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1

Nepheline and sodalite in a barred olivine chondrule from the Allende meteorite  

NASA Astrophysics Data System (ADS)

The discovery of nepheline and sodalite in association with glass in a barred olivine chondrule from the Allende C3V meteorite is reported, and the possible origin of the minerals is discussed. Scanning electron microscope/energy dispersive analysis indicates that the major minerals of the chondrule are olivine, bronzite and chromite, with olivine bars separated by glass of nearly pure plagioclase composition. The olivine is observed to have a composition richer in Fe than that predicted from olivine-liquid equilibria, indicating, along with the presence of plagioclase glass and small amounts of subcalcic diopside, the nonequilibrium crystallization of the barred olivine chondrule. The textural features of the chondrule are consistent with a liquid origin for nepheline and sodalite from the chondrule-forming liquid under nonequilibrium conditions.

Lumpkin, G. R.

1980-06-01

2

Implications for the evolution of chondrules from Agglomeratic olivine chondrules  

NASA Technical Reports Server (NTRS)

There is considerable evidence that chondrules formed by the melting of solid materials and, by default, the early solar nebula is the preferred location for chondrule formation. Agglomeratic olivine (AO) chondrules supply perhaps the most intriguing, direct evidence for chondrule formation from agglomeration of solids. We review the characteristics of AO chondrules and discuss their implications for understanding chondrule precursors and chondrule evolution.

Weisberg, M. K.; Prinz, M.

1994-01-01

3

Formation conditions of pyroxene-olivine and magnesian olivine chondrules  

NASA Technical Reports Server (NTRS)

Dynamic crystallization experiments performed on a Type I and an intermediate Type II/III composition demonstrate chondrule texture is controlled by the abundance of heterogeneous nuclei. This factor is controlled by the maximum initial temperature relative to the olivine disappearance temperature for the given heating time. Glassy and excentroradial textures form from superheated melts with no nuclei, and barred textures form with initial temperatures near the olivine disappearance temperature. Porphyritic and granular textures form with initial temperatures below the liquidus with abundant nuclei. Comparison of zoning characteristics of experimental olivines with those in natural porphyritic olivine chondrules indicates cooling rates of 100 to 1000 C/h, whereas olivine morphology indicates barred olivines cooled at rates of 250 to 1000 C/h. Texture/composition relationships suggest chondrules experienced initial temperatures below 1750 C. These observations are consistent with the idea that chondrules formed by transient heating in dust-rich regions (i.e., in the midplane) of the solar nebula.

Radomsky, Patrick M.; Hewins, Roger H.

1990-01-01

4

Formation conditions of pyroxene-olivine and magnesian olivine chondrules  

SciTech Connect

Dynamic crystallization experiments performed on a Type I and an intermediate Type II/III composition demonstrate chondrule texture is controlled by the abundance of heterogeneous nuclei. This factor is controlled by the maximum initial temperature relative to the olivine disappearance temperature for the given heating time. Glassy and excentroradial textures form from superheated melts with no nuclei, and barred textures form with initial temperatures near the olivine disappearance temperature. Porphyritic and granular textures form with initial temperatures below the liquidus with abundant nuclei. Comparison of zoning characteristics of experimental olivines with those in natural porphyritic olivine chondrules indicates cooling rates of 100 to 1000{degree}C/h, whereas olivine morphology indicates barred olivines cooled at rates of 250 to 1,000{degree}C/h. Texture/composition relationships suggest chondrules experienced initial temperatures below 1,750{degree}C. These observations are consistent with the idea that chondrules formed by transient heating in dust-rich regions (i.e., in the midplane) of the solar nebula.

Radomsky, P.M.; Hewins, R.H. (Rutgers Univ., New Brunswick, NJ (USA))

1990-12-01

5

Formation conditions of pyroxene-olivine and magnesian olivine chondrules  

Microsoft Academic Search

Dynamic crystallization experiments performed on a Type I and an intermediate Type II\\/III composition demonstrate chondrule texture is controlled by the abundance of heterogeneous nuclei. This factor is controlled by the maximum initial temperature relative to the olivine disappearance temperature for the given heating time. Glassy and excentroradial textures form from superheated melts with no nuclei, and barred textures form

P. M. Radomsky; R. H. Hewins

1990-01-01

6

The origin of ferrous zoning in Allende chondrule olivines  

NASA Astrophysics Data System (ADS)

Very similar major and minor element compositions are noted in the ferrous olivine occurring in chondrules at olivine grain boundaries, along cracks in olivine grains, interleaved with enstatite, and in the inner portions of exposed olivine grain surface rims; simultaneous formation by a single process is therefore suggested. The ferrous chondrule olivine probably formed by the reaction of chondrules with very hot nebular vapors over a period of several hours, followed by the condensation of residual metal vapors onto those olivine surfaces that were in direct contact with the gas as the system cooled. The ferrous chondrule olivine that occurs interleaved with enstatite in Allende does not have a composition identical to, and is not the precursor of, matrix olivine.

Peck, J. A.; Wood, J. A.

1987-06-01

7

Crystal Size Distributions from Porphyritic Olivine Chondrules: Insights into Formation Conditions  

NASA Technical Reports Server (NTRS)

Most chondrules preserve, in their texture, a record of their precursor material and the nature and intensity of the nebular events in which they were formed. We have used crystal size distributions (CSDs) together with crystallization experiments to explore the textures of natural chondrules and their relationships to natural formation conditions. Many careful experimental studies have demonstrated fundamental relationships between the texture of a chondrule and its precursor material, melting intensity, and cooling rate. However, until recently most studies have focused on distinctions between textural types (e.g., barred, radial, porphyritic). Previous work has shown that CSDs provide precise, reproducible characterizations of chondrule-scale textures, and can be used together with crystallization experiments to estimate chondrule formation conditions. Here, we expand this study to investigate the link between texture and formation conditions for a range of natural porphyritic olivine (PO) chondrules.

Zieg, M. J.; Lofgren, G. E.

2003-01-01

8

Granoblastic olivine aggregates as precursors of Type I chondrules: An experimental test  

NASA Astrophysics Data System (ADS)

Chondrule formation models involving precursors of granoblastic olivine aggregates (GOA) of either planetesimal or nebular origin have recently been proposed. We have therefore conducted chondrule simulation experiments using mixtures of 100 h-thermally annealed GOA and An + En to test the viability of GOA as predecessors of porphyritic olivine (PO) chondrules. Isothermal runs of less than 5 min at 1350-1550 °C result in GOA disaggregation and Fe-Mg exchange; runs of 0.5-4 h show textures superficially similar to granular and PO chondrules, but with reversely zoned olivine. Charges isothermally heated at 1550 °C for 1 and 4 h before being cooled at 10 and 100 °C/h undergo olivine crystallization and yield classical PO textures. Although most evidence of origin from GOA is erased, the cores of normally zoned euhedral crystals are relict. As 'phenocrysts' in Type I chondrules can be relict such chondrules could have experienced similar peak temperatures to those of Type II chondrules. Chondrules containing GOA with olivine triple junctions resemble experimental charges heated for minutes at temperatures between 1350 and 1450 °C and Type I chondrules with subhedral to anhedral olivine plus GOA relicts resemble charges heated at the same temperatures but for longer duration. Type I chondrules with a mass of granular olivine or irregular, anhedral olivine grains in the center, and much glass nearer the margin, on the other hand, require limited heating at high temperature (1550 °C) while Type I chondrules with euhedral olivines, resemble charges heated at 1550 °C for 4 h. The majority of Type I chondrules in CV chondrites display evidence of derivation from GOA. Many finer-grained chondrules in CR and UOC on the other hand, could not have been derived from such coarse-grained precursors, but could have formed from fine-grained dustballs as stipulated in the standard paradigm. Thus, both GOA and dustballs represent viable chondrule precursors of coarser and finer-grained Type I PO chondrules, respectively.

Whattam, Scott A.; Hewins, Roger H.

2009-09-01

9

The influence of bulk composition and dynamic melting conditions on olivine chondrule textures  

NASA Technical Reports Server (NTRS)

The effects of the bulk composition and the dynamic melting conditions on the texture of olivine chondrules were investigated in a series of heating experiments. It is shown that variations in the olivine chondrule textures can be produced by varying the FeO/(FeO + MgO) ratio between the average Type IA and Type II chondrule compositions, could affect the texture of a chondrule at a constant initial melting temperature and heating time. A range of the heating times and the masses of precursor spheres caused variations in the degree of melting and in chondrule textures. Chondrule textures were distributed on a graph of initial temperatures vs. FeO/(FeO + MgO) ratios as bands parallel to the olivine disappearance curve. This graph could be used to predict chondrule textures from Fe/(FeO + MgO) ratios at specific initial melting temperatures.

Connolly, Harold C., Jr.; Hewins, Roger H.

1991-01-01

10

Experimental constraints on magnetic stability of chondrules and the paleomagnetic significance of dusty olivines  

NASA Astrophysics Data System (ADS)

Dynamic crystallization experiments are conducted under a magnetic field to determine both magnetic and mineralogical properties of chondrules. The experiment reproduced synthetic dusty olivine samples that were formed by a high temperature reduction of an initially fayalitic olivine. Backscattered-electron microscopy observations confirmed that synthetic dusty olivine contains abundant fine, submicron-sized Ni-poor Fe inclusions in the cores of MgO-rich olivine grains, similar to that in natural chondrules. Alternating field demagnetization experiments of dusty olivine samples indicate mean destructive fields of up to 80 mT, suggesting the submicron-sized Fe inclusions are a carrier of stable remanence. In natural chondrules, fine Fe inclusions in the dusty olivine may have been armored against chemical alteration by surrounding host olivine crystals. Since the fine Fe inclusions were probably heated above the Curie temperature during the last chondrule forming events, the fine Fe inclusions in dusty olivine can acquire thermal remanent magnetization during the chondrule formation event. Theoretical time-temperature relation of such fine-grained Fe (kamacite) grains suggested that a paleomagnetic data observed above 490 °C in thermal demagnetization experiments of dusty olivines is reliable despite the low-grade metamorphism of unequilibrated ordinary chondrites (e.g., LL3.0). Therefore, the presence of fine Fe inclusions in dusty olivine in unequilibrated ordinary chondrites constrains that such dusty olivine in chondrules is a good candidate as an un-altered and stable magnetic recorder of the early solar magnetic field.

Uehara, Minoru; Nakamura, Norihiro

2006-10-01

11

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

NASA Astrophysics Data System (ADS)

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

Jones, R. H.; Lofgren, G. E.

1993-06-01

12

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

NASA Technical Reports Server (NTRS)

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

Jones, Rhian H.; Lofgren, Gary E.

1993-01-01

13

Heterogeneity and O-16-Enrichments in Oxygen Isotope Ratios of Olivine from Chondrules in the Mokoia CV3 Chondrite  

NASA Technical Reports Server (NTRS)

Two chondrules from Mokoia contain olivine in which oxygen isotopes are extremely heterogeneous, with some grains highly enriched in O-16. These data provide an important link between CAIs and chondrules. Additional information is contained in the original extended abstract.

Jones, R. H.; Leshin, L. A.; Guan, Y.

2002-01-01

14

Dynamic crystallization of chondrule melts of porphyritic olivine composition - Textures experimental and natural  

NASA Technical Reports Server (NTRS)

A full range of textures characteristic for porphyritic olivine chondrules was reproduced in melts of the same composition, crystallized under dynamic crystallization conditions (under controlled cooling), as determined by electron microprobe analyses. The primary differences between the natural and experimentally produced porphyritic olivine textures were the nature and the extent of matrix crystallization, which reflected the subsolidus or low-temperature cooling history. The most confining limits on the chondrule-forming process were found to be the presence of crystalline precursors for the chondrule melts and the upper temperature limit of melting.

Lofgren, Gary

1989-01-01

15

Olivine-rich rims surrounding chondrules in the Mokoia CV3 carbonaceous chondrite: Further evidence for parent-body processes  

NASA Astrophysics Data System (ADS)

Fine-grained rims surrounding chondrules and inclusions in the Mokoia CV3 carbonaceous chondrite can be divided into phyllosilicate-rich and olivine-rich types. We present a petrographic and electron microscopic study of the olivine-rich rims and their host objects (referred to as chondrules/olivine-rich rims). The olivine-rich rims consist mainly of Fe-rich olivine and very minor phyllosilicate (saponite). Their host chondrules contain minor saponite and phlogopite, which resulted from aqueous alteration of anhydrous silicates. Mineralogical and compositional characteristics of the chondrules/olivine-rich rims suggest that they experienced mild thermal metamorphic effects. The rims commonly contain veins of coarse-grained Fe-rich olivine, magnetite, and Fe-(Ni) sulfides. The chondrules show abundant evidence of alteration along their peripheries, and the alteration textures suggest a mechanism for rim formation by replacement of the chondrules. Initially, enstatite and opaque nodules preferentially reacted to form coarse, platy, Fe-rich olivine crystals, which were subsequently divided into finer grains. Forsterite was also replaced by Fe-rich olivine. As the alteration advanced, these Fe-rich olivines were disaggregated, mixed with simultaneously produced saponite, and formed rims. In contrast, the surrounding matrix shows no evidence of such alteration and metamorphism. These observations indicate that the chondrules/olivine-rich rims did not experience these secondary processes in their present setting. The results suggest that the chondrules/olivine-rich rims experienced extensive replacement reactions in an environment in which aqueous fluids existed but only in minor amounts. They have probably also undergone simultaneous and/or subsequent mild thermal metamorphism. We suggest that the chondrules/olivine-rich rims are actually clasts transported from a relatively dry region in the parent body that was different from the region where Mokoia was finally lithified.

Tomeoka, Kazushige; Ohnishi, Ichiro

2014-07-01

16

A Relict-Grain-Bearing Porphyritic Olivine Compound Chondrule from LL3.0 Semarkona that Experienced Limited Remelting  

NASA Technical Reports Server (NTRS)

Chondrule D8n in LL3.0 Semarkona is a porphyritic olivine (PO) chondrule, 1300 x 1900 microns in size, with a complicated thermal history. The oldest recognizable portion of D8n is a moderately high-FeO, PO chondrule that is modeled as having become enmeshed in a dust ball containing a small, intact, low-FeO porphyritic chondrule and fine-grained material consisting of forsterite, kamacite, troilite, and possibly reduced C. The final chondrule melting event may have been a heat pulse that preferentially melted the low-FeO material and produced a low-FeO, opaque-rich, exterior region, 45-140 microns in thickness, around the original chondrule. Ai one end of the exterior region, a kamacite- and troilite-rich lump 960 pm in length formed. During the final melting event, the coarse, moderately ferroan olivine phenocrysts within the original chondrule appear to have been partly resorbed (These relict phenocrysts have the highest concentrations of FeO, MnO, and Cr2O3-7.5, 0.20, and 0.61 wt%, respectively-in D8n.). Narrow olivine overgrowths crystallized around the phenocrysts following final chondrule melting; their compositions seem to reflect mixing between melt derived from the exterior region and the resorbed margins of the phenocrysts. During the melting event, FeO in the relict phenocrysts was reduced, producing numerous small blebs of Ni-poor metallic Fe along preexisting curvilinear fractures. The reduced olivine flanking the trails of metal blebs has lower FeO than the phenocrysts but virtually identical MnO and Cr2O3 contents. Subsequent parent-body aqueous alteration in the exterior region of the chondrule formed pentlandite and abundant magnetite.

Rubin, Alan E.

2006-01-01

17

Forsterite and Olivine in Sahara-97210 (LL3.2) and Chainpur (LL3.4) Chondrules: Compositional Evolution and the Influence of Melting  

NASA Technical Reports Server (NTRS)

It is generally accepted that chondrules contain relict grains that did not crystallize in situ, and that forsterite is one type of relict grain which is a likely precursor for chondrules. Chemically and morphologically similar forsterite is also found as "isolated grains", especially in carbonaceous chondrites. Using SIMS, we analyzed forsterite, ferrous overgrowths around forsterite, and coexisting normal olivine in 5 chondrules and 2 isolated grains in the Sahara-97210 ('Sahara") LL3.2 chondrite. We earlier used the same methods to study olivine in 3 Chainpur chondrules that contain relict forsterite. Our new data for Sahara provide additional insight into the processes affecting chondrules and their precursors.

Ruzicka, A.; Floss, C.

2004-01-01

18

Suitability of chondrules for studying the magnetic field of the early solar system: an examination of synthetically produced dusty olivine  

Microsoft Academic Search

Chondritic meteorites are rare, yet incredibly valuable windows into the geophysical and geochemical environment of the early solar system. Dusty olivine grains containing exsolved nanometer-scale iron-nickel alloy inclusions are present in many chondritic meteorites and their remanent magnetization may give insight into the strength of the solar dynamo at the time of chondrule formation. Laboratory methods for determining the paleointensity

Y. Hu; J. M. Feinberg; N. Church; G. Bromiley; J. Bowles; M. Jackson; B. M. Moskowitz; R. J. Harrison

2008-01-01

19

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

Microsoft Academic Search

Unequilibrated chromite and olivine margin compositions in type II chondrules are noted to differ systematically among three of the chondrite groups, suggesting that type II liquids differed in composition among the groups. These differences may be interpreted as indicators of different chemical compositions of the precursor solids which underwent melting, or, perhaps, as differences in the extent to which immiscible

C. A. Johnson; M. Prinz

1991-01-01

20

Amoeboid olivine aggregates with low-Ca pyroxenes: a genetic link between refractory inclusions and chondrules?  

NASA Astrophysics Data System (ADS)

Amoeboid olivine aggregates (AOAs) in primitive (unmetamorphosed and unaltered) carbonaceous chondrites are uniformly 16O-enriched (? 17O ˜ -20‰) and consist of forsterite (Fa <2), FeNi-metal, and a refractory component (individual CAIs and fine-grained minerals interspersed with forsterite grains) composed of Al-diopside, anorthite, ±spinel, and exceptionally rare melilite (Åk <15); some CAIs in AOAs have compact, igneous textures. Melilite in AOAs is replaced by a fine-grained mixture of spinel, Al-diopside, and anorthite. Spinel is corroded by anorthite or by Al-diopside. In ˜10% of > 500 AOAs studied in the CR, CV, CM, CO, CH, CB, and ungrouped carbonaceous chondrites Acfer 094, Adelaide, and LEW85332, forsterite is replaced to a various degree by low-Ca pyroxene. There are three major textural occurrences of low-Ca pyroxene in AOAs: (i) thin (<10 ?m) discontinuous layers around forsterite grains or along forsterite grain boundaries in AOA peripheries; (ii) haloes and subhedral grains around FeNi-metal nodules in AOA peripheries, and (iii) thick (up to 70 ?m) continuous layers with abundant tiny inclusions of FeNi-metal grains around AOAs. AOAs with low-Ca pyroxene appear to have experienced melting of various degrees. In the most extensively melted AOA in the CV chondrite Leoville, only spinel grains are relict; forsterite, anorthite and Al-diopside were melted. This AOA has an igneous rim of low-Ca pyroxene with abundant FeNi-metal nodules and is texturally similar to Type I chondrules. Based on these observations and thermodynamic analysis, we conclude that AOAs are aggregates of relatively low temperature solar nebular condensates originated in 16O-rich gaseous reservoir(s), probably CAI-forming region(s). Some of the CAIs were melted before aggregation into AOAs. Many AOAs must have also experienced melting, but of a much smaller degree than chondrules. Before and possibly after aggregation, melilite and spinel reacted with the gaseous SiO and Mg to form Ca-Tschermakite (CaAl 2SiO 6)-diopside (CaMgSi 2O 6) solid solution and anorthite. Solid or incipiently melted olivine in some AOAs reacted with gaseous SiO in the CAI- or chondrule-forming regions to form low-Ca pyroxene: Mg 2SiO 4 + SiO (g) + H 2O (g) = Mg 2Si 2O 6 + H 2(g). Some low-Ca pyroxenes in AOAs may have formed by oxidation of Si-bearing FeNi-metal: Mg 2SiO 4 + Si (in FeNi) + 2H 2O (g) = Mg 2Si 2O 6 + 2H 2(g) and by direct gas-solid condensation: Mg (g) + SiO (g) +H 2O (g) = Mg 2Si 2O 6(s) + H 2(g) from fractionated (Mg/Si ratio < solar) nebular gas. Although bulk compositions of AOAs are rather similar to those of Type I chondrules, on the projection from spinel onto the plane Ca 2SiO 4-Mg 2SiO 4-Al 2O 3, these objects plot on different sides of the anorthite-forsterite thermal divide, suggesting that Type I chondrules cannot be produced from AOAs by an igneous fractionation. Formation of low-Ca pyroxene by reaction of AOAs with gaseous SiO and by melting of silica-rich dust accreted around AOAs moves bulk compositions of the AOAs towards chondrules, and provide possible mechanisms of transformation of refractory materials into chondrules or chondrule precursors. The rare occurrences of low-Ca pyroxene in AOAs may indicate that either AOAs were isolated from the hot nebular gas before condensation of low-Ca pyroxene or that condensation of low-Ca pyroxene by reaction between forsterite and gaseous SiO was kinetically inhibited. If the latter is correct, then the common occurrences of pyroxene-rich Type I chondrules may require either direct condensation of low-Ca pyroxenes or SiO 2 from fractionated nebular gas or condensation of gaseous SiO into chondrule melts.

Krot, Alexander N.; Petaev, Michail I.; Yurimoto, Hisayoshi

2004-04-01

21

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

NASA Technical Reports Server (NTRS)

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

Johnson, Craig A.; Prinz, Martin

1991-01-01

22

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

23

Evidence for fractional crystallization of wadsleyite and ringwoodite from olivine melts in chondrules entrained in shock-melt veins.  

PubMed

Peace River is one of the few shocked members of the L-chondrites clan that contains both high-pressure polymorphs of olivine, ringwoodite and wadsleyite, in diverse textures and settings in fragments entrained in shock-melt veins. Among these settings are complete olivine porphyritic chondrules. We encountered few squeezed and flattened olivine porphyritic chondrules entrained in shock-melt veins of this meteorite with novel textures and composition. The former chemically unzoned (Fa(24-26)) olivine porphyritic crystals are heavily flattened and display a concentric intergrowth with Mg-rich wadsleyite of a very narrow compositional range (Fa(6)-Fa(10)) in the core. Wadsleyite core is surrounded by a Mg-poor and chemically stark zoned ringwoodite (Fa(28)-Fa(38)) belt. The wadsleyite-ringwoodite interface denotes a compositional gap of up to 32 mol % fayalite. A transmission electron microscopy study of focused ion beam slices in both regions indicates that the wadsleyite core and ringwoodite belt consist of granoblastic-like intergrowth of polygonal crystallites of both ringwoodite and wadsleyite, with wadsleyite crystallites dominating in the core and ringwoodite crystallites dominating in the belt. Texture and compositions of both high-pressure polymorphs are strongly suggestive of formation by a fractional crystallization of the olivine melt of a narrow composition (Fa(24-26)), starting with Mg-rich wadsleyite followed by the Mg-poor ringwoodite from a shock-induced melt of olivine composition (Fa(24-26)). Our findings could erase the possibility of the resulting unrealistic time scales of the high-pressure regime reported recently from other shocked L-6 chondrites. PMID:18562280

Miyahara, Masaaki; El Goresy, Ahmed; Ohtani, Eiji; Nagase, Toshiro; Nishijima, Masahiko; Vashaei, Zahra; Ferroir, Tristan; Gillet, Philippe; Dubrovinsky, Leonid; Simionovici, Alexandre

2008-06-24

24

Evidence for fractional crystallization of wadsleyite and ringwoodite from olivine melts in chondrules entrained in shock-melt veins  

PubMed Central

Peace River is one of the few shocked members of the L-chondrites clan that contains both high-pressure polymorphs of olivine, ringwoodite and wadsleyite, in diverse textures and settings in fragments entrained in shock-melt veins. Among these settings are complete olivine porphyritic chondrules. We encountered few squeezed and flattened olivine porphyritic chondrules entrained in shock-melt veins of this meteorite with novel textures and composition. The former chemically unzoned (Fa24–26) olivine porphyritic crystals are heavily flattened and display a concentric intergrowth with Mg-rich wadsleyite of a very narrow compositional range (Fa6–Fa10) in the core. Wadsleyite core is surrounded by a Mg-poor and chemically stark zoned ringwoodite (Fa28–Fa38) belt. The wadsleyite–ringwoodite interface denotes a compositional gap of up to 32 mol % fayalite. A transmission electron microscopy study of focused ion beam slices in both regions indicates that the wadsleyite core and ringwoodite belt consist of granoblastic-like intergrowth of polygonal crystallites of both ringwoodite and wadsleyite, with wadsleyite crystallites dominating in the core and ringwoodite crystallites dominating in the belt. Texture and compositions of both high-pressure polymorphs are strongly suggestive of formation by a fractional crystallization of the olivine melt of a narrow composition (Fa24–26), starting with Mg-rich wadsleyite followed by the Mg-poor ringwoodite from a shock-induced melt of olivine composition (Fa24–26). Our findings could erase the possibility of the resulting unrealistic time scales of the high-pressure regime reported recently from other shocked L-6 chondrites.

Miyahara, Masaaki; El Goresy, Ahmed; Ohtani, Eiji; Nagase, Toshiro; Nishijima, Masahiko; Vashaei, Zahra; Ferroir, Tristan; Gillet, Philippe; Dubrovinsky, Leonid; Simionovici, Alexandre

2008-01-01

25

The formation and alteration of the Renazzo-like carbonaceous chondrites II: Linking O-isotope composition and oxidation state of chondrule olivine  

NASA Astrophysics Data System (ADS)

To better understand the formation conditions of type-I and type-II chondrules in the Renazzo-like carbonaceous (CR) chondrites, an in situ major- and minor-element and O-isotope study was conducted. Twenty-one ferromagnesian chondrules from three CR chondrites (GRA 95229, GRA 06100, and QUE 99177) were analyzed to establish an internally-consistent data set. From this study we infer that type-II chondrule precursors contained enhanced S-bearing dust and ice abundances relative to type-I chondrules. There is a relationship between the O-isotope composition and oxidation state of olivine, which may be related to the amount of 16O-poor ice and reduced carbon accreted by chondrule precursors before melting. Type-II chondrules formed under H2O/H2 ratios of ˜230-740 times solar. In contrast, type-I chondrules formed under more reducing conditions with lower H2O/H2 ratios of ˜10-100 times solar. We find a relationship between type-II chondrule petrology (relict free vs. relict grain-bearing) and O-isotope composition, which is due to degree of melting and exchange with a 16O-poor gas reservoir. The 16O-poor gas that interacted with both type-I and type-II chondrules is estimated to have an isotopic composition between ˜?18Og = 13-27‰ and ?17Og = 10-22‰, different from the O-isotope composition of the water accreted by the CR chondrite parent body. Due to partial melting, type-I chondrules and relict grain-bearing type-II chondrules exchanged with the 16O-poor gas to a lower degree than relict-free type-II chondrules.

Schrader, Devin L.; Connolly, Harold C.; Lauretta, Dante S.; Nagashima, Kazuhide; Huss, Gary R.; Davidson, Jemma; Domanik, Kenneth J.

2013-01-01

26

A New Estimate of the Chondrule Cooling Rate Deduced from an Analysis of Compositional Zoning of Relict Olivine  

NASA Astrophysics Data System (ADS)

Compositional zoning in chondrule phenocrysts records the crystallization environments in the early solar nebula. We modeled the growth of olivine phenocrysts from a silicate melt and proposed a new fractional crystallization model that provides a relation between the zoning profile and the cooling rate. In our model, we took elemental partitioning at a growing solid-liquid interface and time-dependent solute diffusion in the liquid into consideration. We assumed a local equilibrium condition, namely, that the compositions at the interface are equal to the equilibrium ones at a given temperature. We carried out numerical simulations of the fractional crystallization in one-dimensional planar geometry. The simulations revealed that under a constant cooling rate the growth velocity increases exponentially with time and a linear zoning profile forms in the solid as a result. We derived analytic formulae of the zoning profile, which reproduced the numerical results for wide ranges of crystallization conditions. The formulae provide a useful tool to estimate the cooling rate from the compositional zoning. Applying the formulae to low-FeO relict olivine grains in type II porphyritic chondrules observed by Wasson & Rubin, we estimate the cooling rate to be ~200-2000 K s-1, which is greater than that expected from furnace-based experiments by orders of magnitude. Appropriate solar nebula environments for such rapid cooling conditions are discussed.

Miura, H.; Yamamoto, T.

2014-03-01

27

Chondrules in H3 chondrites - Textures, compositions and origins  

NASA Technical Reports Server (NTRS)

Compositional and textural variations among chondrules in unequilibrated (type 3) H-group chondrites are examined in order to determine possible relations between chondrule compositions and textures. Bulk compositions of polished thin sections of 90 individual chondrules and 16 compound chondrule sets from the Sharps, Tieschitz and Bremervorde chondrites were measured by broad-beam electron probe analyses; the chondrules were also classified petrographically as barred olivine, porphyritic olivine, porphyritic pyroxene, barred pyroxene, radiating pyroxene or fine-grained. The mean compositions of each type are found to be distinct as verified by discriminant analysis, despite a large scatter, with the olivine-rich chondrules characterized by low SiO2 and high FeO and MgO contents, greater concentrations of TiO2, Al2O3, Na2O and K2O, and lower Cr2O3 and MnO relative to pyroxene-rich chondrules. Data suggest that composition, together with cooling rate, has played a conspicuous role in producing observed chrondrule textures, and are consistent with chondrule formation from mixtures of differing fractions of high-, intermediate- and low-temperature nebular condensates that underwent melting in space.

Lux, G.; Keil, K.; Taylor, G. J.

1981-01-01

28

Chondrules in H3 chondrites - Textures, compositions and origins  

NASA Astrophysics Data System (ADS)

Compositional and textural variations among chondrules in unequilibrated (type 3) H-group chondrites are examined in order to determine possible relations between chondrule compositions and textures. Bulk compositions of polished thin sections of 90 individual chondrules and 16 compound chondrule sets from the Sharps, Tieschitz and Bremervorde chondrites were measured by broad-beam electron probe analyses; the chondrules were also classified petrographically as barred olivine, porphyritic olivine, porphyritic pyroxene, barred pyroxene, radiating pyroxene or fine-grained. The mean compositions of each type are found to be distinct as verified by discriminant analysis, despite a large scatter, with the olivine-rich chondrules characterized by low SiO2 and high FeO and MgO contents, greater concentrations of TiO2, Al2O3, Na2O and K2O, and lower Cr2O3 and MnO relative to pyroxene-rich chondrules. Data suggest that composition, together with cooling rate, has played a conspicuous role in producing observed chrondrule textures, and are consistent with chondrule formation from mixtures of differing fractions of high-, intermediate- and low-temperature nebular condensates that underwent melting in space.

Lux, G.; Keil, K.; Taylor, G. J.

1981-05-01

29

Demonstration of REE fractionation among individual chondrules from the allende (CV3) chondrite  

SciTech Connect

Abundances of REE, Ba, Sr, Rb, K, Mg and Ca were determined by precise mass spectrometric isotope dilution techniques for 24 chondrules from the Allende (CV3) chondrite. The REE abundances are 2.5-10 {times} CI for barred olivine chondrules, 2-8 {times} CI for porphyritic and nonporphyritic pyroxene chondrules, 0.15-4 {times} CI for porphyritic olivine and porphyritic olivine-pyroxene chondrules and are more or less similarly fractionated. General REE fractionations and large (up to 170%) anomalies of Ce, Eu and Yb occur in all chondrule types, particularly for barred olivine and pyroxene-rich chondrules. Positive correlations of REE with the moderately volatile elements, K and Rb, as well as other refractory elements, Ca, Sr and Ba, are independent of textural type and major chemical compositions. Each type of chondrule has large and systematic abundance variations of K and Rb, but shows a constant K/Rb ratio close to that of CIs. From the these results, the following constraints on the chemical characteristics of precursors and chondrule-forming events are suggested: (1) vaporization loss of alkalis accompanied by K/Rb fractionation did not occur during chondrule-formation melting events, (2) elemental abundances were basically established prior to melting events by accretion of alkali-free component(s) and alkali-bearing refractory precursors with fractionated REE, (3) gas/solid (or liquid) processes yielding REE fractionations took place during the formation of refractory precursors.

Misawa, K; Nakamura, N. (Kobe Univ. (Japan))

1988-06-01

30

Suitability of chondrules for studying the magnetic field of the early solar system: an examination of synthetically produced dusty olivine  

NASA Astrophysics Data System (ADS)

Chondritic meteorites are rare, yet incredibly valuable windows into the geophysical and geochemical environment of the early solar system. Dusty olivine grains containing exsolved nanometer-scale iron-nickel alloy inclusions are present in many chondritic meteorites and their remanent magnetization may give insight into the strength of the solar dynamo at the time of chondrule formation. Laboratory methods for determining the paleointensity of these rare materials must be optimized prior to conducting experiments on actual meteorite samples. To this end, we have used high temperature recrystallization techniques to produce synthetic dusty olivine samples with textures remarkably similar to those observed in chondritic meteorites. The olivine grains used in these annealing experiments are from the 13 kya Haleyjabunga picritic basalt flow in Iceland and have compositions of Fo90, which closely resembles the olivine composition observed in chondritic meteorites. Samples were annealed at 1350°C either under vacuum in the presence of graphite or under controlled oxygen fugacity using pure CO gas. The laboratory-produced magnetic mineral assemblages in two sets of samples have been characterized using low and high temperature remanence and susceptibility measurements, hysteresis loops, FORC diagrams, and scanning electron microscopy. The room-temperature remanence properties of these materials have been explored using stepwise IRM and ARM acquisition and alternating field demagnetization. These synthesis techniques allow us to produce a wide rage of iron-nickel grain sizes with correspondingly large variations in coercivity (between 0 and 500 mT). High temperature measurements of saturation magnetization show that both samples reach their Curie temperatures at ~760°C, consistent with kamacite, a low-Ni high-Fe metal alloy. Multiple experiments have shown that care must be taken to rigorously control the atmosphere in which the samples are heated and cooled in order to avoid forming trace amounts of magnetite on the surface of the samples. Future research will explore the feasibility of using modified Thellier protocols to determine the paleointensity of laboratory-induced thermoremanent magnetizations.

Hu, Y.; Feinberg, J. M.; Church, N.; Bromiley, G.; Bowles, J.; Jackson, M.; Moskowitz, B. M.; Harrison, R. J.

2008-12-01

31

Variations in the O-isotope composition of gas during the formation of chondrules from the CR chondrites  

NASA Astrophysics Data System (ADS)

To better understand the environment of chondrule formation and constrain the O-isotope composition of the ambient gas in the Renazzo-like carbonaceous (CR) chondrite chondrule-forming region, we studied the mineralogy, petrology, and in situ O-isotope compositions of olivine in 11 barred olivine (BO) chondrules and pyroxene and silica in three type I porphyritic chondrules from the CR chondrites Gao-Guenie (b), Graves Nunataks (GRA) 95229, Pecora Escarpment (PCA) 91082, and Shi?r 033. BO chondrules experienced a higher degree of melting than porphyritic chondrules, and therefore, it has been hypothesized that they more accurately recorded the O-isotope composition of the gas in chondrule-forming regions. We studied the O-isotope composition of silica as it has been hypothesized to have formed via direct condensation from the gas.

Schrader, Devin L.; Nagashima, Kazuhide; Krot, Alexander N.; Ogliore, Ryan C.; Hellebrand, Eric

2014-05-01

32

Nonthermal Initiation of Nucleation and Chondrule Texture Development  

NASA Astrophysics Data System (ADS)

The textures of chondrules are almost universally ascribed to the influence of heating and cooling histories of the precursor materials. Many chondrule textures are viewed as constraining the cooling history of precursor droplets of silicate liquid that were initially heated to near liquidus temperatures. The standard thermal model uses a superliquidus silicate droplet that was significantly undercooled to induce nucleation and then cooled, possibly nonlinearly, down a thermal gradient to induce crystal growth in the chondrule. Alternately, nuclei may occur as relicts in the droplet or may be introduced as dust on the surface of the droplet. The means by which the nucleation barrier (the essential first step in the crystal growth history of a chondrule) is overcome has fundamental influence on the subsequent development and type of texture - the development of dendritic and porprhyritic textures reflect quite different nucleation histories. We explore an alternate method of 'jumping' this barrier. Undercooling or, more generally, supersaturation of the liquidus solid, can be induced either by cooling an isochemical system from superliquidus temperatures or by isothermally making the bulk composition of the system more refractory. Removal of some FeO from a liquid of typical chondrule bulk composition increases the liquidus temperature and supersaturates the liquid with the most refractory solid, olivine. FeO is removed easily by reduction to metal. Most chondrules are more magnesian than the solar system composition and indeed most are more magnesian than the host meteorite in which they occur. Clearly the source materials of chondrules have lost Fe relative to either bulk solar system or chondritic precursors. If reduction was involved in chondrule formation then Fe-loss would induce undercooling by forcing the chondrule bulk composition to become more magnesian. (If the Fe-loss occurred prior to the chondrule forming event, then isothermal supersaturation is less likely to occur.) Variability of the degree of Fe-loss dominates much of the compositional range of chondrules with Type I chondrules having the lowest Fe- contents. A plausible mechanism for reduction of the silicate droplets in a chondrule forming region, is gas expansion. During heating, the formation of silicate liquid droplets will occur at equilibrium with the "chondrule" vapor phase and any ambient gas. The vapor+gas cloud associated with the heating cycle of chondrule precursors usually will expand more rapidly than the 'cloud' of liquid droplets it contains. As it expands, the fugacity of most species in the gas cloud, including oxygen species, drops, initiating reduction of the entrained droplets. Surface area/volume considerations require that small droplets (<0.5mm) will react much more rapidly than large droplets (>1mm) and as a result a variety of size sorted compositional groups of chondrules may form. Since reduction is initiated on the outer surface of the droplet, simple diffusional arguments indicate that those outer surfaces will experience reduction induced supersaturation first and can precipitate metal and Mg-rich olivine nuclei from which the texture of the chondrule may grow as diffusion limited reduction proceeds inward. Metal grains may act as nucleation sites for olivine in the chondrule or may be lost from the chondrule because of the differential expansion of metal and silicate. The necessity that precipitation begin on the external surfaces of the droplet suggests that textures characterized by annular structures are likely to be formed by this process. The best example is, of course, classic barred olivine, a texture that is approximated by a variety of dendritic textures in cooling experiments. The production of the characteristic annular shell of olivine enclosing the bars in barred olivine chondrules, may be experimentally difficult in current furnaces but its absence in most experiments may also be the result of inappropriate conditions. The final growth of the chondrule texture must involve a suitable cool

Delaney, J. S.

1995-09-01

33

Ca,Al-rich inclusions, amoeboid olivine aggregates, and Al-rich chondrules from the unique carbonaceous chondrite Acfer 094: I. mineralogy and petrology  

NASA Astrophysics Data System (ADS)

Based on their mineralogy and petrography, ˜200 refractory inclusions studied in the unique carbonaceous chondrite, Acfer 094, can be divided into corundum-rich (0.5%), hibonite-rich (1.1%), grossite-rich (8.5%), compact and fluffy Type A (spinel-melilite-rich, 50.3%), pyroxene-anorthite-rich (7.4%), and Type C (pyroxene-anorthite-rich with igneous textures, 1.6%) Ca,Al-rich inclusions (CAIs), pyroxene-hibonite spherules (0.5%), and amoeboid olivine aggregates (AOAs, 30.2%). Melilite in some CAIs is replaced by spinel and Al-diopside and/or by anorthite, whereas spinel-pyroxene assemblages in CAIs and AOAs appear to be replaced by anorthite. Forsterite grains in several AOAs are replaced by low-Ca pyroxene. None of the CAIs or AOAs show evidence for Fe-alkali metasomatic or aqueous alteration. The mineralogy, textures, and bulk chemistry of most Acfer 094 refractory inclusions are consistent with their origin by gas-solid condensation and may reflect continuous interaction with SiO and Mg of the cooling nebula gas. It appears that only a few CAIs experienced subsequent melting. The Al-rich chondrules (ARCs; >10 wt% bulk Al 2O 3) consist of forsteritic olivine and low-Ca pyroxene phenocrysts, pigeonite, augite, anorthitic plagioclase, ± spinel, FeNi-metal, and crystalline mesostasis composed of plagioclase, augite and a silica phase. Most ARCs are spherical and mineralogically uniform, but some are irregular in shape and heterogeneous in mineralogy, with distinct ferromagnesian and aluminous domains. The ferromagnesian domains tend to form chondrule mantles, and are dominated by low-Ca pyroxene and forsteritic olivine, anorthitic mesostasis, and Fe,Ni-metal nodules. The aluminous domains are dominated by anorthite, high-Ca pyroxene and spinel, occasionally with inclusions of perovskite; have no or little FeNi-metal; and tend to form cores of the heterogeneous chondrules. The cores are enriched in bulk Ca and Al, and apparently formed from melting of CAI-like precursor material that did not mix completely with adjacent ferromagnesian melt. The inferred presence of CAI-like material among precursors for Al-rich chondrules is in apparent conflict with lack of evidence for melting of CAIs that occur outside chondrules, suggesting that these CAIs were largely absent from chondrule-forming region(s) at the time of chondrule formation. This may imply that there are several populations of CAIs in Acfer 094 and that mixing of "normal" CAIs that occur outside chondrules and chondrules that accreted into the Acfer 094 parent asteroid took place after chondrule formation. Alternatively, there may have been an overlap in the CAI- and chondrule-forming regions, where the least refractory CAIs were mixed with Fe-Mg chondrule precursors. This hypothesis is difficult to reconcile with the lack of evidence of melting of AOAs which represent aggregates of the least refractory CAIs and forsterite grains.

Krot, Alexander N.; Fagan, Timothy J.; Keil, Klaus; McKeegan, Kevin D.; Sahijpal, Sandeep; Hutcheon, Ian D.; Petaev, Mikhail I.; Yurimoto, Hisayoshi

2004-05-01

34

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

35

Fayalite-rich rims, veins, and halos around and in forsteritic olivines in CAIs and chondrules in carbonaceous chondrites: Types, compositional profiles and constraints of their formation  

SciTech Connect

Fayalite-rich rims, veins, and halos around and in forsteritic olivines are a wide-spread phenomenon in chondrules, Ca, Al-rich inclusions (CAIs), and single grains in carbonaceous chondrites. The presence of fayalite rod-like crystals and laths in rims, veins, in wall of pores, and as fluffy network bridging neighboring olivines, pyroxenes, feldspars, etc. is strongly suggestive that the fayalitic olivine was formed by condensation presumably from the solar nebula gas. The formation of the fayalitic olivine was probably caused by an increase in the H{sub 2}O/H{sub 2} ratio (to a ratio between 0.1-1) subsequent to condensation of forsterite. At that stage, FeNi inclusions in olivine were also oxidized and fayalitic halos around the metal were then formed Fe diffusion along with addition of SiO{sub 2} from the solar gas or loss of M{sub g}O to the solar gas. The Fa-rich olivine rims and veins display a narrow compositional variation between Fa{sup 34} and Fa{sup 46}. Subsequent to condensation of Fa-rich olivine and oxidation of FeNi metal, Fe diffused in forsterite. This diffusion was probable enhanced due to the presence of point defects in olivine or the formation of a nonstoichiometric phase analogous to laihunite enriched in Al{sub 2}O{sub 3} and Cr{sub 2}O{sub 3}. However, the presence of Al{sub 2}O{sub 3{minus}} and Cr{sub 2}O{sub 3{minus}} rich discrete domains cannot by excluded. Cooling rates calculated by modeling of the diffusion profiles are indicative of rapid cooling subsequent to the condensation of fayalitic olivines. The authors obtain cooling rates ranging from 2000{degree}/day and 10{degree}C/day at an initial temperature of 1200C{degree} and 900C{degree}, respectively.

Hua, X.; Adam, J.; Palme, H.; Goresy, A. E. (Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany, F.R.))

1988-06-01

36

Relict grains in chondrules: Evidence for chondrule recycling  

NASA Technical Reports Server (NTRS)

The presence of relict grains in chondrules, which offers some insight into the degree to which chondrule material was recycled in the chondrule-forming region, is discussed in this report. Relics are grains that clearly did not crystallize in situ in the host chondrule. They represent coarse-grained precursor material that did not melt during chondrule formation, and provide the only tangible record of chondrule precursor grains. Relics are commonly identified by a large difference in size, textural differences, and/or significant compositional differences compared with normal grains in the host chondrule. Two important types of relics are: (1) 'dusty,' metal-bearing grains of olivine and pyroxene; and (2) forsterite (Mg-rich olivine) grains present in FeO-rich chondrules.

Jones, R. H.

1994-01-01

37

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

NASA Technical Reports Server (NTRS)

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

Krot, Alexander N.; Rubin, Alan E.

1993-01-01

38

Chondrule synthesis using fine-grained precursors  

NASA Astrophysics Data System (ADS)

High temperature petrologic experiments have been used in order to reproduce the textures of chondrules, which are rounded to irregularly shaped ferromagnesion silicate objects. Such experiments shed light on the conditions that existed and mechanisms that operated in the early solar nebula, as natural chondrules are believed to have formed there due to some type of heating event. The exact nature of this heating event and the conditions that existed at the time of the formation of the solar nebula are not completely understood. Chondrules, which are believed to be composed of some of the oldest remnants of the solar system, nebular condensates, are the basic components of chondrites. Chondrites comprise ˜82% of all meteorites. Despite years of petrographic examination and experimental petrology, the thermal history of chondrules still remains uncertain. Natural chondrules exhibit a variety of different textures ranging from glassy, barred, porphyritic, microporphyritc to protoporphyritc. Petrologic experiments in a muffle tube furnace under controlled fugacity conditions using type IAB bulk composition analogs have been successful in reproducing each of these textures in the laboratory. Charges are prepared, heated, water quenched, mounted, polished and photographed using back-scattered electron imagery. Subsequent analysis provides numerical data, which can then be used to calculate the nominal grain size of the olivine crystals in each charge. Porphyritic chondrules are the most abundant in nature by far and any model for chondrule formation must be capable of producing porphyritic textures. To reproduce this texture in the laboratory, however, seems to require a very narrow range of maximum temperature and soak time parameters even when using a variety of different types of fine-grained and agglomerated olivine precursor material. Experiments undertaken in this study bring into question some of the basic assumptions of various classical models of chondrule formation, which call for fine-grained precursors (nebular condensates) being processed by a single heating event. In light of these findings, models for chondrule formation that incorporate mechanisms for the recycling of fine-grained precursor material appear to be more favorable.

Fox, George Ernest

2002-11-01

39

Oxygen isotope systematics of chondrule phenocrysts from the CO3.0 chondrite Yamato 81020: Evidence for two distinct oxygen isotope reservoirs  

NASA Astrophysics Data System (ADS)

High-precision oxygen three-isotope measurements of olivine and pyroxene were performed on 33 chondrules in the Yamato 81020 CO3.0 chondrite by secondary ion mass spectrometry. In chondrules where oxygen isotopes were measured in both olivine and pyroxene, the majority of grains have similar values, indicating co-magmatic crystallization. However, many chondrules contain relict grains with unique oxygen isotope ratios. A striking feature of Yamato 81020 chondrules is a bimodal distribution of oxygen isotope ratios, as those with Mg# >97 phenocrysts range in ?17O from -4.8‰ to -6.5‰ ("-5.5‰" group), and those with Mg# 96-36 phenocrysts have ?17O values of -2.1‰ to -3.0‰ ("-2.5‰" group). A single Mg# 99.6 barred olivine chondrule has a ?17O of -3.3‰. We discuss that ?17O ˜-5.5‰ chondrules are derivative of a reservoir with limited dust enrichment (100× Solar System), which yielded a relatively reduced chondrule-forming environment. In contrast, the ?17O ˜-2.5‰ chondrules may have been influenced by 16O-poor H2O ice that sublimed and then homogenized with precursor material. The addition of H2O, when combined with high dust enrichment (1000× Solar System) and greater bulk Fe content, could have induced an oxidized environment at high temperatures, forming Mg# 96-36 chondrules. Among the 33 chondrules studied, the Al-Mg relative ages of 20 had been obtained previously. Comparing the oxygen isotope ratios and the 26Al ages of these chondrules, it is likely that the "-5.5‰" and "-2.5‰" oxygen isotope reservoirs existed contemporaneously. This implies that the snow line was spatially fixed during chondrule formation, and separated the CO chondrite accretion region into two distinct volumes of precursors.

Tenner, Travis J.; Ushikubo, Takayuki; Kurahashi, Erika; Kita, Noriko T.; Nagahara, Hiroko

2013-02-01

40

R-Chondrite Chondrules: New O-Isotopic Compositions  

NASA Astrophysics Data System (ADS)

The high ?17O values in relict olivine phenocrysts in R chondrules (up to 3‰, i.e., higher than OC olivine) contrast with earlier models that held that R-chondrule precursors had OC-chondrule O-isotopic compositions.

Isa, J.; Rubin, A. E.; Marin-Carbonne, J.; McKeegan, K. D.; Wasson, J. T.

2012-09-01

41

The Vaguries of Pyroxene Nucleation and the Resulting Chondrule Textures  

NASA Technical Reports Server (NTRS)

Pyroxene is a major phase in chondrules, but often follows olivine in the crystallization sequence and depending on the melting temperature and time may not nucleate readily upon cooling. Dynamic crystallization experiments based on total or near total melting were used to study PO (porphyritic olivine) and PP (Porphyritic pyroxene) compositions as defined by. The experiments showed that pyroxene nucleated only at subliquidus temperatures in the PP melts and rarely in the PO melts. Porphyritic chondrules with phenocrysts of both olivine and pyroxene (POP chondrules) were not easily produced in the experiments. POP chondrules are common and it is important for deciphering their formation that we understand pyroxene nucleation properties of chondrule melts.

Lofgren, G. E.; Le, L.

2004-01-01

42

Refractory precursor components in an Allende ferromagnesian chondrule  

NASA Technical Reports Server (NTRS)

Chemical and petrological studies of chondrules revealed that they were formed through melting of pre-existing solid precursor materials, and that one of the refractory lithophile precursors was a high temperature condensate from the nebular gas and related to Ca, Al-rich inclusions (CAIs). Sheng et al. found relict spinel grains with isotopically fractionated Mg in plagioclase-olivine inclusions from CV chondrites and suggested that the major fractionation processes were common to CAIs and chondrules. We have determined the Mg isotopic compositon of five barred olivine chondrules and one coarse-grained rim from the Allende (CV3) meteorite. A reproducibility of instrumental isotope fractionation is plus or minus 2 per thousand per amu. The precision of the Mg-26/Mg-24 data after normalization for mass fractionation can be as good as 0.5 per thousand (2 sigma(mean)). The Mg analytical results are given and indicate that delta Mg-25/Mg-24 and sigma Mg-26 of the chondrules are normal within errors.

Misawa, Keiji; Fujita, Takashi; Kitamura, Masao; Nakamura, Noboru

1993-01-01

43

Glass-rich chondrules in ordinary chondrites  

NASA Technical Reports Server (NTRS)

There are two types of glass-rich chondrules in unequilibrated ordinary chondrites (OC): (1) porphyritic chondrules containing 55-85 vol% glass or microcrystalline mesostasis and (2) nonporphyritic chondrules, containing 90-99 vol% glass. These two types are similar in mineralogy and bulk composition to previously described Al-rich chondrules in OC. In addition to Si-, Al- and Na-rich glass or Ca-Al-rich microcrystalline mesostasis, glass-rich chondrules contain dendritic and skeletal crystals of olivine, Al2O3-rich low-Ca pyroxene and fassaite. Some chondrules contain relict grains of forsterite +/- Mg-Al spinel. We suggest that glass-rich chondrules were formed early in nebular history by melting fine-grained precursor materials rich in refractory (Ca, Al, Ti) an moderately volatite (Na, K) components (possibly related to Ca-Al-rich inclusions) admixed with coarse relict forsterite and spinel grains derived from previously disrupted type-I chondrules.

Krot, Alexander N.; Rubin, Alan E.

1994-01-01

44

Retention of sodium during chondrule melting  

NASA Technical Reports Server (NTRS)

Using published data, the differences in Na concentrations in different groups of porphyritic olivine chondrules are analyzed. The results show that Na was incorporated into type II chondrule precursors as albite and was not significantly lost during melting. Type I chondrules, which contain very low concentrations of Na, were also not depleted in Na during melting, as indicated by the lack of correlation between the Na/Al ratios and the liquidus temperatures in type I chondrules. It is concluded that the difference in Na concentration is caused by the abundance of precursor albite in type II chondrules, rather than the loss of Na from the melt.

Hewins, Roger H.

1991-01-01

45

Chondrule formation, metamorphism, brecciation, an important new primary chondrule group, and the classification of chondrules  

NASA Astrophysics Data System (ADS)

The recently proposed compositional classification scheme for meteoritic chondrules divides the chondrules into groups depending on the composition of their two major phases, olivine (or pyroxene) and the mesostasis, both of which are genetically important. The scheme is here applied to discussions of three topics: the petrographic classification of Roosevelt County 075 (the least-metamorphosed H chondrite known), brecciation (an extremely important and ubiquitous process probably experienced by >40% of all unequilibrated ordinary chondrites), and the group A5 chondrules in the least metamorphosed ordinary chondrites which have many similarities to chondrules in the highly metamorphosed 'equilibrated' chondrites. Since composition provides insights into both primary formation properties of the chondrules and the effects of metamorphism on the entire assemblage it is possible to determine the petrographic type of RC075 as 3.1 with unique certainty. Similarly, the new scheme can be applied to individual chondrules without knowledge of the petrographic type of the host chondrite, which makes it especially suitable for studying breccias. Finally, the new scheme has revealed the existence of chondrules not identified by previous techniques and which appear to be extremely important. Like group A1 and A2 chondrules (but unlike group B1 chondrules) the primitive group A5 chondrules did not supercool during formation, but unlike group A1 and A2 chondrules (and like group B1 chondrules) they did not suffer volatile loss and reduction during formation. It is concluded that the compositional classification scheme provides important new insights into the formation and history of chondrules and chondrites which would be overlooked by previous schemes.

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

1995-03-01

46

An olivine-microchondrule-bearing clast in the Krymka meteorite  

SciTech Connect

A small (150 x 200-micron-size) clast consisting of 20 vol pct olivine microchondrules (with barred and granular textures) and 80 vol pct recrystallized silicate matrix material occurs in Krymka (LL3.1). This is the fourth microchondrule-bearing clast to be described. The chondrules are zoned in FeO with concentrations increasing toward the surface. The clast most closely resembles a previously described radial-pyroxene-microchondrule-bearing clast in Piancaldoli (LL3.4). 8 refs.

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

1989-09-01

47

Constraints on the oxidation state of chondrule precursors from titanium XANES analysis of Semarkona Chondrules  

SciTech Connect

The valence of Ti is not easily reset during chondrule formation. To investigate the oxidation state of chondrule precursors, we measured the valence of Ti in olivine, pyroxene and mesostasis in a type I and a type II chondrule in Semarkona. Chondrules are very important because they formed in the solar nebula and are a major component of chondrites, the most common type of meteorite. In unequilibrated chondrites, the ferromagnesian silicates in chondrules exhibit wide ranges of fe (Fe/(Mg + Fe)). On this basis, chondrules can be divided into type I (fe < 0.1) and type II (fe > 0.1). Because a metal must be oxidized to enter a silicate, mafic silicates with low fe's are inferred to have formed in environments where little oxidized iron was available, implying reducing conditions. Therefore, type I and type II chondrules record different oxidation states. A fundamental question in the study of chondrules is whether this difference was established during chondrule formation, or if it reflects differences in their precursors. Last year, we reported the presence of trivalent Ti in refractory forsterite found in the dense fraction of the Tagish Lake CM chondrite. In addition, in the corresponding oral presentation, we reported high Ti{sup 3+}/Ti{sup 4+} in refractory forsterite containing 0.4-0.7 wt% FeO, present in a type I chondrule. Even these low FeO contents reflect a much higher fO{sub 2} than that at which pyroxene with equivalent Ti{sup 3+}/Ti{sup 4+} would be stable. This suggests that either: the equilibrium Ti{sup 3+}/Ti{sup 4+} is higher in olivine than in pyroxene for a given fO{sub 2}; or the grains formed under highly reducing conditions and the valence of Ti in chondrule olivine is a robust recorder of the oxidation state of chondrule precursors, not easily reset during chondrule formation. To improve our understanding of the origin of chondrules we have used XANES (X-ray absorption near edge structure) spectroscopy to measure the valence state of Ti in a type I and a type II chondrule in Semarkona (LL3.0). If olivine from type I chondrules contains Ti{sup 3+} and that from type II chondrules does not, that would tell us that either their precursors formed under different conditions, or that type IIs were more strongly oxidized during formation. If olivine in type II chondrules contains Ti{sup 3+}, that would probably mean that the precursors of these chondrules were originally reduced and that oxidation occurred during chondrule formation.

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

2008-04-28

48

Chondrule formation, metamorphism, brecciation, an important new primary chondrule group, and the classification of chondrules  

NASA Technical Reports Server (NTRS)

The recently proposed compositional classification scheme for meteoritic chondrules divides the chondrules into groups depending on the composition of their two major phases, olivine (or pyroxene) and the mesostasis, both of which are genetically important. The scheme is here applied to discussions of three topics: the petrographic classification of Roosevelt County 075 (the least-metamorphosed H chondrite known), brecciation (an extremely important and ubiquitous process probably experienced by greater than 40% of all unequilibrated ordinary chondrites), and the group A5 chondrules in the least metamorphosed ordinary chondrites which have many similarities to chondrules in the highly metamorphosed 'equilibrated' chondrites. Since composition provides insights into both primary formation properties of the chondruies and the effects of metamorphism on the entire assemblage it is possible to determine the petrographic type of RC075 as 3.1 with unique certainty. Similarly, the near scheme can be applied to individual chondrules without knowledge of the petrographic type of the host chondrite, which makes it especially suitable for studying breccias. Finally, the new scheme has revealed the existence of chondrules not identified by previous techniques and which appear to be extremely important. Like group A1 and A2 chondrules (but unlike group B1 chondrules) the primitive group A5 chondruies did not supercool during formation, but unlike group A1 and A2 chondrules (and like group B1 chondrules) they did not suffer volatile loss and reduction during formation. It is concluded that the compositional classification scheme provides important new insights into the formation and history of chondrules and chondrites which would be overlooked by previous schemes.

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

1995-01-01

49

Mineralogical and isotopic constraints on chondrule formation from shock wave thermal histories  

NASA Astrophysics Data System (ADS)

When a shock wave passes through a nebular gas, increasing water enrichment leads to higher temperatures and post-shock P, but lower cooling rates. A kinetic evaporation model is developed for tracking the chemical and isotopic changes that would occur in a clump of chondrule precursor dust surrounded by nebular gas in a closed system traversed by a nebular shock wave, taking into account effects of non-equilibrium melting and fractional crystallization on the liquid composition and the temperature difference between the gas and the droplet. A range of shock wave temperature-pressure histories computed for systems enriched relative to solar composition by factors of 550 in water, to achieve the redox state of chondrules, and 600 in dust, to retard evaporation, are employed, and redox changes are assumed to occur on the time-scale of heating and cooling in each. Two different system compositions are assumed, with the mean Fe/Si ratios of Types I and II chondrules. Two different textural outcomes are modeled, PO, in which nuclei are preserved and olivine crystallization begins immediately upon reaching saturation, and BO, in which no nuclei are preserved and olivine crystallization begins only after 300-400 K of supersaturation. In all cases, all iron evaporates, regardless of its oxidation state, as well as alkalis and smaller fractions of Mg and Si. In most cases, recondensation occurs on the time-scale of cooling, resulting in droplets whose bulk compositions have small isotopic anomalies in Mg, Si and Fe, comparable to those seen in bulk chondrules. Because fractional crystallization of olivine occurs before recondensation is complete, however, large isotopic variations, especially for iron, would have been recorded both within olivine crystals and between olivine and glass within these objects. Even after diffusive relaxation during crystal growth and cooling, variations in ?25Mg of several tenths of a ‰ to several ‰, in ?29Si of 0.1‰ to several ‰ and in ?56Fe of several ‰ would be measurable within large grains that grew throughout the olivine crystallization interval in many cases, and olivine-glass differences of ?several tenths of a ‰ in ?29Si, and of several ‰ in ?56Fe would be preserved. Such internal isotopic heterogeneities have not yet been observed in chondrules, suggesting that the latter did not form in these shock wave thermal histories. Suppression of production of internal isotopic variations requires heating times that are shorter by a factor of 100, combined with dust enrichments ? 6 × 104 and/or P?10-2 bar. Together with relatively high f, these constraints suggest that chondrules formed in clouds of liquid and vapor generated by impact on ice-rich planetesimals.

Fedkin, Alexei V.; Grossman, Lawrence; Ciesla, Fred J.; Simon, Steven B.

2012-06-01

50

FeO-rich, porphyritic pyroxene chondrules in unequilibrated ordinary chondrites  

Microsoft Academic Search

A suite of FeO-rich (type II), porphyritic, olivine\\/pyroxene (POP) chondrules has been studied in detail. Data for ten chondrules from Semarkona (LL3.0) are emphasized, and one chondrule from Chainpur (LL3.4) and two from Parnallee (LL3.6) are included as further examples of certain properties. The chondrules contain phenocrysts of pyroxene and olivine in varying proportions, and have Fe(Fe + Mg) >

Rhian H. Jones

1996-01-01

51

Fayalite-rich rims, veins, and halos around and in forsteritic olivines in CAIs and chondrules in carbonaceous chondrites - Types, compositional profiles and constraints of their formation  

Microsoft Academic Search

Fayalitic intergrowths in different olivine-bearing objects in the Allende and Groznaya CV3 chondrites were studied in reflected light and with the backscattered-electron-imaging technique and the concentration profiles were measured quantitatively with an automated EMPA. The information was discussed in the framework of the possible conditions and the mechanism of fayalitic olivines formation. The results suggest that the fayalitic olivine was

X. Hua; J. Adam; A. El Goresy; H. Palme

1988-01-01

52

Evidence for secondary origin of chondrules  

NASA Astrophysics Data System (ADS)

Evidence for the formation of chondrules through processes involving precursory materials rather than by direct condensation from the solar nebula is presented. The characteristics of the olivine contained in porphyritic chondrules from the Antarctic meteorite ALH-77015 are discussed, and it is pointed out that several chondrules contain two types of olivine: a type with numerous dusty inclusions and a dirty appearance which is always found near the center of the chondrules, and a second clear euhedral small grain which is found around the first type. The two types of olivine are also noted to have different chemical compositions and crystal structures, indicating that both types could not have crystallized from a liquid in a single process. The dirty, iron-rich olivine is interpreted as a relic mineral which was originally rich in iron and was not completely melted when heated. The relic olivine is thus concluded to be direct evidence for the formation of chondrules through the melting of pre-existing materials.

Nagahara, H.

1981-07-01

53

Shock Effects in Olivine from Mocs Chondrite  

NASA Astrophysics Data System (ADS)

The Mocs (syn. Moci) meteorite, classified as L6 chondrite by Van Schmus and Wood [1] and recently reclassified as L5-6 by Miura et al. [2], fell on February 3, 1882, 16.00 hrs. , over a large area (15 km by 3 km) in Transylvania (Cluj District). Olivine from six fragments of the Mocs chondrite was analyzed by optical microscopy, scanning electron microscopy with energy dispersive X-ray analysis and X-ray powder diffractometry. Olivine occurs as grains in matrix or chondrules: barred olivine chondrules, composed of parallel sets of prismatic olivine crystals and devitrified glass and porphyritic olivine chondrules, which consist mainly of fine-grained olivine crystals and glassy materials of feldspsr composition. In order to determine the mineralogical and chemical effects of shock metamorphism (induced by collisions in space of the Mocs chondrite parent body), in every thin section, ten to twenty of the largest, randomly distributed olivine single crystals were examined by optical polarizing microscope with 20X- or 40X- objectives [3] and with a JEOL JSM-5400 scanning electron microscope for higher magnifications. The mineralogical effects observed are: undulatory extinction, irregular fractures, planar fractures, mosaicism and planar deformation features. These, correlated with the presence of small amounts of maskelynite (An 12-19) indicate that the maximum shock degree this meteorite experienced was S-5 [3]. The quantitative chemical analysis of 77 olivine grains in matrix from all thin sections (6), determined by a JEOL JSM-5400 scanning electron microscope with JED 2001 energy dispersive X-ray analysis at the Yamaguchi University, shows a variation in composition from Fa23 to Fa27 mole % fayalite (Avg. Fa25; PMD 2.3%), indicative of the L-group. The Fayalite content of olivine from chondrules ranges from Fa23 to Fa27 (Avg. Fa25; PMD 1.74%). According to DEER et al. [4], olivine composition can be measured also by X-ray powder diffractometry as Fa (mol per cent) = 100-(4233.91-1494.59 x d130). By using a RIGAKU computer assisted-diffractometer (radiation Cu K alpha = 1.54059) at the Yamaguchi University, the d130 value of olivine from Mocs meteorite was calculated as 2.781 A and the fayalite content as Fa23 mole % fayalite (Forsterite-ferroan as of IMA files, 1993) consistent also with the L-group. The cell parameters and density determined from the X-ray diffraction pattern are: a=4.779; b=10.297; c=6.032; V=296.857 and Dx=3.446 g/cm3. References: [1] Van Schmus W. R. and Wood J. A. (1967) GCA, 31, 747-765. [2] Miura Y. et al. (1995) Proc. NIPR Symp. Antarct. Meteorites, 8, in press. [3] Stoffler D. et al. (1991) GCA, 55, 3845-3867. [4] Deer W. A. et al. (1992) 2nd edition, 4.

Iancu, O. G.; Miura, Y.; Iancu, G.

1995-09-01

54

Vapor saturation of sodium: Key to unlocking the origin of chondrules  

NASA Astrophysics Data System (ADS)

Sodium saturation of the vapor coexisting with chondrules at their liquidus temperatures implies that vapor-condensed phase equilibrium was reached at those temperatures for all elements more refractory than sodium. In order to investigate the possibility that chondrules formed in impact-generated plumes, equilibrium calculations were applied to droplets made from two different target compositions. Combinations of dust enrichment and Ptot were found that lead to sodium saturation, and the subsequent chemical and mineralogical evolution of the droplets was explored at those conditions. If an impact on a body of CI composition caused instantaneous heating, melting and devolatilization of the target rock and ejection of a plume of gaseous, liquid and solid matter that mixed with residual nebular gas at conditions where 50% or 90% of the sodium was retained by the resulting droplets at their liquidus temperature, their mineralogical and chemical properties would strongly resemble those of Type II chondrules. If the droplets cooled and equilibrated with the mixture of residual nebular gas and their devolatilized water, sulfur and alkalis, the fayalite content of the olivine and the chemical compositions of the bulk droplets and their glasses would closely resemble those of Types IIA and IIAB chondrules at CI dust enrichments between 400× and 800×. For 50% sodium retention, the corresponding values of Ptot are 2 bars (for 400×) and 1 bar (for 800×). For 90% retention, they are 25 and 10 bars, respectively. If, instead, the target has an anhydrous, ordinary chondrite-like composition, called H', the ejected droplets are bathed in a gas mix consisting mostly of devolatilized sulfur and alkalis with residual nebular gas, a much more reducing plume. If the conditions were such that sodium were retained by the resulting droplets at their liquidus temperature, the fayalite contents of the olivine and the chemical compositions of the bulk droplets and their glasses would closely resemble those of Types IA and IAB chondrules at H' dust enrichments between 103× and 4 × 103×. For 90% sodium retention, the corresponding values of Ptot are 15 bars (for 103×) and 2 bars (for 4 × 103×). For 50% retention, they are 2 and 8 × 10-2 bars, respectively.

Fedkin, Alexei V.; Grossman, Lawrence

2013-07-01

55

Petrology and thermal history of type IA chondrules in the Semarkona (LL3.0) chondrite  

NASA Technical Reports Server (NTRS)

Detailed petrologic studies have been made of 15 type IA, Fe-poor, porphyritic olivine chondrules in Semarkona (LL3.0). Major and minor element concentrations in olivines, pyroxenes, and mesostases, and bulk composition so the chondrules are measured along with zoning profiles in the olivine and pyroxene crystals. The mineral compositions and textures are best interpreted in terms of closed system crystallization in which the olivines and pyroxenes crystallized in situ from a melt corresponding to the bulk composition of the chondrule. Relict olivine grains are not found in the chondrules. Crystallization probably occurred at a cooling rate of the order of 1000 C/hr. Precursor materials of the chondrules were composed of two components, one refractory Ca-, Al-, and Ti-rich, and one less refractory Si-, Fe-, Cr-, and Mn-rich. The evidence is consistent with Semarkona being one of the least metamorphosed ordinary chondrites.

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

1989-01-01

56

Sulfur and sulfides in chondrules  

NASA Astrophysics Data System (ADS)

The nature and distribution of sulfides within type I PO, POP and PP chondrules of the carbonaceous chondrite Vigarano (CV3) have been studied by secondary electron microscopy and electron microprobe. They occur predominantly as spheroidal blebs composed entirely of low-Ni iron sulfide (troilite, FeS) or troilite + magnetite but in less abundance in association with metallic Fe-Ni beads in opaque assemblages. Troilites are mainly located within the low-Ca pyroxene outer zone and their amounts increase with the abundance of low-Ca pyroxene within chondrules, suggesting co-crystallization of troilite and low-Ca pyroxene during high-temperature events. We show that sulfur concentration and sulfide occurrence in chondrules obey high temperature sulfur solubility and saturation laws. Depending on the fS2 and fO2 of the surrounding gas and on the melt composition, mainly the FeO content, sulfur dissolved in chondrule melts may eventually reach a concentration limit, the sulfur content at sulfide saturation (SCSS), at which an immiscible iron sulfide liquid separates from the silicate melt. The occurrence of both a silicate melt and an immiscible iron sulfide liquid is further supported by the non-wetting behavior of sulfides on silicate phases in chondrules due to the high interfacial tension between their precursor iron-sulfide liquid droplets and the surrounding silicate melt during the high temperature chondrule-forming event. The evolution of chondrule melts from PO to PP towards more silicic compositions, very likely due to high PSiO(g) of the surrounding nebular gas, induces saturation of FeS at much lower S content in PP than in PO chondrules, leading to the co-crystallization of iron sulfides and low-Ca pyroxenes. Conditions of co-saturation of low-Ca pyroxene and FeS are only achieved in non canonical environments characterized by high partial pressures of sulfur and SiO and redox conditions more oxidizing than IW-3. Fe and S mass balance calculations also suggest the occurrence of an external source of iron, very likely gaseous, during chondrule formation. We therefore propose that enrichments in sulfur (and other volatile and moderately volatile elements) from PO to PP type I bulk chondrule compositions towards chondritic values result from progressive reaction between partially depleted olivine-bearing precursors and a volatile-rich gas phase.

Marrocchi, Yves; Libourel, Guy

2013-10-01

57

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

NASA Astrophysics Data System (ADS)

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

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

1986-02-01

58

Lunar and Planetary Science XXXV: Chondrules: The Never-Ending Story  

NASA Technical Reports Server (NTRS)

The session "Chondrules: The Never-Ending Story" included the following reports:Dust Size Distribution in Solar Nebula Inferred from Shock-Wave Heating Model for Chondrule Formation; Collisional Destruction of Chondrules in Shock Waves and Inferred Dust to Gas Mass Ratio; Evaporation and Accompanying Isotopic Fractionation of Sulfur from Fe-S Melt During Shock Wave Heating ; Evaporation During Chondrule Formation, Recondensation as Fine Particles, and the Condensation of S and Other Volatile Elements; Fe Isotopes and the Formation of Chondrules; Pristine and Processed Metal in CR Chondrites: Condensation in the Solar Nebula and Partial Reequilibration During Chondrule Formation; Variation of the Condensation Path of Supercooled Silicate Melt; Volatile and Moderately Volatile Trace Element Composition of Chondrules and Matrix from CM Chondrites: Implications for Chondrule Formation; Opaque Mineral Assemblages at Chondrule Boundaries in the Vigarano CV Chondrite: Evidence for Gas-Solid Reactions Following Chondrule Formation; Forsterite and Olivine in Sahara-97210 (LL3.2) and Chainpur (LL3.4) Chondrules: Compositional Evolution and the Influence of Melting; The Vaguries of Pyroxene Nucleation and the Resulting Chondrule Textures; Contemporaneous Formation of Chondrules in the Al-26-Mg-26 System for Ordinary and CO Chondrites; and Al-Mg Isotopic Systematics in Ferromagnesian Chondrules from the Unequilibrated Ordinary Chondrite.

2004-01-01

59

Kinetics of Melting and Applications to Chondrules  

NASA Astrophysics Data System (ADS)

The congruent melting kinetics of Amelia albite were experimentally determined at 1125o C,/ 1150o C,/ 1175o C, and 1200o C. It was determined that congruent melting is a heterogeneous process. Melting is initiated at external surfaces and cleavage planes. Melting kinetics of albite are best described using a normal growth model. Congruent melting of albite was found to be interface controlled, and rates of melting are directly proportional to the amount of superheat, and inversely proportional to viscosity. Comparison of the results obtained here with previous studies of melting kinetics on other materials (oxides and silicates) finds that the normal growth model can be used to predict melting rates within an order of magnitude. The normal growth model was used to predict congruent melting rates of forsterite and enstatite as well as other minerals which may have been present in the chondrule forming region of the solar nebula. Constraints on the peak temperatures of chondrule formation are thus obtained. Specifically, chondrules containing relict grains of forsteritic olivine and enstatitic pyroxene could not have been heated above 1901o C and 1577o C, respectively, for more than a few seconds. Reanalyses of Na-Al-rich chondrule glasses by EPMA have found that previous EPMA work resulted in loss of Na from the activated volume due to migration in an electrical potential gradient. The Na-Al-rich chondrules have Na/Al ratios of unity, suggesting that they did not lose alkalis during flash heating. Experiments reproduced the chondrule glasses and determined the formational constraints of these chondrules. Specifically, the chondrules needed to have been cooled at low rates (<6o C/hr) at the lower temperature end of chondrule formation.

Greenwood, James Paul

1997-12-01

60

Retention of sodium during chondrule melting  

SciTech Connect

Type I chondrules in unequilibrated ordinary and carbonaceous chondrites tend to be enriched in refractory elements and depleted in volatiles relative to bulk CI. Type II chondrules show chondritic concentrations of major and minor lithophile elements with Na, in particular, at or slightly above the appropriate bulk-rock values. Element ratio diagrams for chondrule bulk compositions show that Type II chondrules plot on a mixing line between forsterite and a Na phase, with Na/Al 1:1, whereas Type I compositions can be explained by mixing forsterite with melilite or CAI or other refractory component with little Na. If their bulk compositions are manipulated, subtracting Ca is diopside and Fe + Mg as olivine, the residue is 90{percent} albite and 10{percent} silica. Albite was incorporated into the precursors of Type II chondrules, which clearly have not been depleted in Na although their initial temperatures overlap with those of Type I. There is no (negative) correlation between Type I liquidus temperatures (1450-1900{degree}C) and Na/Al ratios and hence no indication of Na loss from the melt. If Type I precursors contained albite, the most aluminous chondrules would have suffered the most extreme Na loss, but these have the lowest liquidus temperatures. Their precursors were Na depleted, whereas those of Type II were Na enriched, as a function of the abundance of albite. The simplest way to obtain the bulk compositions of chondrules is to assemble condensates into precursors at different temperatures, and concentration of solids in the nebula or exceptionally rapid heating is required to preserve Na in chondrules after melting. Substantial exchange of Na occurred between chondrules and chondrite matrix during parent-body metamorphism to petrologic type 3.6.

Hewins, R.H. (Rutgers Univ., New Brunswick, NJ (USA))

1991-04-01

61

Non-spherical Lobate Chondrules in CO3.0 Y-81020: General Implications for the Formation of Low-FeO Porphyritic Chondrules in CO Chondrites  

NASA Technical Reports Server (NTRS)

Non-spherical chondrules (arbitrarily defined as having aspect ratios greater than or equal to 1.20) in CO3.0 chondrites comprise multi-lobate, distended, and highly irregular objects with rounded margins; they constitute approx. 70% of the type-I (low-FeO) porphyritic chondrules in Y-81020, approx. 75% of such chondrules in ALHA77307, and approx. 60% of those in Colony. Although the proportion of non-spherical type-I chondrules in LL3.0 Semarkona is comparable (approx. 60%), multi-lobate OC porphyritic chondrules (with lobe heights equivalent to a significant fraction of the mean chondrule diameter) are rare. If the non-spherical type-I chondrules in CO chondrites had formed from totally molten droplets, calculations indicate that they would have collapsed into spheres within approx. 10(exp -3) s, too little time for their 20-micrometer-size olivine phenocrysts to have grown from the melt. These olivine grains must therefore be relicts from an earlier chondrule generation; the final heating episode experienced by the non-spherical chondrules involved only minor amounts of melting and crystallization. The immediate precursors of the individual non-spherical chondrules may have been irregularly shaped chondrule fragments whose fracture surfaces were rounded during melting. Because non-spherical chondrules and circular chondrules form a continuum in shape and have similar grain sizes, mineral and mesostasis compositions, and modal abundances of non-opaque phases, they must have formed by related processes. We conclude that a large majority of low-FeO chondrules in CO3 chondrites experienced a late, low-degree melting event. Previous studies have shown that essentially all type-II (high-FeO) porphyritic chondrules in Y-81020 formed by repeated episodes of low-degree melting. It thus appears that the type-I and type-II porphyritic chondrules in Y-81020 (and, presumably, all CO3 chondrites) experienced analogous formation histories. Because these two types constitute approx. 95% of all CO chondrules, it is clear that chondrule recycling was the rule in the CO chondrule-formation region and that most melting events produced only low degrees of melting. The rarity of significantly non-spherical, multi-lobate chondrules in Semarkona may reflect more-intense heating of chondrule precursors in the ordinary-chondrite region of the solar nebula.

Rubin, Alan E.; Wasson, John T.

2006-01-01

62

Oxygen Isotope Systematics of Chondrules from the Least Equilibrated H Chondrite  

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

63

High precision SIMS oxygen three isotope study of chondrules in LL3 chondrites: Role of ambient gas during chondrule formation  

NASA Astrophysics Data System (ADS)

We report high precision SIMS oxygen three isotope analyses of 36 chondrules from some of the least equilibrated LL3 chondrites, and find systematic variations in oxygen isotope ratios with chondrule types. FeO-poor (type I) chondrules generally plot along a mass dependent fractionation line (? 17O ˜ 0.7‰), with ? 18O values lower in olivine-rich (IA) than pyroxene-rich (IB) chondrules. Data from FeO-rich (type II) chondrules show a limited range of ? 18O and ? 17O values at ? 18O = 4.5‰, ? 17O = 2.9‰, and ? 17O = 0.5‰, which is slightly 16O-enriched relative to bulk LL chondrites (? 17O ˜ 1.3‰). Data from four chondrules show 16O-rich oxygen isotope ratios that plot near the CCAM (Carbonaceous Chondrite Anhydrous Mineral) line. Glass analyses in selected chondrules are systematically higher than co-existing minerals in both ? 18O and ? 17O values, whereas high-Ca pyroxene data in the same chondrule are similar to those in olivine and pyroxene phenocrysts. Our results suggest that the LL chondrite chondrule-forming region contained two kinds of solid precursors, (1) 16O-poor precursors with ? 17O > 1.6‰ and (2) 16O-rich solid precursors derived from the same oxygen isotope reservoir as carbonaceous chondrites. Oxygen isotopes exhibited open system behavior during chondrule formation, and the interaction between the solid and ambient gas might occur as described in the following model. Significant evaporation and recondensation of solid precursors caused a large mass-dependent fractionation due to either kinetic or equilibrium isotope exchange between gas and solid to form type IA chondrules with higher bulk Mg/Si ratios. Type II chondrules formed under elevated dust/gas ratios and with water ice in the precursors, in which the ambient H 2O gas homogenized chondrule melts by isotope exchange. Low temperature oxygen isotope exchange may have occurred between chondrule glasses and aqueous fluids with high ? 17O (˜5‰) in LL the parent body. According to our model, oxygen isotope ratios of chondrules were strongly influenced by the local solid precursors in the proto-planetary disk and the ambient gas during chondrule melting events.

Kita, Noriko T.; Nagahara, Hiroko; Tachibana, Shogo; Tomomura, Shin; Spicuzza, Michael J.; Fournelle, John H.; Valley, John W.

2010-11-01

64

Vesicles in Experimental Chondrules as Clues to Chondrule Precursors  

NASA Astrophysics Data System (ADS)

The processing of chondrule precursors during melting is so extensive that there are few unambiguous indicators of their mineralogical composition. The specific combination of peak temperature and heating time, i.e., the heating mechanism, is also unknown. The general absence of vesicles in chondrules is a potential constraint on both questions. Meteor ablation spherules, whose origins are well understood, differ from chondrules in having abundant vesicles [1]. Chondrules simulated experimentally in a variety of ways have vesicles in many cases, but it has been suggested that the presence of vesicles rules out flash heating [2]. We therefore examine in detail the formation of vesicles in synthetic chondrules. Vesicles have been produced in experiments with long heating times [3] as well as short [2]. They are most prominent in charges that experienced low degrees of melting, probably because of surface tension effects that trap bubbles between relict grains, aided by high melt viscosity. The gas could be derived from air trapped when the powdered sample is prepared, binding agents (acetone, water), or volatiles in the starting minerals (Na, H2O). We have conducted experiments to determine the source of vesicles in synthetic chondrules initially heated slightly below the liquidus and cooled at 500 degrees C/hr. Runs made in pairs included charges with and without acetone binder and charges baked out at 200 degrees C for different lengths of time. Charges with acetone produced more vesicles, which could be avoided to some extent by preliminary baking. Charges with no binder had very few vesicles if baked for 1/2 hour. Vesicles are more prominent when using a well-sorted fine-grained powder than with an unsorted more uniform size distribution. Pulling a vacuum on pellets had no effect on subsequent vesicle development. Vesicles are unlikely to be due to loss of Na from the charge, because vesicles are equally prevalent in flash-heated charges, which retain most of their Na, and earlier experiments that spent longer times at temperature. Experiments with serpentine in the starting materials resulted in a popcorn vesicle texture with voids as large as 3 mm, like some ablation spherules [1]. Trapped air and binding agents cause most vesicles in experimental charges. Chondrule precursors must have consisted of olivine, etc., with no hydrous minerals, assembled at low pressure, or they would have generated vesicles. The absence of vesicles in chondrules does not rule out flash heating mechanisms. References: [1] Brownlee D. E. et al. (1983) In Chondrules and Their Origin (E. A. King, ed.), 10-25, LPI, Houston. [2] Wdowiak T. J. (1983) In Chondrules and Their Origin (E. A. King, ed.), 279-283, LPI, Houston. [3] Radomsky P. M. and Hewins R. H. (1990) GCA, 54, 3475-3490.

Maharaj, S. V.; Hewins, R. H.

1993-07-01

65

Composition of chondrule silicates in LL3-5 chondrites and implications for their nebular history and parent body metamorphism  

NASA Astrophysics Data System (ADS)

The composition of 75 type-IA and type-II porphyritic olivine chondrules from nine LL type 3 to type 5 chondrites was determined and was compared with that of chondrules from the Semarkona type 3.0 meteorite. Chemical data for silicates in the LL3.3-5 chondrites indicated that porphyritic olivine chondrules in these chondrites could be derived from chondrules similar to those from the Semarkona LL3.0, the least metamorphosed one of the known LL chondrites. It is shown that the chemical trends defined by the minerals of type-IA and type-II chondrules can be satisfactorily accounted for by the process of solid-state diffusive equilibration between minerals in chondrules and the opaque matrix rather than by changes in conditions during chondrule crystallization.

McCoy, T. J.; Scott, E. R. D.; Jones, R. H.; Keil, K.; Taylor, G. J.

1991-02-01

66

Petrology of FeO-poor, porphyritic pyroxene chondrules in the Semarkona chondrite  

NASA Astrophysics Data System (ADS)

The mineralogy and petrology of FeO-poor, porphyritic, pyroxene- and olivine-rich chondrules in the Semarkona (LL3.0) chondrite are described in detail. In an extension of the textural classification scheme, these chondrules are designated types IAB and IB. In type IAB chondrules, the proportion of olivine phenocrysts is between 20-80% and in type IB chondrules, olivine constitutes <20% of the phenocryst assemblage. All the chondrules studied are FeO-poor and contain olivine and low-Ca pyroxene phenocrysts in varying proportions. Olivine is present both as chadacrysts enclosed in low-Ca pyroxene and as larger phenocrysts. Ca-rich pyroxene occurs commonly as rims on low-Ca pyroxene phenocrysts. Lamellar zoning in low-Ca pyroxene, observed in backscattered electron images, is interpreted as a primary growth feature. Apparent partition coefficients between phenocrysts and mesostasis for major and minor elements are consistent with crystallization of an essentially molten chondrule at rapid cooling rates (100-1000°C/h). Within the entire type I series, there are continuous changes in textural and compositional properties that suggest common origins for all chondrules in this series. These properties include proportions of olivine and pyroxene phenocrysts, FeO contents of olivine and pyroxene phenocrysts and a complementary relationship between the proportions of refractory elements and Si-, Fe-rich precursor components in chondrule bulk compositions. Observations of the behavior of Na suggest that evaporation and recondensation of volatile elements was not an important process during formation of type I chondrules and that abundances of volatile elements were largely controlled by the abundance of a volatile-rich precursor component.

Jones, Rhian H.

1994-12-01

67

The Formation of Chondrules: Petrologic Tests of the Shock Wave Model  

NASA Technical Reports Server (NTRS)

Chondrules are mm-sized spheroidal igneous components of chondritic meteorites. They consist of olivine and orthopyroxene set in a glassy mesostasis with varying minor amounts of metals, sulfieds, oxides and carbon phases.

Connolly, H. C., Jr.; Love, S. G.

1998-01-01

68

Chondrules and matrix in the ornans CO/sub 3/ meteorite: possible precursor components  

SciTech Connect

Bulk compositions of 17 chondrules and one sample of matrix from CO3 Ornans were determined by instrumental neutron activation analysis. Chondrule precursor components deduced from chondrule compositions are characterized by: (1) common and lightly volatile siderophiles, Cr and chalcophiles, (2) refractory lithophiles and Na, (3) Mn, Si and modal pyroxene, and (4) FeO and olivine. Component 4 may be closely related to matrix material. Precursor components have now been inferred for OC, EH, CV, CM and CO chondrules. A Mn- and Si-rich component occurs exclusively among carbonaceous chondrite chondrules. Although there are significant intergroup differences, common to chondrules in all chondrite groups are refractory-lithophile-rich, common-siderophile-rich, and (with the exception of EH) common-lithophile-rich components. This indicates that the siderophile/lithophile and refractory lithophile/common lithophile fractionations recorded in chondrite whole-rocks were established prior to chondrule formation at all nebular locations.

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

1988-02-01

69

Anorthite-rich chondrules in CR and CH carbonaceous chondrites: Genetic link between Ca,Al-rich inclusions and ferromagnesian chondrules  

NASA Astrophysics Data System (ADS)

Anorthite-rich chondrules in CR and CH carbonaceous chondrites consist of magnesian low-Ca pyroxene and forsterite phenocrysts, FeNi-metal nodules, interstitial anorthite, Al-Ti-Cr-rich low-Ca and high-Ca pyroxenes, and crystalline mesostasis composed of silica, anorthite and high-Ca pyroxene. Three anorthite-rich chondrules contain relic Ca, Al-rich inclusions composed of anorthite, spinel, +/-Al-diopside, and +/-forsterite. A few chondrules contain regions which are texturally and mineralogically similar to magnesian (Type I) chondrules and consist of forsterite, low-Ca pyroxene and abundant FeNi-metal nodules. Anorthite-rich chondrules in CR and CH chondrites are mineralogically similar to those in CV and CO carbonaceous chondrites, but contain no secondary nepheline, sodalite or ferrosilite. Relatively high abundances of moderately-volatile elements such as Cr, Mn and Si in the anorthite-rich chondrules suggest that these chondrules could not have been produced by volatilization of the ferromagnesian chondrule precursors or by melting of the refractory materials only. We infer instead that anorthite-rich chondrules in carbonaceous chondrites formed by melting of the reduced chondrule precursors (olivine, pyroxenes, FeNi-metal) mixed with the refractory materials, including relic CAIs, composed of anorthite, spinel, high-Ca pyroxene and forsterite. The observed mineralogical and textural similarities of the anorthite-rich chondrules in several carbonaceous chondrite groups (CV, CO, CH, CR) may indicate that these chondrules formed in the region(s) intermediate between the regions where CAIs and ferromagnesian chondrules originated. This may explain the relative enrichment of anorthite-rich chondrules in 16O compared to typical ferromagnesian chondrules (Russell et al., 2000).

Krot, Alexander N.; Keil, Klaus

2002-01-01

70

Fe-Mn systematics of type IIA chondrules in unequilibrated CO, CR, and ordinary chondrites  

NASA Astrophysics Data System (ADS)

We have examined Fe/Mn systematics of 34 type IIA chondrules in eight highly unequilibrated CO, CR, and ordinary chondrites using new data from this study and prior studies from our laboratory. Olivine grains from type IIA chondrules in CO chondrites and unequilibrated ordinary chondrites (UOC) have significantly different Fe/Mn ratios, with mean molar Fe/Mn = 99 and 44, respectively. Olivine analyses from both these chondrite groups show well-defined trends in Mn versus Fe (afu) and molar Fe/Mn versus Fe/Mg diagrams. In general, type IIA chondrules in CR chondrites have properties intermediate between those in UOC and CO chondrites. In most UOC and CR type IIA chondrules, the Fe/Mn ratio of olivine decreases during crystallization, whereas in CO chondrites the Fe/Mn ratio does not appear to change. It is difficult to interpret the observed Fe/Mn trends in terms of differing moderately volatile element depletions inherited from precursor materials. Instead, we suggest that significant differences in the abundances of silicates and sulfides ± metals in the precursor material, as well as open-system behavior during chondrule formation, were responsible for establishing the different Fe/Mn trends. Using Fe-Mn-Mg systematics, we are able to identify relict grains in type IIA chondrules, which could be derived from previous generations of chondrules, including chondrules from other chondrite groups, and possibly chondritic reservoirs that have not been sampled previously.

Berlin, Jana; Jones, Rhian H.; Brearley, Adrian J.

2011-04-01

71

Chondrules: Their Diversity and the Role of Open-System Processes during Their Formation  

NASA Astrophysics Data System (ADS)

After classification into compositional groups using their cathodoluminescence properties, chondrules were chiseled from sections of the least metamorphosed ordinary chondrites, Semarkona and Krymka. This technique avoided biases due to size and friability and ensured that all classes were adequately sampled. The chondrules were then analyzed by instrumental neutron activation analysis and their major phases (olivine, pyroxene, metal, mesostasis) were analyzed by electron microprobe. Group A1 and A2 chondrules of Semarkona and group A3 chondrules of Krymka have all the properties expected for chondrules which experienced considerable Fe reduction and evaporative loss during their formation (elemental depletions related to volatility, Fe-poor silicates, Ni-poor metal, significant pyroxene, small sizes). This is not the case for group B1, B2, and A5 chondrules (which have unfractionated bulk silicate compositions, FeO-rich silicates, little or no metal, little pyroxene, large sizes). Group A chondrules in Semarkona generally have thicker metal-sulfide-rich rims than group B chondrules, a situation similar to that of the Murchison CM2 chondrite, except that in Murchison aqueous alteration has destroyed the metal and sulfide. Group A chrondrules sometimes show compositional zoning in their mesostases and we suggest that both mesostasis zoning and chondrule rims are the products of recondensation during chondrule formation. Cooling rates differ considerably with chondrule class. Group A1-3 and A5 chondrules cooled relatively slowly and maintained a degree of equilibrium between melt and phenocrysts, while group B1 and B2 chondrules cooled rapidly and underwent considerable supercooling. The chondrule-forming process, whatever it was, was clearly capable of acting with a variety of intensities and produced a range of cooling rates. We suggest that the diversity of chondrules cannot be attributed mainly to variations in the properties and abundances of precursors, although this can sometimes be a factor, but can be derived from a fairly similar precursor of solar composition.

Huang, Shaoxiong; Lu, Jie; Prinz, Martin; Weisberg, Michael K.; Benoit, Paul H.; Sears, Derek W. G.

1996-08-01

72

Chondrules Formed Through Cementation of Mineral Clusters by Feldspathic Melts  

NASA Astrophysics Data System (ADS)

Several rare chondrules with an unusual combination of phenocryst minerals and mesostases have been found in the Semarkona chondrite. Chondrules SC-28-1, SC-16-2, and SC-16-6 are all POP in texture with unusual CL properties. Their mesostases are greenish yellow in CL, and enclose mineral grains with no CL. The extremely high CaO contents (>17.2 wt%) of the mesostases resemble those of group A1 chondrules. However, the FeO-rich silicates (Fa(sub)>17.0%, FS(sub)>17.0%) are typical of group B1 chondrules (Lu et al., 1991; Sears et al., 1992). Such an unusual combination of melt and phenocrysts is apparent in Fig. 1, in which the CaO/MgO molar ratios in the olivines are plotted against the same ratios for the coexisting mesostasis. Most of the chondrules cluster in a well-defined region that shows a positive correlation between olivine and mesostasis CaO/MgO, suggesting that the phenocrysts were formed in situ. The three unusual chondrules, however, plot outside of this region and have unusually high CaO/MgO ratios for their mesostases. A close examination of the largest chondrule (SC-28-1) reveals that the olivines are either poikilitically enclosed in pyroxenes or form discrete clusters. All the olivines have resorbed and rounded edges. The textures are those expected from incomplete melting of pre-existing mineral clusters. Unlike the strongly zoned olivines in group B1 chondrules, olivines in this chondrule are rather uniform in composition. The pyroxenes are highly FeO-rich (Fs(sub)17.4Wo(sub)1.9) and have high-Ca pyroxene rims (Fs(sub)12.4Wo(sub)38.9) when they are in contact with the mesostasis. The mesostases of these chondrules are highly anorthitic (normative An > 80 wt%). More importantly, a sightly MgO-rich relic pyroxene core (Fs(sub)13.8Wo(sub)0.4) was found inside the FeO-rich pyroxene, which also encloses some poikilitic olivines (Fig. 2). The olivines and pyroxenes are closely associated and have Fs/Fa ratios close to one. However, the pyroxenes are not at equilibrium with the coexisting mesostases. Although the olivine compositions and textures are similar to the relic grains described by Nagahara (1983), the association of "incompatible" phenocrysts and melts in these unusual chondrules suggests that they were formed through cementation of unmelted mineral clusters by non-cogenetic melts. Considering the high CaO contents of group A1 and A2 chondrules, the viscosity of the melts must be much lower than the SiO(sub)2-rich melts of group B1 chondrules. It is therefore possible that some of these low viscosity melts may spin off from their host droplets and cement the FeO-rich mineral clusters in the vicinity. The presence of these unusual chondrules suggests that chondrule-forming processes were very dynamic and that while most chondrules were formed through in situ melting of pre-existing solid material, possibly accompanied by reduction and volatilization, some chondrules could have been formed through cementation of unmelted mineral clusters by feldspathic melts. Lu J., Sears D.W.G., Benoit P.H., Prinz M. and Weisberg M.K. (1991) Meteoritics 26, 367. Sears D.W.G., Lu J., Benoit P.H., DeHart J.M. and Lofgren G.E. (1992) Nature, in press. Nagahara H. (1983) Chondrules and Their Origins (ed. King E.A.), Lunar and Planet. Inst., Houston, 211-222. Figure 1, which in the hard copy appears here, shows CaO/MgO (molar) in olivine vs. CaO/MgO (molar) in mesostasis for Semarkona chondrules. Figure 2, which in the hard copy appears here, shows a BSE image of a fragment of chondrule SC-28-1 chiseled from Semarkona. ol = olivine, py = pyroxene (gray), rpy = relic pyroxene (dark gray), m = mesostasis.

Lu, J.

1992-07-01

73

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

NASA Astrophysics Data System (ADS)

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

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

1982-06-01

74

Composition of chondrule silicates in LL3-5 chondrites and implications for their nebular history and parent body metamorphism  

SciTech Connect

The authors petrologic studies of 75 type 1A and type 2 porphyritic olivine chondrules in nine selected LL group chondrites of type 3.3 to type 5 and comparisons with published studies of chondrules in Semarkona (LL3.0) show that compositions of silicates and bulk chondrules, but not overall chondrule textures, vary systematically with the petrologic type of the condrite. These compositional trends are due to diffusive exchange between chondrule silicates and other phases (e.g., matrix), such as those now preserved in Semarkona, during which olivines in both chondrule types gained Fe{sup 2+} and Mn{sup 2+} and lost Mg{sup 2+}, Cr{sup 3+}, and Ca{sup 2+}. In a given LL4-5 chondrite, the olivines from the two chondrule types are identical in composition. Enrichments of Fe{sup 2+} in olivine are particularly noticeable in type 1A chondrules from type 3.3-3.6 chondrites, especially near grain edges, chondrule rims, grain boundaries, and what appear to be annealed cracks. Compositional changes in low-Ca pyroxene lag behind those in coexisting olivine, consistent with its lower diffusion rates. With increasing petrologic type, low-Ca pyroxenes in type 1A chondrules become enriched in Fe{sup 2+} and Mn{sup 2+} and depleted in Mg{sup 2+}, Cr{sup 3+}, and Al{sub 3+}. These compositional changes are entirely consistent with mineral equilibration in chondritic material during metamorphism. From these compositional data alone they cannot exclude the possibility that chondritic material was metamorphosed to some degree in the nebula, but they see no evidence favoring nebula over asteroidal metamorphism, nor evidence that the chondrule reacted with nebular gases after crystallization.

McCoy, T.J. (Univ. of Hawaii, Honolulu (USA) Univ. of New Mexico, Albuquerque (USA)); Scott, E.R.D.; Keil, K.; Taylor, G.J. (Univ. of Hawaii, Honolulu (USA)); Jones, R.H. (Univ. of New Mexico, Albuquerque (USA))

1991-02-01

75

Petrology and mineralogy of Type II, FeO-rich chondrules in Semarkona (LL3.0) - Origin by closed-system fractional crystallization, with evidence for supercooling  

NASA Technical Reports Server (NTRS)

The petrology of type II porphyritic olivine chondrules in Semarkona (LL3.0) has been studied in detail. Olivines in these chondrules are euhedral, Fe-rich, and are strongly zoned from cores to rims of grains in FeO (Fa10-30), Cr2O3 (0.2-0.6 wt pct), MnO (0.2-0.7 wt pct), and CaO (0.1-0.4 wt pct). Interstitial mesostasis is rich in Si, Al, and Ca and is glassy with abundant microcrystallites. Minor minerals include troilite, Fe,Ni metal, and chromite. Some olivine grains contain euhedral, fayalite-rich cores that are probably produced during initial supercooling of the chondrule melt. Rare relict grains of forsteritic olivine have compositions very similar to olivines in type IA chondrules in Semarkona and may result from disaggregation of such chondrules. Apart from these relics, all properties of type II chondrules can be described by closed-system fractional crystallization of droplets which were essentially entirely molten. Type IA chondrules may have formed from type II chondrules by loss of Fe and volatiles. Alternatively, the two chondrule types may have formed in regions of considerable diversity in the solar nebula from precursor materials with different Fe/Mg ratios.

Jones, Rhian H.

1990-01-01

76

Fayalitic Olivine in Matrix of the Krymka LL3.1 Chondrite  

NASA Astrophysics Data System (ADS)

INTRODUCTION. Matrix persists as one of the most poorly characterized chondritic components. Its aggregational nature makes it an excellent place to search for primitive chondritic components that prevailed in the nebula during and after chondrule formation as well as components recording processes that predated and postdated accretion. In this study we focus on the occurrence and formation of the fayalitic olivine in the matrix of the Krymka LL3.1 unequilibrated ordinary chondrite. RESULTS. We limited our study to matrix areas clearly sandwiched between chondrules and did not include chondrule rims. In Krymka, matrix is coarser-grained and more Fe-rich than the rim material. Matrix is also highly variable in the size, shape and composition of its components, whereas chondrule rims appear more uniform. Krymka matrix is an aggregation of diverse mineral and lithic components. Mineral components include olivine, enstatite, diopsidic pyroxene, Ti-Al-rich Ca-pyroxene, hedenbergite, amorphous silicate material, spinel, oxides, troilite, and metal. Olivine is clearly dominant (~75% normative) and occurs in a variety of textures and compositions. Fayalitic olivine (Fa(sub)(58-94), avg.=Fa(sub)(72)) is ubiquitous throughout the matrix and occurs as (1) Isolated platelets (typically 1-3 micrometers x 3-5 micrometers, with some up to 10 micrometers in length), (2) Platelet clusters, which include randomly oriented platelets and/or intergrown platelets, (3) Platelet overgrowths which are overgrowths of parallel platelets on surfaces of larger (10-300 micrometers), more magnesian (Fa(sub)(4-34), avg.=Fa(sub)(19)) olivine fragments, (4) Euhedral-subhedral crystals (1-10 micrometers) which are often associated with and compositionally similar to platelets, and (5) Fluffy aggregates - irregularly shaped porous aggregates of submicron crystals. TEM study of the overgrowths reveals that the direction of elongation of the fayalitic platelets is along the c axis corresponding with the c direction of the larger olivine substrate. The larger, more magnesian olivine fragments are generally single crystals, but in some cases are associated with pyroxene (Fs(sub)(5-27),Wo(sub)(0.5-2)) or high-Ca pyroxene. These larger olivines are compositionally similar to chondrule olivines, whereas the fayalitic platelets are texturally and compositionally unlike olivines in chondrules. Fayalitic olivine with morphologies similar to those in Krymka matrix occur in the Chainpur LL3.4 and Ngawi LL3 matrix, but are much less common. These textures may have been characteristic of all primitive ordinary chondrite matrix, but were generally overprinted by metamorphic recrystallization. DISCUSSION: Fayalitic olivine in Krymka matrix records a process that has important implications for understanding the evolution of ordinary chondrites. It may form under oxidizing nebular conditions through solid state reactions in the presence of free silica, or vapor-solid reactions in a gas with a high silica activity [1,2]. Textural observations have been used to support a nebular origin for similar fayalitic olivine in CV3 matrix, and thermodynamic calculations indicate it could form in a nebula with a supersolar H2O/H2 ratio [3]. Vaporization experiments show that at ~10^(-6) bar and ~1650K olivine evaporates incongruently to produce a fayalitic vapor [4]. However, textural arguments favoring post-accretion formation of the fayalitic olivine in ordinary chondrite matrix and in CV3 dark inclusions have also been presented [5,6]. Thus, we consider three hypotheses for the formation of the fayalitic olivine in Krymka matrix: (1) vapor-solid reactions between a silica-rich vapor and metallic Fe degrees in the nebula, (2) vaporization of olivine-rich material to produce a fayalite vapor, followed by recondensation, or (3) parent body heating/dehydration of pre-existing phyllosilicates. Although the platy layered structure of some of the fayalitic olivine is suggestive of the layered structures of phyllosilicates and some fayalitic olivine texturally resembles saponite replacing ol

Weisberg, M. K.; Zolensky, M. E.; Prinz, M.

1995-09-01

77

Silica Under- and Oversaturated Mineral Assemblages in Chondrule Mesostases  

NASA Astrophysics Data System (ADS)

In chondrules of unequilibrated ordinary chondrites (UOC's), mesostases sometimes have compositions that are not in equilibrium with the co-existing minerals. Examples include highly silica-oversaturated mesostases in porphyritic olivine chondrules and feldspathoid-bearing mesostases in radiating pyroxene (enstatite) chondrules [1]. As part of a larger study of chondrules and clasts in UOC's, we report the results of a survey of the mineral assemblages in mesostases. Silica enrichment can manifest itself in mesostasis glass, with SiO2 contents up to 73wt%, or as silica polymorphs. Neither of these assemblages are in equilibrium with the olivine phenocrysts which comprise the bulk of the chondrules. Chondrule CC35 (type IIA [2]) separated from Chainpur (LL3.4) is an example of the latter. Mesostasis comprising 10% of CC35 contains An(sub)69-83, Ca-px (En(sub)44-52, Fs(sub)17-18, Wo(sub)31-39) and a silica polymorph. Silica oversaturation in chondrules can readily be attributed to abundant metastable olivine crystallisation, which drives residua towards quartz-, diopside- and feldspar-rich normative compositions. This could occur in chondrules crystallising as closed systems, so sampling of a larger, chemically fractionated reservoir need not necessarily be invoked, although silica-rich clasts provide evidence that an analogous process occurred in larger, open igneous systems [3]. Some silica undersaturated mineral assemblages in mesostases may also be explained by closed system crystallisation within chondrules. A radiating pyroxene chondrule in Chainpur (Chr1) contains interstitial nepheline and scapolite. Metastable crystallisation of enstatite from an initially chondritic melt composition, at low pressure, can create silica undersaturated residua. The LREE-enriched abundances of the Chr1 mesostasis minerals are consistent with this, having up to 19 x OC La and Eu/Eu* = 10 [4]. Similarly nepheline-bearing mesostasis identified in two Parnallee (LL3.6) chondrules (P6, P22), may have crystallised from residual chondrule liquid. Other feldspathoid occurrences in chondrule mesostases cannot be explained in this way. Chondrule CC1 (type IIAB, Chainpur) consists of sodalite (<= 7wt% Cl), nepheline, An(sub)88-91 and pyroxene (En(sub)75, Fs(sub)16, Wo(sub)9) dendrites in a texture suggesting devitrification. This alkaline assemblage cannot simply be a residuum following crystallisation of the phenocrysts, because they are predominantly olivine. Mobilisation of alkali fluids within UOC parent bodies, after the formation of chondrules, is probably responsible for "white matrix" [4] but low temperature metasomatism cannot be invoked for CC1 because its texture indicates that the mesostasis assemblage is derived from a melt. Instead, there could have been a late influx of alkali elements into the precursor melt. A similar conclusion was reached for the FELINE nepheline-rich clast [5] and the feldspathoid-bearing SA-1 basaltic clast [6]. If true, the CC1 precursor melt may, like that of FELINE, have originated within an open igneous system on a planetary body. Oxygen isotopic data is being collected on these and other samples in order to help ascertain whether the alkali-enriched melts envisaged are from normal OC reservoirs or exotic sources [5]. References: [1] Alexander C. M. O'D. et al. (1994) LPS XXV, 11-12. [2] Scott E. R. D. et al. (1994) GCA, 58, 1203-1209. [3] Bridges J. C. et al. (1995) Meteoritics, submitted. [4] Hutchison R. et al. (1994) Meteoritics, 29, 476-477. [5] Bridges J. C. et al. (1995) Proc. NIPR Symp. Antarct. Met., 8, in press. [6] Kennedy A. K. and Hutcheon I. D. (1992) Meteoritics, 27, 539-554.

Bridges, J. C.; Hutchison, R.

1995-09-01

78

Three Unusual Chondrules in the Bovedy (L3) Chondrite  

NASA Astrophysics Data System (ADS)

The Bovedy (L3) chondrite [1] has recently been studied petrographically using SEM and EMPA as part of a general review of the Irish meteorites. The following chondrules are notable: Chondrule 1. A covered thin-section of the Bovedy (Sprucefield) meteorite contains a very highly-strained, ellipsoidal, radiating pyroxene chondrule with a semi-major axis of 2mm. The elongation ratio, 2.6 x, is higher than values published elsewhere [2]. Chondrule 2. A slab of Bovedy (~48 cm^2) contains an exceptionally large, ellipsoidal, porphyritic olivine chondrule (semi-major axis = 1.4 cm, minor axis = 0.8 cm). This is among the largest droplet chondrule on record [2]. The chondrule is texturally identical to other PO chondrules in the meteorite. Chondrule 3. A polished thin-section, prepared from the above slab, contains an ellipsoidal-to-irregular shaped glassy chondrule (Fig. 1). SEM and EMPA confirm a composition of pyroxenitic glass (brown) with globular and elongate inclusions of silica glass (colorless). Representative EMPA of the brown glass (in wt%) is: SiO2 57.49, Al2O3 0.93, Cr2O3 0.38, FeO 14.22, MnO 0.63, MgO 23.32, CaO 2.69, Na2O 1.03 (no other elements detected). This can be recast as a pyroxene with formula Ca(sub)0.10 Na(sub)0.07 Fe(sub)0.43Mg(sub)1.26Al(sub)0.04 Cr(sub)0.01Mn(sub)0.02Si(sub)2.08O(sub)6. The composition corresponds closely with that reported by [3] for a silica pyroxenite clast from the same meteorite. It suggests that the chondrule was derived by rapid melting of the material represented by the clast, which has been interpreted as an igneous fractionate formed in a planetary environment. References: [1] Graham A. L. et al. (1976) GCA, 40, 529-535. [2] Grossman J. N. et al. (1988) In Meteorites and the Early Solar System (J. F. Kerridge and M. S. Matthews, eds.), 619-659, Univ. Arizona. [3] Ruzicka A. and Boynton W. V. (1992) Meteoritics, 27, 283. Fig. 1, which appears here in the hard copy, shows a photograph of chondrule 3 photographed in plane polarized light. Darker areas within chondrule boundary are pyroxenitic glass. The (white) globular and elongate inclusions are silica glass. The width of the image is 1.7 mm across.

Hill, H. G. M.

1993-07-01

79

Temperature conditions for chondrule formation  

NASA Technical Reports Server (NTRS)

An attempt is made to constrain the chondrule-forming process from dynamic crystallization experiments on chondrule analogs and from correlations between texture and bulk composition in natural chondrules. Liquidus temperatures for chondrules from unequilibrated chondrites are calculated using Herzberg's (1979) method. The paper then infers whether each chondrule formed above, at, or below its liquidus based on textures produced in experiments. A range of temperatures to which chondrules may have been initially heated is then derived from the texture-composition-temperature relationships. Finally, the role of dust seeding, or external heterogeneous nucleation, in producing chondrule textures is examined.

Hewins, Roger H.; Radomsky, Patrick M.

1990-01-01

80

Experimental petrology of meteorites: Phosphorus and oxygen isotopes in olivine  

NASA Astrophysics Data System (ADS)

Experiments have been conducted to investigate the exchange and behavior of phosphorus and oxygen isotopes in olivine of extraterrestrial materials. The first project concentrated on determining the conditions necessary for the formation of phosphoran olivine in pallasite meteorites. Results indicate that phosphoran olivine forms during rapid crystallization and not subsolidus diffusion. Phosphoran olivine does not persist if the system closely approaches equilibrium. Models proposing that pallasites represent samples of a core- mantle boundary of a differentiated asteroid are inconsistent with these results. The second and third projects involved the exchange of oxygen isotopes in chondrules at nebular pressures and temperatures, first observing gas-melt exchange, then olivine-melt exchange. In the gas-melt exchange experiments, a low pressure flow of carbon monoxide gas was reacted with an olivine-normative melt to simulate exchange with a nebular gas in the early solar system. No isotopic exchange between carbon monoxide and olivine-rich melt was detected. However, the experiments did demonstrate for the first time, the kinetic evaporation of oxygen. It was proposed that water vapor was likely the major oxygen-bearing species to exchange oxygen in the early solar nebula and carbon monoxide contributed to this only through reactions with the water vapor or ambient hydrogen. The final experiments involved exchange of oxygen between relict chondrule olivine, their overgrowths, and the chondrule melt. It was determined that Fe-Mg diffusion can obscure relict grains during chondrule crystallization. However, the original oxygen isotopic composition of those grains will remain intact. Durations of weeks at high temperature are required to obscure the oxygen signature by diffusion. Relict olivine grains are more prevalent than previously estimated and probably occur in more than 30% of all chondrules.

Boesenberg, Joseph S.

81

A RELICT Spinel Grain in an Allende Ferromagnesian Chondrule  

NASA Astrophysics Data System (ADS)

It is suggested that one of the refractory lithophile precursors in CV-CO chondrules was a hightemperature condensate from the nebular gas and was related to Ca,Al-rich inclusions (CAIs) [1-3]. However, little is known about refractory siderophile precursors in chondrules [4]. Allende barred olivine chondrule R-11 consists mainly of olivine (Fa(sub)7- 18), pyroxene (En(sub)93Fs(sub)1Wo(sub)6, En(sub)66Fs(sub)1Wo(sub)33), plagioclase (An(sub)80), Fe-poor spinel, and alkali-rich glass. The CI- chondrite normalized REE pattern of the chondrule, excluding a spinel grain, are fractionated, HREEdepleted (4.6-7.8 x CI) with a large positive Yb anomaly. The REE abundances are hump-shaped functions of elemental volatility, moderately refractory REE-enriched, suggesting that the refractory lithophile precursor component of R-11 could be a condensate from the nebular gas and related to Group 11 CAIs [1,2]. An interior portion of spinel is almost Fe-free, but in an outer zone (2040 micrometers in width) FeO contents increase rapidly. TiO(sub)2, Cr(sub)2O(sub)3, and V(sub)2O(sub)3 contents in core spinel are less than 0.5%, which is different from the V-rich nature of spinel in fluffy Type A CAIs [5]. The Fe-Mg zoning of spinel may have been generated by diffusional emplacement of Mg and Fe during chondrule-forming events. The spinel contains silicate inclusions and tiny metallic grains. The largest silicate inclusion is composed of Al,Ti-rich pyroxene and Ak 40 melilite. One of the submicrometersized grains was analyzed by SEM-EDS and found to be composed of refractory Pt-group metals with minor amounts of Fe and Ni. This is the first occurrence of refractory Pt-group metal nuggets in a ferromagnesian chondrule from the Allende meteorite. Tungsten, Os, Ir, Mo, and Ru are enriched 2-6 x 10^5 relative to CIs, and abundances of Pt and Rh decrease 2-10 x 10^4 with increasing volatility. In addition, abundances of Fe and Ni in the nugget are equal to or less than that CI chondrites. A depletion of Mo relative to other refractory metals may have resulted from high- temperature oxidation [6]. Chondrule R-11 exhibits both similarities (spinel and plagioclase chemistry; Group II REE pattern) and differences (fassaite chemistry; existence of refractory Pt-group metal nuggets and melilite) with respect to POIs [3] carrying isotopically fractionated Mg. Refractory Pt-group metal nuggets in CAIs are considered to have been produced during high-temperature events (at least 1300 degrees C) before total condensation of Fe in the early solar nebula [8-10]. In analogy with the formation history with CAIs, we suggest that one of the refractory siderophile precursor components of Allende chondrules is a high-temperature condensate from the nebular gas and is associated with refractory oxide and silicates. References: [1] Misawa K. and Nakamura N. (1988) GCA, 52, 1669. [2] Misawa K. and Nakamura N. (1988) Nature, 334, 47. [3] Sheng Y. J. et al. (1991) GCA, 55, 581. [4] Grossman J. N. et al. (1988) In Meteorites and the Early Solar System (J. F. Kerridge and M. S. Matthews, eds.), 619, Univ. of Arizona. [5] MacPherson G. J. and Grossman L. (1984) GCA, 48, 29. [6] Fegley B. Jr. and Palme H. (1985) EPSL, 72, 311. [7] Wark D. A. and Lovering J. F. (1976) LS VII, 912. [8] Palme H. and Wlotzka F. (1976) EPSL, 33, 45. [9] El Goresy A. et al. (1978) Proc. LPSC 9th, 1279. [10] Blander M. and Fuchs L. H. (1980) Proc. LPSC 11th, 929.

Misawa, K.; Fujita, T.; Kitamura, M.; Nakamura, N.; Yurimoto, H.

1993-07-01

82

Are some chondrule rims formed by impact processes? Observations and experiments.  

PubMed

Observations and experimental evidence are presented to support the hypothesis that high-speed impact into a parent body regolith can best explain certain textures and compositions observed for rims on some chondrules. A study of 19 interclastic rimmed chondrules in the Weston (H 3/4) ordinary chondrite shows that two main rim types are present on porphyritic olivine-pyroxene (POP) and porphyritic pyroxene (PP) chondrules: granular and opaque rims. Granular rims are composed of welded, fine-grained host chondrule fragments. Bulk compositions of granular rims vary among chondrules, but each rim is compositionally dependent on that of the host chondrule. Opaque rims contain mineral and glass compositions distinctly different from those of the host, partially reacted chondrule mantle components, and some matrix grains. Opaque rims are greatly enriched in FeO (up to 63 wt%). The original chondrule pyroxene compositional zonation patterns and euhedral grain outlines are discontinuous at the chondrule/rim interface. Opaque rims are dominated by fayalitic olivine (Fa92-56), with high Al2O3 content (0.78-3.15%), which makes them distinctly different from primary olivine, but similar to Fe-olivine in chondrule rims of other meteorites. Thin zones of chondrule minerals adjacent to the present rims are intermediate in FeO content between the Mg-rich interior and the Fe-rich rim, which indicates a reaction relationship. Regardless of conclusions drawn regarding other types of rims, granular and opaque rim characteristics appear to be inconsistent with nebular condensation, in that host and matrix fragments are included within the rim. We have initiated a series of experiments, using the Ames two-stage light gas gun, to investigate the hypothesis that the Weston chondrule rims are the result of thermal and mechanical alteration upon impact into a low-density medium. Clusters of approximately 200-micron-sized silicate particles were fired into aerogel (density = 0.1 g cm-3) at velocities of 5.6, 4.7, and 2.2 km sec-1. Recovered grains show characteristics that range from fragmented projectile grains mixed with melted aerogel that nearly rim the grains to grains that have melted aerogel clumps mixed with partially melted projectile. These experimental results demonstrate that rim-like thermal and mechanical alteration of projectiles can result from a high-velocity encounter with a low-density target. Therefore, experiments using appropriately chosen projectile and target materials can provide a test of the hypothesis that chondrule rims common to Weston and possibly other ordinary chondrites were formed by such a process. PMID:11538105

Bunch, T E; Schultz, P; Cassen, P; Brownlee, D; Podolak, M; Lissauer, J; Reynolds, R; Chang, S

1991-01-01

83

High Cooling Rates of Type-II Chondrules: Limited Overgrowths on Phenocrysts Following the Final Melting Event  

NASA Technical Reports Server (NTRS)

In a study of type-II chondrules in Y81020 Wasson and Rubin (2003) described three kinds of evidence indicating that only minor (4-10 m) olivine growth occurred following the final melting event: 1) Nearly all (>90%) type-II chondrules in CO3.0 chondrites contain low-FeO relict grains; overgrowths on these relicts are narrow, in the range of 2-12 m. 2) Most type-II chondrules contain small (10-20 m) FeO-rich olivine grains with decurved surfaces and acute angles between faces indicating that the grains are fragments from an earlier generation of chondrules; the limited overgrowth thicknesses following the last melting event are too thin to disguise the shard-like nature of these small grains. 3) Most type-II chondrules contain many small (<20 m) euhedral or subhedral phenocrysts with central compositions that are much more ferroan than the centers of the large phenocrysts; their small sizes document the small amount of growth that occurred following the final melting event.We have additional data on chondrules in Y81020 and Semarkona, and we have reinterpreted observations of Jones (1990). The striking feature of this chondrule is the large number of tiny fragments. The chondrule precursor initially consisted of crushed olivine.

Wasson, John T.; Rubin, Alan E.

2003-01-01

84

Chondrule Crystallization Experiments  

NASA Technical Reports Server (NTRS)

Given the great diversity of chondrules, laboratory experiments are invaluable in yielding information on chondrule formation process(es) and for deciphering their initial conditions of formation together with their thermal history. In addition, they provide some critical parameters for astrophysical models of the solar system and of nebular disk evolution in particular (partial pressures, temperature, time, opacity, etc). Most of the experiments simulating chondrules have assumed formation from an aggregate of solid grains, with total pressure of no importance and with virtually no gain or loss of elements from or to the ambient environment. They used pressed pellets attached to wires and suffered from some losses of alkalis and Fe.

Hweins, R. H.; Connolly, H. C., Jr.; Lofgren, G. E.; Libourel, G.

2004-01-01

85

Micromagnetic and Microstructural Analyses in Chondrules of the Allende Chondritic Meteorite  

NASA Astrophysics Data System (ADS)

Results of micromagnetic and microstructural studies of individual chondrules from the Allende carbonaceous meteorite are presented. Allende is a CV3 carbonaceous chondrite consisting mainly of chondrules, matrix with CAIs, olivine inclusions, opaque minerals, and lithic and mineral fragments. The macroscopic texture of Allende reflects abundance of chondrules of sub-millimeter size within the aphanitic black matrix. Allende is part of the oxidized chondrites with an anhydrous mineralogy, with hydrous phases restricted to chondrules and CAIs. Studies indicate secondary alteration processes affecting Allende mineralogy and composition. Chondrules separated for this study have diameters varying from 0.08 to 0.45 cm. Micromagnetic analyses in the chondrules identify magnetite as a main magnetic phase. Magnetic hysteresis data in terms of plots of parameter ratios suggest pseudo-single domain and multidomain states. Relationships of hysteresis parameters with chondrule size, mass, density and shape are obtained. Morphology, internal structure and elemental composition are investigated by scanning electron microscope and WDS spectrometer analyses using a JEOL microprobe. Relationships are correlated to the internal microstructures and elemental compositional variation within the chondrules. Results show distinct mineralogical assemblages with spatial compositional variation, which are correlated to chondrule size and shape.

Floresgutierrez, D.; Urrutia Fucugauchi, J.

2008-12-01

86

Volatiles in Chainpur chondrules  

NASA Technical Reports Server (NTRS)

A study of volatile element concentrations in individual chondrules in the Chainpur LL3 chondrite is presented. Volatile elements differing in geochemical behavior tended to vary randomly and correlated variations were observed only for those elements inferred to occupy similar mineral sites. Variations in Co and Ni in kamacite show that metal in chondrule interiors has not approached equilibrium, and that postformational element distribution has mainly altered siderophile concentrations in surface metal grains, and has probably left ionic species unaltered. Etching to remove 3 to 5% of the chondrule dissolved siderophiles, enhanced Zn and Na volatiles relative to nonvolatile Cr in the etch, and produced a large Cd enhancement. If metamorphic redistribution of nonsiderophile volatiles was neglible, their high concentrations are inconsistent with chondrule formation by direct condensation, and models involving sudden melting of preexisting solids can explain the observations but require rapid cooling to prevent volatile loss.

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

1979-01-01

87

Primordial oxygen isotope reservoirs of the solar nebula recorded in chondrules in Acfer 094 carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

Highly precise and accurate ion microprobe analyses of oxygen three-isotope ratios in chondrules from the Acfer 094, one of the most primitive carbonaceous chondrites, show that chondrules preserve evidence for oxygen isotope heterogeneity in chondrule-forming regions of the solar nebula. Identical ?17O values in most minerals and glass within each chondrule indicate that the oxygen isotope ratio in chondrule melt did not change during or after crystallization. Nearly half of the chondrules studied contain small amounts of olivine grains that have an oxygen isotope anomaly relative to other minerals and glass in the same chondrule. Most chondrules in Acfer 094 can be classified into two oxygen isotope groups (?17O ˜ -2‰ and ?17O ˜ -5‰) indicating that the final melting of chondrules occurred within two distinct oxygen isotope reservoirs, probably representing the local protoplanetary disk immediately before planetesimal formation. One of these reservoirs (?17O ˜ -2‰) is observed from chondrules in other carbonaceous chondrites and from crystalline silicates in comet Wild 2, suggesting that crystalline silicates formed in an oxygen isotope reservoir of ?17O ˜ -2‰ were widely distributed in the outer asteroid belt and throughout the outer solar nebula. Oxygen three-isotope ratios of minerals in chondrules from Acfer 094 are distributed along a newly defined Primitive Chondrule Minerals (PCM) line, which has slope ˜1 [?17O = (0.987 ± 0.013) × ?18O - (2.70 ± 0.11)] and intersects the terrestrial fractionation line at ?18O = 5.8 ± 0.4‰. These data are distinct from, and plot between, the CCAM, and Young and Russell lines. The PCM line is interpreted to represent the mixing trend of extreme oxygen isotope reservoirs in the early solar system that were the primary oxygen isotope reservoir of solids that accreted to form planets including the Earth.

Ushikubo, Takayuki; Kimura, Makoto; Kita, Noriko T.; Valley, John W.

2012-08-01

88

Ubiquitous low-FeO relict grains in type II chondrules and limited overgrowths on phenocrysts following the final melting event  

Microsoft Academic Search

Type II porphyritic chondrules commonly contain several large (>40 ?m) olivine phenocrysts; furnace-based cooling rates based on the assumption that these phenocrysts grew in a single-stage melting-cooling event yield chondrule cooling-rate estimates of 0.01–1 K s?1. Because other evidence indicates much higher cooling rates, we examined type II chondrules in the CO3.0 chondrites that have experienced only minimal parent-body alteration.

John T. Wasson; Alan E. Rubin

2003-01-01

89

Deformation and thermal histories of chondrules in the Chainpur (LL3. 4) chondrite  

SciTech Connect

The results of optical and TEM studies of chondrules in the Chainpur (LL3.4) chondrite are presented. Results were obtained, using a microprobe, from quantitative microchemical analyses for Mg, Fe, Si, and Ca for the chondrule olivine and pyroxene, showing that chondrules in the Chainpur chondrite experienced varied degrees of annealing and deformation. It is suggested that Chainpur may be an agglomerate of a breccia that experienced little overall deformation or heating during and after the final accumulation and compaction of its constituents. 75 refs.

Ruzicka, A. (Arizona Univ., Tucson (USA))

1990-06-01

90

Deformation and thermal histories of chondrules in the Chainpur (LL3.4) chondrite  

NASA Astrophysics Data System (ADS)

The results of optical and TEM studies of chondrules in the Chainpur (LL3.4) chondrite are presented. Results were obtained, using a microprobe, from quantitative microchemical analyses for Mg, Fe, Si, and Ca for the chondrule olivine and pyroxene, showing that chondrules in the Chainpur chondrite experienced varied degrees of annealing and deformation. It is suggested that Chainpur may be an agglomerate of a breccia that experienced little overall deformation or heating during and after the final accumulation and compaction of its constituents.

Ruzicka, A.

1990-06-01

91

Chondrule rims and interchondrule matrix in UOC  

NASA Technical Reports Server (NTRS)

Opaque rims around chondrules and clasts were distinguished from opaque, interchondrule matrix apparently unrelated spatially to chondrules and clasts. Microprobe and electron microscope techniques were used. The mean chemical composition for dark rim and matrix in Bishunpur and Tieschitz are similar to the opaque matrix of Huss, et al. However, the mean dark rim compositions in Bishunpur have significantly higher Fe, and lower Na, K, Al and Si than opaque interchondrule matrix. The opaque matrix of Huss, et al, essentially lies between these compositions. In Tieschitz only rim material was observed. In Tieschitz the rims are Si-poor and dominated by normative olivine (Fo50). Again there is an Na, K, Al component but is often nepheline normative rather than albitic. It too is probably present as glass, Ashworth (pers.comm.). In Bishunpur rims as well as the silicate-FeS, FeNi layering described by Allen, et al, discontinuous layering was observed within the silicate portion. This is apparently due to variations in the proportions of the components, particularly in the glassy phase. In Bishunpur there is a strong genetic link between matrix and rims, although rims seem to have formed under different, possibly more oxidizing, conditions. Also the presence of the same component in rims, matrix chondrules, and clasts suggests a common source.

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

1984-01-01

92

Petrology and oxygen isotope compositions of chondrules in E3 chondrites  

NASA Astrophysics Data System (ADS)

Chondrules in E3 chondrites differ from those in other chondrite groups. Many contain near-pure endmember enstatite (Fs <1). Some contain Si-bearing FeNi metal, Cr-bearing troilite, and, in some cases Mg, Mn- and Ca-sulfides. Olivine and more FeO-rich pyroxene grains are present but much less common than in ordinary or carbonaceous chondrite chondrules. In some cases, the FeO-rich grains contain dusty inclusions of metal. The oxygen three-isotope ratios (? 18O, ? 17O) of olivine and pyroxene in chondrules from E3 chondrites, which are measured using a multi-collection SIMS, show a wide range of values. Most enstatite data plots on the terrestrial fractionation (TF) line near whole rock values and some plot near the ordinary chondrite region on the 3-isotope diagram. Pyroxene with higher FeO contents (˜2-10 wt.% FeO) generally plots on the TF line similar to enstatite, suggesting it formed locally in the EC (enstatite chondrite) region and that oxidation/reduction conditions varied within the E3 chondrite chondrule-forming region. Olivine shows a wide range of correlated ? 18O and ? 17O values and data from two olivine-bearing chondrules form a slope ˜1 mixing line, which is approximately parallel to but distinct from the CCAM (carbonaceous chondrite anhydrous mixing) line. We refer to this as the ECM (enstatite chondrite mixing) line but it also may coincide with a line defined by chondrules from Acfer 094 referred to as the PCM (Primitive Chondrite Mineral) line ( Ushikubo et al., 2011). The range of O isotope compositions and mixing behavior in E3 chondrules is similar to that in O and C chondrite groups, indicating similar chondrule-forming processes, solid-gas mixing and possibly similar 16O-rich precursors solids. However, E3 chondrules formed in a distinct oxygen reservoir. Internal oxygen isotope heterogeneity was found among minerals from some of the chondrules in E3 chondrites suggesting incomplete melting of the chondrules, survival of minerals from previous generations of chondrules, and chondrule recycling. Olivine, possibly a relict grain, in one chondrule has an R chondrite-like oxygen isotope composition and may indicate limited mixing of materials from other reservoirs. Calcium-aluminum-rich inclusions (CAIs) in E3 chondrites have petrologic characteristics and oxygen isotope ratios similar to those in other chondrite groups. However, chondrules from E3 chondrites differ markedly from those in other chondrite groups. From this we conclude that chondrule formation was a local event but CAIs may have all formed in one distinct place and time and were later redistributed to the various chondrule-forming and parent body accretion regions. This also implies that transport mechanisms were less active at the time of and following chondrule formation.

Weisberg, Michael K.; Ebel, Denton S.; Connolly, Harold C.; Kita, Noriko T.; Ushikubo, Takayuki

2011-11-01

93

Chondrules and the Protoplanetary Disk  

NASA Astrophysics Data System (ADS)

Part I. Introduction: 1. Chondrules and the protoplanetary disk: An overview R. H. Hewins; Part. II. Chonrules, Ca-Al-Rich Inclusions and Protoplanetary Disks: 2. Astronomical observations of phenomena in protostellar disks L. Hartmann; 3. Overview of models of the solar nebula: potential chondrule-forming environments P. Cassen; 4. Large scale processes in the solar nebula A. P. Boss; 5. Turbulence, chondrules and planetisimals J. N. Cuzzi, A. R. Dobrovolskis and R. C. Hogan; 6. Chondrule formation: energetics and length scales J. T. Wasson; 7. Unresolved issues in the formation of chondrules and chondrites J. A. Wood; 8. Thermal processing in the solar nebula: constraints from refractory inclusions A. M. Davis and G. J. MacPherson; 9. Formation times of chondrules and Ca-Al-Rich inclusions: constraints from short-lived radionuclides T. D. Swindle, A. M. Davis, C. M. Hohenberg, G. J. MacPherson and L. E. Nyquist; 10. Formation of chondrules and chondrites in the protoplanetary nebula E. R. D. Scott, S. G. Love and A. N. Krot; Part III. Chondrule precursors and multiple melting: 11. Origin of refractory precursor components of chondrules K. Misawa and N. Nakamura; 12. Mass-independent isotopic effects in chondrites: the role of chemical processes M. H. Thiemens; 13. Agglomeratic chondrules: implications for the nature of chondrule precursors and formation by incomplete melting M. K. Weisberg and M. Prinz; 14. Constraints on chondrule precursors from experimental Data H. C. Connolly Jr. and R. H. Hewins; 15. Nature of matrix in unequilibrated chondrites and its possible relationship to chondrules A. J. Brearly; 16. Constraints on chondrite agglomeration from fine-grained chondrule Rims K. Metzler and A. Bischoff; 17. Relict grains in chondrules: evidence for chondrule recycling R. H. Jones; 18. Multiple heating of chondrules A. E. Rubin and A. N. Krot; 19. Microchondrule-bearing chondrule rims: constraints on chondrule formation A. N. Krot and A. E. Rubin; Part IV. Heating, Cooling and Volatiles: 20. A dynamic crystallization model for chondrule melts G. E. Lofgren; 21. Peak temperatures of flash-melted chondrules R. H. Hewins and H. C. Connolly Jr.; 22. Congruent melting kinetics: constraints on chondrule formation J. P. Greenwood and P. C. Hess; 23. Sodium and sulfur in chondrules: heating time and cooling curves Y. Yu, R. H. Hewins and B. Zanda; 24. Open-system behaviour during chondrule formation D. W. G. Sears, S. Huang and P. H. Benoit; 25. Recycling and volatile loss in chondrule formation C. M. O'D. Alexander; 26. Chemical fractionations of chondrites: signatures of events before chondrule formation J. N. Grossmann; Part V. Models of Chondrule Formation: 27. A concise guide to chondrule formation models A. P. Boss; 28. Models for multiple heating mechanisms L. L. Hood and D. A. Kring; 29. Chondrule formation in the accretional shock T. V. Ruzmaikina and W. H. Ip; 30. The protostellar jet model of chondrule formation K. Liffman and M. Brown; 31. Chondrule formation in lightning discharges: status of theory and experiments M. Horanyi and S. Robertson; 32. Chondrules and their associates in ordinary chondrites: a planetary connection? R. Hutchinson; 33. Collision of icy and slightly differentiated bodies as an origin for unequilibriated ordinary chondrites M. Kitamura and A. Tsuchiyama; 34. A chondrule-forming scenario involving molten planetisimals I. S. Sanders.

Hewins, R. H.; Jones, Rhian; Scott, Ed

2011-03-01

94

Origin of magnetite in oxidized CV chondrites: in situ measurement of oxygen isotope compositions of Allende magnetite and olivine  

Microsoft Academic Search

Magnetite in the oxidized CV chondrite Allende mainly occurs as spherical nodules in porphyritic-olivine (PO) chondrules, where it is associated with Ni-rich metal and\\/or sulfides. To help constrain the origin of the magnetite, we measured oxygen isotopic compositions of magnetite and coexisting olivine grains in PO chondrules of Allende by an in situ ion microprobe technique. Five magnetite nodules form

Byeon-Gak Choi; Kevin D. McKeegan; Laurie A. Leshin; John T. Wasson

1997-01-01

95

Evidence for primitive nebular components in chondrules from the Chainpur chondrite  

NASA Astrophysics Data System (ADS)

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

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

1982-06-01

96

Experimental investigation of the nebular formation of chondrule rims and the formation of chondrite parent bodies  

NASA Astrophysics Data System (ADS)

We developed an experimental setup to test the hypothesis that accretionary rims around chondrules formed in the solar nebula by accretion of dust on the surfaces of hot chondrules. Our experimental method allows us to form dust rims around chondrule analogs while levitated in an inert-gas flow. We used micrometer-sized powdered San Carlos olivine to accrete individual dust particles onto the chondrule analogs at room temperature (20 °C) and at 1100 °C. The resulting dust rims were analyzed by means of two different techniques: non-destructive micro computer tomography, and scanning electron microscopy. Both methods give very similar results for the dust rim structure and a mean dust rim porosity of 60% for the hot coated samples, demonstrating that both methods are equally well suited for sample analysis. The chondrule analog's bulk composition has no measurable impact on the accretion efficiency of the dust. We measured the chemical composition of chondrule analog and dust rim to check whether elemental exchange between the two components occurred. Such a reaction zone was not found; thus, we can experimentally confirm the sharp border between chondrules and dust rims described in the literature. We adopted a simple model to derive the degree of post-accretionary compaction for different carbonaceous chondrites. Moreover, we measured the rim porosity of a fragment of Murchison meteorite, analyzed it with micro-CT and found rim porosities with this technique that are comparable to those described in the literature.

Beitz, E.; Blum, J.; Mathieu, R.; Pack, A.; Hezel, D. C.

2013-09-01

97

The formation of chondrules by open-system melting of nebular condensates  

NASA Astrophysics Data System (ADS)

Experiments were conducted under canonical nebular conditions to see whether the chemical compositions of the various chondrule types can be derived from a single CI-like starting material by open-system melting and evaporation. Experimental charges, produced at 1580 °C and P H2 of 1.31×10 -5 atm over 1 to 18 hours, consisted of only two phases, porphyritic olivine crystals in glass. Sulfur, metallic-iron and alkalis were completely evaporated in the first minutes of the experiments and subsequently the main evaporating liquid oxides were FeO and SiO 2. Olivines from short runs (2-4 hours) have compositions of Fo 83-Fo 89, as in Type IIA chondrules, while longer experimental runs (12-18 hours) produce ˜Fo 99 olivine, similar to Type IA chondrules. The concentration of CaO in both olivine (up to 0.6 wt.%) and glass, and their Mg#, increased with increasing heating duration. Natural chondrules also show increasing CaO with decreasing S, alkalis, FeO and SiO 2. The similarities in bulk chemistry, mineralogy and textures between Type IIA and IA chondrules and the experimental charges demonstrate that these chondrules could have formed by the evaporation of CI precursors. The formation of silica-rich chondrules (IIB and IB) by evaporation requires a more pyroxene-rich precursor. Based on the FeO evaporation rates measured here, Type IIA and IA chondrules, were heated for at least ˜0.5 and ˜3.5 h, respectively, if formed at 1580 °C and P H2 of 1.31×10 -5 atm. Type II chondrules may have experienced higher cooling-rates and less evaporation than Type I. The experimental charges experienced free evaporation and exhibited heavy isotopic enrichments in silicon, as well as zero concentrations of S, Na and K, which are not observed in natural chondrules. However, experiments on potassium-rich melts at the same pressure but in closed capsules showed less evaporation of K, and less K isotopic mass fractionation, than expected as a function of decreasing cooling rate. Thus the environment in which chondrules formed is as important as the kinetic processes they experienced. If chondrule formation occurred under conditions in which evaporated gases remained in the vicinity of the residual melts, the extent of evaporation would be reduced and back reaction between the gas and the melt could contribute to the suppression of isotopic mass fractionation. Hence chondrule formation could have involved evaporative loss without Rayleigh fractionation. Volatile-rich Type II and volatile-poor Type I chondrules may have formed in domains with high and low chondrule concentrations, and high partial pressures of lithophile elements, respectively.

Cohen, Bosmat A.; Hewins, Roger H.; Alexander, Conel M. O.'D.

2004-04-01

98

A Parent Magma for the Nakhla Martian Meteorite: Reconciliation of Estimates from 1-Bar Experiments, Magmatic Inclusions in Olivine, and Magmatic Inclusions in Augite  

NASA Technical Reports Server (NTRS)

The composition of the parent magma for the Nakhla (martian) meteorite has been estimated from mineral-melt partitioning and from magmatic inclusions in olivine and in augite. These independent lines of evidence have converged on small range of likely compositions. Additional information is contained in the original extended abstract.

Treiman, Allan H.; Goodrich, Cyrena Anne

2001-01-01

99

Sibling and Independent Compound Chondrules  

NASA Astrophysics Data System (ADS)

We studied compound chondrules in 79 cm2 of ordinary chondrite (OC) thin sections. Compound chondrules consist of a primary that solidified first and one or more secondaries attached to the primary. Sibling compound chondrules have very similar textures and compositions; most, perhaps all, seem to consist of chondrules melted in the same heating event. About 1.4% of all chondrules are the primaries of sibling compound chondrules. A smaller fraction, 1.0%, of all chondrules are the primaries of independent chondrules, the members of which were melted in separate heating events. Independent chondrules show appreciable differences in texture and/or composition. We propose that sibling chondrules originated when numerous chondrules were created from one large, more-or-less homogeneous, precursor assemblage that was flash-melted to produce a large set (perhaps 100-1000) of chondrules; some of these collided while molten, probably within several centimeters of the production site. We envision that small radial velocities were imparted to the members of the set, with small differences in velocity causing collisions among those few in intersecting trajectories. If all chondrules were produced this way, the collision efficiency was 1.4%; if only 10% were produced in this fashion, the efficiency rises to 14%. The original Gooding-Keil model of independent compound chondrule formation calls for random collisions to occur while the secondaries were molten. This appears improbable because the mean period between collisions in the dusty midplane of the nebula is estimated to be hours (or days), orders of magnitude longer than the period during which chondrules could have retained low viscosities following a flash-heating event in a cool (<700 K) nebula. We suggest that most independent compound chondrules formed by the mechanism that accounts for chondrules with relict grains and for chondrules with coarse- grained rims: the primary chondrule was embedded in a porous dust assemblage at the time of the second heating event; it experienced minimal melting because melting efficiency increases with increasing surface/volume ratio. There is a minor tendency for the FeO/(FeO+MgO) ratio in independent secondaries to be higher than in primaries, as expected if this ratio increased with time in the nebular dust. However, Monte Carlo calculations confirm that the compositions of independent secondaries are not randomly distributed, but related to those of primaries. Some exchange probably occurred during the fusion of the two chondrules, but this mechanism seems unable to account for the general similarity of independent primary/secondary compositions. This suggests that, in the environment where, at any one time, chondrules were forming (perhaps the interface between the gaseous nebula and the dusty midplane), the dust composition was more uniform than it was in the central midplane at a later time when agglomeration occurred.

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

1993-07-01

100

Chronology of the early Solar System from chondrule-bearing calcium-aluminium-rich inclusions.  

PubMed

Chondrules and Ca-Al-rich inclusions (CAIs) are high-temperature components of meteorites that formed during transient heating events in the early Solar System. A major unresolved issue is the relative timing of CAI and chondrule formation. From the presence of chondrule fragments in an igneous CAI, it was concluded that some chondrules formed before CAIs (ref. 5). This conclusion is contrary to the presence of relict CAIs inside chondrules, as well as to the higher abundance of 26Al in CAIs; both observations indicate that CAIs pre-date chondrules by 1-3 million years (Myr). Here we report that relict chondrule material in the Allende meteorite, composed of olivine and low-calcium pyroxene, occurs in the outer portions of two CAIs and is 16O-poor (Delta17O approximately -1 per thousand to -5 per thousand). Spinel and diopside in the CAI cores are 16O-rich (Delta17O up to -20 per thousand), whereas diopside in their outer zones, as well as melilite and anorthite, are 16O-depleted (Delta17O = -8 per thousand to 2 per thousand). Both chondrule-bearing CAIs are 26Al-poor with initial 26Al/27Al ratios of (4.7 +/- 1.4) x 10(-6) and <1.2 x 10(-6). We conclude that these CAIs had chondrule material added to them during a re-melting episode approximately 2 Myr after formation of CAIs with the canonical 26Al/27Al ratio of 5 x 10(-5). PMID:15846340

Krot, Alexander N; Yurimoto, Hisayoshi; Hutcheon, Ian D; MacPherson, Glenn J

2005-04-21

101

Iodine-xenon, chemical, and petrographic studies of Semarkona chondrules - Evidence for the timing of aqueous alteration  

NASA Technical Reports Server (NTRS)

The relationship of the I-Xe system of the Semarkona meteorite to other measured properties is investigated via INAA, petrographic, and noble-gas analyses on 17 chondrules from the meteorite. A range of not less than 10 Ma in apparent I-Xe ages is observed. The three latest apparent ages fall in a cluster, suggesting the possibility of a common event. It is argued that the initial I-129/I-127 ratio (R0) is related to chondrule type and/or mineralogy, with nonporphyritic and pyroxene-rich chondrules showing evidence for lower R0s than porphyritic and olivine-rich chondrules. Chondrules with sulfides on or near the surface have lower R0s than other chondrules. The He-129/Xe-132 ratio in the trapped Xe component anticorrelates with R0, consistent with the evolution of a chronometer in a closed system or in multiple systems. It is concluded that the variations in R0 represent variations in ages, and that later events, possibly aqueous alteration, preferentially affected chondrules with nonporphyritic textures and/or sulfide-rich exteriors about 10 Ma after the formation of the chondrules.

Swindle, T. D.; Grossman, J. N.; Olinger, C. T.; Garrison, D. H.

1991-01-01

102

Origin of plagioclase-olivine inclusions in carbonaceous chondrites  

SciTech Connect

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, and abundance of olivine and aluminousenstatite. Rare accessory minerals including armalcolite, zirconolite, rutile, and sapphirine are found in several POIs. The petrographic and chemical properties of POIs indicate that they are not condensates or evaporative residues but formed by melting or partial melting of pre-existing solids. Seven of fourteen POIs contain isotopically fractionated Mg, and despite their textures these POIs are not isotopically homogeneous. A comparison of the essential characteristics of POIs and CAIs suggests that the major processes leading to formation of POIs - including condensation, dust/gas fractionation, aggregation of chemically and isotopically disparate materials, and partial melting - are common to most CAIs and chondrules. We present a scenario for the formulation of these objects and conclude that the homogeneity of the final assemblage - CAI, POI, or chondrule - is primarily a reflection of the thermal history rather than the nature of precursor materials.

Sheng, Y.J.; Hutcheon, I.D.; Wasserburg, G.J. (California Inst. of Tech., Pasadena (USA))

1991-02-01

103

Producing chondrules by recycling and volatile loss  

NASA Technical Reports Server (NTRS)

Interelement correlations observed in bulk chondrule INAA data, particularly between the refractory lithophiles, have led to the now generally accepted conclusion that the chondrule precursors were nebular condensates. However, it has been recently suggested that random sampling of fragments from a previous generation of chondrules could reproduce much of the observed range of bulk chondrule composition.

Alexander, C. M. O.

1994-01-01

104

A chondrule-like object captured by space-exposed aerogel on the international space station  

NASA Astrophysics Data System (ADS)

Here we report on the mineralogy, petrography, and oxygen-isotope compositions of a micrometeoroid captured on the international space station. This micrometeoroid has the texture of a porphyritic olivine chondrule. Because hydrated phases were not identified in the micrometeoroid and because Ni-rich sulfide in it does not show exsolution of pentlandite on the TEM scale, the micrometeoroid probably escaped low temperature events such as aqueous alteration on its parent body. However, the mean value and standard deviation of Cr 2O 3 wt.% in olivine in the micrometeoroid suggest that the micrometeoroid experienced weak thermal metamorphism. Oxygen isotope ratios of pyroxene and olivine in the micrometeoroid are similar to those of chondrule-like objects in comet 81P/Wild2 and coarse-grained crystalline micrometeorites as well as those in chondrules in major types of carbonaceous chondrites. These data suggest that the micrometeoroid is a fragment of a chondrule-like object that was derived from a primitive parent body that experienced thermal metamorphism.

Noguchi, T.; Nakamura, T.; Ushikubo, T.; Kita, N. T.; Valley, J. W.; Yamanaka, R.; Kimoto, Y.; Kitazawa, Y.

2011-09-01

105

Ubiquitous Low-FeO Relict Grains in Type II Chondrules and Limited Overgrowths on Phenocrysts Following the Final Melting Event  

NASA Technical Reports Server (NTRS)

Type II porphyritic chondrules commonly contain several large (>40 microns) olivine phenocrysts; furnace-based cooling rates based on the assumption that these phenocrysts grew in a single-stage melting-cooling event yield chondrule cooling-rate estimates of 0.01-1 K per second. Because other evidence indicates much higher cooling rates, we examined type II chondrules in the CO3.0 chondrites that have experienced only minimal parent-body alteration. We discovered three kinds of evidence indicating that only minor (4-10 microns) olivine growth occurred after the final melting event: (1) Nearly all (>90%) type II chondrules in CO3.0 chondrites contain low-FeO relict grains; overgrowths on these relicts are narrow, in the range of 2-12 microns. (2) Most type II chondrules contain some FeO-rich olivine grains with decurved surfaces and acute angles between faces indicating that the grains are fragments from an earlier generation of chondrules; the limited overgrowth thicknesses following the last melting event are too thin to disguise the shard-like nature of these grains. (3) Most type II chondrules contain many small (<20 micron) euhedral or subhedral phenocrysts with central compositions that are much more ferroan than the centers of the large phenocrysts: their small sizes document the small amount of growth that occurred after the final melting event. If overgrowth thicknesses were small (4-10 microns) after the final melting event, it follows that large fractions of coarse (>40 microns) high-FeO phenocrysts are relicts from earlier generations of chondrules, and that cooling rates after the last melting event were much more rapid than indicated by models based on a single melting event. These observations are thus inconsistent with the classic igneous model of formation of type II porphyritic chondrules by near-total melting of a precursor mix followed by olivine nucleation on a very limited number of nuclei (say, less than or equal to 10) and by growth to produce the large phenocrysts during a period of monotonic (and roughly linear) cooling. Our observations that recycled chondrule materials constitute a large component of the phenocrysts of type II chondrules also imply that this kind of chondrule formed relatively late during the chondrule-forming period.

Wasson, John T.; Rubin, Alan E.

2003-01-01

106

Ubiquitous low-FeO relict grains in type II chondrules and limited overgrowths on phenocrysts following the final melting event  

NASA Astrophysics Data System (ADS)

Type II porphyritic chondrules commonly contain several large (>40 ?m) olivine phenocrysts; furnace-based cooling rates based on the assumption that these phenocrysts grew in a single-stage melting-cooling event yield chondrule cooling-rate estimates of 0.01-1 K s -1. Because other evidence indicates much higher cooling rates, we examined type II chondrules in the CO3.0 chondrites that have experienced only minimal parent-body alteration. We discovered three kinds of evidence indicating that only minor (4-10 ?m) olivine growth occurred after the final melting event: (1) Nearly all (>90%) type II chondrules in CO3.0 chondrites contain low-FeO relict grains; overgrowths on these relicts are narrow, in the range of 2-12 ?m. (2) Most type II chondrules contain some FeO-rich olivine grains with decurved surfaces and acute angles between faces indicating that the grains are fragments from an earlier generation of chondrules; the limited overgrowth thicknesses following the last melting event are too thin to disguise the shard-like nature of these grains. (3) Most type II chondrules contain many small (<20 ?m) euhedral or subhedral phenocrysts with central compositions that are much more ferroan than the centers of the large phenocrysts; their small sizes document the small amount of growth that occurred after the final melting event. If overgrowth thicknesses were small (4-10 ?m) after the final melting event, it follows that large fractions of coarse (>40 ?m) high-FeO phenocrysts are relicts from earlier generations of chondrules, and that cooling rates after the last melting event were much more rapid than indicated by models based on a single melting event. These observations are thus inconsistent with the "classic" igneous model of formation of type II porphyritic chondrules by near-total melting of a precursor mix followed by olivine nucleation on a very limited number of nuclei (say, ?10) and by growth to produce the large phenocrysts during a period of monotonic (and roughly linear) cooling. Our observations that recycled chondrule materials constitute a large component of the phenocrysts of type II chondrules also imply that this kind of chondrule formed relatively late during the chondrule-forming period.

Wasson, John T.; Rubin, Alan E.

2003-06-01

107

Ubiquitous Low-FeO Relict Grains in Type II Chondrules and Limited Overgrowths on Phenocrysts Following the Final Melting Event  

NASA Technical Reports Server (NTRS)

Type II porphyritic chondrules commonly contain several large (>40 microns) olivine phenocrysts; furnace-based cooling rates based on the assumption that these phenocrysts grew in a single-stage melting-cooling event yield chondrule cooling-rate estimates of 0.01-1 K/s. Because other evidence indicates much higher cooling rates, we examined type 11 chondrules in the CO3.0 chondrites that have experienced only minimal parent-body alteration. We discovered three kinds of evidence indicating that only minor (4-10 microns) olivine growth occurred after the final melting event: (1) Nearly all (>90%) type II chondrules in CO3.0 chondrites contain low-FeO relict grains; overgrowths on these relicts are narrow, in the range of 2-12 microns. (2) Most type II chondrules contain some FeO-rich olivine grains with decurved surfaces and acute angles between faces indicating that the grains are fragments from an earlier generation of chondrules; the limited overgrowth thicknesses following the last melting event are too thin to disguise the shard-like nature of these grains. (3) Most type II chondrules contain many small (<20 microns) euhedral or subhedral phenocrysts with central compositions that are much more ferroan than the centers of the large phenocrysts; their small sizes document the small amount of growth that occurred after the final melting event. If overgrowth thicknesses were small (4-10 microns) after the final melting event, it follows that large fractions of coarse (>40 microns) high-FeO phenocrysts are relicts from earlier generations of chondrules, and that cooling rates after the last melting event were much more rapid than indicated by models based on a single melting event. These observations are thus inconsistent with the "classic" igneous model of formation of type II porphyritic chondrules by near-total melting of a precursor mix followed by olivine nucleation on a very limited number of nuclei (say, <10) and by growth to produce the large phenocrysts during a period of monotonic (and roughly linear) cooling. Our observations that recycled chondrule materials constitute a large component of the phenocrysts of type II chondrules also imply that this kind of chondrule formed relatively late during the chondrule-forming period.

Wasson, John T.; Rubin, Alan E.

2006-01-01

108

Crystallization of chondrules in ordinary chondrites  

NASA Astrophysics Data System (ADS)

The process of crystallization and the origin of chondrules are discussed, in terms of the phase relations of the minerals in chondrules in six ordinary chondrites of the Yamato-74 meteorites, especially the Yamato-74191 (L3). Chondrules are classified into six types. The bulk compositions of chondrules projected onto the MgO-FeO-SiO2 system show that the compositions of chondrules vary widely. Investigations by means of the MgO-Al2O3-SiO2 system indicate that porphyritic chondrules can be regarded as products of supercooling crystallization. The difference between types of chondrules is interpreted in terms of the compositions of chondrules and the nucleation temperatures of the supercooled droplets. The impact and dust fusion theories do not appear to be plausible. Only a liquid condensation theory can well explain the characteristic features and the process of the crystallization of chondrules.

Kimura, M.; Yagi, K.

1980-04-01

109

Little Chondrules and Giant Impacts  

NASA Astrophysics Data System (ADS)

Alexander (Sasha) Krot (University of Hawaii), Yuri Amelin (University of Toronto), Pat Cassen (SETI Institute), and Anders Meibom (Museum National d'Histoire Naturelle, Paris) studied and then extracted frozen droplets of molten silicate (chondrules) from unusual meteorites rich in metallic iron-nickel. Called CB (Bencubbin-like) chondrites, these rare but fascinating meteorites contain chondrules with different properties than those in other types of chondrites. Most notably, the chondrules contain very small concentrations of volatile elements and variable concentrations of refractory elements. (Volatile elements condense from a gas at a relatively low temperature, or are boiled out of solids or liquids at relatively low temperature. Refractory elements are the opposite.) Some of the metal grains in CB chondrites are chemically zoned, indicating that they formed by condensation in a vapor cloud. The most intriguing feature of chondrules in CB chondrites is their relatively young age. Lead-lead isotopic dating of chondrules separated from two CB chondrites show that they formed 5 million years after formation of the first solids in the solar system (calcium-aluminum-rich inclusions), which is about at least two million years after formation of other chondrules, and after energetic events in the solar nebula stopped. Krot and his colleagues suggest that the CB chondrules formed as the result of an impact between Moon- to Mars-sized protoplanets. Such impacts were so energetic that huge amounts of material were vaporized and then condensed as chondrules or chemically zoned metal grains. This event enriched refractory elements and depleted volatile elements. Such large impacts appear to play important roles in planet formation, including the formation of the Moon.

Taylor, G. J.

2005-10-01

110

Evidence in CO3.0 Chondrules for a drift in the O Isotopic Composition of the Solar Nebula  

NASA Technical Reports Server (NTRS)

Several recent studies have shown that materials such as magnetite that formed in asteroids tend to have higher Delta O-17 (=delta O-17 -0.52 delta O-18) values than those recorded in unaltered chondrules. Other recent studies have shown that, in sets of chondrules from carbonaceous chondrites, Delta O-17 tends to increase as the FeO contents of the silicates increase. We report a comparison of the O isotopic composition of olivine phenocrysts in low-FeO (Fal5) type II porphyritic chondrules in the highly primitive C03.0 chondrite Yamato-81020. In agreement with a similar study of chondrules in C03.0 ALH A77307 by Jones et al., Delta O-17 tends to increase with increasing FeO. We find that Delta O-17 values are resolved (but only marginally) between the two sets of olivine phenocrysts. In two of the high-FeO chondrules, the difference between Delta O-17 of the late-formed, high-FeO phenocryst olivine and those in the low-FeO cores of relict grains is well-resolved (although one of the relicts is interpreted to be a partly melted amoeboid olivine inclusion by Yurimoto and Wasson). It appears that, during much of the chondrule-forming period, there was a small upward drift in the Delta O-17 of nebular solids and that relict cores preserve the record of a different (and earlier) nebular environment.

Wasson, John T.; Rubin, Alan E.; Yurimoto, Hisayoshi

2006-01-01

111

The influence of gravitational body force in meteoritic chondrule and lunar glass formation  

NASA Technical Reports Server (NTRS)

The effects of gravitational body force must be considered in the formation of extraterrestrial materials such as meteoritic chondrules and lunar glasses. Solidification experiments conducted in microgravity as well as g values greater than Earth's gravitational force have demonstrated that gravitational force can have profound and sometimes unexpected effects upon the way materials solidify and, therefore, upon their physical and mechanical properties. Solutal, thermal and sedimentation effects differ from those experienced on Earth. Because buoyancy forces are reduced, materials of different densities may remain in close proximity. The spherical morphology of chondrules and many lunar glasses may reflect the tendency for free floating liquids to form spherical droplets in a microgravity environment, a form which minimizes surface energy. Under these conditions, surface energy forces dominate gravity forces. The formation of two common chondrule textures, barred and radiating chondrules, can be explained using observations from glass science.

Budka, P. Z.

1984-01-01

112

The effect of Na vapor on the Na content of chondrules  

NASA Technical Reports Server (NTRS)

Chondrules contain higher concentrations of volatiles (Na) than expected for melt droplets in the solar nebula. Recent studies have proposed that chondrules may have formed under non-canonical nebular conditions such as in particle/gas-rich clumps. Such chondrule formation areas may have contained significant Na vapor. To test the hypothesis of whether a Na-rich vapor would minimize Na volatilization reaction rates in a chondrule analog and maintain the Na value of the melt, experiments were designed where a Na-rich vapor could be maintained around the sample. A starting material with a melting point lower that typical chondrules was required to keep the logistics of working with Na volatilization from NaCl within the realm of feasibility. The Knippa basalt, a MgO-rich alkali olivine basalt with a melting temperature of 1325 +/- 5 C and a Na2O content of 3.05 wt%, was used as the chondrule analog. Experiments were conducted in a 1 atm, gas-mixing furnace with the fO2 controlled by a CO/CO2 gas mixture and fixed at the I-W buffer curve. To determine the extent of Na loss from the sample, initial experiments were conducted at high temperatures (1300 C - 1350 C) for duration of up to 72 h without a Na-rich vapor present. Almost all (up to 98%) Na was volatilized in runs of 72 h. Subsequent trials were conducted at 1330 C for 16 h in the presence of a Na-rich vapor, supplied by a NaCl-filled crucible placed in the bottom of the furnace. Succeeding Knudsen cell weight-loss mass-spectrometry analysis of NaCl determined the P(sub Na) for these experimental conditions to be in the 10(exp -6) atm range. This value is considered high for nebula conditions but is still plausible for non-canonical environments. In these trials the Na2O content of the glass was maintained or in some cases increased; Na2O values ranged from 2.62% wt to 4.37% wt. The Na content of chondrules may be controlled by the Na vapor pressure in the chondrule formation region. Most heating events capable of producing chondrules are sufficient to volatile Na. Sodium volatilization reaction rates will be reduced to varying degrees from melt droplets, depending on the magnitude of the P(sub Na) generated. A combination of Na vapor during, and Na diffusion back into chondrules after, formation could maintain and/or enrich Na concentrations in chondrules.

Lewis, R. Dean; Lofgren, Gary E.; Franzen, Hugo F.; Windom, Kenneth E.

1993-01-01

113

Conference on Chondrules and Their Origins  

NASA Technical Reports Server (NTRS)

Chondrule parent materials, chondrule formation, and post-formational history are addressed. Contributions involving mineralogy petrology, geochemistry, geochronology, isotopic measurements, physical measurements, experimental studies, and theoretical studies are included.

Hrametz, K.

1983-01-01

114

Constraints on chondrule agglomeration from fine-grained chondrule rims  

NASA Technical Reports Server (NTRS)

Fine-grained rims around chondrules, Ca,Al-rich inclusions, and other coarse-grained components occur in most types of unequilibrated chondrites, most prominently in carbonaceous chondrites of the CM group. Based on mineralogical and petrographic investigations, it was suggested that rim structures in unequilibrated ordinary chondrites could have formed in the solar nebula by accretion of dust on the surfaces of the chondrules. Dust mantles in CM chondrites seem to have formed by accretion of dust on the surfaces of chondrules and other components during their passage through dust-rich regions in the solar nebula. Concentric mantles with compositionally different layers prove the existence of various distinct dust reservoirs in the vicinity of the accreting parent body. Despite mineralogical and chemical differences, fine-grained rims from other chondrite groups principally show striking similarities to dust mantle textures in CM chondrite. This implies that the formation of dust mantles was a cosmically significant event like the chondrule formation itself. Dust mantles seem to have formed chronologically between chondrule-producing transient heating events and the agglomeration of chondritic parent bodies. For this reason the investigation of dust mantle structures may help to answer the question of how a dusty solar nebula was transformed into a planetary system.

Metzler, K.; Bischoff, A.

1994-01-01

115

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

NASA Technical Reports Server (NTRS)

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

Johnson, M. C.

1986-01-01

116

An Evaluation of Quantitative Methods of Determining the Degree of Melting Experienced by a Chondrule  

NASA Technical Reports Server (NTRS)

Many workers have considered the degree to which partial melting occurred in chondrules they have studied, and this has led to attempts to find reliable methods of determining the degree of melting. At least two quantitative methods have been used in the literature: a convolution index (CVI), which is a ratio of the perimeter of the chondrule as seen in thin section divided by the perimeter of a circle with the same area as the chondrule, and nominal grain size (NGS), which is the inverse square root of the number density of olivines and pyroxenes in a chondrule (again, as seen in thin section). We have evaluated both nominal grain size and convolution index as melting indicators. Nominal grain size was measured on the results of a set of dynamic crystallization experiments previously described, where aliquots of LEW97008(L3.4) were heated to peak temperatures of 1250, 1350, 1370, and 1450 C, representing varying degrees of partial melting of the starting material. Nominal grain size numbers should correlate with peak temperature (and therefore degree of partial melting) if it is a good melting indicator. The convolution index is not directly testable with these experiments because the experiments do not actually create chondrules (and therefore they have no outline on which to measure a CVI). Thus we had no means to directly test how well the CVI predicted different degrees of melting. Therefore, we discuss the use of the CVI measurement and support the discussion with X-ray Computed Tomography (CT) data.

Nettles, J. W.; Lofgren, G. E.; Carlson, W. D.; McSween, H. Y., Jr.

2004-01-01

117

MAGNESIUM ISOTOPE EVIDENCE FOR SINGLE STAGE FORMATION OF CB CHONDRULES BY COLLIDING PLANETESIMALS  

SciTech Connect

Chondrules are igneous spherical objects preserved in chondritic meteorites and believed to have formed during transient heating events in the solar protoplanetary disk. Chondrules present in the metal-rich CB chondrites show unusual chemical and petrologic features not observed in other chondrite groups, implying a markedly distinct formation mechanism. Here, we report high-precision Mg-isotope data for 10 skeletal olivine chondrules from the Hammadah al Hamra 237 (HH237) chondrite to probe the formation history of CB chondrules. The {sup 27}Al/{sup 24}Mg ratios of individual chondrules are positively correlated to their stable Mg-isotope composition (?{sup 25}Mg), indicating that the correlated variability was imparted by a volatility-controlled process (evaporation/condensation). The mass-independent {sup 26}Mg composition (?{sup 26}Mg*) of chondrules is consistent with single stage formation from an initially homogeneous magnesium reservoir if the observed ?{sup 25}Mg variability was generated by non-ideal Rayleigh-type evaporative fractionation characterized by a ? value of 0.5142, in agreement with experimental work. The magnitude of the mass-dependent fractionation (?300 ppm) is significantly lower than that suggested by the increase in {sup 27}Al/{sup 24}Mg values, indicating substantial suppression of isotopic fractionation during evaporative loss of Mg, possibly due to evaporation at high Mg partial pressure. Thus, the Mg-isotope data of skeletal chondrules from HH237 are consistent with their origin as melts produced in the impact-generated plume of colliding planetesimals. The inferred ?{sup 26}Mg* value of –3.87 ± 0.93 ppm for the CB parent body is significantly lower than the bulk solar system value of 4.5 ± 1.1 ppm inferred from CI chondrites, suggesting that CB chondrites accreted material comprising an early formed {sup 26}Al-free component.

Olsen, Mia B.; Schiller, Martin; Krot, Alexander N.; Bizzarro, Martin [Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350 (Denmark)] [Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350 (Denmark)

2013-10-10

118

Plagioclase-rich chondrules in the reduced CV chondrites: Evidence for complex formation history and genetic links between calcium-aluminum-rich inclusions and ferromagnesian chondrules  

NASA Astrophysics Data System (ADS)

Plagioclase-rich chondrules (PRCs) in the reduced CV chondrites Efremovka, Leoville, Vigarano and Grosvenor Mountains (GRO) 94329 consist of magnesian low-Ca pyroxene, Al-Ti-Cr-rich pigeonite and augite, forsterite, anorthitic plagioclase, FeNi-metal-sulfide nodules, and crystalline mesostasis composed of silica, anorthitic plagioclase and Al-Ti-Cr-rich augite. The silica grains in the mesostases of the CV PRCs are typically replaced by hedenbergitic pyroxenes, whereas anorthitic plagioclase is replaced by feldspathoids (nepheline and minor sodalite). Some of the PRCs contain regions that are texturally and mineralogically similar to type I chondrules and consist of forsterite, low-Ca pyroxene and abundant FeNi-metal nodules. Several PRCs are surrounded by igneous rims or form independent compound objects. Twelve PRCs contain relic calcium-aluminum-rich inclusions (CAIs) composed of anorthite, spinel, high-Ca pyroxene, ?forsterite, and ?Al-rich low-Ca pyroxene. Anorthite of these CAIs is generally more heavily replaced by feldspathoids than anorthitic plagioclase of the host chondrules. This suggests that either the alteration predated formation of the PRCs or that anorthite of the relic CAIs was more susceptible to the alteration than anorthitic plagioclase of the host chondrules. These observations and the presence of igneous rims around PRCs and independent compound PRCs suggest that the CV PRCs may have had a complex, multistage formation history compared to a more simple formation history of the CR PRCs. Relatively high abundances of moderately-volatile elements such as Cr, Mn and Si in the PRCs suggests that these chondrules could not have been produced by volatilization of ferromagnesian chondrule precursors or by melting of refractory materials only. We infer instead that PRCs in carbonaceous chondrites formed by melting of the reduced chondrule precursors (magnesian olivine and pyroxene, FeNi-metal) mixed with refractory materials (relic CAIs) composed of anorthite, spinel, high-Ca pyroxene, and forsterite. The mineralogical, chemical and textural similarities of the PRCs in several carbonaceous chondrite groups (CV, CO, CH, CR) and common presence of relic CAIs in these chondrules suggest that PRCs may have formed in the region(s) intermediate between the regions where CAIs and ferromagnesian chondrules originated.

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

2002-02-01

119

Mn-Cr ages of Fe-rich olivine in two Rumuruti (R) chondrites  

NASA Astrophysics Data System (ADS)

Mn-Cr systematics in olivine of two Rumuruti (R) chondrites was investigated. Mn/52Cr ratios up to 1800 and 1300, and ?53Cr of up to 25° and 7° were observed for NWA 753 and Sahara 99531, respectively. All data points of NWA 753 show a linear correlation between ?53Cr values and Mn/52Cr ratios on the isochron diagram. The inferred initial 53Mn/55Mn ratio for NWA 753 is (1.84 ± 0.42(2?)) × 10-6. In the case of Sahara 99531, a positive correlation interpreted as an isochron for 53Mn/55Mn = 2.75 ± 1.55 (2?) × 10-6 was obtained for only one chondrule. Data from other chondrules in Sahara 99531 give an upper limit of 53Mn/55Mn = 0.49 × 10-6. The Mn-Cr ages of NWA 753 and a chondrule in Sahara 99531 are slightly older than that of the angrite LEW 86010 (Lugmair and Shukolyukov, 1998). Other chondrules in Sahara 99531 are at least 5 Ma younger than the LEW 86010. The Mn-Cr ages of olivine in R chondrites correspond to the time when olivine became a closed system either during slow cooling from the peak metamorphic temperature or during rapid cooling by impact excavation. In either case the olivine closure occurred earlier than the final assembly of the brecciated chondrites.

Sugiura, N.; Miyazaki, A.

2006-05-01

120

Olivine Thermometry  

NSDL National Science Digital Library

This assignment is ostensibly about geothermometry, but is also part of a sequence of assignments where students learn about mineral components â what they represent (in regards to solid solution phenomena especially), and how they calculated. I begin with olivine because its components are simple, and reasonably good thermometers do not require long equations. I also use this assignment to teach about binary solid solutions and phase diagrams, though the interpretations of such are based within other assignments. This is part of a sequence of assignments where students learn about mineral components â what they represent (in regards to solid solution phenomena especially), and how they calculated. Though students will not use a binary solid solution diagram per se, I use this HW assignment to re-emphasize such concepts. This assignment also allows students to begin tests of equilibrium, so they must understand the concept and use of an equilibrium constant.

Putirka, Keith

121

Chondrules born in plasma? Simulation of gas-grain interaction using plasma arcs with applications to chondrule and cosmic spherule formation  

NASA Astrophysics Data System (ADS)

Abstract-We are investigating <span class="hlt">chondrule</span> formation by nebular shock waves, using hot plasma as an analog of the heated gas produced by a shock wave as it passes through the protoplanetary environment. Precursor material (mainly silicates, plus metal, and sulfide) was dropped through the plasma in a basic experimental set-up designed to simulate gas-grain collisions in an unconstrained spatial environment (i.e., no interaction with furnace walls during formation). These experiments were undertaken in air (at atmospheric pressure), to act as a "proof-of-principle"—could <span class="hlt">chondrules</span>, or <span class="hlt">chondrule</span>-analog objects (CAO), be formed by gas-grain interaction initiated by shock fronts? Our results showed that if accelerating material through a fixed plasma field is a valid simulation of a supersonic shock wave traveling through a cloud of gas and dust, then CAO certainly could be formed by this process. Melting of and mixing between starting materials occurred, indicating temperatures of at least 1266 °C (the <span class="hlt">olivine</span>-feldspar eutectic). The production of CAO with mixed mineralogy from monomineralic starting materials also shows that collisions between particles are an important mechanism within the <span class="hlt">chondrule</span> formation process, such that dust aggregates are not necessarily required as <span class="hlt">chondrule</span> precursors. Not surprisingly, there were significant differences between the synthetic CAO and natural <span class="hlt">chondrules</span>, presumably mainly because of the oxidizing conditions of the experiment. Results also show similarity to features of micrometeorites like cosmic spherules, particularly the dendritic pattern of iron oxide crystallites produced on micrometeorites by oxidation during atmospheric entry and the formation of vesicles by evaporation of sulfides.</p> <div class="credits"> <p class="dwt_author">Morlok, A.; Sutton, Y. C.; Braithwaite, N. St. J.; Grady, Monica M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">122</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950012913&hterms=Benoit&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DBenoit"> <span id="translatedtitle">Open-system behavior during <span class="hlt">chondrule</span> formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The question of whether <span class="hlt">chondrules</span> behaved as open systems during formation is crucial to our understanding of both <span class="hlt">chondrule</span> and chondrite formation. The very large range of <span class="hlt">chondrule</span> types is best summarized by the compositional classification scheme, wherein the primitive <span class="hlt">chondrule</span> groups (i.e., those not produced by metamorphic processes) are A1, A2, A5, and B1. In the Semarkona (LL3.0) chondrite, 10.5%, 25.0%, 5.0%, and 56.9% (by number) of the <span class="hlt">chondrules</span> are groups A1, A2, A5, and B1, respectively. We argue that groups A1 and A2 were produced by reduction and evaporation during <span class="hlt">chondrule</span> formation of material originally resembling group B1 <span class="hlt">chondrules</span>.</p> <div class="credits"> <p class="dwt_author">Sears, D. W. G.; Shaoxiong, H.; Benoit, P. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">123</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013GeCoA.102..261W"> <span id="translatedtitle">Petrology, trace element abundances and oxygen isotopic compositions of a compound CAI-<span class="hlt">chondrule</span> object from Allende</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report the petrology, trace element abundances and oxygen isotopic characteristics of a compound CAI-<span class="hlt">chondrule</span> object, WI-025, found in the Allende CV3 chondrite. The WI-025 is an irregularly shaped inclusion consisting of three texturally and chemically distinct portions: the interior portion, the igneous rim and the intermediate zone located between these two portions. The interior portion consists of anorthite, spinel, <span class="hlt">olivine</span> and Al-bearing low-Ca pyroxene. The major element chemistry of the interior portion corresponds to that of Al-rich <span class="hlt">chondrules</span> and is of intermediate character between fine-grained spinel-rich CAIs and ferromagnesian <span class="hlt">chondrules</span>. The interior portion has abundant 16O-rich spinel (?17O = -14.2 to -24.7) and displays a group II CAI-like REE composition. These observations indicate that the interior portion contains a CAI component formed by fractional condensation. The major and trace element chemistry of the interior portion indicate that the CAI had subsequently assimilated <span class="hlt">chondrule</span> materials through partial melting. The maximum heating temperature of the partial melting is estimated at approximately 1400 °C, similar to the maximum heating temperature of Type-B CAIs. The oxygen isotopic compositions of the <span class="hlt">olivine</span> and low-Ca pyroxene (?17O = -6.3) in the interior portion indicate that the partial melting and <span class="hlt">chondrule</span> assimilation took place under a moderately 16O-poor nebular gas. The igneous rim is texturally and chemically similar to ferromagnesian <span class="hlt">chondrules</span> and entirely surrounds the interior portion. The oxygen isotopic compositions of the <span class="hlt">olivine</span> and low-Ca pyroxene in the igneous rim are indistinguishable from those of the interior <span class="hlt">olivine</span> and Al-bearing low-Ca pyroxenes. These observations indicate that a <span class="hlt">chondrule</span> material, which was melted in the same nebular gas as the interior portion, was accreted to the interior portion. The intermediate zone represents a reaction zone accompanying the igneous rim formation. The formation history of WI-025 can be summarized by the following processes: (1) original CAI formation, (2) partial melting and <span class="hlt">chondrule</span> assimilation, (3) igneous rim formation and (4) secondary alteration on the parent body.</p> <div class="credits"> <p class="dwt_author">Wakaki, S.; Itoh, S.; Tanaka, T.; Yurimoto, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">124</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/11540500"> <span id="translatedtitle">Origin of magnetite in oxidized CV chondrites: in situ measurement of oxygen isotope compositions of Allende magnetite and <span class="hlt">olivine</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Magnetite in the oxidized CV chondrite Allende mainly occurs as spherical nodules in porphyritic-<span class="hlt">olivine</span> (PO) <span class="hlt">chondrules</span>, where it is associated with Ni-rich metal and/or sulfides. To help constrain the origin of the magnetite, we measured oxygen isotopic compositions of magnetite and coexisting <span class="hlt">olivine</span> grains in PO <span class="hlt">chondrules</span> of Allende by an in situ ion microprobe technique. Five magnetite nodules form a relatively tight cluster in oxygen isotopic composition with delta 18O values from -4.8 to -7.1% and delta 17O values from -2.9 to -6.3%. Seven coexisting <span class="hlt">olivine</span> grains have oxygen isotopic compositions from -0.9 to -6.3% in delta 18O and from -4.6 to -7.9% in delta 17O. The delta 17O values of the magnetite and coexisting <span class="hlt">olivine</span> do not overlap; they range from -0.4 to -2.6%, and from -4.0 to -5.7%, respectively. Thus, the magnetite is not in isotopic equilibrium with the <span class="hlt">olivine</span> in PO <span class="hlt">chondrules</span>, implying that it formed after the <span class="hlt">chondrule</span> formation. The delta 17O of the magnetite is somewhat more negative than estimates for the ambient solar nebula gas. We infer that the magnetite formed on the parent asteroid by oxidation of metal by H2O which had previously experienced minor O isotope exchange with fine-grained silicates. PMID:11540500</p> <div class="credits"> <p class="dwt_author">Choi, B G; McKeegan, K D; Leshin, L A; Wasson, J T</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">125</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20040121339&hterms=magnetite+solar&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dmagnetite%2Bsolar"> <span id="translatedtitle">Origin of magnetite in oxidized CV chondrites: in situ measurement of oxygen isotope compositions of Allende magnetite and <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Magnetite in the oxidized CV chondrite Allende mainly occurs as spherical nodules in porphyritic-<span class="hlt">olivine</span> (PO) <span class="hlt">chondrules</span>, where it is associated with Ni-rich metal and/or sulfides. To help constrain the origin of the magnetite, we measured oxygen isotopic compositions of magnetite and coexisting <span class="hlt">olivine</span> grains in PO <span class="hlt">chondrules</span> of Allende by an in situ ion microprobe technique. Five magnetite nodules form a relatively tight cluster in oxygen isotopic composition with delta 18O values from -4.8 to -7.1% and delta 17O values from -2.9 to -6.3%. Seven coexisting <span class="hlt">olivine</span> grains have oxygen isotopic compositions from -0.9 to -6.3% in delta 18O and from -4.6 to -7.9% in delta 17O. The delta 17O values of the magnetite and coexisting <span class="hlt">olivine</span> do not overlap; they range from -0.4 to -2.6%, and from -4.0 to -5.7%, respectively. Thus, the magnetite is not in isotopic equilibrium with the <span class="hlt">olivine</span> in PO <span class="hlt">chondrules</span>, implying that it formed after the <span class="hlt">chondrule</span> formation. The delta 17O of the magnetite is somewhat more negative than estimates for the ambient solar nebula gas. We infer that the magnetite formed on the parent asteroid by oxidation of metal by H2O which had previously experienced minor O isotope exchange with fine-grained silicates.</p> <div class="credits"> <p class="dwt_author">Choi, B. G.; McKeegan, K. D.; Leshin, L. A.; Wasson, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">126</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1993Metic..28Q.434S"> <span id="translatedtitle">The Compositional Classification of <span class="hlt">Chondrules</span> and the Petrologic Type of an Especially Primitive H Chondrite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">While LL chondrites of petrologic type <3.4 are relatively common, it has been only recently that a few H chondrites of type <3.4 have been reported. One of them is the heavily weathered Roosevelt County 075 [1]. Weathering and the lack of equilibration make classification uncertain, but it is probably an H chondrite. Weathering also makes it very difficult to assign a petrologic type. For example, removal of the weathering products by acid washing increased the TL sensitivity of RC075 by a factor of ~7, equivalent to a change in petrologic type estimate from 3.0 to 3.3, a major difference. The compositional classification scheme for <span class="hlt">chondrules</span> [2,3] summarizes considerably more information than previous schemes [4-6], not least being that it tracks metamorphic effects as well as more thoroughly monitoring primary <span class="hlt">chondrule</span> differences. It is also very easy to apply and almost 100% of the <span class="hlt">chondrules</span> can be classified. As an example of its utility, we here show that application of the scheme to the <span class="hlt">chondrules</span> in RC075 provides the best means of determining the petrologic type of this highly weathered, but very important, unequilibrated chondrite. The compositional classification scheme for <span class="hlt">chondrules</span> divides them into eight classes (A1, A2, A3, A4, A5, B1, B2, B3) on the basis of the composition of the two major phases (phenocrysts and mesostasis) [2,3]. Among the changes that occur during metamorphism, <span class="hlt">olivines</span> lose CaO and acquire uniform FeO, while the mesostases acquire oligoclase compositions having originally included compositions that were SiO2 rich (the B series), CaO rich (the A series), and Na2O rich (A5). These changes give rise to CL properties that can be used as an alternative to microprobe analysis and which, like microprobe data, are insensitive to weathering. Thus we were able to assign all of the almost 100 <span class="hlt">chondrules</span> present in a 7 x 5-mm section of RC075 to compositional classes. The results are shown in Fig. 1, along with similar data from [3]. The relative abundance and classes of <span class="hlt">chondrules</span> present provides an excellent method of assigning petrographic type. The relative abundance of group B <span class="hlt">chondrules</span> in RC075 is less than Semarkona (3.0), and comparable with the higher types, while the abundance of A5 <span class="hlt">chondrules</span> is comparable to that in Krymka (3.1) and intermediate between that in Semarkona and Chainpur (3.4). Most significantly, the fraction of A1 <span class="hlt">chondrules</span> is very large and comparable (within error) to that of Semarkona, while the large number of group A3 <span class="hlt">chondrules</span> is comparable only to Krymka. Apparently, RC075 is intermediate to Semarkona and Chainpur and comparable to Krymka in its petrologic type. McCoy et al. [1] report means ranging from 0.07 to 7.2 mol% Fa and 0.11 to 0.36 wt% CaO for <span class="hlt">olivine</span> in six type-IA <span class="hlt">chondrules</span> and 12.3-20.2 mol% Fa for five type-II <span class="hlt">chondrules</span> in RC075 [1]. Four of the type IA <span class="hlt">chondrules</span> resembled those of Semarkona in <span class="hlt">olivine</span> composition (<2 mol% Fa). Unlike the compositional classification scheme, which leads fairly simply to unambiguous petrologic type assignment, it seems difficult to assign RC075 to a petrologic type on the basis of <span class="hlt">olivine</span> compositions and texture alone. Other advantages of the new scheme are (1) that it applies to individual <span class="hlt">chondrules</span> and makes no assumptions about average response of <span class="hlt">chondrules</span> to metamorphism; (2) it is insensitive to brecciation, which is common in UOC [7]; and (3) it is quantitative, and does not require subjective evaluations of texture, although textural descriptions may be used with the compositional class (just as they are for chondrites). The compositional classification scheme is certainly subject to improvement(e.g. class A5, both in type 3 and higher types). However, as it currently stands the scheme clearly provides the best way of not only describing individual <span class="hlt">chondrules</span>, but of assessing primary <span class="hlt">chondrule</span> properties and the extent of changes experienced during metamorphism. Thus it provides the best method for assigning the weathered and highly unequilibrated RC075 meteorite to a petrologic ty</p> <div class="credits"> <p class="dwt_author">Sears, D. W. G.; Huang, S.; Benoit, P. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">127</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AGUFMGP51B..05C"> <span id="translatedtitle">Spatially resolved NRM of the Bishunpur LL3.1 chondrite measured by scanning SQUID microscopy: implications for <span class="hlt">chondrule</span> formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Chondrites represent the building blocks of the solar system and the factors controlling their formation have implications for processes within the protoplanetary disk and interactions between the solar nebula and the early Sun. However, the source of the flash heating that formed the constituent <span class="hlt">chondrules</span> is a subject of debate, with proposed mechanisms including various forms of convection drawing nebular dust towards and ejecting it away from the Sun, or alternatively extra-nebular energy pulses that require no interaction with the young star. Because the Sun was strongly magnetic early in its life, paleointensity measurements of <span class="hlt">chondrules</span> can be used to determine the distance at which they cooled through their Curie temperature, providing evidence about which formation mechanism caused their melting and potentially shedding light on accretionary processes within the protoplanetary disk. The Bishunpur LL3.1 meteorite is among the most pristine ordinary chondrites, having both limited thermal and aqueous alteration and a known (magnetic) history on Earth. As such, its <span class="hlt">chondrules</span> have the potential to preserve primary remanence from their formation if the recorders are capable of maintaining a stable magnetic state over timescales greater than 4.6 Ga. Previous work has shown that dusty <span class="hlt">olivine</span>—iron nanoparticle-bearing silicate that constitutes a proportion of the <span class="hlt">chondrules</span> of Bishunpur—is an stable recorder over these timescales even at temperatures approaching the Curie temperature of iron. In bulk measurements, however, the paleointensity signal from the <span class="hlt">chondrules</span> is masked by magnetic phases on <span class="hlt">chondrule</span> rims and in the matrix, necessitating a technique that allows the contribution of different signals to be distinguished. Scanning SQUID microscopy presents an ideal solution as it produces a map of magnetic field measurements with a spatial resolution of 10s of ?m from which the absolute magnetization can be calculated, allowing the paleointensity and demagnetization behavior of the <span class="hlt">chondrules</span> to be directly observed. This work presents the demagnetization sequence of a thin section of Bishunpur as well as rock magnetic measurements acquired on the scanning SQUID microscope and a bulk moment magnetometer. Bulk measurements of the NRM are dominated by signal from the matrix and <span class="hlt">chondrule</span> rim, but the sensitivity of the scanning SQUID technique allows weak signals from individual <span class="hlt">chondrules</span> to be identified which are stable in alternating-field demagnetization through 290 mT. These signals can be modeled as single dipoles, which means the magnetization of dusty <span class="hlt">olivine</span> regions can be quantitatively measured. Calibration curves from synthetic analogues will permit the paleointensity of these regions to be determined and combined with SEM observations of the microstructure, used to provide a unique line of evidence about <span class="hlt">chondrule</span> formation and the process of accretion in the solar nebula.</p> <div class="credits"> <p class="dwt_author">Church, N. S.; Andrade Lima, E.; Lappe, S. L.; Russell, S.; Weiss, B. P.; Harrison, R. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">128</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1992Metic..27R.281R"> <span id="translatedtitle">Magnetite-Pentlandite <span class="hlt">Chondrules</span> in CK Chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Opaque-mineral-rich <span class="hlt">chondrules</span> are among the least common <span class="hlt">chondrule</span> types and have received scant attention since their discovery by Gustav Rose in 1864. This category includes <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> in Karoonda (CK4), PCA82500 (CK4/5) and EET90007 (CK5). The <span class="hlt">chondrules</span> range in size from 225x255 micrometers to 440x570 micrometers and have ellipsoidal or spheroidal morphologies. All are concentrically layered: five of the <span class="hlt">chondrules</span> have 20-60-micrometer-thick magnetite rims surrounding pentlandite-rich cores or mantles; two of the <span class="hlt">chondrules</span> have thin pentlandite rims surrounding magnetite-rich cores and mantles. One <span class="hlt">chondrule</span> from Karoonda has four distinct alternating layers of magnetite and pentlandite. Accessory phases, which occur in one or more of the <span class="hlt">chondrules</span>, include pyrrhotite, chlorapatite, ilmenite, and chalcopyrite. The <span class="hlt">chondrules</span> have finely to coarsely granular textures; in the center of one <span class="hlt">chondrule</span> from PCA82500 there is a 25x100 micrometers subhedral crystal of pentlandite. All of the <span class="hlt">chondrules</span> appear to be recrystallized, presumably due to metamorphism of their host rocks. The magnetite-pentlandite <span class="hlt">chondrules</span> are very similar to the magnetite-pentlandite-rich nodules within mafic silicate <span class="hlt">chondrules</span> 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 <span class="hlt">chondrule</span> has four concentric layers of magnetite+-pentlandite. The nodules probably formed from immiscible sulfide-oxide droplets within their molten silicate <span class="hlt">chondrule</span> hosts during <span class="hlt">chondrule</span> 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 <span class="hlt">chondrules</span>. The similarities in size, shape, mineralogy, and texture between the magnetite-pentlandite <span class="hlt">chondrules</span> and nodules indicate that these <span class="hlt">chondrules</span> constitute the set of immiscible nodule droplets that were lost to their mafic silicate <span class="hlt">chondrule</span> hosts after melting. The occurrence of magnetite-pentlandite <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> and destroyed the evidence for rhythmic layering. The intactness of the <span class="hlt">chondrules</span> and nodules implies that the oxidation of fine-grained metallic Fe-Ni into magnetite probably occurred before agglomeration, either during <span class="hlt">chondrule</span> formation in a region of high fo(sub)2 or within porous <span class="hlt">chondrule</span>-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</p> <div class="credits"> <p class="dwt_author">Rubin, A. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">129</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=N9519338"> <span id="translatedtitle"><span class="hlt">Chondrule</span> Precursors and Cooling Paths: The Sulfur Evidence.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The behavior of moderately volatile elements (Na and S) is controversial but critical in understanding <span class="hlt">chondrule</span> precursors and heating processes. Sulfide appeared to be present in most <span class="hlt">chondrules</span>, but S should have been vaporized during <span class="hlt">chondrule</span> formati...</p> <div class="credits"> <p class="dwt_author">B. Zanda Y. Yu M. Bourot-denise R. H. Hewins H. C. Connolly</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">130</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930069284&hterms=olivine&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dolivine"> <span id="translatedtitle">Effect of metamorphism on isolated <span class="hlt">olivine</span> grains in CO3 chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The presence of a metamorphic sequence in the CO3 chondrite group has been shown previously to result in changes in properties of <span class="hlt">chondrule</span> silicates. However, the role of isolated <span class="hlt">olivine</span> grains during metamorphism of these chondrites has not been addressed. Isolated <span class="hlt">olivine</span> grains in two metamorphosed CO3 chondrites, Lance and Isna, have been investigated in this study in order to assess the compositional properties of isolated <span class="hlt">olivine</span> grains that may be attributable to metamorphism. Compositional changes in isolated <span class="hlt">olivines</span> with increasing petrologic subtype are very similar to changes in <span class="hlt">chondrule</span> <span class="hlt">olivines</span> in the same chondrites. <span class="hlt">Olivine</span> compositions from all occurrences (<span class="hlt">chondrules</span>, isolated grains, and matrix) converge with increasing petrologic subtype. The degree of equilibration of minor elements is qualitatively related to the diffusion rate of each element in <span class="hlt">olivine</span>, suggesting that diffusion-controlled processes are the most important processes responsible for compositional changes within the metamorphic sequence. The data are consistent with metamorphism taking place in a closed system on the CO3 chondrite parent body. Fe-poor <span class="hlt">olivine</span> grains in metamorphosed chondrites are characterized by an Fe-rich rim, which is the result of diffusion of Fe into the grains from Fe-rich matrix. In some instances, 'complex', Fe-rich rims have been identified, which appear to have originated as igneous overgrowths and subsequently to have been overprinted by diffusion processes during metamorphism. Processes experienced by CO3 chondrites are more similar to those experienced by the ordinary chondrites than to those encountered by other carbonaceous chondrites, such as the CV3 group.</p> <div class="credits"> <p class="dwt_author">Jones, Rhian H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">131</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19820048215&hterms=fasano&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dfasano"> <span id="translatedtitle">Conditions of formation of pyroxene excentroradial <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Understanding the exact mechanism of origin of <span class="hlt">chondrules</span> and the attendant physical conditions remains a key factor in understanding the early evolution of the solar system. The present investigation is concerned with an interpretation of the range of cooling histories needed to make <span class="hlt">chondrules</span>. <span class="hlt">Chondrule</span>-like spherules were formed in dynamic crystallization experiments, using gas-mixing facilities. It is found that textures in pyroxene-rich <span class="hlt">chondrules</span> are well reproduced in the laboratory by cooling melts of <span class="hlt">chondrule</span> composition from just above the liquidus. The range of pyroxene dendrite widths is slightly greater for natural <span class="hlt">chondrules</span> than for droplets cooled from 50 C/hr to greater than 3000 C/hr. A blanketing medium of variable thickness explains the cooling rates lower than expected for radiative cooling. Experimental results, textures indicating incomplete melting, and isotopic disequilibrium are compatible with reheating of primitive material in the early solar nebula.</p> <div class="credits"> <p class="dwt_author">Hewins, R. H.; Klein, L. C.; Fasano, B. V.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">132</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1126/science.1156561"> <span id="translatedtitle">The formation conditions of <span class="hlt">chondrules</span> and chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary"><span class="hlt">Chondrules</span>, 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 <span class="hlt">chondrule</span> formation remain poorly understood. Here we show that the abundance of the volatile element sodium remained relatively constant during <span class="hlt">chondrule</span> formation. Prevention of the evaporation of sodium requires that <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> and also implies that <span class="hlt">chondrule</span> and planetesimal formation were linked.</p> <div class="credits"> <p class="dwt_author">Alexander, C. M. O'D.; Grossman, J. N.; Ebel, D. S.; Ciesla, F. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">133</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/18566282"> <span id="translatedtitle">The formation conditions of <span class="hlt">chondrules</span> and chondrites.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><span class="hlt">Chondrules</span>, 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 <span class="hlt">chondrule</span> formation remain poorly understood. Here we show that the abundance of the volatile element sodium remained relatively constant during <span class="hlt">chondrule</span> formation. Prevention of the evaporation of sodium requires that <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> and also implies that <span class="hlt">chondrule</span> and planetesimal formation were linked. PMID:18566282</p> <div class="credits"> <p class="dwt_author">Alexander, C M O'D; Grossman, J N; Ebel, D S; Ciesla, F J</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-06-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">134</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19920044034&hterms=chromite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dchromite"> <span id="translatedtitle">Spinel-bearing, Al-rich <span class="hlt">chondrules</span> in two chondrite finds from Roosevelt County, New Mexico - Indicators of nebular and parent body processes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Two rare spinel-bearing Al-rich <span class="hlt">chondrules</span> are identified in chondrite finds from Roosevelt County, New Mexico-RC 071 (L4) and RC 072 (L5). These <span class="hlt">chondrules</span> have unusual mineralogies dominated by highly and asymmetrically zoned Al-Cr-rich spinels. Two alternatives exist to explain the origin of this zoning-fractional crystallization or metamorphism. Fractional crystallization formed the zoning of the trivalent cations and caused a localized depletion in chromites around the large Al-Cr-rich spinels. Diffusive exchange and partitioning of Fe and Mg between <span class="hlt">olivine</span> and spinel during parent-body metamorphism can explain the asymmetric zoning of these elements. The bulk compositions of the <span class="hlt">chondrules</span> suggest affinities with the Na-Al-Cr-rich <span class="hlt">chondrules</span>, as would be expected from the abundance of Al-Cr-rich spinels. The most important factors are the temperature to which the molten <span class="hlt">chondrule</span> was heated and the cooling rate during crystallization. These two <span class="hlt">chondrules</span> cooled rapidly from near the liquidus, as indicated by the zoning, occurrence and sizes of spinels, radiating <span class="hlt">chondrule</span> textures and localized chromite depletions.</p> <div class="credits"> <p class="dwt_author">Mccoy, Timothy J.; Pun, Aurora; Keil, Klaus</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">135</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19890039063&hterms=difference+rocks+minerals&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Ddifference%2Brocks%2Bminerals"> <span id="translatedtitle"><span class="hlt">Chondrules</span> in the Sharps H3 chondrite - Evidence for intergroup compositional differences among ordinary chondrite <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Bulk compositions of 19 <span class="hlt">chondrules</span> 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 <span class="hlt">chondrule</span> types; e.g., in H3 as well as L3 and LL3 chondrites, porphyritic <span class="hlt">chondrules</span> are more refractory than nonporphyritic <span class="hlt">chondrules</span>. Precursor components of H3 <span class="hlt">chondrules</span> are closely related to those of LL3 <span class="hlt">chondrules</span>. The mean Ir/Ni, Ir/Co, and Ir/Au ratios of H3 <span class="hlt">chondrules</span> differ from the corresponding ratios of LL3 <span class="hlt">chondrules</span> at the 99, 90, and 79 percent confidence levels, respectively. The ratios in H3 <span class="hlt">chondrules</span> exceed those in LL3 <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span>. These differences support the inference that <span class="hlt">chondrule</span> formation occurred after major nebular fractionation events had established the observed bulk compositional differences among OC groups.</p> <div class="credits"> <p class="dwt_author">Rubin, Alan E.; Pernicka, Ernst</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">136</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010GeCoA..74.2190K"> <span id="translatedtitle">Oxygen isotopic compositions of <span class="hlt">chondrules</span> from the metal-rich chondrites Isheyevo (CH/CB b), MAC 02675 (CB b) and QUE 94627 (CB b)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">It has been recently suggested that (1) CH chondrites and the CB b/CH-like chondrite Isheyevo contain two populations of <span class="hlt">chondrules</span> formed by different processes: (i) magnesian non-porphyritic (cryptocrystalline and <span class="hlt">barred</span>) <span class="hlt">chondrules</span>, which are similar to those in the CB chondrites and formed in an impact-generated plume of melt and gas resulted from large-scale asteroidal collision, and (ii) porphyritic <span class="hlt">chondrules</span> formed by melting of solid precursors in the solar nebula. (2) Porphyritic <span class="hlt">chondrules</span> in Isheyevo and CH chondrites are different from porphyritic <span class="hlt">chondrules</span> in other carbonaceous chondrites ( Krot et al., 2005, 2008a,b). In order to test these hypotheses, we measured in situ oxygen isotopic compositions of porphyritic (magnesian, Type I and ferroan, Type II) and non-porphyritic (magnesian and ferroan cryptocrystalline) <span class="hlt">chondrules</span> from Isheyevo and CB b chondrites MAC 02675 and QUE 94627, paired with QUE 94611, using a Cameca ims-1280 ion microprobe. On a three-isotope oxygen diagram ( ?17O vs. ?18O), compositions of <span class="hlt">chondrules</span> measured follow approximately slope-1 line. Data for 19 magnesian cryptocrystalline <span class="hlt">chondrules</span> from Isheyevo, 24 magnesian cryptocrystalline <span class="hlt">chondrules</span> and 6 magnesian cryptocrystalline silicate inclusions inside chemically-zoned Fe,Ni-metal condensates from CB b chondrites have nearly identical compositions: ?17O = -2.2 ± 0.9‰, -2.3 ± 0.6‰ and -2.2 ± 1.0‰ (2 ?), respectively. These observations and isotopically light magnesium compositions of cryptocrystalline magnesian <span class="hlt">chondrules</span> in CB b chondrites ( Gounelle et al., 2007) are consistent with their single-stage origin, possibly as gas-melt condensates in an impact-generated plume. In contrast, ?17O values for 11 Type I and 9 Type II <span class="hlt">chondrules</span> from Isheyevo range from -5‰ to +4‰ and from -17‰ to +3‰, respectively. In contrast to typical <span class="hlt">chondrules</span> from carbonaceous chondrites, seven out of 11 Type I <span class="hlt">chondrules</span> from Isheyevo plot above the terrestrial fractionation line. We conclude that (i) porphyritic <span class="hlt">chondrules</span> in Isheyevo belong to a unique population of objects, suggesting formation either in a different nebular region or at a different time than <span class="hlt">chondrules</span> from other carbonaceous chondrites; (ii) Isheyevo, CB and CH chondrites are genetically related meteorites: they contain non-porphyritic <span class="hlt">chondrules</span> produced during the same highly-energetic event, probably large-scale asteroidal collision; (iii) the differences in mineralogy, petrography, chemical and whole-rock oxygen isotopic compositions between CH and CB chondrites are due to various proportions of the nebular and the impact-produced materials.</p> <div class="credits"> <p class="dwt_author">Krot, Alexander N.; Nagashima, Kazuhide; Yoshitake, Miwa; Yurimoto, Hisayoshi</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">137</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19800060501&hterms=1103&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3D1103"> <span id="translatedtitle"><span class="hlt">Olivines</span> and <span class="hlt">olivine</span> coronas in mesosiderites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The paper presents a study of <span class="hlt">olivines</span> and their surrounding coronas in mesosiderites texturally and compositionally using optical and microprobe methods. <span class="hlt">Olivine</span> composition ranges from Fo(58-92) and shows no consistent pattern of distribution within and between mesosiderites; <span class="hlt">olivine</span> occurs as large single crystals or as partially recrystallized mineral clasts, except for two lithic clasts. These are Emery and Vaca Muerta, and both are shock-modified <span class="hlt">olivine</span> orthopyroxenites. Fine-grained coronas surround <span class="hlt">olivine</span>, except for those in impact-melt group mesosiderites and those without tridymite in their matrices. Coronas consist largely of orthopyroxene, plagioclase, clinopyroxene, chromite, merillite, and ilmenite, and are similar to the matrix, but lack metal and tridymite. Texturally the innermost parts of the corona can be divided into three stages of development: (1) radiating acicular, (2) intermediate, and (3) granular.</p> <div class="credits"> <p class="dwt_author">Nehru, C. E.; Zucker, S. M.; Harlow, G. E.; Prinz, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">138</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1980GeCoA..44.1103N"> <span id="translatedtitle"><span class="hlt">Olivines</span> and <span class="hlt">olivine</span> coronas in mesosiderites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The paper presents a study of <span class="hlt">olivines</span> and their surrounding coronas in mesosiderites texturally and compositionally using optical and microprobe methods. <span class="hlt">Olivine</span> composition ranges from Fo(58-92) and shows no consistent pattern of distribution within and between mesosiderites; <span class="hlt">olivine</span> occurs as large single crystals or as partially recrystallized mineral clasts, except for two lithic clasts. These are Emery and Vaca Muerta, and both are shock-modified <span class="hlt">olivine</span> orthopyroxenites. Fine-grained coronas surround <span class="hlt">olivine</span>, except for those in impact-melt group mesosiderites and those without tridymite in their matrices. Coronas consist largely of orthopyroxene, plagioclase, clinopyroxene, chromite, merillite, and ilmenite, and are similar to the matrix, but lack metal and tridymite. Texturally the innermost parts of the corona can be divided into three stages of development: (1) radiating acicular, (2) intermediate, and (3) granular.</p> <div class="credits"> <p class="dwt_author">Nehru, C. E.; Zucker, S.; Harlow, G. E.; Prinz, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">139</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050162083&hterms=shock+wave&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dshock%2Bwave"> <span id="translatedtitle">The Collisions of <span class="hlt">Chondrules</span> Behind Shock Waves</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">One of the reasons that the mechanism(s) responsible for the formation of <span class="hlt">chondrules</span> has remained so elusive is that each proposed mechanism must be able to explain a large number of features observed in <span class="hlt">chondrules</span>. Most models of <span class="hlt">chondrule</span> formation focus on matching the expected thermal histories of <span class="hlt">chondrules</span>: rapid heating followed by cooling during crystallization at rates between approx. 10-1000 K/hr [1], and references therein]. Thus far, only models for large shock waves in the solar nebula have quantitatively shown that the thermal evolution of millimeter-sized particles in the nebula can match these inferred thermal histories [2-4]. While this is a positive step for the shock wave model, further testing is needed to see if other properties of <span class="hlt">chondrules</span> can be explained in the context of this model. One area of interest is understanding the collisional evolution of <span class="hlt">chondrules</span> after they encounter a shock wave. These collisions could lead to sticking, destruction, or bouncing. Here we focus on understanding what conditions are needed for these different outcomes to occur and try to reconcile the seemingly contradictory conclusions reached by studies of compound <span class="hlt">chondrule</span> formation and <span class="hlt">chondrule</span> destruction by collisions behind a shock wave.</p> <div class="credits"> <p class="dwt_author">Ciesla, F. J.; Hood, L. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">140</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20140000237&hterms=self+study&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dself%2Bstudy"> <span id="translatedtitle">A Microanalytical (TEM) Study of Fine-grained <span class="hlt">Chondrule</span> Rims in NWA 5717</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Northwest Africa (NWA) 5717 is a highly primitive ordinary chondrite of petrologic type 3.05 with ubiquitous fine-grained <span class="hlt">chondrule</span> rims [1, 2]. Rims appear around approximately 60% of <span class="hlt">chondrules</span> and are comprised of micron-sized mineral and lithic fragments and microchondrules that are embdedded in an FeO-rich submicron groundmass that compositionally resembles fayalitic <span class="hlt">olivine</span>. Some rim clasts appear overprinted with FeO-rich material, suggesting secondary alteration that postdates rim formation. Here we present a microanalytical (TEM) study of the submicron component (i.e. the groundmass) of the rims in order to determine the crystal structures and compositions of their constituent phases and decipher the accretion and alteration history recorded in rims.</p> <div class="credits"> <p class="dwt_author">Bigolski, J. N.; Frank, D. R.; Zolensky, Michael E.; Weisberg, M. K.; Ebel, D. S.; Rahman, Z.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_6");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_7");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a style="font-weight: bold;">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_9");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">141</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20060049107&hterms=pyroxene&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dpyroxene"> <span id="translatedtitle">Aluminian Low-Ca Pyroxene in a Ca-Al-rich <span class="hlt">Chondrule</span> from the Semarkona Meteorite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A Ca-AI-rich <span class="hlt">chondrule</span> (labeled G7) from the Semarkona LL3.0 ordinary chondrite (OC) consists of 73 vol% glassy mesostasis, 22 vol% skeletal forsterite. 3 vol% fassaite (i.e., Al-Ti diopside), and 2 vol% Al-rich, low-Ca pyroxene. The latter phase, which contains up to 16.3 wt% A1203, is among the most AI-rich, low-Ca pyroxene grains ever reported. It is inferred that 20% of the tetrahedral sites and 13% of the octahedral sites in this grain are occupied by Al. Approximately parallel optical extinction implies that the Al-rich, low-Ca pyroxene grains are probably orthorhombic, consistent with literature data that show that A1203 stabilizes the orthoenstatite structure relative to protoenstatite at low pressure. The order of crystallization in the <span class="hlt">chondrule</span> was forsterite, AI-rich low-Ca pyroxene, and fassaite; the residual liquid vitrified during <span class="hlt">chondrule</span> quenching. Phase relationships indicate that, for a G7-composition liquid at equilibrium, spinel and anorthite should crystallize early and orthopyroxene should not crystallize at all. The presence of AI-rich orthopyroxene in G7 is due mainly to the kinetic failure of anorthite to crystallize; this failure was caused by quenching of the G7 precursor droplet. Aluminum preferentially enters the relatively large B tetrahedra of orthopyroxene; because only one tetrahedral size occurs in fassaite, this phase contains higher mean concentrations of Al2O3 than the Al-rich orthopyroxene (17.8 and 14.7 wt%, respectively). <span class="hlt">Chondrule</span> G7 may have formed by remelting an amoeboid <span class="hlt">olivine</span> inclusion that entered the OC region of the solar nebula during an episode of <span class="hlt">chondrule</span> formation.</p> <div class="credits"> <p class="dwt_author">Rubin, Alan E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">142</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20060049098&hterms=oxidation&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Doxidation"> <span id="translatedtitle">Relationships Among Intrinsic Properties of Ordinary Chondrites: Oxidation State, Bulk Chemistry, Oxygen-isotopic Composition, Petrologic Type, and <span class="hlt">Chondrule</span> Size</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The properties of ordinary chondrites (OC) reflect both nebular and asteroidal processes. OC are modeled here as having acquired nebular water, probably contained within phyllosilicates, during agglomeration. This component had high Ai70 and acted like an oxidizing agent during thermal metamorphism. The nebular origin of this component is consistent with negative correlations in H, L, and LL chondrites between oxidation state (represented by <span class="hlt">olivine</span> Fa) and bulk concentration ratios of elements involved in the metal-silicate fractionation (e.g., NdSi, Ir/Si, Ir/Mn, Ir/Cr, Ir/Mg, Ni/Mg, As/Mg, Ga/Mg). LL chondrites acquired the greatest abundance of phyllosilicates with high (delta)O-17 among OC (and thus became the most oxidized group and the one with the heaviest O isotopes); H chondrites acquired the lowest abundance, becoming the most reduced OC group with the lightest O isotopes. <span class="hlt">Chondrule</span> precursors may have grown larger and more ferroan with time in each OC agglomeration zone. Nebular turbulence may have controlled the sizes of <span class="hlt">chondrule</span> precursors. H-chondrite <span class="hlt">chondrules</span> (which are the smallest among OC) formed from the smallest precursors. In each OC region, low-FeO <span class="hlt">chondrules</span> formed before high-FeO <span class="hlt">chondrules</span> during repeated episodes of <span class="hlt">chondrule</span> formation. During thermal metamorphism, phyllosilicates were dehydrated; the liberated water oxidized metallic Fe-Ni. This caused correlated changes with petrologic type including decreases in the modal abundance of metal, increases in <span class="hlt">olivine</span> Fa and low-Ca pyroxene Fs, increases in the <span class="hlt">olivine</span>/pyroxene ratio, and increases in the kamacite Co and Ni contents. As water (with its heavy 0 isotopes) was lost during metamorphism, inverse correlations between bulk (delta)O-18 and bulk (delta)O-17 with petrologic type were produced. The H5 chondrites that were ejected from their parent body approx.7.5 Ma ago during a major impact event probably had been within a few kilometers of each other since they accreted approx.4.5 Ga ago. There are significant differences in the <span class="hlt">olivine</span> compositional distributions among these rocks; these reflect stochastic nebular sampling of the oxidant (Le., phyllosilicates with high (delta)O-17) on a 0.1-1 km scale during agglomeration.</p> <div class="credits"> <p class="dwt_author">Rubin, Alan E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">143</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005GeCoA..69.4907R"> <span id="translatedtitle">Relationships among intrinsic properties of ordinary chondrites: Oxidation state, bulk chemistry, oxygen-isotopic composition, petrologic type, and <span class="hlt">chondrule</span> size</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The properties of ordinary chondrites (OC) reflect both nebular and asteroidal processes. OC are modeled here as having acquired nebular water, probably contained within phyllosilicates, during agglomeration. This component had high ? 17O and acted like an oxidizing agent during thermal metamorphism. The nebular origin of this component is consistent with negative correlations in H, L, and LL chondrites between oxidation state (represented by <span class="hlt">olivine</span> Fa) and bulk concentration ratios of elements involved in the metal-silicate fractionation (e.g., Ni/Si, Ir/Si, Ir/Mn, Ir/Cr, Ir/Mg, Ni/Mg, As/Mg, Ga/Mg). LL chondrites acquired the greatest abundance of phyllosilicates with high ? 17O among OC (and thus became the most oxidized group and the one with the heaviest O isotopes); H chondrites acquired the lowest abundance, becoming the most reduced OC group with the lightest O isotopes. <span class="hlt">Chondrule</span> precursors may have grown larger and more ferroan with time in each OC agglomeration zone. Nebular turbulence may have controlled the sizes of <span class="hlt">chondrule</span> precursors. H-chondrite <span class="hlt">chondrules</span> (which are the smallest among OC) formed from the smallest precursors. In each OC region, low-FeO <span class="hlt">chondrules</span> formed before high-FeO <span class="hlt">chondrules</span> during repeated episodes of <span class="hlt">chondrule</span> formation. During thermal metamorphism, phyllosilicates were dehydrated; the liberated water oxidized metallic Fe-Ni. This caused correlated changes with petrologic type including decreases in the modal abundance of metal, increases in <span class="hlt">olivine</span> Fa and low-Ca pyroxene Fs, increases in the <span class="hlt">olivine</span>/pyroxene ratio, and increases in the kamacite Co and Ni contents. As water (with its heavy O isotopes) was lost during metamorphism, inverse correlations between bulk ? 18O and bulk ? 17O with petrologic type were produced. The H5 chondrites that were ejected from their parent body ˜7.5 Ma ago during a major impact event probably had been within a few kilometers of each other since they accreted ˜4.5 Ga ago. There are significant differences in the <span class="hlt">olivine</span> compositional distributions among these rocks; these reflect stochastic nebular sampling of the oxidant (i.e., phyllosilicates with high ? 17O) on a 0.1-1 km scale during agglomeration.</p> <div class="credits"> <p class="dwt_author">Rubin, Alan E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">144</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19790065612&hterms=paleomagnetism&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dpaleomagnetism"> <span id="translatedtitle">On the origin of <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A new mechanism for primordial melting of <span class="hlt">chondrules</span> based upon heating by relativistic electrons accelerated by reconnecting magnetic field lines is discussed. This mechanism is free of the creation-annihilation problem of collisions used for heating. The basic requirements for reconnection are an interplanetary magnetic field with regions of reversals. An early magnetic field is inferred from the paleomagnetism of meteorites and the requirements of solar spin-down, while the field reversals upon which the reconnection is based are a common property of the present epoch solar wind.</p> <div class="credits"> <p class="dwt_author">Sonett, C. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1979-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">145</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19940007705&hterms=roger+hewins&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Droger%2Bhewins"> <span id="translatedtitle">Flash melting of <span class="hlt">chondrule</span> precursors in excess of 1600 C. Series 1: Type 2 (B1) <span class="hlt">chondrule</span> composition experiments</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Several questions in <span class="hlt">chondrule</span> production remain an enigma despite years of experiments. What were the melting temperatures experienced by <span class="hlt">chondrules</span>? What were the physical characteristics of <span class="hlt">chondrule</span> precursors? How and why did volatile elements (i.e. Na) found within <span class="hlt">chondrules</span> survive the formation process? We present the initial results of a series of experiments designed to investigate the above questions by using flash melting to duplicate the melting stage of <span class="hlt">chondrule</span> formation.</p> <div class="credits"> <p class="dwt_author">Connolly, Harold C., Jr.; Hewins, Roger H.; Lofgren, Gary E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">146</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050165557&hterms=genetics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dgenetics"> <span id="translatedtitle">Genetic Relationships Between <span class="hlt">Chondrules</span>, Rims and Matrix</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The most primitive chondrites are composed of <span class="hlt">chondrules</span> and <span class="hlt">chondrule</span> fragments, various types of inclusions, discrete mineral grains, metal, sulfides, and fine-grained materials that occur as interchondrule matrix and as <span class="hlt">chondrule</span>/inclusion rims. Understanding how these components are related is essential for understanding how chondrites and their constituents formed and were processed in the solar nebula. For example, were the first generations of <span class="hlt">chondrules</span> formed by melting of matrix or matrix precursors? Did <span class="hlt">chondrule</span> formation result in appreciable transfer of <span class="hlt">chondrule</span> material into the matrix? Here, we consider three types of data: 1) compositional data for bulk chondrites and matrix, 2) mineralogical and textural information, and 3) the abundances and characteristics of presolar materials that reside in the matrix and rims. We use these data to evaluate the roles of evaporation and condensation, <span class="hlt">chondrule</span> formation, mixing of different nebular components, and secondary processing both in the nebula and on the parent bodies. Our goal is to identify the things that are reasonably well established and to point out the areas that need additional work.</p> <div class="credits"> <p class="dwt_author">Huss, G. R.; Alexander, C. M. OD.; Palme, H.; Bland, P. A.; Wasson, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">147</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20040059901&hterms=cu+zn&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dcu%2Bzn"> <span id="translatedtitle">Metallic <span class="hlt">Chondrules</span> in NWA1390 (H3-6): Clues to Their History from Metallic Cu</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A recent study of ordinary chondrites suggests that many long-recognized shock indicators in <span class="hlt">olivine</span> and pyroxene minerals may be erased by post-shock annealing. Therefore, the presence of other indicators of shock, which can not be erased by subsequent heating, are important to fully characterize the history of chondritic meteorites. One such proposed indicator is metallic Cu, which occurs in at least 2/3 of ordinary chondrites. Here we present a comparative study of two metallic <span class="hlt">chondrules</span> in the NWA1390 ordinary chondrite, both of which contain appreciable Cu in the Fe,Ni metal phase and one that is partially rimmed by metallic Cu.</p> <div class="credits"> <p class="dwt_author">LaBlue, A. R.; Lauretta, D. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">148</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950012891&hterms=hutchison&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dhutchison"> <span id="translatedtitle"><span class="hlt">Chondrules</span> and their associates in ordinary chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A theory for the origin of the ordinary chondrites (OC's) must account for the origin(s) of their constituents. If the OC's accreted in a protoplanetary disk, their components represent the variety of materials that coexisted in it, which constrains their possible origins. The following discussion excludes gas-rich meteorites that formed after any disk had dissipated. This discussion entails: (1) ordinary chondrites' physical properties; (2) textural relationships between <span class="hlt">chondrules</span>; (3) textures within <span class="hlt">chondrules</span>; (4) chemical composition; (5) igneous fragments; (6) <span class="hlt">chondrule</span> rims and interchonrule matrix; and (7) ages of chondrites and inclusions.</p> <div class="credits"> <p class="dwt_author">Hutchison, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">149</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/9445468"> <span id="translatedtitle">The origin of <span class="hlt">chondrules</span> at jovian resonances</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Isotopic dating indicates that <span class="hlt">chondrules</span> were produced a few million years after the solar nebula formed. This timing is incompatible with dynamical lifetimes of small particles in the nebula and short time scales for the formation of planetesimals. Temporal and dynamical constraints can be reconciled if <span class="hlt">chondrules</span> were produced by heating of debris from disrupted first-generation planetesimals. Jovian resonances can excite planetesimal eccentricities enough to cause collisional disruption and melting of dust by bow shocks in the nebular gas. The ages of <span class="hlt">chondrules</span> may indicate the times of Jupiter's formation and dissipation of gas from the asteroidal region. PMID:9445468</p> <div class="credits"> <p class="dwt_author">Weidenschilling; Marzari; Hood</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-30</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">150</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1998M%26PS...33.1087W"> <span id="translatedtitle">Fayalitic <span class="hlt">olivine</span> in CV3 chondrite matrix and dark inclusions: A nebular origin</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Fayalitic <span class="hlt">olivine</span> (Fa>32) is the major component of the matrices and Dark Inclusions (DI) of CV3 and other unequilibrated chondrites. It occurs most commonly as rims, veins and halos in and around <span class="hlt">chondrule</span> silicates in the Allende-type (CV3OxA) chondrites and to a much lesser extent in the reduced (CV3R) and Bali-type (CV3OxB) chondrites. The <span class="hlt">olivines</span> have distinctive platy, tabular and lath- or irregular-shaped crystals, with the ratio the two types varying widely. In CV3OxB chondrites, matrix fayalitic <span class="hlt">olivines</span> range up to Fa99.9, whereas in the other CV3 chondrites the range is much smaller. The platy and tabular anisotropic forms of the fayalitic <span class="hlt">olivines</span> strongly suggest growth from a vapor and the nature of occurrences suggests that CV3 matrices are unequilibrated mixtures of nebular materials. We argue that the parent body hydration/dehydration model has numerous inconsistencies that make this hypothesis highly unlikely. These include: (1) There is no direct evidence linking fayalitic <span class="hlt">olivine</span> to precursor phyllosilicates. (2) Dehydration of phyllosilicates cannot explain the wide range of morphologies of the fayalitic <span class="hlt">olivines</span>. (3) Fayalitic <span class="hlt">olivine</span> clearly predates the formation of the hydrous phases in CV3 chondrites and is one of the phases that breaks down to form phyllosilicates (Keller et al., 1994). (4) The unequilibrated nature of the matrix, including fine scale zoning in 10=B5-sized fayalitic <span class="hlt">olivine</span> crystals, would not survive the parent body metamorphism required in the dehydration model. (5) A DI in the Ningqiang chondrite contains fayalitic <span class="hlt">olivine</span> rimmed by glassy and microcrystalline material (Zolensky et al., 1997), which probably formed by radiation damage. This indicates that the fayalitic <span class="hlt">olivine</span> was exposed to solar radiation in a nebular setting. (6) Some Allende <span class="hlt">chondrules</span> contain unaltered primary, anhydrous glassy mesostasis in contact with the host matrix (e.g., Ikeda and Kimura, 1995). <span class="hlt">Chondrule</span> mesostases would not have survived parent body hydration without becoming hydrated and would probably not survive the metamorphic heating required in the dehydration scenario. (7) Single platy and barrel-shaped crystals of fayalitic <span class="hlt">olivine</span> are present in accretionary rims in CAIs (MacPherson and Davis, 1997), which developed in the nebula. (8) Matrix lumps completely encased in <span class="hlt">chondrules</span> in ordinary chondrites contain mainly fayalitic <span class="hlt">olivine</span> (Scott et al., 1984), indicating a nebular origin. (9) Oxygen isotopic compositions of Allende matrix and DIs strongly indicate little or no hydration for Allende and its components (Clayton, 1997). We favor a nebular vaporization/recondensation model in which vaporization of chondritic dust produced a fayalite-rich vapor, followed by formation of the fayalitic <span class="hlt">olivine</span> by direct recondensation from the vapor, epitactic growth on surfaces of existing forsterite and enstatite in <span class="hlt">chondrules</span>, and replacement of existing forsterite and enstatite by gas-solid exchange.</p> <div class="credits"> <p class="dwt_author">Weisberg, Michael K.; Prinz, Martin</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">151</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014Icar..232..176J"> <span id="translatedtitle">The quasi-universality of <span class="hlt">chondrule</span> size as a constraint for <span class="hlt">chondrule</span> formation models</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Primitive meteorites are dominated by millimeter-size silicate spherules called <span class="hlt">chondrules</span>. The nature of the high-temperature events that produced them in the early Solar System remains enigmatic. Beside their thermal history, one important clue is provided by their size which shows remarkably little variation (less than a factor of 6 for the mean <span class="hlt">chondrule</span> radius of most chondrites) despite the extensive range of ages and heliocentric distances sampled. It is however unclear whether <span class="hlt">chondrule</span> size is due to the <span class="hlt">chondrule</span> melting process itself, or has been simply inherited from the precursor material, or yet results from some sorting process. I examine these different possibilities in terms of their analytical size predictions. Unless the <span class="hlt">chondrule</span>-forming “window” was very narrow, radial sorting can be excluded as a size-determining process because of the large variations it would predict. Molten planetesimal collision or impact melting models, which derive <span class="hlt">chondrules</span> from the fragmentation of larger melt bodies, would likewise predict too much size variability by themselves; more generally any size modification during <span class="hlt">chondrule</span> formation is limited in extent by evidence from compound <span class="hlt">chondrules</span> and the considerable compositional variability of <span class="hlt">chondrules</span>. Turbulent concentration would predict a low size variability but lack of evidence of any accretion bias in carbonaceous chondrites may be difficult to reconcile with any form of local sorting upon agglomeration. Growth by sticking (especially if bouncing-limited) of aggregates as <span class="hlt">chondrule</span> precursors would yield limited variations of their final radius in space and time, and would be consistent with the relatively similar size of other chondrite components such as refractory inclusions. This suggests that the <span class="hlt">chondrule</span>-melting process(es) simply melted such nebular aggregates with little modification of mass.</p> <div class="credits"> <p class="dwt_author">Jacquet, Emmanuel</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">152</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950012924&hterms=H3&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DH3"> <span id="translatedtitle">Textural variability of ordinary chondrite <span class="hlt">chondrules</span>: Implications of their formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Scanning electron microscopy (SEM) and microprobe examination of the Raguli H3-4, Saratov L3, and Fucbin L5-6 ordinary chondrites and the analysis of preexisted data on other meteorites have shown that the variety of textural types of <span class="hlt">chondrules</span> depends on the chemical composition of the <span class="hlt">chondrules</span>. The comparison of bulk-rock chemistries of the <span class="hlt">chondrules</span> by major components demonstrates that they apparently fall, like basic-ultrabasic rock, into groups of dunitic and pyroxenitic composition. This separation is further validated by the character of zoning in <span class="hlt">chondrules</span> of the intermediate, peridotitic type. The effect is vividly demonstrated by the '<span class="hlt">chondrule-in-chondrule</span>' structure.</p> <div class="credits"> <p class="dwt_author">Zinovieva, N. G.; Mitreikina, O. B.; Granovsky, L. B.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">153</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1995Metic..30..599W"> <span id="translatedtitle">I-Xe Dating of Small <span class="hlt">Chondrules</span> from the Bjurbole Meteorite Using RELAX</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Chondrules</span> from the Bjurbole L4 meteorite have been widely used as a standard for I-Xe dating because of the good high temperature 129Xe-128Xe correlation [1] and small spread in their apparent ages determined by this technique. As part of an ongoing study [2,3], I-Xe analyses have been performed on several Bjurbole <span class="hlt">chondrules</span> of sizes smaller than have hitherto been studied in order to determine if the <span class="hlt">chondrules</span> and their constituent minerals are isochronous on a small scale. Use has been made of the ultra-sensitive RELAX resonance ionization xenon mass spectrometer, in conjunction with a laser probe for low-blank sample extraction [4] to analyse <span class="hlt">chondrule</span> aliquots ranging in mass from 54 micrograms to 306 micrograms. Using data from five <span class="hlt">chondrules</span> a spread of ages of 5Ma about the mean has been observed (129I t1/2=1.7x10^7 Ma), with specific excess (over the ordinary chondrite value [6]) 129Xe contents in the range 10x10^-12 to 1200x10^-12 cm3 STP g-1, consistent with previously reported values [2,5]. All the <span class="hlt">chondrules</span> were completely molten at the highest laser probe powers used, hence it may be assumed that they were completely outgassed, in contrast to the data presented in [2]. This assumption is born out by the magnitudes of the specific excess 129Xe release. The smaller <span class="hlt">chondrules</span> showed a sharper 129Xe release as a function of laser power as would be expected from the discussion of temperature gradients in [2]. Good isochrons were obtained except in the case of one sample (ABjC19) which contained very little excess 129Xe. The figure shows data from sample ABjC22, a 54 microgram aliquot from a 336 microgram <span class="hlt">chondrule</span>. Excess 129Xe release and the ratio of excess 129Xe to excess 128Xe are plotted against extraction number (higher numbers correspond to higher temperatures). The fourth extraction gave rise to a 129Xe*/128Xe* ratio significantly different from the mean (error <span class="hlt">bars</span> are one standard deviation) corresponding to an age apparently 3Ma older than the plateau. The reason for this is unclear, although the presence in the sample of material with an older closure age is a possible explanation and may account for the observed spread in I-Xe ages of Bjurbole <span class="hlt">chondrules</span>. Two of the <span class="hlt">chondrules</span> analysed (ABjC33, ABjC22) exhibited a good correlation between excess 128Xe and 131Xe, in agreement with some prior observations [2,3], suggesting that in some <span class="hlt">chondrules</span> the iodine bearing phase may be intimately mixed with a phase containing barium or tellurium. Aliquots of all the <span class="hlt">chondrules</span> analysed have been retained for mineralogical characterization. References: [1] Turner G. (1965) JGR, 70, 5433-5445. [2] Gilmour J. D. et al. (1995) Meteoritics, in press. [3] Gilmour J. D. and Turner G. (1994) Noble Gas Geochemistry and Cosmochemistry (J. Matsuda, ed.). [4] Gilmour J. D. et al. (1994) Rev. Sci. Instrum., 65, 617-625. [5] Caffee et al. (1982) Proc. LPSC 13th, in JGR, 87, A303-A317. [6] Lavielle B. and Marti K. (1992) JGR, 97, 20875-20881.</p> <div class="credits"> <p class="dwt_author">Whitby, J. A.; Gilmour, J. D.; Ash, R. D.; Turner, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">154</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19850007296&hterms=sulphide&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3D%2522sulphide%2522"> <span id="translatedtitle"><span class="hlt">Chondrules</span> in the bishunpur L13 chondrite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Twenty-six <span class="hlt">chondrules</span>, <span class="hlt">chondrule</span> fragments or clasts were analyzed. An automated wavelength dispersive instrument with a 90 micrometer beam integrated a series of analyses in traverses across each object. Depending on the size of the cross-sectional area, from 1 to 21 analyses were performed for each bulk analysis. Si, Ti, Al, Cr, Fe, Ni, Mn, Mg, Ca, Na, K and S were determined, and an analyzed augite was used as a secondary standard before and after each set of analyses. The work is part of a study of <span class="hlt">chondrule</span> rims, interchondrule matrix, <span class="hlt">chondrules</span> and clasts in unequilibrated ordinary chondrites. Only two of the twenty-six objects analyzed have Ca/Al atomic ratios greater than the ordinary chondritic average of 0.74. The bulk meteorite has a normal Ca/Al ratio, so presumably a Ca-rich, Al-poor component must be present to compensate for <span class="hlt">chondrules</span> and chlasts. This component is unlikely to be rim or matrix, but may be phosphate associated with metal or sulphide. Na/Al ratios range from 1 to almost zero, but there is no hiatus as in a suite of Manych <span class="hlt">chondrules</span> and glasses.</p> <div class="credits"> <p class="dwt_author">Hutchison, R.; Alexander, C.; Barber, D. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">155</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19940007699&hterms=pallasite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2522pallasite%2522"> <span id="translatedtitle"><span class="hlt">Olivine</span>-rich asteroids, pallasitic <span class="hlt">olivine</span> and <span class="hlt">olivine</span>-metal mixtures: Comparisons of reflectance spectra</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The recent acquisition of high resolution 0.3 - 2.6 micron reflectance spectra for a number of <span class="hlt">olivine</span>-rich asteroids permits the analysis of their surface compositions to be made on the basis of new and existing laboratory spectral data for pallasitic <span class="hlt">olivines</span> and <span class="hlt">olivine</span>-metal mixtures. Analysis of the spectral data for the latter has revealed a number of spectral parameters which can be used to constrain <span class="hlt">olivine</span> and metal abundances, grain sizes, and <span class="hlt">olivine</span> compositions. The following topics are discussed in greater detail: pallasite <span class="hlt">olivine</span> spectra, <span class="hlt">olivine</span>-metal mixture spectra, and <span class="hlt">olivine</span>-rich asteroid spectra.</p> <div class="credits"> <p class="dwt_author">Cloutis, E. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">156</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950012909&hterms=ip&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dip"> <span id="translatedtitle"><span class="hlt">Chondrule</span> formation in the radiative accretional shock</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The physical, mineralogical, and isotopic properties of <span class="hlt">chondrules</span> strongly indicate that they were formed by the rapid melting and resolidification of preexisting solids composed of primitive material. The <span class="hlt">chondrule</span> precursors were heated to temperatures of about 1800 K in short high-temperature events, followed by cooling with a rate of 10(exp 2)-10(exp 3) K/hr. A heat input of about 1500 J/g is required to heat <span class="hlt">chondrule</span> precursors to such a temperature and melt them. Lightning discharges and flares in the solar nebula, and heating of the <span class="hlt">chondrule</span> precursors by friction with gas decelerated in the accretional shock or in a shock (of unspecified origin) within the solar nebula, have been discussed as possible mechanisms for <span class="hlt">chondrule</span> formation. One advantage of <span class="hlt">chondrule</span> formation in large-scale shocks is that a lot of dust material can be processed. An accretional shock, which is produced by infalling gas of the presolar cloud when it collides with the solar nebula, belongs to this type of shock. In 1984 Wood considered the possibility of <span class="hlt">chondrule</span> formation in the accretional shock by heating of <span class="hlt">chondrule</span> precursors by gas drag. He concluded that the density in the accreting material is much lower than needed to melt silicates at the distance of the asteroid belt if the accreting matter had the cosmic ratio of dust to gas, and the mass of the solar nebula did not exceed 2 solar mass units. Melting of <span class="hlt">chondrule</span> precursors is difficult because of their effective cooling by thermal radiation. Suppression of the radiative cooling of individual grains in dust swarms, which are opaque to thermal emission, was considered to be the only possible means of <span class="hlt">chondrule</span> formation in solar nebula shocks. Previous models of solid grain melting in solar nebula shocks have neglected gas cooling behind the shock front, i.e., they considered adiabatic shocks. In this paper we show that large dust grains could be heated much stronger than was supposed by these authors, because of effects associated with the gas cooling.</p> <div class="credits"> <p class="dwt_author">Ruzmaikina, T. V.; Ip, W.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">157</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20040059896&hterms=quantitative+methods&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522quantitative%2Bmethods%2522"> <span id="translatedtitle">Lunar and Planetary Science XXXV: <span class="hlt">Chondrules</span> and CAIs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The session "<span class="hlt">Chondrules</span> and CAI's" included the following reports:Metallic <span class="hlt">Chondrules</span> in NWA 1390 (H3-6): Clues to Their History from Metallic Cu; Relationship Between Bulk Chemical Composition and Formation Age of <span class="hlt">Chondrules</span> in Bishunpur and Krymka; Relict Forsterite in <span class="hlt">Chondrules</span>: Implications for Cooling Rates; An Evaluation of Quantitative Methods of Determining the Degree of Melting Experienced by a <span class="hlt">Chondrule</span>; Rare Earth Element Fractionation in <span class="hlt">Chondrules</span>; Mineralogy and Petrology of <span class="hlt">Chondrules</span> in Carbonaceous Chondrite NWA 770; Isotopic Cosmobarometry: A Synthesis of Concepts and Implications for <span class="hlt">Chondrule</span> and CAI Formation Mechanisms; Further Investigations of Minor Element Distributions in Spinels in Type B CAIs; and Trace Element Compositions of the Sublayers Making Up W-L Rims on CAI .</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">158</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41055163"> <span id="translatedtitle">Petrologic, geochemical and experimental constraints on models of <span class="hlt">chondrule</span> formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The petrologic and geochemical properties of <span class="hlt">chondrules</span> as well as results of experimental studies provide strong constraints on <span class="hlt">chondrule</span>-formation models. Nebular formation is indicated by the non-mass-fractionated oxygen isotopic compositions of bulk <span class="hlt">chondrules</span>. <span class="hlt">Chondrule</span> formation from a melt is required by the prototypical spheroidal shapes and the presence of euhedral phenocrysts and glassy mesostases. Incomplete melting is indicated by the</p> <div class="credits"> <p class="dwt_author">Alan E. Rubin</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">159</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40919070"> <span id="translatedtitle">Chromite and chromite <span class="hlt">chondrules</span> in meteorites--I</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In a number of chondrites, several <span class="hlt">chondrules</span> have been found containing chromite as a major component. The second, most common mineral in these <span class="hlt">chondrules</span> is usually an albite-like plagioclase. Besides coarse grains of chromite, many <span class="hlt">chondrules</span> contain fine chromite grains, intergrown with feldspar as pseudomorphs after a previously decomposed mineral, probably kosmochlor. Transitions to chromite aggregates, which may represent deformed</p> <div class="credits"> <p class="dwt_author">Paul Ramdohr</p> <p class="dwt_publisher"></p> <p class="publishDate">1967-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">160</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www2.mnhn.fr/hdt205/leme/doc/2001%20Shu%20et%20al%20ApJ.pdf"> <span id="translatedtitle">The Origin of <span class="hlt">Chondrules</span> and Refractory Inclusions in Chondritic Meteorites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Examples of calcium-aluminum-rich inclusions (CAIs) surrounded by thick <span class="hlt">chondrule</span> mantles have been found in chondritic meteorites and cast doubt on the conventional belief that CAIs and <span class="hlt">chondrules</span> possessed different spacetime origins in the primitive solar nebula. We study specific processes by which such objects, and the more common ordinary CAIs and <span class="hlt">chondrules</span>, might have formed by flare heating of primitive</p> <div class="credits"> <p class="dwt_author">Hsien Shang; Matthieu Gounelle; Alfred E. Glassgold; Typhoon Lee</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_7");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return 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id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_8");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a style="font-weight: bold;">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_10");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">161</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011M%26PS...46..857N"> <span id="translatedtitle">Ion microprobe analyses of oxygen three-isotope ratios of <span class="hlt">chondrules</span> from the Sayh al Uhaymir 290 CH chondrite using a multiple-hole disk</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The ion microprobe is the only technique capable of determining high-precision stable isotope ratios in individual tiny extraterrestrial particles (?100 ?m in diameter), but these small samples present special analytical challenges. We produced a new sample holder disk with multiple holes (three holes and seven holes), in which epoxy disks containing a single unknown sample and a standard grain are cast and polished. Performance tests for oxygen two-isotope analyses using San Carlos <span class="hlt">olivine</span> standard grains show that the new multiple-hole disks allow accurate analysis of tiny particles if the particles are located within the 500 ?m and 1 mm radius of the center of holes for seven-hole and three-hole disks, respectively. Using the new seven-hole disk, oxygen three-isotope ratios of eight magnesian cryptocrystalline <span class="hlt">chondrules</span> (approximately 100 ?m in diameter) from the Sayh al Uhaymir (SaU) 290 CH chondrite were analyzed by ion microprobe at the University of Wisconsin. Five out of eight <span class="hlt">chondrules</span> have nearly identical oxygen isotope ratios (?17O = -2.2 ± 0.6‰; 2SD), which is consistent with those of magnesian cryptocrystalline <span class="hlt">chondrules</span> in CH/CB and CB chondrites, suggesting a genetic relationship, i.e., formation by a common (possibly impact) heating event. The other three <span class="hlt">chondrules</span> have distinct oxygen isotope ratios (?17O values from -6.4‰ to +2.2‰). Given that similar variation in ?17O values was observed in type I porphyritic <span class="hlt">chondrules</span> in a CH/CB chondrite, the three <span class="hlt">chondrules</span> may have formed in the solar nebula, similar to the type I porphyritic <span class="hlt">chondrules</span>.</p> <div class="credits"> <p class="dwt_author">Nakashima, Daisuke; Ushikubo, Takayuki; Gowda, Rudraswami N.; Kita, Noriko T.; Valley, John W.; Nagao, Keisuke</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">162</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003LPI....34.1451K"> <span id="translatedtitle">Silica-rich Igneous Rims Around Magnesian <span class="hlt">Chondrules</span> in CR Carbonaceous Chondrites: Evidence for Fractional Condensation During <span class="hlt">Chondrule</span> Formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Type I <span class="hlt">chondrules</span> in CRs are surrounded by silica-rich igneous rims which may have formed by gas-solid condensation of SiO2-rich materials onto <span class="hlt">chondrule</span> surfaces and subsequent incomplete melting, or by direct SiO condensation into <span class="hlt">chondrule</span> melts.</p> <div class="credits"> <p class="dwt_author">Krot, A. N.; Libourel, G.; Goodrich, C. A.; Petaev, M. I.; Killgore, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">163</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2000Icar..143..106L"> <span id="translatedtitle"><span class="hlt">Chondrule</span> Fine-Grained Mantle Formation by Hypervelocity Impact of <span class="hlt">Chondrules</span> with a Dusty Gas</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">At some stage during the <span class="hlt">chondrule</span> (and refractory inclusion) formation process, many of these objects accreted fine-grained mantles of dust. Observations suggest that the mantle thickness is directly proportional to the <span class="hlt">chondrule</span>-core radius. Following the proposal of H. C. Connolly, Jr., and S. G. Love (1998, Science280, 62-67), we demonstrate numerically how this effect can be produced by the hypersonic interaction between a <span class="hlt">chondrule</span> and a mixture of gas and dust. This result is of relevance to the shock and jet models of <span class="hlt">chondrule</span> formation, and places limits on both models. In particular, we use this result to constrain our version of the jet theory of <span class="hlt">chondrule</span> formation, where <span class="hlt">chondrules</span> are formed at the base of a bipolar solar jet and then ejected to the outer regions of a magnetically confined solar nebula, where they impact at hypersonic speeds into the nebula. We find that the observed linear correlation between mantle thickness and <span class="hlt">chondrule</span>-core radius requires a dust-to-gas mass ratio of approximately 0.5-1.0, provided that the dust-<span class="hlt">chondrule</span> sticking coefficient, Q, was in the range 0.5-1.0. We suggest that the settling of dust ejected from the jet could produce such high ratios in the inner regions of the nebula. Another constraint on the <span class="hlt">chondrule</span> formation process is the observed structure of fine-grained rims around igneous rims, but not the other way around. We argue that this observation can be readily explained by the jet model, but poses a challenge for the shock model. As a consequence of this study, we show that the standard drag coefficient for a sphere moving through rarefied gas is approximately 70% of the physically correct value. We also derive a simple form for the drag coefficient which describes the interaction between dust grains and a macroscopic sphere.</p> <div class="credits"> <p class="dwt_author">Liffman, Kurt; Toscano, Maurizio</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">164</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2001Sci...291.1776K"> <span id="translatedtitle">A New Astrophysical Setting for <span class="hlt">Chondrule</span> Formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Chondrules</span> in the metal-rich meteorites Hammadah al Hamra 237 and QUE 94411 have recorded highly energetic thermal events that resulted in complete vaporization of a dusty region of the solar nebula (dust/gas ratio of about 10 to 50 times solar). These <span class="hlt">chondrules</span> formed under oxidizing conditions before condensation of iron-nickel metal, at temperatures greater than or equal to 1500 K, and were isolated from the cooling gas before condensation of moderately volatile elements such as manganese, sodium, potassium, and sulfur. This astrophysical environment is fundamentally different from conventional models for <span class="hlt">chondrule</span> formation by localized, brief, repetitive heating events that resulted in incomplete melting of solid precursors initially residing at ambient temperatures below approximately 650 K.</p> <div class="credits"> <p class="dwt_author">Krot, Alexander N.; Meibom, Anders; Russell, Sara S.; O'D. Alexander, Conel M.; Jeffries, Timothy E.; Keil, Klaus</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">165</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950012898&hterms=love&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dlove"> <span id="translatedtitle">Formation of <span class="hlt">chondrules</span> by electrical discharge heating</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A possible mechanism for making <span class="hlt">chondrules</span> in the solar nebula is electrical discharge ('lightning') heating, which can create high-temperature (greater than 1600 K), short-duration (approximately 10 s) thermal events as indicated by the chondritic record. Lightning occurs in many diverse terrestrial and planetary settings, and may have occurred in the solar nebula; it is thus worthwhile to investigate its implications for <span class="hlt">chondrule</span> formation. Nebular discharges do not appear a viable source of heat for melting <span class="hlt">chondrule</span> precursors, regardless of the uncertainty in the details of the mode. Nonetheless, we believe nebular lightning worthy of further investigation than what is presented here. Experiments analogous to those currently underway to investigate terrestrial thunderstorm lightning could be fruitful in refining nebular lightning models, and would be double interesting in application to nonthunderstorm and planetary lightnings.</p> <div class="credits"> <p class="dwt_author">Love, S. G.; Keil, K.; Scott, E. R. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">166</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFMMR13C1397C"> <span id="translatedtitle">REE Diffusion in <span class="hlt">Olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Diffusion of rare earth elements has been characterized in synthetic forsterite and natural <span class="hlt">olivine</span> (Fo90) under dry conditions. The source of diffusant was a mixture of REE aluminate garnet powder and synthetic forsterite powder in 3:1 proportions. Experiments were prepared by enclosing source material and polished forsterite in platinum capsules, which were crimped shut. For experiments on natural <span class="hlt">olivine</span>, samples were placed with the source in AgPd capsules, which were sealed under vacuum in silica glass ampoules with a solid buffer to buffer at NNO. Prepared capsules were then annealed in 1 atm furnaces for times ranging from an hour to several weeks, at temperatures from 850 to 1300°C. REE distributions in the <span class="hlt">olivine</span> were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for Dy diffusion in forsterite: D = 2.3x10-10 exp(-273 kJ mol-1/RT) m2sec-1. Diffusivities of Yb and La in forsterite appear similar, and preliminary results for Dy diffusion in natural <span class="hlt">olivine</span> also suggest similar diffusivities. REE diffusivities in forsterite are about an order of magnitude faster than those of REE+3 in enstatite (Cherniak and Liang, 2007). However, if the Arrhenius relation above is extrapolated up to 1450C, it yields diffusivities about three orders of magnitude smaller than those determined for REE diffusion in <span class="hlt">olivine</span> by Spandler et al. (2007). Work is currently underway in further characterizing diffusion in Fe-bearing <span class="hlt">olivine</span>. If an Arrhenius relation similar to that for forsterite is found to apply, timescales for preservation of REE signatures in <span class="hlt">olivine</span>-hosted melt inclusions may be relatively long. Cherniak and Liang (2007) GCA 71, 1324-1340; Spandler et al. (2007) Nature 447, 303-306.</p> <div class="credits"> <p class="dwt_author">Cherniak, D. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">167</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19740005450&hterms=forsterite+thesis&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dforsterite%2Bthesis"> <span id="translatedtitle">Artificial meteor ablation studies: <span class="hlt">Olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Artificial meteor ablation was performed on a Mg-rich <span class="hlt">olivine</span> sample using an arc-heated plasma of ionized air. Experimental conditions simulated a meteor traveling about 12 km/sec at an altitude of 70 km. The mineral content of the original <span class="hlt">olivine</span> sample was 98% <span class="hlt">olivine</span> (including traces of <span class="hlt">olivine</span> alteration products) and 2% chromite. Forsterite content of the original <span class="hlt">olivine</span> was Fo-89. After ablation, the forsterite content had increased to Fo-94 in the recrystallized <span class="hlt">olivine</span>. In addition, lamella-like intergrowths of magnetite were prevalent constituents. Wherever magnetite occurred, there was an increase in Mg and a corresponding decrease in Fe for the recrystallized <span class="hlt">olivine</span>. The Allende fusion crust consisted of a recrystallized <span class="hlt">olivine</span>, which was more Mg-rich and Fe-deficient than the original meteorite's <span class="hlt">olivine</span>, and abundant magnetite grains. Although troilite and pentlandite were the common opaque mineral constituents in this meteorite, magnetite was the principal opaque mineral found in the fusion crust.</p> <div class="credits"> <p class="dwt_author">Blanchard, M. B.; Cunningham, G. G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1973-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">168</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1987GeCoA..51.1923R"> <span id="translatedtitle"><span class="hlt">Chondrules</span>, matrix and coarse-grained <span class="hlt">chondrule</span> rims in the Allende meteorite - Origin, interrelationships, and possible precursor components</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">INAA and broad-beam EMPA are used to determine the bulk compositions of 20 <span class="hlt">chondrules</span>, 13 coarse-grained <span class="hlt">chondrule</span> rims, and one nonporphyritic CV <span class="hlt">chondrule</span> (NPCVC) from CV3 Allende (and of one NPCVC each from Leoville and Vigarano). The data are presented in extensive tables and graphs and analyzed in detail. Five probable <span class="hlt">chondrule</span> precursor components are deduced, and the solar-nebula processes giving rise to them (and probably to the coarse-grained rims as well) are discussed. It is suggested that the formation of the rimmed <span class="hlt">chondrules</span> involved nebular reheating in space, after the accretion of dusty coatings.</p> <div class="credits"> <p class="dwt_author">Rubin, A. E.; Wasson, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">169</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/n889506n72763871.pdf"> <span id="translatedtitle">Sintering of <span class="hlt">olivine</span> and <span class="hlt">olivine</span>-basalt aggregates</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The sintering behavior of <span class="hlt">olivine</span> and <span class="hlt">olivine</span>-basalt aggregates has been examined at temperatures near 1,300° C. Experimental factors contributing to rapid sintering kinetics and high-density, fine-grained specimens include: (i) the uniform dispersion of basalt throughout the specimen, (ii) a very fine, uniform particle size for the <span class="hlt">olivine</span> powder, (iii) oxygen fugacities near the high PO2 end of the <span class="hlt">olivine</span> stability</p> <div class="credits"> <p class="dwt_author">R. F. Cooper; D. L. Kohlstedt</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">170</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20020046273&hterms=Reproduction&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DReproduction"> <span id="translatedtitle">Experimental Reproduction of Type 1B <span class="hlt">Chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">We have replicated type 1B <span class="hlt">chondrule</span> textures and compositions with crystallization experiments in which UOC material was melted at 1400 deg.C and cooled at 5-1000 deg.C/hr using graphite crucibles in evacuated silica tubes to provide a reducing environment. Additional information is contained in the original extended abstract.</p> <div class="credits"> <p class="dwt_author">Lofgren, G. E.; Le, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">171</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1996LPI....27..485H"> <span id="translatedtitle">High C and H Contents of <span class="hlt">Chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Carbon and hydrogen concentrations (reported hereafter as in ppm C and [H] in ppm H2O) of 33 <span class="hlt">chondrules</span> of all petrological types and sizes, and belonging to some of the least altered and metamorphosed chondrites were determined with the CRPG Nancy ion-microprobe. Special care was taken in order to efficiently get rid of the terrestrial contamination. Before analysis, each sampling area (0~25 micrometers and ~50 micrometers for the smaller <span class="hlt">chondrules</span>) was sputtered by the O^2- primary beam (20nA) for 5 minutes. Precise chemical concentrations for H and C were obtained for a -60V offset applied to the sample, along with an energy filtering of +/- 10V. Mass resolution (M/Delta M) of 1800 is sufficient to discriminate the 24Mg++ signal from the 12C+. Mid-ocean ridge basalts were used for calibration of C and H. Major element concentrations in phases were obtained by electron probe analysis. Then, in each <span class="hlt">chondrule</span>, phase proportions were visually estimated allowing the calculation of a bulk concentration for the major elements. [C] and [H] were obtained by two methods : 1) using internal <span class="hlt">chondrule</span> correlations between individual ion-probe spots for carbon (or H) and major elements contents or 2) by averaging all ion-probe [C] and [H] determinations. _</p> <div class="credits"> <p class="dwt_author">Hanon, P.; Chaussidon, M.; Robert, F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">172</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010PhDT.......173L"> <span id="translatedtitle">Magnetic reconnection as a <span class="hlt">chondrule</span> heating mechanism</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The origin of <span class="hlt">chondrules</span> (sub-millimeter inclusions found in stony meteorites) remains today an open question despite over century of examination. The age of these proto-solar relics shows a well defined cutoff of around 4.5 billion years ago. This places them as the oldest solids in the solar system. Chemical examination indicates that they experienced heating events on the order of 5000 K/hr for periods of around 30 minutes, followed by extending periods of cooling. Additional examination indicates the presence of large magnetic fields during their formation. Most attempts to explain <span class="hlt">chondrule</span> formation in the proto-solar nebula neglect the existence of a plasma environment, with even less mention of dust being a charge carrier (dusty plasma). Simulations of magnetic reconnection in a dusty plasma are forwarded as a mechanism for <span class="hlt">chondrule</span> formation in the proto-solar nebula. Here large dust-neutral relative velocities are found in the reconnection region. These flows are associated with the dynamics of reconnection. The high Knudsen number of the dust particles allows for a direct calculation of frictional heating due to collisions with neutrals (allowing for the neglect of boundary layer formation around the particle). Test particle simulations produce heating equivalent to that recorded in the <span class="hlt">chondrule</span> mineral record. It is shown that magnetic reconnection in a dusty plasma is of fundamental importance to the formation of the most primitive solids in the solar system.</p> <div class="credits"> <p class="dwt_author">Lazerson, Samuel A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">173</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950035331&hterms=fractional+condensation&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522fractional%2Bcondensation%2522"> <span id="translatedtitle">Silica-merrihueite/roedderite-bearing <span class="hlt">chondrules</span> and clasts in ordinary chondrites: New occurrences and possible origin</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Merrihueite (K,Na)2(Fe,Mg)5Si12O30 (na less than 0.5, fe greater than 0.5, where na = Na/(Na + K), fe = Fe/(Fe + Mg) in atomic ratio) is a rare mineral described only in several <span class="hlt">chondrules</span> and irregularly-shaped fragments in the Mezo-Madaras L3 chondrite (Dodd et al., 1965; Wood and Holmberg, 1994). Roedderite (Na,K)2(Mg,Fe)5Si12O30 (na greater than 0.5, fe less than 0.5) has been found only in enstatite chondrites and in the reduced, subchondritic silicate inclusions in IAB irons (Fuchs, 1966; Rambaldi et al., 1984; Olsen, 1967). We described silica-roedderite-bearing clasts in L/LL3.5 ALHA77011 and LL3.7 ALHA77278, a silica-roedderite-bearing <span class="hlt">chondrule</span> in L3 Mezo-Madaras, and a silica-merrihueite-bearing <span class="hlt">chondrule</span> in L/LL3.5 ALHA77115. The findings of merrihueite and roedderite in ALHA77011, ALHA77115, ALHA77278 and Mezo-Madaras fill the compositional gap betweeen previously described roedderite in enstatite chondrites and silicate inclusions in IAB irons and merrihueite in Mezo-Madaras, suggesting that there is a complete solid solution of roedderite and merrihueite in meteorites. We infer that the silica- and merrihueite/roedderite-bearing <span class="hlt">chondrules</span> and clasts experienced a complex formational history including: (a) fractional condensation in the solar nebular that produced Si-rich and Al-poor precursors, (b) melting of fractionated nebular solids resulting in the formation of silica-pyroxene <span class="hlt">chondrules</span>, (c) in some cases, fragmentation in the nebula or on a parent body, (d) reaction of silica with alkali-rich gas that formed merrihueite/roedderite on a parent body, (e) formation of fayalitic <span class="hlt">olivine</span> and feerosilite-rich pyroxene due to reaction of silica with oxidized Fe on a parent body, and (f) minor thermal metamorphism, possibly generated by impacts.</p> <div class="credits"> <p class="dwt_author">Krot, Alexander N.; Wasson, John T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">174</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1996LPI....27.1257S"> <span id="translatedtitle">New Evidence for 26Al in CAI and <span class="hlt">Chondrules</span> from Type 3 Ordinary Chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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 <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span>. Also, metamorphism can erase the evidence in high-AI/Mg phases. To address these issues, we have conducted a search for <span class="hlt">chondrules</span> 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, <span class="hlt">olivine</span>-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 <span class="hlt">chondrules</span> from ordinary chondrites of low metamorphic grade and have found clear evidence for 26A1 in both CAI and in two <span class="hlt">chondrules</span>.</p> <div class="credits"> <p class="dwt_author">Srinivasan, G.; Russell, S. S.; MacPherson, G. J.; Huss, G. R.; Wasserburg, G. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">175</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004M%26PS...39.1809C"> <span id="translatedtitle">Evaluating planetesimal bow shocks as sites for <span class="hlt">chondrule</span> formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We investigate the possible formation of <span class="hlt">chondrules</span> by planetesimal bow shocks. The formation of such shocks is modeled using a piecewise parabolic method (PPM) code under a variety of conditions. The results of this modeling are used as a guide to study <span class="hlt">chondrule</span> formation in a one-dimensional, finite shock wave. This model considers a mixture of <span class="hlt">chondrule</span>-sized particles and micron-sized dust and models the kinetic vaporization of the solids. We found that only planetesimals with a radius of ˜1000 km and moving at least ˜8 km/s with respect to the nebular gas can generate shocks that would allow <span class="hlt">chondrule</span>-sized particles to have peak temperatures and cooling rates that are generally consistent with what has been inferred for <span class="hlt">chondrules</span>. Planetesimals with smaller radii tend to produce lower peak temperatures and cooling rates that are too high. However, the peak temperatures of <span class="hlt">chondrules</span> are only matched for low values of <span class="hlt">chondrule</span> wavelength-averaged emissivity. Very slow cooling (<˜100s of K/hr) can only be achieved if the nebular opacity is low, which may result after a significant amount of material has been accreted into objects that are <span class="hlt">chondrule</span>-sized or larger, or if <span class="hlt">chondrules</span> formed in regions of the nebula with small dust concentrations. Large shock waves of approximately the same scale as those formed by gravitational instabilities or tidal interactions between the nebula and a young Jupiter do not require this to match the inferred thermal histories of <span class="hlt">chondrules</span>.</p> <div class="credits"> <p class="dwt_author">Ciesla, Fred J.; Hood, Lon L.; Weidenschilling, Stuart J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">176</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://serc.carleton.edu/NAGTWorkshops/mineralogy/activities/10074.html"> <span id="translatedtitle"><span class="hlt">Olivine</span> Crystal Structure</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">This exercise is based on recent crystallographic research on the <span class="hlt">olivine</span> crystal structure published by Redfern et al. (2000). The authors of this study synthesized Fa50 <span class="hlt">olivine</span> <span class="hlt">olivine</span> (MgFeSiO4) in an experimental apparatus at temperatures ranging from 100 to 1250 °C, quenched the experiments, and used in situ neutron powder diffraction techniques to investigate changes in the synthesized <span class="hlt">olivines</span> as a function of temperature. While this study reports cutting-edge materials research carried out with the latest crystallographic techniques, the results are educationally instructive and illustrate important concepts normally covered in an undergraduate mineralogy course. In this exercise, students are guided into the American Mineralogist Crystal Structure Database to retrieve and download published crystal structure data for viewing in either the CrystalMaker or XtalDraw visualization software packages. The students are instructed on how to manipulate the structures and are asked to plot some of the crystallographic data from this study on graphs using a spreadsheet program such as Excel.</p> <div class="credits"> <p class="dwt_author">Ratajeski, Kent</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">177</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19980037669&hterms=ELEMENT+104+254&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DELEMENT%2B104%2B254"> <span id="translatedtitle">Partitioning of Moderately Siderophile Elements Among <span class="hlt">Olivine</span>, Silicate Melt, and Sulfide Melt: Constraints on Core Formation in the Earth and Mars</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">This study investigates the effects of Variations in the fugacities of oxygen and sulfur on the partitioning of first series transition metals (V, Cr, Mn, Fe, Co, Ni. and Cu) and W among coexisting sulfide melt, silicate melt, and <span class="hlt">olivine</span>. Experiments were performed at 1 atm pressure, 1350 C, with the fugacities of oxygen and sulfur controlled by mixing CO2, CO, and SO2 gases. Starting compositions consisted of a CaO-MgO-Al2O3-SiO2-FeO-Na2O analog for a <span class="hlt">barred</span> <span class="hlt">olivine</span> <span class="hlt">chondrule</span> from an ordinary chondrite and a synthetic komatiite. The f(sub O2)/f(sub S2), conditions ranged from log of f(sub O2) = -7.9 to - 10.6, with log of f(sub S2) values ranging from - 1.0 to -2.5. Our experimental results demonstrate that the f(sub O2)/f(sub S2) dependencies of sulfide melt/silicate melt partition coefficients for the first series transition metals arc proportional to their valence states. The f(sub O2)/f(sub S2) dependencies for the partitioning of Fe, Co, Ni, and Cu are weaker than predicted on the basis of their valence states. Variations in conditions have no significant effect on <span class="hlt">olivine</span>/melt partitioning other than those resulting from f(sub O2)-induced changes in the valence state of a given element. The strong f(sub O2)/f(sub S2) dependence for the <span class="hlt">olivine</span>/silicate melt partitioning of V is attributable to a change of valence state, from 4+ to 3+, with decreasing f(sub O2). Our experimentally determined partition coefficients are used to develop models for the segregation of sulfide and metal from the silicate portion of the early Earth and the Shergottite parent body (Mars). We find that the influence of S is not sufficient to explain the overabundance of siderophile and chalcophile elements that remained in the mantle of the Earth following core formation. Important constraints on core formation in Mars are provided by our experimental determination of the partitioning of Cu between silicate and sulfide melts. When combined with existing estimates for siderophile element abundances in the Martian mantle and a mass balance constraint from Fe, the experiments allow a determination of the mass of the Martian core (approx. 17 to 22 wt% of the planet) and its S content (approx.0.4 wt%). These modeling results indicate that Mars is depleted in S, and that its core is solid.</p> <div class="credits"> <p class="dwt_author">Gaetani, Glenn A.; Grove, Timothy L.</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">178</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1991GeCoA..55..581S"> <span id="translatedtitle">Origin of plagioclase-<span class="hlt">olivine</span> inclusions in carbonaceous chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The origin of plagioclase-<span class="hlt">olivine</span> inclusions (POIs) from three CV chondrites and one ungrouped chondrite was investigated by examining the chemical, mineralogical, and isotopic characteristics of a group of POIs from these chondrites. Results of these analyses demonstrate that the mixing and the partial melting processes in these inclusions were superimposed on more ancient isotopically heterogeneous material. A comparison of the essential characteristics of POIs and CAIs suggests that the major processes leading to the formation of POIs (such as condensation, dust/gas fractionation, aggregation of chemically and isotopically disparate materials, and partial melting) are common to most CAIs and <span class="hlt">chondrules</span>. A scenario for the origin of POIs is proposed, showing that the homogeneity of the final assemblage (whether a POI, a CAI, or a chondrite) is primarily a reflection of the thermal history rather than the nature of precursor materials.</p> <div class="credits"> <p class="dwt_author">Sheng, Y. J.; Hutcheon, I. D.; Wasserburg, G. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">179</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011JGRE..11612007E"> <span id="translatedtitle">Magnetic characteristics of CV <span class="hlt">chondrules</span> with paleointensity implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have conducted a detailed magnetic study on 45 <span class="hlt">chondrules</span> from two carbonaceous chondrites of the CV type: (1) Mokoia and (2) Allende. Allende has been previously extensively studied and is thought to have a high potential of retaining an extra-terrestrial paleofield. Few paleomagnetic studies of Mokoia have previously been undertaken. We report a range of magnetic measurements including hysteresis, first-order reversal curve analysis (FORCs), demagnetization characteristics, and isothermal remanent (IRM) acquisition behavior on both Mokoia and Allende <span class="hlt">chondrules</span>. The Mokoia <span class="hlt">chondrules</span> displayed more single domain-like behavior than the Allende <span class="hlt">chondrules</span>, suggesting smaller grain sizes and higher magnetic stability. The Mokoia <span class="hlt">chondrules</span> also had higher average concentrations of magnetic minerals and a larger range of magnetic characteristics than the Allende <span class="hlt">chondrules</span>. IRM acquisition analysis found that both sets of <span class="hlt">chondrules</span> have the same dominant magnetic mineral, likely to be a FeNi phase (taenite, kamacite, and/or awaruite) contributing to 48% of the Mokoia <span class="hlt">chondrules</span> and 42% of the Allende <span class="hlt">chondrule</span> characteristics. FORC analysis revealed that generally the Allende <span class="hlt">chondrules</span> displayed low-field coercivity distributions with little interactions, and the Mokoia <span class="hlt">chondrules</span> show clear single-domain like distributions. Paleointensity estimates for the two meteorites using the REMc and Preisach methods yielded estimates between 13 and 60 ?T and 3-56 ?T, respectively, for Allende and 3-140 ?T and 1-110 ?T, respectively, for Mokoia. From the data, we suggest that Mokoia <span class="hlt">chondrules</span> carry a non-primary remagnetization, and while Allende is more likely than Mokoia to retain its primary magnetization, it also displays signs of post accretionary magnetization.</p> <div class="credits"> <p class="dwt_author">Emmerton, Stacey; Muxworthy, Adrian R.; Hezel, Dominik C.; Bland, Philip A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">180</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19850044381&hterms=mito&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dmito"> <span id="translatedtitle">Oxygen isotopic compositions of <span class="hlt">chondrules</span> in Allende and ordinary chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The ferromagnesian <span class="hlt">chondrules</span> in Allende follow a trend in the oxygen three-isotope plot that diverges significantly from the 16-O mixing line defined by light and dark inclusions and the matrix of the meteorite. The trend probably results from isotopic exchange with an external gaseous reservoir during the process of <span class="hlt">chondrule</span> formation sometime after the establishment of the isotopic compositions of the inclusions and matrix. The Allende <span class="hlt">chondrules</span> approach, but do not reach, the isotopic compositions of <span class="hlt">chondrules</span> in unequilibrated ordinary chondrites, implying exchange with a similar ambient gas, but isotopically different solid precursors for the two types of meteorite.</p> <div class="credits"> <p class="dwt_author">Clayton, R. N.; Mayeda, T. K.; Hutcheon, I. D.; Molini-Velsko, C.; Onuma, N.; Ikeda, Y.; Olsen, E. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_8");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_11");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">181</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1994LPICo.844...30P"> <span id="translatedtitle">Formation of <span class="hlt">chondrules</span> and CAIs by nebular processes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Chondrules</span> are essential components of most chondritic meteorites. Carbonaceous chondrites, with the exception of CI chondrites, contain 30-50% <span class="hlt">chondrules</span>, ordinary and enstatite chondrites even more. A better understanding of <span class="hlt">chondrule</span> formation will therefore lead to an improved understanding of the origin of meteorites. Most studies of <span class="hlt">chondrules</span> are, however, concerned with their texture and mineralogy. As <span class="hlt">chondrules</span>, by definition, passed through a molten stage, their present texture and mineralogy can only provide information on conditions of crystallization from a melt and the subsequent solid-state cooling history. Information concerning <span class="hlt">chondrule</span> formation is contained in their chemical and isotopic composition. The two most important observations relevant to the chemistry of the <span class="hlt">chondrules</span> are their generally low Fe content and the large compositional variability of <span class="hlt">chondrules</span> from a single meteorite, reflected in major variations of Mg/Si ratios, of Al and other refractory element abundances, total Fe, metal (Fe, Ni), and sulfide. This large compositional variability is surprising considering the uniform and nearly solar composition of bulk chondrites, which, in some cases, consist of more than 90% of <span class="hlt">chondrules</span>.</p> <div class="credits"> <p class="dwt_author">Palme, H.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">182</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40927927"> <span id="translatedtitle">A short duration of <span class="hlt">chondrule</span> formation in the solar nebula: evidence from 26Al in Semarkona ferromagnesian <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The 26Al–26Mg systems of five ferromagnesian <span class="hlt">chondrules</span> from the least metamorphosed ordinary chondrite Semarkona (LL3.0) were studied using a secondary ion mass spectrometer. Their glass or plagioclase portions contain excesses of 26Mg, and in two <span class="hlt">chondrules</span> the 26Mg excesses are well correlated with 27Al\\/24Mg, which demonstrates the in-situ decay of 26Al. The initial 26Al\\/27Al ratios in these <span class="hlt">chondrules</span> obtained from</p> <div class="credits"> <p class="dwt_author">Noriko T. Kita; Hiroko Nagahara; Shigeko Togashi; Yuichi Morishita</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">183</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/26374105"> <span id="translatedtitle"><span class="hlt">Olivine</span>-type cathodes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The recent progress at Sony in the design of practical <span class="hlt">olivine</span>-type cathodes is reviewed briefly. First principle calculations revealed LiFePO4 is a semiconductor with ca. 0.3eV band gap and LiMnPO4 is an insulator with ca. 2eV band gap, which seems the major intrinsic obstacle to a smooth redox reaction at 4V in the Mn-rich phase. Attention is also focused on</p> <div class="credits"> <p class="dwt_author">Atsuo Yamada; Mamoru Hosoya; Sai-Cheong Chung; Yoshihiro Kudo; Koichiro Hinokuma; Kuang-Yu Liu; Yoshio Nishi</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">184</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/jb/v077/i014/JB077i014p02483/JB077i014p02483.pdf"> <span id="translatedtitle">Electrical Conductivity of <span class="hlt">Olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The electrical conductivity a of single crystals of <span class="hlt">olivine</span> of 0, 7.7, 8.2, 9.4, and 26.4 mole % fayalite has been measured up to 1200øC and 7.5 kb. Samples from different localities with approximately the same fayalite content and impurity levels have electrical conductivities that differ by 2-3 orders of magnitude. It is proposed that the oxidation state of the</p> <div class="credits"> <p class="dwt_author">Al Duba</p> <p class="dwt_publisher"></p> <p class="publishDate">1972-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">185</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5556116"> <span id="translatedtitle">Constraints on <span class="hlt">chondrule</span> origin from petrology of isotopically characterized <span class="hlt">chondrules</span> in the Allende meteorite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The petrologic and chemical properties of the ferromagnesian <span class="hlt">chondrules</span> in the Allende carbonaceous chondrite were examined in terms of the isotopic composition and the correlations between isotopic patterns. Areas of thin sections were studied with a SEM and bulk chemical fractions of 12 constituents were quantified to calculate correlations with petrologic features. A possible correlation between (CaO + Al2O2)/MgO and oxygen isotopes imply the formation of oxygen isotopic compositions in the <span class="hlt">chondrules</span> by exchanges between isotopically heavy nebular gases and O-16 enriched solids. Different rates of gaseous exchange occurred with the various types of <span class="hlt">chondrules</span>. Factors which may have controlled the exchanges are discussed. 21 references.</p> <div class="credits"> <p class="dwt_author">Mcsween, H.Y. Jr.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">186</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6996620"> <span id="translatedtitle"><span class="hlt">Chondrules</span>, matrix and coarse-grained <span class="hlt">chondrule</span> rims in the allende meteorite: origin, interrelationships and possible precursor components</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Bulk compositions of 20 <span class="hlt">chondrules</span>, 13 coarse-grained <span class="hlt">chondrule</span> rims and two composite samples of matrix material from CV3 Allende were determined by instrumental neutron activation analysis. Three rare nonporphyritic CV <span class="hlt">chondrules</span> (from Allende, Leoville and Vigarano) were analyzed by broad-beam electron microprobe analysis. <span class="hlt">Chondrule</span> precursor components deduced from <span class="hlt">chondrule</span> compositions are characterized by: (1) refractory and semi-refractory lithophiles with low FeO, (2) common siderophiles and chalcophiles, (3) common to slightly volatile lithophiles (Si, Cr, Mn), and modal pyroxene with moderately high FeO/(FeO + MgO), (4) moderately volatile siderophiles and (5) alkalies. These precursor components can be explained by plausible processes occurring in the solar nebula. In general, the compositions of coarse-grained rims are more similar to the mean <span class="hlt">chondrule</span> composition than to those of the <span class="hlt">chondrules</span> they enclose. Several <span class="hlt">chondrules</span> and rims have fractionated rare-earth patterns and may have been affected by metamorphism. The enclosure of some coarse-grained rims by fine-grained matrix-like rims indicates that coarse-grained rims were also formed in the nebula. Two matrix samples are similar in composition to some coarse-grained rims, suggesting that matrix was derived from similar compositional reservoirs of nebular dust. <span class="hlt">Chondrules</span> with coarse-grained rims were reheated in space following the accretion of dusty coatings.</p> <div class="credits"> <p class="dwt_author">Rubin, A.E.; Wasson, J.T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">187</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050174600&hterms=chondrites&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2522R%2Bchondrites%2522"> <span id="translatedtitle">Porphyritic <span class="hlt">Olivine</span>-Pyroxene Clast in Kaidun: First Discovery of an Ordinary Chondrite Clast?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Kaidun is an enigmatic meteorite showing a micro-brecciated texture composed of variable kinds of lithic clasts and mineral fragments. The constituent components range from primitive chondritic materials to differentiated achondritic materials, and thus believed to have originated from a large parent body accumulating materials from many different bodies in the asteroid belt. One of the interesting observations is that no ordinary chondrite component has been found yet, although C and E chondrites components are abundant. In this abstract, we report mineralogy of the clast (Kaidun #15415- 01.3.13a) showing a porphyritic <span class="hlt">olivine</span>-pyroxene <span class="hlt">chondrule</span>-like texture similar to those found in unequilibrated ordinary chondrites.</p> <div class="credits"> <p class="dwt_author">Mikouchi, T.; Makishima, J.; Koizumi, E.; Zolensky, M. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">188</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1984Metic..19...79R"> <span id="translatedtitle">Minor elements in Marjalahti <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Precise microprobe determinations of minor elements in <span class="hlt">olivine</span> from Marjalahti show averages of 0.0267 percent CaO; 0.0211 percent Cr2O3; less than 0.0045 percent TiO2; 0.288 percent MnO; and 30 ppm Ni. The calcium is as high as in some terrestrial plutonic <span class="hlt">olivines</span> (e.g. Stillwater) but lower than in terrestrial nodule (high-temperature mantle?) <span class="hlt">olivines</span>, consistent with very slow cooling to low temperatures. The chromium is discrepant with some earlier determinations, and possibly chromium is zoned in most pallasitic <span class="hlt">olivines</span>. The Ti, Mn, and Ni data are consistent with previous determinations.</p> <div class="credits"> <p class="dwt_author">Ryder, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">189</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013M%26PSA..76.5149K"> <span id="translatedtitle">Primary Oxygen Isotope Signatures of <span class="hlt">Chondrules</span> in R Chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Chondrules</span> in R3 clast from NWA 753 (R3-5) breccia show oxygen isotope ratios similar to those in LL3 chondrites. ?^17O values of most <span class="hlt">chondrules</span> distribute between 0‰ and +1.5‰, significantly lower than that of bulk R chondrites (~2.7‰).</p> <div class="credits"> <p class="dwt_author">Kita, N. T.; Tenner, T. J.; Nakashima, D.; Ushikubo, T.; Bischoff, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">190</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1994Metic..29Q.487K"> <span id="translatedtitle">Coarse-grained rims on magnesium-rich and magnesium-poor <span class="hlt">chondrules</span> in ordinary chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Chondrules</span> with igneous rims and enveloping compound <span class="hlt">chondrules</span> in ordinary chondrites (OC) preserve the record of solids that were present at different times or in different regions of the solar nebula during <span class="hlt">chondrule</span> formation. These objects demonstrate that OC <span class="hlt">chondrules</span> experienced multiple episodes of <span class="hlt">chondrule</span> formation. This conclusion is consistent with the presence of relict grains in <span class="hlt">chondrules</span> that were probably produced by disaggregation of <span class="hlt">chondrules</span> of a previous generation, small range in OC <span class="hlt">chondrule</span> O isotope composition, and interelement correlations in bulk <span class="hlt">chondrule</span> data that can be interpreted as the random sampling of a previous generation of <span class="hlt">chondrules</span>. Rims around <span class="hlt">chondrules</span> can be divided into two major categories: fine-grained rims (FGR), typically opaque and Fe rich and relatively coarse-grained rims. Thirteen CGR on Mg-rich <span class="hlt">chondrules</span> (type I, Fa/Fs less than 10 mol%) and nine rims on Mg-poor <span class="hlt">chondrules</span> (type II, Fa/Fs greater than 10 mol%) were studied petrographically, by electron microprobe analysis, and scanning electron microscopy. Many of the CGR on type I <span class="hlt">chondrules</span> show evidence of significant and, in many cases, complete melting. Similar Fa and Fs contents in mafic minerals of OC igneous rims and their type I <span class="hlt">chondrule</span> hosts indicate that many OC <span class="hlt">chondrules</span> experienced multiple heating events during a time short compared to the time necessary for appreciable evolution in the mean Fa or Fs of the nebular solids, and were than withdrawn from the <span class="hlt">chondrule</span>-forming region. Type II <span class="hlt">chondrules</span> and their CGR formed from more oxidized material mixed with fragments of type I <span class="hlt">chondrules</span> and were heated to lower temperatures than type I <span class="hlt">chondrules</span> and their CGR. Type I and type II <span class="hlt">chondrules</span> may have formed in different OC nebular subregions or at different times and were mixed together before or during agglomeration to form chondrites.</p> <div class="credits"> <p class="dwt_author">Krot, A. N.; Watson, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">191</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.V43D..02C"> <span id="translatedtitle">Helium Diffusion in <span class="hlt">Olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Diffusion of helium has been characterized in natural Fe-bearing <span class="hlt">olivine</span> (~Fo90) and synthetic forsterite. Polished, oriented slabs of <span class="hlt">olivine</span> were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted <span class="hlt">olivine</span> were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950°C: D = 3.91x10-6exp(-159 ± 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700°C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in <span class="hlt">olivine</span>. Diffusion in Fe-bearing <span class="hlt">olivine</span> (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm experiments, indicating that the results reported here can be reasonably applied to modeling He transport in the upper mantle. The insensitivity of He diffusion to pressure over the investigated range of conditions suggests that compression of the mineral lattice is not sufficient to significantly influence migration of the relatively small helium atoms, which likely diffuse via crystal interstices. The He diffusivities in this work are generally consistent with results from the study of Futagami et al. (1993), who measured He diffusion in natural <span class="hlt">olivine</span> by outgassing 4He implanted samples, and with the diffusivities measured by bulk-release of 4He and 3He by Shuster et al. (2003), but are about 2 orders of magnitude slower than the recent findings of Tolstikhin et al. (2010) and Blard et al. (2008) . An up-temperature extrapolation of our data also show reasonable agreement with the higher-temperature measurements of Hart (1984). Blard et al. (2008) GCA 72, 3788-3803; Futagami et al. (1993) GCA 57, 3177-3194; Hart (1984) EPSL 70, 297-302; Shuster et al.( 2003) EPSL 217, 19-32; Tolstikhin et al. (2010) GCA 74, 1436-1447</p> <div class="credits"> <p class="dwt_author">Cherniak, D. J.; Watson, E. B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">192</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20060049099&hterms=high+content+data&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dhigh%2Bcontent%2Bdata"> <span id="translatedtitle">Oxygen-isotopic Compositions of Low-FeO relicts in High-FeO Host <span class="hlt">Chondrules</span> in Acfer 094, a Type 3.0 Carbonaceous Chondrite Closely Related to CM</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">With one exception, the low-FeO relict <span class="hlt">olivine</span> grains within high-FeO porphyritic <span class="hlt">chondrules</span> in the type 3.0 Acfer 094 carbonaceous chondrite have DELTA O-17 ( = delta O-17 - 0.52 X delta O-18) values that are substantially more negative than those of the high-FeO <span class="hlt">olivine</span> host materials. These results are similar to observations made earlier on <span class="hlt">chondrules</span> in C03.0 chondrites and are consistent with two independent models: (1) Nebular solids evolved from low-FeO, low-DELTA O-17 compositions towards high-FeO, more positive DELTA O-17 compositions; and (2) the range of compositions resulted from the mixing of two independently formed components. The two models predict different trajectories on a DELTA O-17 vs. log Fe/Mg (<span class="hlt">olivine</span>) diagram, but our sample set has too few values at intermediate Fe/Mg ratios to yield a definitive answer. Published data showing that Acfer 094 has higher volatile contents than CO chondrites suggest a closer link to CM chondrites. This is consistent with the high modal matrix abundance in Acfer 094 (49 vol.%). Acfer 094 may be an unaltered CM chondrite or an exceptionally matrix-rich CO chondrite. <span class="hlt">Chondrules</span> in Acfer 094 and in CO and CM carbonaceous chondrites appear to sample the same population. Textural differences between Acfer 094 and CM chondrites are largely attributable to the high degree of hydrothermal alteration that the CM chondrites experienced in an asteroidal setting.</p> <div class="credits"> <p class="dwt_author">Rubin, Alan E.; Kunihiro, Tak; Wasson, John T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">193</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19730055761&hterms=Osborn&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DOsborn"> <span id="translatedtitle">Elemental composition of individual <span class="hlt">chondrules</span> from ordinary chondrites.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Sequential nondestructive neutron activation analysis was used to determine the bulk abundance of Fe, Al, Na, Mn, Cr, Sc, Co, and Ir in approximately 300 individual <span class="hlt">chondrules</span> from 16 chondrites representing the H(3-5), L4, and LL(3-6) compositional and petrologic classes. The histograms indicate that the most probable abundances for lithophilic elements, except Cr, are enriched in the <span class="hlt">chondrules</span>, while the siderophilic elements are depleted in the <span class="hlt">chondrules</span> compared to the whole chondrite. Some of the abundance populations, such as Al and Fe, appear to be multimodal. Systematic variations in the composition of the <span class="hlt">chondrules</span> with increasing petrologic type were observed; most consistent are an increasing Na-Al and Cr-Al correlation, a decreasing Na-Mn correlation, increasing Na abundance, and decreasing Na and Mn dispersions among <span class="hlt">chondrules</span>.</p> <div class="credits"> <p class="dwt_author">Osborn, T. W.; Schmitt, R. A.; Smith, R. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1973-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">194</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1987GeCoA..51.3003G"> <span id="translatedtitle">Compositional evidence regarding the origins of rims on Semarkona <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">This paper presents results on neutron activation analyses of the interiors and the abraded surfaces of seven <span class="hlt">chondrules</span> from Semarkona chondrite. The results showed that six of seven <span class="hlt">chondrule</span> rims have enhanced contents of siderophiles and chalcophiles relative to <span class="hlt">chondrule</span> interiors, indicating that, during <span class="hlt">chondrule</span> formation, metal/sulfide melts migrated to the exterior of the <span class="hlt">chondrule</span>; later reheating caused this material to spread out into fine-grained rim material. For nonvolatile elements, the lithophile and siderophile element abundance patterns in the surfaces are generally similar to those in the corresponding interiors, indicating that the surface and the interior metal might have originated from a single precursor. The volatile to moderately-volatile elements K, As, and Zn tend to be enriched in the surface, compared with other elements of similar mineral affinity.</p> <div class="credits"> <p class="dwt_author">Grossman, J. N.; Wasson, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">195</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007LPI....38.2312W"> <span id="translatedtitle">Implications of Textural Distributions for <span class="hlt">Chondrule</span> Formation: A Survey of CR <span class="hlt">Chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The common (>95% low-FeO) <span class="hlt">chondrules</span> in CR chondrites have two main textures: round shapes with minimal interior metal, and irregular shapes with abundant, small, interior metal. These reflect large differences in degree of melting, and thus in mean maxim</p> <div class="credits"> <p class="dwt_author">Wasson, J. T.; Rubin, A. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">196</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22037092"> <span id="translatedtitle"><span class="hlt">CHONDRULE</span> FORMATION IN BOW SHOCKS AROUND ECCENTRIC PLANETARY EMBRYOS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Recent isotopic studies of Martian meteorites by Dauphas and Pourmand have established that large ({approx}3000 km radius) planetary embryos existed in the solar nebula at the same time that <span class="hlt">chondrules</span>-millimeter-sized igneous inclusions found in meteorites-were forming. We model the formation of <span class="hlt">chondrules</span> by passage through bow shocks around such a planetary embryo on an eccentric orbit. We numerically model the hydrodynamics of the flow and find that such large bodies retain an atmosphere with Kelvin-Helmholtz instabilities allowing mixing of this atmosphere with the gas and particles flowing past the embryo. We calculate the trajectories of <span class="hlt">chondrules</span> flowing past the body and find that they are not accreted by the protoplanet, but may instead flow through volatiles outgassed from the planet's magma ocean. In contrast, <span class="hlt">chondrules</span> are accreted onto smaller planetesimals. We calculate the thermal histories of <span class="hlt">chondrules</span> passing through the bow shock. We find that peak temperatures and cooling rates are consistent with the formation of the dominant, porphyritic texture of most <span class="hlt">chondrules</span>, assuming a modest enhancement above the likely solar nebula average value of <span class="hlt">chondrule</span> densities (by a factor of 10), attributable to settling of <span class="hlt">chondrule</span> precursors to the midplane of the disk or turbulent concentration. We calculate the rate at which a planetary embryo's eccentricity is damped and conclude that a single planetary embryo scattered into an eccentric orbit can, over {approx}10{sup 5} years, produce {approx}10{sup 24} g of <span class="hlt">chondrules</span>. In principle, a small number (1-10) of eccentric planetary embryos can melt the observed mass of <span class="hlt">chondrules</span> in a manner consistent with all known constraints.</p> <div class="credits"> <p class="dwt_author">Morris, Melissa A.; Desch, Steven J.; Athanassiadou, Themis [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404 (United States); Boley, Aaron C., E-mail: melissa.a.morris@asu.edu [Department of Astronomy University of Florida, Gainesville, FL 32611 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-06-10</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">197</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6200697"> <span id="translatedtitle">Electrical conduction in <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This paper reports detailed measurements of electrical conductivitysigma and thermoelectric effect /ital S/ in the mineral <span class="hlt">olivine</span> and in syntheticforsterite as functions of temperature in the range from 1000/degree/ to1500 /degree/C and oxygen partial pressure in the range from 10/sup /minus/10/ to10/sup 4/ Pa. The two most striking observations are strong conductivityanisotropy in forsterite and a sign change in /ital S/ in <span class="hlt">olivine</span> at 1390 /degree/C.These results are interpreted to show that both materials have mixed ionic andextrinsic electronic conduction under these conditions. On the basis ofthese interpretations, we infer that forsterite conductivity is dominatedby electronic conduction in the /ital a/ and /ital b/ directions and probably bymovement involving magnesium vacancies in the /ital c/ direction, wherefar higher /ital P//sub O/sub 2//-independent conductivity is observed. Olivineappears to show mixed conduction under all the circumstances observed; at low temperature, electron holes dominate but are superseded bymagnesium vacancies at high temperatures./copyright/ American Geophysical Union 1989</p> <div class="credits"> <p class="dwt_author">Schock, R. N.; Duba, A. G.; Shankland, T. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-05-10</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">198</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930028355&hterms=analogue+metal&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DW%2Banalogue%2Bmetal"> <span id="translatedtitle">The effect of oxygen fugacity on the partitioning of nickel and cobalt between <span class="hlt">olivine</span>, silicate melt, and metal</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The effect of oxygen fugacity, f(O2), on the partitioning behavior of Ni and Co between <span class="hlt">olivine</span>, silicate melt, and metal was investigated in the CaO-MgO-Al2O3-SiO2-FeO-Na2O system, an analogue of a <span class="hlt">chondrule</span> composition from an ordinary chondrite. The conditions were 1350 C and 1 atm, with values of f(O2) varying between 10 exp -5.5 and 10 exp -12.6 atm (i.e., the f(O2) range relevant for crystal/liquid processes in terrestrial planets and meteorite parent bodies). Results of chemical analysis showed that the values of the Ni and Co partitioning coefficients begin to decrease at values of f(O2) that are about 3.9 log units below the nickel-nickel oxide and cobalt-cobalt oxide buffers, respectively, near the metal saturation for the <span class="hlt">chondrule</span> analogue composition.</p> <div class="credits"> <p class="dwt_author">Ehlers, Karin; Grove, Timothy L.; Sisson, Thomas W.; Recca, Steven I.; Zervas, Deborah A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">199</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19940016315&hterms=forsterite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dforsterite"> <span id="translatedtitle">Fe/Mn in <span class="hlt">olivine</span> of carbonaceous meteorites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><span class="hlt">Olivines</span> in primitive meteorites show a range of Fe/Mn both within one grain and among grains suggesting that they have recorded changing conditions during or after growth. Because <span class="hlt">olivine</span> should be an early forming phase, Fe/Mn is used here to infer these earliest conditions. Initial Fe/Mn in cores of isolated, euhedral forsterite in both C2 and C3 meteorites ranges from 25 to 35 but differs at grain edge. Murchison (C2) forsterites show Fe/Mn approaching 1.0 at the grain edge while Ornans Fe/Mn is near 60 at grain edge. These values are lower than the matrix Fe/Mn for both meteorites and the distinct difference in zoning profile indicates different processes operating during and after grain growth. The Fe/Mn of bulk samples from a particular source such as the Moon is nearly constant. Individual samples show variation suggesting that there is some fractionation of Mn from Fe. Minerals have their individual ranges of Fe/Mn which has been used to recognize different types of <span class="hlt">olivine</span> within one meteorite. Extreme values of Fe/Mn below 1.0 occur in forsterite from some IDP's, UOC matrix, and C1 meteorites. There are apparently no detailed studies of Fe/Mn variation within single <span class="hlt">olivine</span> grains. Forsterite grains in C2 and C3 carbonaceous chondrites show complex zoning, and the nearly pure forsterites (Fo greater than approximately 99.5) have high levels of some minor elements including Ti, Al, V, and Sc. There is disagreement on the original source of these grains and both <span class="hlt">chondrule</span> and vapor growth have been proposed. In addition, there is clear evidence that diffusion has affected the outer margins but in some cases the whole grain. Within the cores, the FeO range is limited, and if growing under constant conditions, the Fe/Mn should be near constant as there is little fractionation of Mn from Fe by forsterite. Additionally, there are apparently no co-crystallizing phases as evidenced by a lack of common inclusions in the forsterites. These observations are now followed by analyses of isolated <span class="hlt">olivine</span> grains in C2 and C3 meteorites.</p> <div class="credits"> <p class="dwt_author">Steele, Ian M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">200</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19940011872&hterms=fraction-a&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522fraction-a%2522"> <span id="translatedtitle">On origin of the <span class="hlt">olivine</span> inclusions from the Kainsaz CO carbonaceous chondrite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><span class="hlt">Olivine</span> inclusions and <span class="hlt">chondrules</span> of Kainsaz were formed in a unique process of dust matter melting. The elemental abundances of four fractions of <span class="hlt">olivine</span> (01) inclusions from Kainsaz were analyzed by INAA. The inclusions of fraction A (160 less than d less than 260 microns) have Fe-Ni grains, the inclusions of fractions B (100 less than d less than 160 microns), C (160 less than d less than 260 microns), and D (260 less than d less than 360 microns) do not. The average elemental enrichment factors relative to CI chondrite for each fraction and <span class="hlt">chondrules</span> of Kainsaz is shown. The enrichment factors of siderophile Co, Ni, Ir, Au, and non-refractory Na in all fractions are less than 1. The factors of refractory Ca, Sc, La, Sm, and Yb are comparative with the corresponding values of O1 aggregates of Allende CV (average 4.76). For <span class="hlt">chondrules</span> of Kainsaz these values are lower. Fraction A is enriched in Co, Ir, Au, and relative Ni and CI chondrites: Ir greater than Au greater than Co. The values of (Me/Ni)inc/(Me/Ni)CI are equal to 3.25 for Ir, 2.1 for Au, and 1.2 for Co. The superabundances in Ir and Au relative to Ni witness to formation of Fe-Ni grains of O1 inclusions by agglomeration of grains enriched in refractory metal with grains enriched in non-refractory metal (Au). The enrichments of fraction A in Ca, Sc, La, Sm, and Yb witness about presence of high-temperature phases in O1 inclusions.</p> <div class="credits"> <p class="dwt_author">Lavrukhina, A. K.; Lavrentjeva, Z. A.; Ljul, A. YU.; Ignatenko, K. I.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_9");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_10");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a style="font-weight: bold;">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_12");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">201</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950012922&hterms=sodium&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dsodium"> <span id="translatedtitle">Flash heating is required to minimize sodium losses from <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><span class="hlt">Chondrules</span> were formed by high-temperature melting events, but do not always show Na depletion compared to CI chondrites, though extensive Na loss has been found in previous isothermal experiments. While Na loss can be prevented by high partial pressure of Na in the nebula, many people favor a flash-heating mechanism to reduce the Na loss from <span class="hlt">chondrule</span> melts. To examine the validity of the flash-heating hypothesis, we have conducted a series of flash-heating experiments and observed Na loss rate under different conditions. Our results support the flash heating as a plausible heating mechanism to form <span class="hlt">chondrules</span>.</p> <div class="credits"> <p class="dwt_author">Yu, Y.; Hewins, R. H.; Connolly, H. C., Jr.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">202</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050165560&hterms=DSL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3D%2522DSL%2522"> <span id="translatedtitle"><span class="hlt">Chondrules</span> and Isolated Grains in the Fountain Hills Bencubbinite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The Fountain Hills (FH) meteorite was recently classified as a Bencubbin-like (CB(sub a)) chondrite, which are part of the CR clan [1]. The FH O-isotopic composition is indistinguishable from CB(sub a) chondrites. Metal and silicate compositions are consistent with the CB(sub a) classification. Significant differences between FH and the other CB(sub a) chondrites were noted. These include abundant porphyritic <span class="hlt">chondrules</span> and complete lack of sulfide minerals. We are furthering this investigation by analyzing silicate <span class="hlt">chondrules</span> and isolated grains in FH to determine more about its composition, thermal history, and implications for <span class="hlt">chondrule</span> formation in the early solar system.</p> <div class="credits"> <p class="dwt_author">LaBlue, A. R.; Lauretta, D. S.; Killgore, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">203</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19830034138&hterms=age+range&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dage%2Brange"> <span id="translatedtitle">I-Xe ages of individual Bjurbole <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Initial iodine isotopic compositions have been obtained for 10 individual <span class="hlt">chondrules</span> from the meteorite Bjurbole, with a total range in well determined values of 6.5%, which would correspond to an age difference of 1.6 m.y. These results can be interpreted as distinct formation ages, metamorphic ages, or isotopic inhomogeneities in the early solar system, and can serve to constrain models for <span class="hlt">chondrule</span> formation. Two of the <span class="hlt">chondrules</span> show evidence of either isotopic inhomogeneities or disturbances of their I-Xe systems.</p> <div class="credits"> <p class="dwt_author">Caffee, M. W.; Hohenberg, C. M.; Swindle, T. D.; Hudson, B.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">204</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1993Metic..28R.384K"> <span id="translatedtitle">Silica-Fayalite-bearing <span class="hlt">Chondrules</span> in Ordinary Chondrites: Evidence of Oxidation in the Solar Nebula</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Most ordinary chondrite (OC) <span class="hlt">chondrules</span> have compositions similar to those of bulk OC in terms of lithophile-element abundances. There are only a few rare <span class="hlt">chondrule</span> classes that deviate significantly from OC-like compositions; these include Al-rich <span class="hlt">chondrules</span>, chromitic and chromite-bearing silicate <span class="hlt">chondrules</span>, and silica-rich <span class="hlt">chondrules</span>. We studied 41 thin sections of unequilibrated OC and found 82 silica-bearing <span class="hlt">chondrules</span> that can be divided into two major categories: silica-pyroxene <span class="hlt">chondrules</span> and silica-fayalite- pyroxene <span class="hlt">chondrules</span>. These <span class="hlt">chondrules</span> are more common in H (>3/cm^2) than in L and LL chondrites (<1/cm^2). Silica-pyroxene <span class="hlt">chondrules</span> consist mainly of low-Ca pyroxene and silica and have radial and porphyritic textures. Silica-bearing radial pyroxene (RP) <span class="hlt">chondrules</span> contain 5-10 vol% silica grains; the low-Ca pyroxene is uniform in individual <span class="hlt">chondrules</span> but varies from one <span class="hlt">chondrule</span> to another (Fs(sub)10.2- Fs(sub)31.5). Silica-bearing porphyritic pyroxene (PP) <span class="hlt">chondrules</span> contain 15- 40 vol% silica; the low-Ca pyroxene varies in composition within individual PP <span class="hlt">chondrules</span> and tends to be more magnesian than in the silica-bearing RP <span class="hlt">chondrules</span> (Fs(sub)5.0-Fs(sub)21.1). Petrographic observations suggest that some PP <span class="hlt">chondrules</span> were not completely molten; they appear to have cooled more slowly than the silica-bearing RP <span class="hlt">chondrules</span>. Silica-fayalite-pyroxene <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> can be divided into two types: (1) radial or porphyritic silica-fayalite-pyroxene <span class="hlt">chondrules</span> containing 5-40 vol% silica and (2) granular silica-fayalite-pyroxene <span class="hlt">chondrules</span> consisting almost entirely (90-95 vol%) of silica. Silica-fayalite-bearing pyroxene <span class="hlt">chondrules</span> are texturally and compositionally similar to the silica-bearing pyroxene <span class="hlt">chondrules</span> 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 <span class="hlt">chondrule</span> 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 <span class="hlt">chondrules</span>. Fragments of granular silica <span class="hlt">chondrules</span> occur as relict clasts within two pyroxene <span class="hlt">chondrules</span> in Sharps. These fragments were altered after <span class="hlt">chondrule</span> solidification. Conclusions: (1) Silica-bearing <span class="hlt">chondrules</span> have similar textures to common mafic silicate <span class="hlt">chondrules</span> and were formed by melting silica-rich precursor material that possibly formed by nonequilibrium condensation. (2) The higher abundance of silica-bearing <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> formed by alteration of silica-bearing <span class="hlt">chondrules</span>. The common occurrence of both categories within the same chondrite suggests that oxidation and fayalite formation by nebular gas was an inefficient process.</p> <div class="credits"> <p class="dwt_author">Krot, A. N.; Wasson, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">205</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19890005672&hterms=settling+rate&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dsettling%2Brate"> <span id="translatedtitle">Experimental constraints on the origin of <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Chrondule formation was an important (perhaps ubiguitous) process in the early solar system, yet their origins remain elusive. Some points, however, are clear. The precursor material of chondules (dust) was rapidly heated at rates of perhaps thousands of degrees per second and was cooled more slowly. It was proposed to investigate <span class="hlt">chondrule</span> formation in the Space Station environment via a dust-box (a chamber in which dust can be suspended, heated, and cooled. A microgravity environment is conducive to this kind of experiment because of the significant retardation of settling rates compared with a terrestrial laboratory environment. These long-duration experiments might require the development of technologies to counteract even the small, but finite and permanent gravitation field of the Space Station. Simple, but interesting experiments on dust suspensions immediately present themselves.</p> <div class="credits"> <p class="dwt_author">Boynton, W. V.; DRAKE; HILDEBRAND; JONES; LEWIS; TREIMAN; WARK</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">206</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20030065978&hterms=long+distance+relationships&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dlong%2Bdistance%2Brelationships"> <span id="translatedtitle">Mineralogy and Petrology of Amoeboid <span class="hlt">Olivine</span> Inclusions in CO3 Chondrites: Relationship to Parent-Body Aqueous Alteration</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Petrographic and mineralogic studies of amoeboid <span class="hlt">olivine</span> inclusions (AOIs) in CO3 carbonaceous chondrites reveal that they are sensitive indicators of parent-body aqueous and thermal alteration. As the petrologic subtype increases from 3.0 to 3.8, forsteritic <span class="hlt">olivine</span> (Fa(sub 0-1)) is systematically converted into ferroan <span class="hlt">olivine</span> (Fa(sub 60-75)). We infer that the Fe, Si and O entered the assemblage along grain boundaries, forming ferroan <span class="hlt">olivine</span> that filled fractures and voids. As temperatures increased, Fe(+2) from the new <span class="hlt">olivine</span> exchanged with Mg(+2) from the original AOI to form diffusive haloes around low-FeO cores. Cations of Mn(+2), Ca(+2) and Cr(+3) were also mobilized. The systematic changes in AOI textures and <span class="hlt">olivine</span> compositional distributions can be used to refine the classification of CO3 chondrites into subtypes. In subtype 3.0, <span class="hlt">olivine</span> occurs as small forsterite grains (Fa(sub 0-1)), free of ferroan <span class="hlt">olivine</span>. In petrologic subtype 3.2, narrow veins of FeO-rich <span class="hlt">olivine</span> have formed at forsterite grain boundaries. With increasing alteration, these veins thicken to form zones of ferroan <span class="hlt">olivine</span> at the outside AOI margin and within the AOI interior. By subtype 3.7, there is a fairly broad <span class="hlt">olivine</span> compositional distribution in the range Fa(sub 63-70), and by subtype 3.8, no forsterite remains and the high-Fa peak has narrowed, Fa(sub 64-67). Even at this stage, there is incomplete equilibration in the chondrite as a whole (e.g., data for coarse <span class="hlt">olivine</span> grains in Isna (CO3.8) <span class="hlt">chondrules</span> and lithic clasts show a peak at Fa(sub39)). We infer that the mineral changes in A01 identified in the low petrologic types required aqueous or hydrothermal fluids whereas those in subtypes greater than or equal to 3.3 largely reflect diffusive exchange within and between mineral grains without the aid of fluids.</p> <div class="credits"> <p class="dwt_author">Chizmadia, Lysa J.; Rubin, Alan E.; Wasson, John T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">207</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012M%26PSA..75.5228W"> <span id="translatedtitle">Petrology of <span class="hlt">Chondrules</span> and a Diopside-Rich Inclusion in the MAC 88136 EL3 Chondrite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">MAC 88136 (EL3) contains densely-packed enstatite-rich <span class="hlt">chondrules</span>, metal-rich nodules intergrown with silicate and an unusual large, diopside-rich <span class="hlt">chondrule</span>-like object. Petrologic and chemical features suggest hot accretion for its components.</p> <div class="credits"> <p class="dwt_author">Weisberg, M. K.; Ebel, D. S.; Kimura, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">208</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19940007704&hterms=post+production&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dpost%2Bproduction"> <span id="translatedtitle">The experimental production of matrix lumps within <span class="hlt">chondrules</span>: Evidence of post-formational processes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The processes that acted upon <span class="hlt">chondrules</span> after their formation are as important clues to the nature of the early solar nebula as are the exact processes that formed the <span class="hlt">chondrules</span>. Recent experiments have studied the rim forming processes and the effects the processes have on <span class="hlt">chondrules</span>. We present below information on how matrix inclusions found within <span class="hlt">chondrules</span> may have been formed and the potential usefulness of this information.</p> <div class="credits"> <p class="dwt_author">Connolly, Harold C., Jr.; Hewins, Roger H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">209</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/15056715"> <span id="translatedtitle">The Formation of <span class="hlt">Chondrules</span> at High Gas Pressures in the Solar Nebula</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">High-precision magnesium isotope measurements of whole <span class="hlt">chondrules</span> from the Allende carbonaceous chondrite meteorite show that some aluminum-rich Allende <span class="hlt">chondrules</span> formed at or near the time of formation of calcium-aluminum-rich inclusions and that some others formed later and incorporated precursors previously enriched in magnesium-26. <span class="hlt">Chondrule</span> magnesium-25\\/magnesium-24 correlates with [magnesium]\\/[aluminum] and size, the aluminum-rich, smaller <span class="hlt">chondrules</span> being the most enriched in the</p> <div class="credits"> <p class="dwt_author">Albert Galy; Edward D. Young; Richard D. Ash; R. Keith O'Nions</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">210</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19940030915&hterms=roger+hewins&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Droger%2Bhewins"> <span id="translatedtitle">On the possible role of elemental carbon in the formation of reduced <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Recent experiments have been designed to produce <span class="hlt">chondrule</span> textures via flash melting while simultaneously studying the nature of <span class="hlt">chondrule</span> precursors. However, these experiments have only been concerned with silicate starting material. This is a preliminary report concerning what effects elemental carbon, when added to the silicate starting material, has on the origin of <span class="hlt">chondrules</span> produced by flash melting.</p> <div class="credits"> <p class="dwt_author">Connolly, Harold C., Jr.; Hewins, Roger H.; Ash, Richard D.; Lofgren, Gary E.; Zanda, Brigitte</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">211</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950047183&hterms=forsterite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dforsterite"> <span id="translatedtitle">Two <span class="hlt">chondrule</span> groups each with distinctive rims in Murchison recognized by cathodoluminescence</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Two groups of <span class="hlt">chondrules</span> in the Murchison CM chondrite, which have previously been identified on the basis of FeO in the <span class="hlt">chondrule</span> grains, are readily identified from cathodoluminescence (CL) and belong to those of the ordinary chondrite group A and B <span class="hlt">chondrules</span> of Sears et al. (1992a). All <span class="hlt">chondrules</span> are surrounded by fine-grained rims containing forsterite with bright red CL, but on group A <span class="hlt">chondrules</span> an outer thin rim grades into a much thicker rim, with a lower density of forsterite grains, which in turn grades into the central <span class="hlt">chondrule</span>. Group B <span class="hlt">chondrules</span> have only the thin outer rim with a high density of small forsterite grains. This is the first time an unequivocal correlation has been observed between <span class="hlt">chondrule</span> rim thickness and the composition of the object on which the rim is located. We suggest that while all objects in the meteorite (group B <span class="hlt">chondrules</span>, refractory inclusions, mineral and <span class="hlt">chondrule</span> fragments, clasts) acquired a very thin rim during processing in a wet regolith, the thick rims on group A <span class="hlt">chondrules</span> were formed by aqueous alteration of precursor metal- and sulfide-rich rims which are a characteristic of group A <span class="hlt">chondrules</span> in ordinary chondrites.</p> <div class="credits"> <p class="dwt_author">Sears, Derek W. G.; Benoit, Paul H.; Jie, LU</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">212</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ia.usu.edu/viewproject.php?project=ia:3034"> <span id="translatedtitle"><span class="hlt">Bar</span> Graphs!</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">Mrs. Kohlar has been working with you on <span class="hlt">bar</span> graphs. Here are a couple of games for you to play to help you practice using them. Catch all the Bugs in the system and put them in the correct column of the <span class="hlt">bar</span> graph. Answer the questions about the bugs in the graph. You can play the game twice if you wish. Do these <span class="hlt">bar</span> graph activities and have some <span class="hlt">bar</span> graph fun! Don\\'t worry about the last question, just answer ...</p> <div class="credits"> <p class="dwt_author">Pocock, Mrs.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-10-26</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">213</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008GeCoA..72.4756C"> <span id="translatedtitle"><span class="hlt">Olivine</span> dissolution in basaltic melt</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The main purpose of this work is to understand and quantify diffusive and convective <span class="hlt">olivine</span> dissolution in basaltic melt. Crystal dissolution and growth in a magma chamber is often accompanied by the descent or ascent of the crystal in the chamber due to gravity. The motion induces convection that enhances mass transport. Such convective dissolution and growth rates have not been quantified before. MgO diffusivity in the melt ( DMgO), MgO concentration of the interface melt ( C0) and the effective thickness of the compositional boundary layer (?) are necessary parameters to model the convective dissolution. Experiments of non-convective <span class="hlt">olivine</span> dissolution in a basaltic melt were conducted at 1271-1480 °C and 0.47-1.42 GPa in a piston-cylinder apparatus. At specific temperature and pressure conditions, multiple experiments of different durations show that the interface melt reaches near-saturation within 2 min. Therefore, diffusion, not interface reaction, is the rate-controlling step for non-convective <span class="hlt">olivine</span> dissolution in basaltic melt. The compositional profile length and <span class="hlt">olivine</span> dissolution distance are proportional to the square root of experimental duration, consistent with diffusive dissolution. DMgO and C0 are obtained from the experimental results. DMgO displays Arrhenian dependence on temperature, but the pressure dependence is small and not resolved. C0 increases with increasing temperature and decreases with increasing pressure. Comparison with literature data shows that DMgO depends strongly on the initial melt composition, while C0 does not. ? is estimated from fluid dynamics. DMgO/?, which characterizes the kinetic and dynamic aspects of convective crystal dissolution, is parameterized as a function of temperature, pressure, and <span class="hlt">olivine</span> composition. Convective <span class="hlt">olivine</span> dissolution rate in basaltic melt can be conveniently calculated from the model results. Application to convective crystal growth and xenolith digestion is discussed.</p> <div class="credits"> <p class="dwt_author">Chen, Yang; Zhang, Youxue</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">214</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20040062235&hterms=glass+reflect&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dglass%2Breflect"> <span id="translatedtitle"><span class="hlt">Chondrule</span> Glass Alteration in Type IIA <span class="hlt">Chondrules</span> in the CR2 Chondrites EET 87770 and EET 92105: Insights into Elemental Exchange Between <span class="hlt">Chondrules</span> and Matrices</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">CR2 carbonaceous chondrites are a primitive group of meteorites that preserve evidence of a variety of processes that occurred in the solar nebula as well as on asteroidal parent bodies. CR2 chondrites are distinct from other carbonaceous chondrites by (among other properties) their relatively high abundance of <span class="hlt">chondrules</span> (50-60 vol. %) and Fe,Ni metal (5-8 vol. %) [1]. Like the CM2 chondrites, the CRs have been affected by aqueous alteration and according to [2] show a range of degrees of alteration. In weakly- altered CR chondrites, fine-grained matrices and <span class="hlt">chondrule</span> rims have been partially altered and <span class="hlt">chondrule</span> mesostases show evidence of incipient aqueous alteration. In these meteorites, glassy mesostasis is still common. However, some CR chondrites, (e.g. Renazzo and Al Rais) show evidence of much more extensive alteration with complete replacement of <span class="hlt">chondrule</span> mesostasis [2] by chlorite and serpentine. Although the general characteristics of alteration of the CR chondrites have been described, the details of alteration reactions in these meteorites remain unclear. In addition, the setting for aqueous alteration is poorly understood: both asteroidal and preaccretionary alteration scenarios have been proposed [2].</p> <div class="credits"> <p class="dwt_author">Burger, Paul V.; Brearley, Adrian J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">215</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://geosci-webdev.uchicago.edu/~grossman/GS76GCA.pdf"> <span id="translatedtitle">Amoeboid <span class="hlt">olivine</span> aggregates in the Allende meteorite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Greyish-brown irregularly-shaped aggregates composed predominantly of <span class="hlt">olivine</span> make up nearly 2% of the Allende meteorite by volume. Many of the aggregates are constructed of subspherical lumps of micron-sized crystals of <span class="hlt">olivine</span>, pyroxene, nepheline and sodalite surrounded by coarser-grained <span class="hlt">olivine</span>. Rarely, anorthite, spinel and perovskite are also present. The <span class="hlt">olivine</span> ranges in composition from Fo64 to Fo99. Pyroxenes range from aluminous</p> <div class="credits"> <p class="dwt_author">L. Grossman; I. M. Steele</p> <p class="dwt_publisher"></p> <p class="publishDate">1976-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">216</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950012897&hterms=Thermostats&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DThermostats"> <span id="translatedtitle">Implications of a phase-transition thermostat for <span class="hlt">chondrule</span> melting</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">It is widely accepted that <span class="hlt">chondrules</span> were formed in brief, localized nebular heating episodes. Given the apparent (at least local) high efficiency of <span class="hlt">chondrule</span> formation, these thermal events seem to have occurred at a large number of different times and/or azimuthal locations in the solar nebula. It is reasonable to expect that the <span class="hlt">chondrule</span>-forming events, whatever their underlying cause, were not all identical, but instead occurred with some spread of heating intensities. If this was so, it is puzzling that compositional and textural evidence points to peak temperatures certainly within 1400 - 1750 C, and in most cases within 1500 - 1550 C. This problem is addressed in this article and a possible explanation for this restricted range of peak temperatures is discussed.</p> <div class="credits"> <p class="dwt_author">Love, S. G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">217</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1007079"> <span id="translatedtitle">Shape, metal abundance, chemistry, and origin of <span class="hlt">chondrules</span> in the Renazzo (CR) chondrite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We used synchrotron X-ray microtomography to image in 3-dimensions (3D) eight whole <span class="hlt">chondrules</span> in a {approx}1 cm{sup 3} piece of the Renazzo (CR) chondrite at {approx}17 {micro}m per volume element (voxel) edge. We report the first volumetric (3D) measurement of metal/silicate ratios in <span class="hlt">chondrules</span> and quantify indices of <span class="hlt">chondrule</span> sphericity. Volumetric metal abundances in whole <span class="hlt">chondrules</span> range from 1 to 37 volume % in 8 measured <span class="hlt">chondrules</span> and by inspection in tomography data. We show that metal abundances and metal grain locations in individual <span class="hlt">chondrules</span> cannot be reliably obtained from single random 2D sections. Samples were physically cut to intersect representative <span class="hlt">chondrules</span> multiple times and to verify 3D data. Detailed 2D chemical analysis combined with 3D data yield highly variable whole-<span class="hlt">chondrule</span> Mg/Si ratios with a supra-chondritic mean value, yet the chemically diverse, independently formed <span class="hlt">chondrules</span> are mutually complementary in preserving chondritic (solar) Fe/Si ratios in the aggregate CR chondrite. These results are consistent with localized <span class="hlt">chondrule</span> formation and rapid accretion resulting in <span class="hlt">chondrule</span> + matrix aggregates (meteorite parent bodies) that preserve the bulk chondritic composition of source regions.</p> <div class="credits"> <p class="dwt_author">Ebel, D.S.; Weisberg, M.K.; Hertz, J.; Campbell, A.J. (AMNH)</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-03-31</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">218</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950012874&hterms=precipitation+isotope&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dprecipitation%2Bisotope"> <span id="translatedtitle">Papers presented to the Conference on <span class="hlt">Chondrules</span> and the Protoplanetary Disk</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The following topics are covered in the presented papers: (1) producing <span class="hlt">chondrules</span>; (2) carbons, CAI's, and <span class="hlt">chondrules</span>; (3) large scale processes in the solar nebula; (4) <span class="hlt">chondrule</span>-matrix relationships in chondritic meteorites; (5) overview of nebula models; (6) constraints placed on the nature of <span class="hlt">chondrule</span> precursors; (7) turbulent diffusion and concentration of <span class="hlt">chondrules</span> in the protoplanetary nebula; (8) heating and cooling in the solar nebula; (9) crystallization trends of precursor pyroxene in ordinary chondrites; (10) precipitation induced vertical lightning in the protoplanetary nebula; (11) the role of <span class="hlt">chondrules</span> in nebular fractionations of volatiles and other elements; (12) astronomical observations of phenomena in disks; (13) experimental constraints on models for origins of <span class="hlt">chondrules</span>, and various other topics.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">219</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1991LPSC...21..513B"> <span id="translatedtitle">PIXE analyses of <span class="hlt">olivine</span> grains in Semarkona - Microdistribution and correlation of trace elements</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Results are reported from proton-induced X-ray emission (PIXE) studies of trace elements (20-100 ppm) in isolated and <span class="hlt">chondrule</span> <span class="hlt">olivines</span> (IOs and COs) from the Semarkona chondrite (LL3.0). The experimental procedures are described, and the results are presented in extensive tables, graphs, and micrographs and discussed in detail. The absolute concentrations of Ca, Ti, V, Cr, Mn, Fe, and Ni in small IOs are found to be similar to those in Fe-rich COs, whereas those in large IOs are between those of Fe-rich and Fe-poor COs. It is inferred that the large IOs were briefly exposed to high temperatures and ambient gas pressures.</p> <div class="credits"> <p class="dwt_author">Bajt, S.; Pernicka, E.; Traxel, K.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">220</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012LPI....43.2127T"> <span id="translatedtitle">Oxygen Isotopes of <span class="hlt">Chondrules</span> in the Queen Alexandra Range 99177 CR3 Chondrite: Further Evidence for Systematic Relationships Between <span class="hlt">Chondrule</span> Mg# and ?^1^7O and the Role of Ice During <span class="hlt">Chondrule</span> Formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">QUE 99177 <span class="hlt">chondrules</span> steadily rise in ?^1^7O (-5 to -1 ‰) as Mg# decreases (99 to 97). Addition of +?1^7O H_2O ice to dry precursors could reduce <span class="hlt">chondrule</span> Mg# (by oxidation during formation) while increasing ?^1^7O. Estimated H_2O ice ?^1^7O is 0.5 to 6‰.</p> <div class="credits"> <p class="dwt_author">Tenner, T. J.; Nakashima, D.; Ushikubo, T.; Kita, N. T.; Weisberg, M. K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_10");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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style="font-weight: bold;">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_13");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">221</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050206573&hterms=dante&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Ddante"> <span id="translatedtitle">Supernova <span class="hlt">olivine</span> from cometary dust</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">An interplanetary dust particle contains a submicrometer crystalline silicate aggregate of probable supernova origin. The grain has a pronounced enrichment in 18O/16O (13 times the solar value) and depletions in 17O/16O (one-third solar) and 29Si/28Si (<0.8 times solar), indicative of formation from a type II supernova. The aggregate contains <span class="hlt">olivine</span> (forsterite 83) grains <100 nanometers in size, with microstructures that are consistent with minimal thermal alteration. This unusually iron-rich <span class="hlt">olivine</span> grain could have formed by equilibrium condensation from cooling supernova ejecta if several different nucleosynthetic zones mixed in the proper proportions. The supernova grain is also partially encased in nitrogen-15-rich organic matter that likely formed in a presolar cold molecular cloud.</p> <div class="credits"> <p class="dwt_author">Messenger, Scott; Keller, Lindsay P.; Lauretta, Dante S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">222</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/15994379"> <span id="translatedtitle">Supernova <span class="hlt">olivine</span> from cometary dust.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">An interplanetary dust particle contains a submicrometer crystalline silicate aggregate of probable supernova origin. The grain has a pronounced enrichment in 18O/16O (13 times the solar value) and depletions in 17O/16O (one-third solar) and 29Si/28Si (<0.8 times solar), indicative of formation from a type II supernova. The aggregate contains <span class="hlt">olivine</span> (forsterite 83) grains <100 nanometers in size, with microstructures that are consistent with minimal thermal alteration. This unusually iron-rich <span class="hlt">olivine</span> grain could have formed by equilibrium condensation from cooling supernova ejecta if several different nucleosynthetic zones mixed in the proper proportions. The supernova grain is also partially encased in nitrogen-15-rich organic matter that likely formed in a presolar cold molecular cloud. PMID:15994379</p> <div class="credits"> <p class="dwt_author">Messenger, Scott; Keller, Lindsay P; Lauretta, Dante S</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-07-29</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">223</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012CoMP..163..701P"> <span id="translatedtitle">The legacy of crystal-plastic deformation in <span class="hlt">olivine</span>: high-diffusivity pathways during serpentinization</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Crystal-plastic <span class="hlt">olivine</span> deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence of asthenospheric mantle flow. Although crystal-plastic deformation and serpentinization are spatio-temporally decoupled, we identified compositional readjustments expressed on the micrometric level as a striped Fe-enriched ( <span class="hlt">bar</span>{X}_{text{Fe}} = 0.24 ± 0.02 (zones); 0.12 ± 0.02 (bulk)) or Fe-depleted ( <span class="hlt">bar</span>{X}_{text{Fe}} = 0.10 ± 0.01 (zones); 0.13 ± 0.01 (bulk)) zoning in partly serpentinized <span class="hlt">olivine</span> grains from two upper mantle sections in Norway. Focused ion beam sample preparation combined with transmission electron microscopy (TEM) and aberration-corrected scanning TEM, enabling atomic-level resolved electron energy-loss spectroscopic line profiling, reveals that every zone is immediately associated with a subgrain boundary. We infer that the zonings are a result of the environmental Fe2+Mg-1 exchange potential during antigorite serpentinization of <span class="hlt">olivine</span> and the drive toward element exchange equilibrium. This is facilitated by enhanced solid-state diffusion along subgrain boundaries in a system, which otherwise re-equilibrates via dissolution-reprecipitation. Fe enrichment or depletion is controlled by the silica activity imposed on the system by the local <span class="hlt">olivine</span>/orthopyroxene mass ratio, temperature and the effect of magnetite stability. The Fe-Mg exchange coefficients K_{text{D}}^{{{text{Atg}}/{text{Ol}}}} between both types of zoning and antigorite display coalescence toward exchange equilibrium. With both types of zoning, Mn is enriched and Ni depleted compared with the unaffected bulk composition. Nanometer-sized, heterogeneously distributed antigorite precipitates along <span class="hlt">olivine</span> subgrain boundaries suggest that water was able to ingress along them. Crystallographic orientation relationships gained via electron backscatter diffraction between <span class="hlt">olivine</span> grain domains and different serpentine vein generations support the hypothesis that serpentinization was initiated along <span class="hlt">olivine</span> subgrain boundaries.</p> <div class="credits"> <p class="dwt_author">Plümper, Oliver; King, Helen E.; Vollmer, Christian; Ramasse, Quentin; Jung, Haemyeong; Austrheim, Håkon</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">224</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010LPI....41.1315K"> <span id="translatedtitle"><span class="hlt">Chondrule</span> Tieschitz XII Revisited: Reading a Very Old Logbook</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Chondrule</span> Tieschitz XII (Tie XII) was recently re-investigated with an ion micro-probe. Tie XII perfectly fit the PLC model (Varela and Kurat, 2009) and the theoretical predictions of phase condensation in a non-canonical solar nebula [Ebel 2006].</p> <div class="credits"> <p class="dwt_author">Kurat, G.; Varela, M. E.; Zinner, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">225</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20020046214&hterms=primary&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3D%2522primary%2522"> <span id="translatedtitle">Sulfur Isotope Composition of Putative Primary Troilite in <span class="hlt">Chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Sulfur isotope compositions of putative primary troilites in <span class="hlt">chondrules</span> from Bishunpur were measured by ion probe. These primary troilites have the same S isotope compositions as matrix troilites and thus appear to be isotopically unfractionated. Additional information is contained in the original extended abstract.</p> <div class="credits"> <p class="dwt_author">Tachibana, Shogo; Huss, Gary R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">226</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19830034153&hterms=refractory+production&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Drefractory%2Bproduction"> <span id="translatedtitle">Refractory residues, condensates and <span class="hlt">chondrules</span> from solar furnace experiments</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Vertical access solar furnace experiments have produced refractory residues, condensates and <span class="hlt">chondrules</span> that are similar to components of chondritic meteorites. In particular, Ca-Al-rich refractory residues similar in chemistry to inclusions in carbonaceous chondrites have been produced by partial evaporation of basaltic bulk rock samples. Fe-Mg-Si-rich condensates with distinctive microbotryoidal morphology have been collected from the same sample runs. Particle coatings and aggregates with virtually identical microbotryoidal morphology and major element chemistry have been identified in both the Allende and Murchison meteorites. Spattered drops from melt beads undergoing heating and partial evaporation resemble some meteoritic <span class="hlt">chondrules</span> in their mineralogies, textures, grain size, and sorting. The spatter mechanism is highly efficient in the production of <span class="hlt">chondrules</span>. If any of the refractory inclusions in chondrites are, in fact, partial evaporation residues, many meteoritic fluid drop <span class="hlt">chondrules</span> must have been formed by this process. The hot central portion of the solar nebula, acting on a cloud of dust and gas, is the probable source of heat required to produce the fractionated chemistry and physical state of many of the components of chondritic meteorites.</p> <div class="credits"> <p class="dwt_author">King, E. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">227</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JGRB..117.4102M"> <span id="translatedtitle">Serpentinization of oceanic peridotites: 2. Kinetics and processes of San Carlos <span class="hlt">olivine</span> hydrothermal alteration</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The kinetics of the reaction (Mg,Fe)-<span class="hlt">olivine</span> + H2O ? serpentine + magnetite + brucite + H2 were investigated at 500 <span class="hlt">bars</span> in the 250-350°C range using natural <span class="hlt">olivine</span> (San Carlos; Fo91) with grain sizes between 1 and 150 ?m and for run durations up to 514 d. The amount of magnetite produced, which directly relates to reaction progress, was accurately monitored using up to 24 time-resolved magnetic measurements per experiment. Eighty percent of serpentinization was achieved after 60 d for <span class="hlt">olivine</span> grain sizes of 5-15?m and after 500 d for grain sizes of 50-63 ?m. Serpentinization kinetics were found to be inversely proportional to the geometrical surface area of the starting <span class="hlt">olivine</span> grains. They were one or two orders of magnitude slower than serpentinization kinetics commonly used for modeling serpentinization-related processes. The nature of the serpentine mineral product depended on the initial <span class="hlt">olivine</span> grain size (IGS); for IGS in the 5-150?m range lizardite formed, and <span class="hlt">olivine</span> dissolution was the rate-limiting process. At IGS below 5?m, chrysotile crystallized instead of lizardite, and the relationship between <span class="hlt">olivine</span> surface area and reaction kinetics no longer held. We infer that for such small <span class="hlt">olivine</span> grain sizes dissolution is no longer the rate-limiting process. Serpentinization in our experiments was associated with the creation of new reactive surface area according to two cooperative processes: etch pits formation associated with dissolution and grain fracturing for IGS above 20?m. Interestingly, fractures and etch pits with similar geometry and sizes were also observed for residual <span class="hlt">olivine</span> (with a typical grain size of 50 ?m) in serpentinized peridotite samples from the Southwest Indian Ridge. This suggests that the processes governing <span class="hlt">olivine</span> serpentinization kinetics in our experiments are similar to those prevailing in natural systems. We therefore suggest that the new kinetic data set that we present here, which encompasses a range of <span class="hlt">olivine</span> grain sizes and reaction temperatures, is relevant to the serpentinization of <span class="hlt">olivine</span> in the oceanic crust insofar as water is available.</p> <div class="credits"> <p class="dwt_author">Malvoisin, Benjamin; Brunet, Fabrice; Carlut, Julie; RouméJon, StéPhane; Cannat, Mathilde</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">228</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20040068145&hterms=Si+Al+Ca&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DSi%252C%2BAl%252C%2BO%252C%2BCa"> <span id="translatedtitle">Contemporaneous Formation of <span class="hlt">Chondrules</span> in the Al-26-MG-26 System for Ordinary and CO Chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Chronometer using the short-lived extinct-nuclide (26)Al has been applied to <span class="hlt">chondrules</span> in order to obtain of their formation ages. Previous studies were mostly performed on Al-rich <span class="hlt">chondrules</span>, which constitute only 1% of all <span class="hlt">chondrules</span>, because of their high Al/Mg ratios. Recently, (26)Al ages of major ferromagnesian <span class="hlt">chondrules</span> in least equilibrated ordinary chondrites (OC) have been obtained. However, (26)Al ages of ferromagnesian <span class="hlt">chondrules</span> in least equilibrated carbonaceous chondrites (CC) are very limited. Particularly, age data of FeO-poor (Type I) <span class="hlt">chondrules</span> in CC have been scarcely obtained, because of their fine textures and lack of phases with high Al/Mg (>100) ratios. In order to clarify the origin and formation processes of <span class="hlt">chondrules</span>, we started systematic investigations on Type I <span class="hlt">chondrules</span> in the most pristine CC (CO3.0 Yamato-81020), by examining textures, bulk chemical compositions, (26)Al ages and oxygen isotopic compositions. We find Type I <span class="hlt">chondrules</span> in CC formed contemporaneously with ferromagnesian <span class="hlt">chondrules</span> in OC.</p> <div class="credits"> <p class="dwt_author">Kurahashi, E.; Kita, N. T.; Nagahara, H.; Morishita, Y.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">229</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014M%26PS..tmp...79M"> <span id="translatedtitle">Noble gases in individual <span class="hlt">chondrules</span> of the Allende CV3 chondrite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We analyzed noble gases in nine individual <span class="hlt">chondrules</span>, an assemblage of small <span class="hlt">chondrules</span>, and four whole-rock samples of the Allende CV3 chondrite. Major elements were also determined for five <span class="hlt">chondrules</span>. The cosmic ray exposure ages are calculated from cosmogenic 3He to be 5.17 ± 0.38 and 5.15 ± 0.25 Myr for the averages of the <span class="hlt">chondrules</span> and whole rocks, respectively, showing no significant pre-exposure evidence for the studied <span class="hlt">chondrules</span>. Large amounts of 36Ar, 80,82Kr, and 128Xe produced by neutron capture are observed in most samples; the abundances of these nuclides are correlated among the samples. The epithermal neutron flux and neutron slowing down density are calculated based on [80Kr]n, from which a sample depth of about 30 cm can be calculated. The measured <span class="hlt">chondrules</span> contain variable amounts of radiogenic 129Xe. The abundance ratios of radiogenic 129Xe to neutron capture-produced 128Xe are rather constant among the studied <span class="hlt">chondrules</span>; four <span class="hlt">chondrules</span> give more precise ratios at the high-temperature fractions, ranging from 1920 ± 80 to 2280 ± 140, which corresponds to a time difference of 3.9 ± 2.4 Myr. It is noticeable that most <span class="hlt">chondrules</span> also contain 244Pu-derived fission Xe. The average 244Pu/238U ratio for nine <span class="hlt">chondrules</span> is 0.0069 ± 0.0018, which agrees well with the preferred ratio reported for chondrites.</p> <div class="credits"> <p class="dwt_author">Miura, Yayoi N.; Nagao, Keisuke; Kimura, Makoto</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">230</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/39669966"> <span id="translatedtitle">Surface destabilization and laboratory-induced non-stoichiometry in San Carlos <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Annealing experiments on natural <span class="hlt">olivine</span> (Mg1-xFex)2SiO4 (with x˜0.11) crystals (San Carlos, Arizona, spinel-lherzolite context) have been performed between T=1,100° C and 1,500° C for oxygen partial pressures pO2=10-3 to 10-13 <span class="hlt">bar</span> and times of 1 to 140 h in CO\\/CO2 or H2\\/H2O gas mixtures. Even specimens annealed within the T-pO2theoretical stability field (TSF) calculated for stoichiometric <span class="hlt">olivine</span> (Nitsan 1974) show</p> <div class="credits"> <p class="dwt_author">O. Jaoul; B. Houlier; M. Cheraghmakani; R. Pichon; R. C. Liebermann</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">231</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20040140879&hterms=magnetite+solar&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dmagnetite%2Bsolar"> <span id="translatedtitle">Opaque Minerals in the Matrix of the Bishunpur (LL3.1) Chondrite: Constraints on the <span class="hlt">Chondrule</span> Formation Environment</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The chemistry and mineralogy of a group of opaque mineral assemblages in the matrix of the Bishunpur LL3.1 ordinary chondrite provide insight into the nebular environment in which they formed. The assemblages consist of a kamacite (Fe,Ni) core that is rimmed by troilite (FeS) and fayalite (Fe2Si04). Accessory phases in the rims include silica (Si02), chromite (FeCr204), whitlockite (Ca3(P04)2), maricite (FeNaP04), magnetite (Fe304), and tetrataenite (FeNi). We suggest that the metal melted in and equilibrated with an igneous <span class="hlt">chondrule</span> under high- temperature, reducing conditions. In this environment the molten alloys incorporated varied amounts of Si, Ni, P, Cr, and Co, depending on the oxygen fugacity and temperature of the melt. Some of the metal was subsequently expelled from the <span class="hlt">chondrule</span> interiors into the surrounding nebular gas. As the temperature dropped, the alloy solidified and volatile elements corroded the metal. The main reaction products were troilite and fayalite. Thermodynamic equilibrium calculations are used to constrain the conditions under which these two phases can form simultaneously in the solar nebula. Kinetic factors are used to place a lower limit on the formation temperature. We determine that the metal corroded between 1173 and 1261 K at a total pressure in the range of 1025.0 to 1024.1 <span class="hlt">bars</span> and a dust/gas ratio of 302 to 355 x relative to solar composition. These conditions are consistent with our model that the metal corroded in a dust- rich region of the solar nebula that was cooling after a <span class="hlt">chondrule</span> formation event.</p> <div class="credits"> <p class="dwt_author">Lauretta, D. S.; Buseck, P. R.; Zega, T. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">232</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014GeCoA.139..131K"> <span id="translatedtitle">Amoeboid <span class="hlt">olivine</span> aggregates from CH carbonaceous chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Amoeboid <span class="hlt">olivine</span> aggregates (AOAs) in CH carbonaceous chondrites are texturally and mineralogically similar to those in other carbonaceous chondrite groups. They show no evidence for alteration and thermal metamorphism in an asteroidal setting and consist of nearly pure forsterite (Fa<3; in wt%, CaO = 0.1-0.8, Cr2O3 = 0.04-0.48; MnO < 0.5), anorthite, Al-diopside (in wt%, Al2O3 = 0.7-8.1; TiO2 < 1), Fe,Ni-metal, spinel, and, occasionally, low-Ca pyroxene (Fs1Wo2-3), and calcium-aluminum-rich inclusions (CAIs). The CAIs inside AOAs are composed of hibonite, grossite, melilite (Åk13-44), spinel, perovskite, Al,Ti-diopside (in wt%, Al2O3 up to 19.6; TiO2 up to 13.9), and anorthite. The CH AOAs, including CAIs within AOAs, have isotopically uniform 16O-rich compositions (average ?17O = -23.4 ± 2.3‰, 2SD) and on a three-isotope oxygen diagram plot along ?slope-1 line. The only exception is a low-Ca pyroxene-bearing AOA 1-103 that shows a range of ?17O values, from -24‰ to -13‰. Melilite, grossite, and hibonite in four CAIs within AOAs show no evidence for radiogenic 26Mg excess (?26Mg). In contrast, anorthite in five out of six AOAs measured has ?26Mg corresponding to the inferred initial 26Al/27Al ratio of (4.3 ± 0.7) × 10-5, (4.2 ± 0.6) × 10-5, (4.0 ± 0.3) × 10-5, (1.7 ± 0.2) × 10-5, and (3.0 ± 2.6) × 10-6. Anorthite in another AOA shows no resolvable ?26Mg excess; an upper limit on the initial 26Al/27Al ratio is 5 × 10-6. We infer that CH AOAs formed by gas-solid condensation and aggregation of the solar nebula condensates (forsterite and Fe,Ni-metal) mixed with the previously formed CAIs. Subsequently they experienced thermal annealing and possibly melting to a small degree in a 16O-rich gaseous reservoir during a brief epoch of CAI formation. The low-Ca pyroxene-bearing AOA 1-103 may have experienced incomplete melting and isotope exchange in an 16O-poor gaseous reservoir. The lack of resolvable ?26Mg excess in melilite, grossite, and hibonite in CAIs within AOAs reflects heterogeneous distribution of 26Al in the solar nebula during this epoch. The observed variations of the inferred initial 26Al/27Al ratios in anorthite of the mineralogically pristine and uniformly 16O-rich CH AOAs could have recorded (i) admixing of 26Al in the protoplanetary disk during the earliest stages of its evolution and/or (ii) closed-system Mg-isotope exchange between anorthite and Mg-rich minerals (spinel, forsterite, and Al-diopside) during subsequent prolonged (days-to-weeks) thermal annealing at high temperature (?1100 °C) and slow cooling rates (?0.01 K h-1) that has not affected their O-isotope systematics. The proposed thermal annealing may have occurred in an impact-generated plume invoked for the origin of non-porphyritic magnesian <span class="hlt">chondrules</span> and Fe,Ni-metal grains in CH and CB carbonaceous chondrites about 5 Myr after formation of CV CAIs.</p> <div class="credits"> <p class="dwt_author">Krot, Alexander N.; Park, Changkun; Nagashima, Kazuhide</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">233</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6951678"> <span id="translatedtitle"><span class="hlt">Olivine</span>-Pyroxene-PtFe alloy as an oxygen geobarometer</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">An equilibrium assemblage of <span class="hlt">olivine</span>, Ca-free pyroxene, and PtFe alloy can be used to calculate oxygen fugacity at a known temperature and pressure. This oxygen geobarometer has been tested T = 1,300-1,450C, P = 1 <span class="hlt">bar</span> and 10 kbar. The calculated log fO{sub 2} may be compared with that determined by the CO{sub 2}-H{sub 2} mixture used to control the furnace atmosphere in the 1 <span class="hlt">bar</span> experiments and, in the case of the 10 kbar experiments, the log fO{sub 2} determined from the graphite-fluid equilibrium. The average deviation of the calculated log fO{sub 2} determined from the graphite-fluid equilibrium. The average deviation of the calculated log fO{sub 2} and that determined by other means is 0.2; the maximum absolute difference is 0.4. The distribution coefficient (K{sub d}) for Fe and Mg between coexisting <span class="hlt">olivine</span> and pyroxene was found to range from 1.14 at x{sub Fe{sub 2}SiO{sub 4}}{sup ol} = 0.164 to 1.54 at x{sub Fe{sub 2}SiO{sub 4}}{sup ol} = 0.655, and varies systematically with the Fe/(Fe + Mg) of the phases.</p> <div class="credits"> <p class="dwt_author">Jamieson, H.E.; Roeder, P.L.; Grant, A.H. (Queen's Univ., Kingston, Ontario (Canada))</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">234</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.shodor.org/interactivate/activities/BarGraph/"> <span id="translatedtitle"><span class="hlt">Bar</span> Graph</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">In this activity, students use preset data or input their own data to be represented by a <span class="hlt">bar</span> graph. This activity allows students to explore <span class="hlt">bar</span> graphs and how changing scales will alter how their data is represented. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">235</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013M%26PS...48..432R"> <span id="translatedtitle">An amoeboid <span class="hlt">olivine</span> inclusion (AOI) in CK3 NWA 1559, comparison to AOIs in CV3 Allende, and the origin of AOIs in CK and CV chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">An amoeboid <span class="hlt">olivine</span> inclusion in CK3 NWA 1559 (0.54 × 1.3 mm) consists of a diopside-rich interior (approximately 35 vol%) and an <span class="hlt">olivine</span>-rich rim (approximately 65 vol%). It is the first AOI to be described in CK chondrites; the apparent paucity of these inclusions is due to extensive parent-body recrystallization. The AOI interior contains irregular 3-15 ?m-sized Al-bearing diopside grains (approximately 70 vol%), 2-20 ?m-sized pores (approximately 30 vol%), and traces of approximately 2 ?m plagioclase grains. The 75-160 ?m-thick rim contains 20-130 ?m-sized ferroan <span class="hlt">olivine</span> grains, some with 120º triple junctions. A few coarse (25-50 ?m-sized) patches of plagioclase with 2-18 ?m-thick diopside rinds occur in several places just beneath the rim. The occurrence of <span class="hlt">olivine</span> rims around AOI-1 and around many AOIs in CV3 Allende suggests that CK and CV AOIs formed by the acquisition of porous forsteritic rims around fine-grained, rimless CAIs that consisted of diopside, anorthite, melilite, and spinel. Individual AOIs in carbonaceous chondrites may have formed after transient heating events melted their <span class="hlt">olivine</span> rims as well as portions of the underlying interiors. In AOI-1, coarse plagioclase grains with diopside rinds crystallized immediately below the <span class="hlt">olivine</span> rim. Secondary parent-body alteration transformed forsterite in the rims of CV and CK AOIs into more-ferroan <span class="hlt">olivine</span>. Some of the abundant pores in the interior of AOI-1 may have formed during aqueous alteration after fine-grained melilite and anorthite were leached out. Chondrite groups with large <span class="hlt">chondrules</span> tend to have large AOIs. AOIs that formed in dust-rich nebular regions (where CV and CK chondrites later accreted) tend to be larger than AOIs from less-dusty regions.</p> <div class="credits"> <p class="dwt_author">Rubin, Alan E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">236</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950060235&hterms=love&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dlove"> <span id="translatedtitle">Electrical discharge heating of <span class="hlt">chondrules</span> in the solar nebula</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">We present a rudimentary theoretical assessment of electrical discharge heating as a candidate mechanism for the formation of <span class="hlt">chondrules</span> in the solar nebula. The discharge model combines estimates of the properties of the nebula, a mechanism for terrestrial thunderstorm electrification, and some fundamental electrical properties of gases. Large uncertainties in the model inputs limit these calculations to order-or-magnitude accuracy. Despite the uncertainty, it is possible to estimate an upper limit to the efficiency of nebular discharges at melting millimeter-sized stony objects. We find that electrical arcs analogous to terrestrial lightning could have occurred in the nebula, but that under most conditions these discharges probably could not have melted <span class="hlt">chondrules</span>. Despite our difficulties, we believe the topic worthy of further investigation and suggest some experiments which could improve our understanding of nebular discharges.</p> <div class="credits"> <p class="dwt_author">Love, Stanley G.; Keil, Klaus; Scott, Edward R. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">237</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014IAUS..299..228S"> <span id="translatedtitle">Magnetocentrifugal jets and <span class="hlt">chondrule</span> formation in protostellar disks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Chondrite meteorites are the building blocks of the solar nebula, out of which our Solar System formed. They are a mixture of silicate and oxide objects (<span class="hlt">chondrules</span> and refractory inclusions) that experienced very high temperatures, set in a matrix that remained cold. Their prevalence suggests that they formed through a very general process, closely related to stellar and planet formation. However the nature and properties of the responsible mechanism have remained unclear. The evidence for a hot solar nebula provided by this material seems at odds with astrophysical observations of forming stars. These indicate that the typical temperatures of protostellar disks are too low to melt and vapourise silicate minerals at the radial distances sampled by <span class="hlt">chondrule</span>-bearing meteorites. Here, we show that processing of precursors in a protostellar outflow at radial distances of about 1 - 3 AU can heat them to their melting points and explain their basic properties, while retaining association with the colder matrix.</p> <div class="credits"> <p class="dwt_author">Salmeron, Raquel; Ireland, Trevor</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">238</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20040084634&hterms=Pat+Kyle&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DPat%2BKyle"> <span id="translatedtitle">Turbulent Concentration of <span class="hlt">Chondrules</span>: Size Distribution and Multifractal Scaling</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Size-selective concentration of particles in 3D turbulence may be related to collection of <span class="hlt">chondrules</span> and other constituents into primitive bodies in a weakly turbulent protoplanetary nebula. In the terrestrial planet region, both the characteristic size and narrow size distribution of <span class="hlt">chondrules</span> are explained, whereas "fluffier" particles would be concentrated in lower density, or more intensely turbulent, regions of the nebula. The spatial distribution of concentrated particle density obeys multifractal scaling, suggesting a dose tie to the turbulent cascade process. This scaling behavior allows predictions of the concentration probabilities to be made in the protoplanetary nebula, which are so large (> 10(exp 3) - 10(exp 4)) that further studies must be made of the role of mass loading.</p> <div class="credits"> <p class="dwt_author">Cuzzi, Jeffrey N.; Hogan, Robert C.; Paque, Julie M.; Dobrovolskis, Anthony R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">239</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013M%26PSA..76.5294T"> <span id="translatedtitle">^60Fe-^60Ni Systematics of <span class="hlt">Chondrules</span> from UOC QUE 97008: Comparing Results from In Situ and Bulk Analyses</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In order to better understand discrepancies between ^60Fe-^60Ni systematics of in situ and bulk <span class="hlt">chondrule</span> measurements, we analyzed two <span class="hlt">chondrules</span> from QUE 97008 (LL3.05) that were previously measured using TIMS.</p> <div class="credits"> <p class="dwt_author">Telus, M.; Huss, G. R.; Nagashima, K.; Ogliore, R. C.; Chen, J. H.; Papanasstassiou, D. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">240</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1008908"> <span id="translatedtitle"><span class="hlt">Chondrule</span> formation by current sheets in protoplanetary disks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We numerically explore where, when and if magnetorotational instability in protoplanetary disks can produce current sheets that could form <span class="hlt">chondrules</span>. Results are tested against astronomical, meteoritic, thermodynamic, and experimental evidence. Theories of protoplanetary disk evolution require that the viscosity of the differentially rotating disk (the resistance of the disk to shear forces) be sufficient for stellar accretion on timescales of 106 years. With only molecular (frictional) viscosity, accretion takes 103 times longer. Vertical turbulent convection cannot provide the needed viscosity. The leading mechanisms for disk viscosity are (a) gravitational instability, which would drive density waves in the disk, and (b) coupling of the disk rotation to its magnetic field. In cold disk regions with a high mass density, gravitational instabilities could occur, and drive <span class="hlt">chondrule</span>-forming shocks. Alternatively, magnetorotational instability (MRI) is predicted to occur in regions of the disk where the gas is ionized enough to couple to magnetic fields. Like spiral density waves, MRI effectively transfers angular momentum outward in the disk. The MRI also produces magnetic field gradients. In weakly ionized regions where neutral particles can slip through ions (i.e.-where ambipolar diffusion occurs), magnetic field gradients are predicted to grow steeper with time, producing sheets of strong electrical current. We propose that these current sheets could melt <span class="hlt">chondrule</span> precursors. Unlike mechanisms involving accumulation and dissipation of charge (nebular 'lightning', e.g.-[11]), the MRI is driven by the abundant energy of the differential rotation of the disk itself. Furthermore, current sheets are predicted to occur in different regions over the lifetime of the disk. Which disk regions make current sheets, when, and where might they form <span class="hlt">chondrules</span>? Because current sheet thermal profiles are qualitatively similar to those of shocks, our results are testable against meteoritic evidence by techniques analogous to those used by [6].</p> <div class="credits"> <p class="dwt_author">Ebel, D.S.; Joung, M.K.R.; McLow, M.-M. (AMNH); (Columbia)</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-10</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_11");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return 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id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_12");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a style="font-weight: bold;">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_14");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">241</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1008888"> <span id="translatedtitle">Unambiguous voids in Allende <span class="hlt">chondrules</span> and refractory inclusions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Void space can be caused by thin section preparation. 3-dimensional tomographic analysis, prior to sectioning, shows that several very different types of voids are abundant in Allende meteorite inclusions. Formation models are proposed for each type. Void spaces in the components of chondritic meteorites have received little attention, perhaps due to ambiguities attendant upon their very existence, and also their origin. Computer-aided microtomography allows the 3-dimensional imaging and analysis of void spaces within solid objects. Several striking examples of void spaces, apparently enclosed by solid material, resulted from our observations of large <span class="hlt">chondrules</span> and CAIs from the Allende (CV3) meteorite. These voids are 'unambiguous' because their existence cannot be ascribed to plucking during sample preparation, as would be the case in traditional 2-dimensional thin section petrography. Although we focus on large objects in Allende, preliminary observations indicate that void spaces are prevalent in <span class="hlt">chondrules</span> and refractory inclusions in many meteorites. Voids remain ambiguous, however, because their structure and appearance vary between <span class="hlt">chondrules</span> and CAIs, suggesting there may be different causes of void formation in particular objects. Some voids appear to have formed as a result of dilation during cooling. Others are evidence of hydrothermal leaching on the parent body followed by partial chemical replacement. Alternatively, vapor-mediated leaching and replacement may have occurred in the nebula. Yet another possibility is internal brecciation caused by impact, while the object was still free floating in the nebula, and perhaps still partially molten.</p> <div class="credits"> <p class="dwt_author">Murray, J.; Boesenberg, J.S.; Ebel, D.S. (AMNH)</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-03-26</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">242</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/1022895"> <span id="translatedtitle">Extremely NA and CL Rich <span class="hlt">Chondrule</span> AL3509 from the Allende Meteorite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We report on the mineralogy, petrology, chemistry, oxygen isotopes, {sup 26}Al-{sup 26}Mg and {sup 36}Cl-{sup 36}S isotope systematics of the Allende <span class="hlt">chondrule</span> Al3509 discovered and described by [1] and [2]. This spherical object ({approx}1cm {phi}) contains {approx}10% Na and 1% Cl, and nearly pure {sup 129}Xe [({sup 129}Xe/{sup 127}I) = 1.1 x 10{sup -4} (3)]. This high enrichment in halogens makes it of interest in searching for radiogenic {sup 36}S from {sup 36}Cl (t{sub 1/2} {approx} 0.3 Ma) decay. While there is strong evidence for the presence of {sup 36}Cl in sodalite and wadalite in CV CAIs [4,5], some sodalites show no evidence for excesses of {sup 36}S ({sup 36}S*). In contrast, high inferred initial {sup 36}Cl/{sup 35}Cl = 2 x 10{sup -5} has been found in wadalite from the Allende CAI AJEF [5]. The observed {sup 36}S excesses in sodalite are not correlated with radiogenic {sup 26}Mg, decay product of {sup 26}Al (t{sub 1/2} {approx} 0.72 Ma) [4]. From the inferred initial {sup 36}Cl/{sup 35}Cl ratios and consideration of both AGB and SNe stellar sources, {sup 36}Cl must be the product of charged particle irradiation within the early solar system. However, neither the specific nuclear production mechanism nor the irradiation site have been identified. Both sodalite and wadalite are found as late stage alteration products of CAIs together with grossular, monticellite, Al-rich pyroxene, wollastonite, nepheline, ferroan <span class="hlt">olivine</span>, and ferroan pyroxenes. This late-stage alteration has been found to extensively change some CAIs in Allende, but clear residues of spinel, hibonite and Wark-Lovering rims are recognizable remnants of the original CAIs. The nature of the widespread volatile alteration process as well as that of the fluid phase remain controversial.</p> <div class="credits"> <p class="dwt_author">Wasserburg, G J; Hutcheon, I D; Aleon, J; Ramon, E C; Krot, A N; Nagashima, K; Brearley, A J</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-04-07</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">243</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20040065904&hterms=magnetite+solar&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dmagnetite%2Bsolar"> <span id="translatedtitle">Clear Evidence for Fe-60 in Silicate from a Semarkona <span class="hlt">Chondrule</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Fe-60 (t(sub 1/2) = 1.5 Ma) is key to understanding the sources of short-lived radionuclides in the early solar system because it is the only one among those known from meteoritic material that is produced only in stars [1]. Within the last year, it has become clear that Fe-60 was present in sulfides from primitive ordinary and enstatite chondrites in amounts sufficient to require a recent stellar input [2-5]. The sulfide data indicate an initial Fe-60/Fe-56 ratio for the early solar system of between approx. 3 10(exp -7) and approx. 1.6 10(exp -6) [2-4]. However, iron (and nickel?) in sulfides is easily mobilized by very mild heating [e.g., 6], so there is considerable uncertainty over the true initial ratio. To resolve this uncertainty, we have begun a search for evidence of Fe-60 in silicates from primitive chondrites. In <span class="hlt">olivine</span> from type 3.0-3.1 ordinary chondrites, diffusive exchange of iron and magnesium has not occurred to any significant degree, and diffusive exchange in pyroxene is slower [7]. However, the relatively small elemental fractionation of iron from nickel in silicates, coupled with the fact that the daughter nuclide, Ni-60, makes up approx. 26 % of normal nickel, make detection of excesses of radiogenic Ni-60 very difficult. Fortunately, we have found a fine-grained radiating-pyroxene <span class="hlt">chondrule</span> in Semarkona (LL3.0) with a very high Fe/Ni ratio that gives clear evidence of Fe-60.</p> <div class="credits"> <p class="dwt_author">Huss, G. R.; Tachibana, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">244</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/42296699"> <span id="translatedtitle">Oxygen isotopic compositions of <span class="hlt">chondrules</span>: Implications for evolution of oxygen isotopic reservoirs in the inner solar nebula</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We review the oxygen isotopic compositions of minerals in <span class="hlt">chondrules</span> and compound objects composed of a <span class="hlt">chondrule</span> and a refractory inclusion, and bulk oxygen isotopic compositions of <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> from primitive (unmetamorphosed)</p> <div class="credits"> <p class="dwt_author">Alexander N. Krot; Hisayoshi Yurimoto; Kevin D. McKeegan; Laurie Leshin; Marc Chaussidon; Guy Libourel; Miwa Yoshitake; Gary R. Huss; Yunbin Guan; Brigitte Zanda</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">245</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/u4124347234g0102.pdf"> <span id="translatedtitle">Mg tracer diffusion in synthetic forsterite and San Carlos <span class="hlt">olivine</span> as a function of P, T and fO 2</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We present new experimental data on Mg tracer diffusion in oriented single crystals of forsterite (Fo100) and San Carlos <span class="hlt">olivine</span> (Fo92) between 1000–1300° C. The activation energies of diffusion are found to be 400 (±60) kJ\\/mol (˜96 kcal\\/mol) and 275 (±25) kJ\\/mol (˜65 kcal\\/ mol) in forsterite and San Carlos <span class="hlt">olivine</span>, respectively, along [001] at a fO2 of 10-12 <span class="hlt">bars</span>.</p> <div class="credits"> <p class="dwt_author">Sumit Chakraborty; John R. Farver; Richard A. Yund; David C. Rubie</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">246</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40922926"> <span id="translatedtitle">Dynamic crystallization of <span class="hlt">chondrule</span> melts of porphyritic and radial pyroxene composition</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Dynamic crystallization experiments in which heterogeneous nucleation is an important variable have been completed on four melts of <span class="hlt">chondrule</span> composition. Compositions were chosen to best represent <span class="hlt">chondrules</span> with porphyritic pyroxene and radial pyroxene textures. Experimental results show that heterogeneous nucleation is essential for the formation of porphyritic textures. Without preexisting nuclei, too much supercooling is established before crystallization is initiated</p> <div class="credits"> <p class="dwt_author">G. Lofgren; W. J. Russell</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">247</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48949531"> <span id="translatedtitle">Micromagnetic coercivity distributions and interactions in <span class="hlt">chondrules</span> with implications for paleointensities of the early solar system</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Chondrules</span> in chondritic meteorites record the earliest stages of formation of the solar system, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 <span class="hlt">chondrules</span> from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the</p> <div class="credits"> <p class="dwt_author">Gary Acton; Qing-Zhu Yin; Kenneth L. Verosub; Luigi Jovane; Alex Roth; Benjamin Jacobsen; Denton S. Ebel</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">248</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19780032327&hterms=common+genetic+variation&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dcommon%2Bgenetic%2Bvariation"> <span id="translatedtitle">Chemical and petrographic constraints on the origin of <span class="hlt">chondrules</span> and inclusions in carbonaceous chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Bulk chemical compositions of the various petrographic types of <span class="hlt">chondrules</span> and inclusions in Type 3 carbonaceous chondrites (excluding those affected by metamorphism) have been determined by microprobe defocused-beam analysis. Inclusion compositions follow approximately the theoretical compositional trajectory for equlibrium condensation. <span class="hlt">Chondrules</span> occurring in the same meteorites have higher silica contents and show only slight overlap with inclusion compositions. Dust fusion is apparently an inadequate mechanism for producing the wide chemical variations observed among <span class="hlt">chondrules</span>. Impact-melting models require sampling of complex target rocks which are unknown as components of meteorites; this mechanism also demands efficient mechanical processing of <span class="hlt">chondrules</span> before accretion. A genetic relationship between <span class="hlt">chondrules</span> and inclusions in carbonaceous chondrites is suggested by the compositional continuum between these objects. A condensation sequence which dips into the liquid stability field at lower temperatures is advocated for the production of both inclusions and <span class="hlt">chondrules</span>. Textural relationships between intergrown <span class="hlt">chondrules</span> and inclusions support such a sequence. This model suggests that the assembled components (inclusions and <span class="hlt">chondrules</span>) of carbonaceous chondrites are related by a common process.</p> <div class="credits"> <p class="dwt_author">Mcsween, H. Y., Jr.</p> <p class="dwt_publisher"></p> <p class="publishDate">1977-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">249</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41335347"> <span id="translatedtitle">Gas dynamic heating of <span class="hlt">chondrule</span> precursor grains in the solar nebula</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In the present investigation of solar nebula gasdynamic processes which may account for the melting of <span class="hlt">chondrule</span> precursor grains, both drag heating due to grain relative motion and heating due to collisions with gas molecules in thermal motion are considered in conjunction with the effect of thermally emitted radiation on grain heating and cooling. The melting of <span class="hlt">chondrule</span>-sized grains is</p> <div class="credits"> <p class="dwt_author">L. L. Hood; M. Horanyi</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">250</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1980GeCoA..44..841L"> <span id="translatedtitle">Metamorphism of the H-group chondrites - Implications from compositional and textural trends in <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The paper discusses element bulk compositions of 373 <span class="hlt">chondrules</span> from 18 H3 to H6 chondrites determined by broad-beam electron probe analysis. Bulk <span class="hlt">chondrule</span> FeO and Al2O3 amounts increase and TiO2 and Cr2O3 decrease with increasing petrologic type; normative faylite, albite, and plagioclase amounts increase through the petrologic sequence. <span class="hlt">Chondrule</span> diameters correlate with phenocryst sizes in porphyritic <span class="hlt">chondrules</span> of type 3 chondrites, but this correlation is diminished in the higher petrologic types. The compositional trends in <span class="hlt">chondrules</span> through the petrologic sequence are attributed to diffusion and equilibration among <span class="hlt">chondrules</span>, and between <span class="hlt">chondrules</span> and matrix in response to increasing degrees of thermal metamorphism. It is suggested that H-group chondrites are formed by accretion of high-temperature (<span class="hlt">chondrules</span>) and low-temperature (matrix) materials. Internal reheating of the parent materials to different temperatures caused compositional equilibration, grain coarsening, and reduction of FeO to Fe(0) by carbon.</p> <div class="credits"> <p class="dwt_author">Lux, G.; Keil, K.; Taylor, G. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">251</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1985GeCoA..49..925G"> <span id="translatedtitle">The origin and history of the metal and sulfide components of <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Instrumental and radiochemical neutron activation analysis is used to determine the concentrations of 14 siderophile and other nonlithophilic elements in 31 <span class="hlt">chondrules</span> from the extremely unequilibrated chondrite Semarkona. The results are presented in tables and graphs, characterized in detail, and compared with the results obtained for lithophile elements in the same samples by Grossman and Wasson (1983). The elements studied are found to be significantly more fractionated than the lithophile elements, with variations in <span class="hlt">chondrule</span>/whole-rock abundances of up to a factor of 1000, a mean ratio of 0.2, and differences between Ni-rich and Ni-depleted <span class="hlt">chondrules</span>. It is argued that the metal and sulfides in the <span class="hlt">chondrules</span> represent the composition of the solar nebula before <span class="hlt">chondrule</span> formation and already contained the siderophile and chalcophile elements, although some Fe was contained in silicates along with Ni, Co, Au, Ge and Se. The segregation of metals during a molten stage is considered of minor importance.</p> <div class="credits"> <p class="dwt_author">Grossman, J. N.; Wasson, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">252</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1984E%26PSL..68...43K"> <span id="translatedtitle"><span class="hlt">Chondrules</span> from Chainpur (LL-3) - Reduced parent rocks and vapor fractionation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Nineteen <span class="hlt">chondrules</span> from the Chainpur chondrite have been analyzed for their bulk lithophile element content and mineral chemistry. The most refractory <span class="hlt">chondrules</span> are depleted in K, leading to the conclusion that this group was mainly produced by vapor fractionation during the chrondule-forming event. The majority of <span class="hlt">chondrules</span> are enriched in Na but fractionated in K. A separation mechanism via alkali sulfides is suggested for the fractionation of K from Na. It is concluded that the pre-Chainpur matter went through highly reducing conditions before being sampled by the <span class="hlt">chondrule</span>-forming process. Melting occurred under oxidizing conditions in a dense atmosphere with high partial pressure of volatile elements, leading to a conversion of sulfides into oxides, providing FeO in almost constant amounts, and enriching the <span class="hlt">chondrules</span> in volatiles compared to bulk chondrite compositions.</p> <div class="credits"> <p class="dwt_author">Kurat, G.; Pernicka, E.; Herrwerth, I.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">253</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014Icar..228..288S"> <span id="translatedtitle"><span class="hlt">Olivine</span>-dominated asteroids: Mineralogy and origin</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Olivine</span>-dominated asteroids are a rare type of objects formed either in nebular processes or through magmatic differentiation. The analysis of meteorite samples suggest that at least 100 parent bodies in the main belt experienced partial or complete melting and differentiation before being disrupted. However, only a few <span class="hlt">olivine</span>-dominated asteroids, representative of the mantle of disrupted differentiated bodies, are known to exist. Due to the paucity of these objects in the main belt their origin and evolution have been a matter of great debate over the years. In this work we present a detailed mineralogical analysis of twelve <span class="hlt">olivine</span>-dominated asteroids. We have obtained near-infrared (NIR) spectra (0.7-2.4 ?m) of asteroids (246) Asporina, (289) Nenetta, (446) Aeternitas, (863) Benkoela, (4125) Lew Allen and (4490) Bamberry. Observations were conducted with the Infrared Telescope Facility (IRTF) on Mauna Kea, Hawai'i. This sample was complemented with spectra of six other <span class="hlt">olivine</span>-dominated asteroids including (354) Eleonora, (984) Gretia, (1951) Lick, (2501) Lohja, (3819) Robinson and (5261) Eureka obtained by previous workers. Within our sample we distinguish two classes, one that we call monomineralic-<span class="hlt">olivine</span> asteroids, which are those whose spectra only exhibit the 1 ?m feature, and another referred to as <span class="hlt">olivine</span>-rich asteroids, whose spectra exhibit the 1 ?m feature and a weak (Band II depth ˜4%) 2 ?m feature. For the monomineralic-<span class="hlt">olivine</span> asteroids the <span class="hlt">olivine</span> chemistry was found to range from ˜Fo49 to Fo70, consistent with the values measured for brachinites and R chondrites. In the case of the <span class="hlt">olivine</span>-rich asteroids we determined their <span class="hlt">olivine</span> and low-Ca pyroxene abundance using a new set of spectral calibrations derived from the analysis of R chondrites spectra. We found that the <span class="hlt">olivine</span> abundance for these asteroids varies from 0.68 to 0.93, while the fraction of low-Ca pyroxene to total pyroxene ranges from 0.6 to 0.9. A search for dynamical connections between the <span class="hlt">olivine</span>-dominated asteroids and asteroid families found no genetic link (of the type core-mantel-crust) between these objects.</p> <div class="credits"> <p class="dwt_author">Sanchez, Juan A.; Reddy, Vishnu; Kelley, Michael S.; Cloutis, Edward A.; Bottke, William F.; Nesvorný, David; Lucas, Michael P.; Hardersen, Paul S.; Gaffey, Michael J.; Abell, Paul A.; Corre, Lucille Le</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">254</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012M%26PS...47.2193M"> <span id="translatedtitle">Ultrarapid chondrite formation by hot <span class="hlt">chondrule</span> accretion? Evidence from unequilibrated ordinary chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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 <span class="hlt">chondrules</span>. 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 <span class="hlt">chondrule</span> 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 <span class="hlt">chondrule</span> 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 <span class="hlt">chondrules</span> is about 50%, a value which seemingly cannot be exceeded due to geometric limitations. Both viscous and brittle <span class="hlt">chondrule</span> deformation is observed. A model for cluster chondrite formation is proposed where hot and deformable <span class="hlt">chondrules</span> 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 <span class="hlt">chondrule</span> 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 <span class="hlt">chondrule</span>-forming conditions. Cluster chondrites would document local <span class="hlt">chondrule</span> formation, where <span class="hlt">chondrule</span>-forming heating events and the accretion of chondritic bodies were closely linked in time and space.</p> <div class="credits"> <p class="dwt_author">Metzler, Knut</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">255</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009Litho.112..201B"> <span id="translatedtitle">Origin of <span class="hlt">olivine</span> in kimberlite: Phenocryst or impostor?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Kimberlite hosts two populations of <span class="hlt">olivine</span> that are distinguished on the basis of grain size and morphology; the populations are commonly described genetically as xenocrysts and phenocrysts. <span class="hlt">Olivine</span> xenocrysts or macrocrysts are thought to derive from disaggregation of mantle xenoliths whereas the smaller, euhedral <span class="hlt">olivine</span> crystals are presumed entirely cognate to the kimberlite melt. Recent studies of zoning patterns of euhedral <span class="hlt">olivine</span> in kimberlite have, however, cast doubt on the actual origins of the smaller <span class="hlt">olivine</span> crystals. Here, we elucidate the nature and origins of the textural and chemical zonation that characterize both populations of <span class="hlt">olivine</span>: macrocrysts (<span class="hlt">olivine</span>-I) and euhedral crystals (<span class="hlt">olivine</span>-II). Specifically, we show that both <span class="hlt">olivine</span>-I and <span class="hlt">olivine</span>-II feature chemically distinct overgrowths resulting from heterogeneous crystallization onto pre-existing <span class="hlt">olivine</span> xenocrysts. Our analysis limits the total volume of <span class="hlt">olivine</span> crystallized during transport to ? 5% in contrast to previous estimates of ~ 25%. The reduced extent of <span class="hlt">olivine</span> crystallization allows for closer reconciliation of crystallized <span class="hlt">olivine</span> compositions and estimates of Mg#s for primitive kimberlite melts. It also places constraints on processes involving orthopyroxene assimilation by kimberlite melt. If <span class="hlt">olivine</span> crystallization and orthopyroxene assimilation are coupled, then orthopyroxene assimilation is limited to ~ 7%. Larger masses of orthopyroxene assimilation (i.e. 25%) are possible only if kimberlite magmas originate at super-liquidus (> 100 ºC) conditions and sub-equal amounts of <span class="hlt">olivine</span> crystallization occurs.</p> <div class="credits"> <p class="dwt_author">Brett, R. C.; Russell, J. K.; Moss, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">256</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/39659752"> <span id="translatedtitle">Cations in <span class="hlt">olivine</span>, Part 2: Diffusion in <span class="hlt">olivine</span> xenocrysts, with applications to petrology and mineral physics</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Diffusivities for calcium, iron, magnesium, manganese and aluminum have been measured for St. John's <span class="hlt">olivine</span> undergoing cation exchange with synthetic basaltic melts. The variety of temperature, pressure and fO2 conditions under which the diffusivities were measured complement the equilibrium-partitioning study of calcium in <span class="hlt">olivine</span>-bearing basalts by Jurewicz and Watson, 1988. <span class="hlt">Olivine</span> was found to be anisotropic with respect to the</p> <div class="credits"> <p class="dwt_author">Amy J. G. Jurewicz; E. Bruce Watson</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">257</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19940011937&hterms=takeda&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3D%2522takeda%2522"> <span id="translatedtitle">Exsolved kirschsteinite in angrite LEW86010 <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Mineralogy of kirschsteinite exsolution in <span class="hlt">olivine</span> from Antarctic meteorite LEW86010 has been studied by single crustal X-ray diffraction technique. The LEW86010 <span class="hlt">olivine</span> crystals have exsolution lamellae of kirschteinite about 15 microns wide. Determination of crystallographic orientation of exsolved kirschsteinite in an <span class="hlt">olivine</span> grain has been made. Weak reflections of exsolved kirschsteinite share common crystallographic orientation with the host <span class="hlt">olivine</span>. The cell dimensions of the exsolved phase (a - 4.87 plus or minus 0.05A, b - 11.14 plus or minus 0.10A, c - 6.36 plus or minus 0.05A) and intensities were in well accord with those of kirschsteinite previously reported. Oriented section perpendicular to the a axis shows exsolution lamellae in two directions parallel to (031) and (031). The lamellae are up to 10 microns in width and spacings between them are usually 50-100 microns.</p> <div class="credits"> <p class="dwt_author">Mikouchi, Takashi; Takeda, Hiroshi; Mori, Hiroshi; Miyamoto, Masamichi; Mckay, Gordon</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">258</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19840057214&hterms=H3&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DH3"> <span id="translatedtitle">Chemical and physical studies of type 3 chondrites. III <span class="hlt">Chondrules</span> from the Dhajala H3.8 chondrite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Thermoluminescence (TL) properties have been measured in 58 <span class="hlt">chondrules</span> separated from the Dhajala H3.8 chondrite. The pyrolytic <span class="hlt">chondrules</span> are noted to have higher mass-normalized TL values than nonpyrolytic ones. Significant correlations are noted between log(TL) and the bulk CaO, Al2O3, and MnO content of the <span class="hlt">chondrules</span>. These, together with correlations of log(TL) with the CaO, Al2O3, SiO2 and normative anorthite content of the <span class="hlt">chondrule</span> glass, indicate an association of the TL and the abundance and position of mesostasis. It is suggested that the TL level in a given <span class="hlt">chondrule</span> is governed by its bulk composition and metamorphism, and it is hypothesized that the devitrification resistance of unequilibrated <span class="hlt">chondrule</span> mesostasis explains the unequilibration of certain <span class="hlt">chondrules</span> in type 3 ordinary chondrites.</p> <div class="credits"> <p class="dwt_author">Sears, D. W. G.; Sparks, M. H.; Rubin, A. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">259</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AGUFMMR11A2469D"> <span id="translatedtitle">Effect of fO2 on the incorporation and diffusivity of Li in <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Over the last decade the geochemical behaviour of Li has become of special interest since it was speculated that Li stable isotopes could be a promising tracer for subduction zone processes. However, there have been many studies of natural samples but our experimental and theoretical basis for interpreting these data is still lacking. Two diffusion mechanisms were identified for Li in <span class="hlt">olivine</span> [1]. Their contribution to the net flux of Li in <span class="hlt">olivine</span> depends on the vacancy concentration on the metal sites, which is sensitive to the fO2. Therefore we have studied the effect of fO2 on Li solubility and diffusion in <span class="hlt">olivine</span>. Experimental approach: thin plates of crushed, natural <span class="hlt">olivine</span> single crystals were embedded into two different kind of powders, ground plagioclase with about 2.5 ppm Li or a pre-annealed powder mixture of San Carlos <span class="hlt">olivine</span> and isotopically enriched Li. All runs were performed in a gas-mixing furnace with fO2 controlled by flowing CO/CO2 mixture. In each run we simultaneously annealed about 100 micrometer-sized samples of Pakistan <span class="hlt">olivine</span> and San Carlos <span class="hlt">olivine</span>. In addition we have added to each run a mm sized crystallographically oriented parallelepiped of San Carlos <span class="hlt">olivine</span>. For each powder reservoir we have performed a set of three anneals at 1200 C and different fO2. Cross sections of the run products were polished and analyzed with LA-ICP-MS. Results: In all cases the Li isotopes and concentrations were homogeneous in the 100 micrometer sized grains with one exception, the experiment at 1.e-10 <span class="hlt">bar</span> with the highly enriched Li reservoir. The final Li concentration was slightly lower in the Pakistan than San Carlos <span class="hlt">olivine</span> and was much lower in general if buffered by the plagioclase powder. Most importantly, the Li concentration increased systematically with increasing oxygen fugacity, indicating that the incorporation of Li in <span class="hlt">olivine</span> is fO2 dependent. The mm-sized, oriented crystal was in most cases zoned and the extent of zoning depends on the diffusion direction. In addition the profiles became systematically longer with decreasing fugacity and at the most reducing conditions the crystal was almost homogenous. However, the isotopes were in all cases completely homogenized and equilibrated with the isotopically enriched reservoir. Thermodynamic model: We extended the quantitative point defect model for <span class="hlt">olivine</span> [2] and reproduced the effect of fO2 on the solubility of Li when we assume it is mainly on the metal site and charge balanced by the formation of Fe3+ on the metal site. Conclusions: Our results strongly indicate that incorporation of Li is dependent on the fO2, less dependent on the trace element content. Diffusion of Li in <span class="hlt">olivine</span> is anisotropic and dependent on fO2. Our quantitative point defect model for <span class="hlt">olivine</span> underpins the experimental results. This will allow us to develop a multi-component diffusion model considering relevant point defects, e.g. Fe3+ and metal vacancies. Such a model will hopefully help us to simulate diffusion of Li at various natural circumstances including fO2 as a critical parameter. References: [1] Dohmen et al. (2010) Geochim Cosmochim Acta 74, 274-292; [2] Dohmen and Chakraborty (2007), Phys Chem Minerals 34, 597- 598.</p> <div class="credits"> <p class="dwt_author">Dohmen, R.; Coogan, L. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">260</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.V43F..07P"> <span id="translatedtitle">Atom Probe Tomography of <span class="hlt">Olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Here we present atom probe tomographic (APT) analyses of natural <span class="hlt">olivine</span>. APT provides three-dimensional trace element and isotopic analysis with sub-nanometer spatial resolution. It has been used for many years in engineering and materials science, but has not been applied to geological materials because traditional APT can only be used on conducting (usually metal) samples. The recent development of laser assisted APT has changed this situation, and now semi-conductors and insulators can be analyzed (Marquis et al., 2009, Kelly et al 2007). Potentially, this opens APT to extensive use in geoscience as many Fe-bearing silicates are semi-conductors. In this study, we explore the capability of the new class of APT instrumentation to analyze geological materials. APT involves the controlled evaporation of small, cylindrical specimens (100's nm in diameter) within an electric field. Specimens are typically prepared using in-situ focused-ion-beam (FIB) liftout and shaping techniques. Evaporated atoms are accelerated to a detector plate that records the position of the atom with sub-nm precision. Evaporated atoms are measured using time-of-flight mass spectrometry, allowing both elemental and isotopic determination. Since the method progressively ablates into the needle, the final analytical result is a nm-scale 3-dimensional image in which the position and identity of each detected atom is known. Typical mass resolution is between 200 and 1200 (full-width at half maximum) and typical concentration detection limits are 10 ppm. The number of potential applications of APT to igneous, metamorphic and sedimentary materials is large, ranging from studies of mineral and melt inclusions, to fine scale layering in minerals, to reaction surfaces and diffusion profiles. Much recent progress in the geochemical and petrologic fields has been driven by the increasing spatial resolution of the ion probe and laser ablation ICPMS. The ability of APT to provide atom-scale mass spectrometry should continue this trend. The main limitations to atom probe analysis of geological materials are the ability to control heat flow during laser pulsing and the associated ability to control clustering during field evaporation. Both of these factors can be controlled through specimen preparation and varying the atom probe experimental factors. <span class="hlt">Olivine</span> specimens were properly analyzed using laser pulsed APT through the use of shallow (nominally 1mm) FIB liftouts and wide shank angle specimen apices. APT settings were found to give the best mass resolution using low specimen temperatures, 0.2 nJ laser energy, and 50 kHz pulse repetition rate. Increasing any of these values increases the amount of thermal tails due to excessive heat buildup, reducing the mass spectrum resolution, and ultimately affecting the spatial resolution of the reconstruction. Marquis EA, Miller MK, Blavette D, Ringer SP, Sudbrack CK and Smith DW (2009). MRS Bulletin 34: 725-730. Thomas F. Kelly, David J. Larson, Keith Thompson, Roger L. Alvis, Joseph H. Bunton, Jesse D. Olson, Brian P. Gorman, Ann. Rev. Mat. Res. 37: 681-727.</p> <div class="credits"> <p class="dwt_author">Parman, S. W.; Gorman, B.; Jackson, C.; Cooper, R. F.; Jaeger, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_12");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_13");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a style="font-weight: bold;">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_15");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">261</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.V41F..06Y"> <span id="translatedtitle">Incompatible Trace Element Abundances in Hawaiian <span class="hlt">Olivines</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Our understanding of trace elements partitioning between <span class="hlt">olivine</span> and silicate melt is clouded by large variations in values of partition coefficients presented in the literature. In general, partition coefficients from phenocryst-matrix results are higher than those from experimental equilibration and in-situ measurements (such as LA-ICP-MS and Ion-probe) (Blard and Farley, 2008; Lee et al., 2007). This discrepancy is possibly caused by the presence of melt or micromineral inclusions in the analyzed phenocrysts, or contamination of grain boundaries by enriched glasses or accessory phases or uranium pick up from alteration of <span class="hlt">olivines</span>. To further investigate why analysis of natural phenocrysts usually results in relative high apparent D’s for incompatible trace elements, six aliquots of <span class="hlt">olivine</span> grains from a single sediment sample of Waimea river watershed, on the western side of the island of Kauai, Hawaii, were analyzed by solution ICP-MS at Harvard University for trace element concentrations. Two aliquots of <span class="hlt">olivines</span> were leached in 1% oxalic acid for 45-60 min at 90 OC before dissolution. Leached and unleached <span class="hlt">olivines</span> mostly show positive linear correlations in plots of incompatible trace elements versus La, which possibly indicates mixing lines between <span class="hlt">olivine</span> and one end-member with higher incompatible element concentration (possibly melt inclusion). Assuming La concentration in <span class="hlt">olivine</span> is zero, we estimate concentration of other incompatible elements in <span class="hlt">olivines</span> using intercepts of these mixing lines. We obtain that U and Th concentration in the <span class="hlt">olivines</span> to be about 1 ppb and 0.1 ppb respectively, corresponding to apparent DUol/melt and DThol/melt of 0.003 and 0.0001 if host lave has U of 0.3 ppm and Th of 1ppm (Gayer et al.,2008). Recently, helium isotopic measurements were made in these <span class="hlt">olivines</span> (Gayer et al., 2008) and the results yield a basin-wide average erosion rate of 0.056 mma-1 for Waimea river watershed. Gayer et al. (2008) argued that radiogenic 4He in these ~4.5 Ma old <span class="hlt">olivines</span> is negligible using DUol/melt=2×10-5 and DThol/melt=5×10-5 (Beattie 1993; Kennedy et al., 1993) and 0.3 ppm U and 1 ppm Th for host lavas. This assumption has been challenged by Blard and Farley (2008), who argued that radiogenic 4He in these <span class="hlt">olivines</span> are significant and could affect the calculated erosion rate by a factor of 10-100. They used apparent DUol/melt and DThol/melt ranging between 0.03 and 0.1, which were obtained from analyses of whole natural phenocrysts and host lava (Blard and Farley, 2008). In contrast, using our measured U and Th contents in the Kauai <span class="hlt">olivines</span> suggest revisions to erosion rates on order of only 15%. Therefore, Blard and Farley (2008)’s apparent D values may not be representative of Kauai <span class="hlt">olivines</span> and their assertion that Gayer et al. (2008)’s erosion rates from Hawaii require revision by more than a factore of 10 is incorrect.</p> <div class="credits"> <p class="dwt_author">Yu, G.; Huang, S.; Mukhopadhyay, S.; Jacobsen, S. B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">262</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19910025734&hterms=Rajan&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DRajan"> <span id="translatedtitle"><span class="hlt">Chondrule</span>-like objects and brown glasses in howardites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Chondrulelike objects and brown glasses were analyzed in the howardites, Bununu, Malvern, Monticello, Pavlovka, and Yamato 7308. The objects are very similar to <span class="hlt">chondrules</span> in ordinary and carbonaceous chondrites. Like the brown glasses, the chondrulelike objects could have been produced by impact melting that left some crystalline nuclei, followed by a slower cooling rate than for the glasses. Alternatively, these objects are <span class="hlt">chondrules</span> implanted from chondrite impactors. They are, however, without rims or any adhering matrix. The brown glasses appear to represent melting of average regolithic surface material, except for Monticello and Y7308, both of which have some siliceous glasses. The siliceous glasses could not have been produced by vapor fractionation but by melting of differentiated lithologies such as fayalitic granites. Impact mechanics indicates that howardites with abundant brown glasses came from an asteroid larger than Vesta (greater than 400 km radius), upon which impacts occurred at relative velocities of up to 5 km/s. Howardites with little or no brown glasses came from a smaller parent body. It is concluded that at least two parent bodies are likely sources for the basaltic achondrites.</p> <div class="credits"> <p class="dwt_author">Olsen, Edward J.; Fredriksson, Kurt; Rajan, Sundar; Noonan, Albert</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">263</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1992Metic..27R.256M"> <span id="translatedtitle">Constraints to the Formation of Matrix Reduced <span class="hlt">Olivine</span> in Yamato-691 (EH3) Chondrite: Implications for the Evolution of EH Chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In order to understand the origin of oxidized components in enstatite chondrites, matrix reduced <span class="hlt">olivine</span> (RO) (<~60 micrometers in diameter) in Yamato-691 (EH3) chondrite has been examined in detail using EPMA. It commonly shows a lamellar structure, composed of alternation (with the spacing of about 1 micrometer) of "reduced <span class="hlt">olivine</span>," which is a mixture of forsterite, metallic Fe, and probably unreacted <span class="hlt">olivine</span> (relict), and sub-grain boundaries (SB) partly filled with decomposition products (Fe-metal, troilite, enstatite, and siliceous melt) due to reduction, strongly suggesting that the reduction of high-FeO <span class="hlt">olivine</span> took place along SB (Boland and Duba, 1986). The presence of RO with bended SB is also suggestive of plastic deformation of the <span class="hlt">olivine</span> before reduction. We estimated the rate of reduction of (Mg,Fe)-<span class="hlt">olivine</span> as a function of temperature, composition of <span class="hlt">olivine</span> (X(sub)Fe) and PO(sub)2 of reducing gas. We assumed that PO(sub)2 of the reducing gas was buffered by Si-bearing Fe-Ni metal + quartz assemblage. A mean Si- and Ni-contents of kamacite in Y-691 (Si=2.09 wt%; Ni=2.90 wt%) was adopted (El Goresy et al., 1988). To form RO with the SB spacing of 1 micrometer within 10^6-7 yr, which is a typical time-scale of thermal metamorphism at shallow parts of meteorite parent bodies (Wood, 1979), the temperature during reduction must have exceeded 700 K. From these results, the formational history of matrix RO and other coexisting phases in Y-691 could be summarized as follows: (1) High-FeO <span class="hlt">chondrule</span> <span class="hlt">olivines</span> crystallized in <span class="hlt">chondrule</span> melts enriched in oxidized components. (2a) A severe impact process deformed them plastically and generated numerous dislocations (>10^9/cm^2) in them. (2b) Post-shock high-T (>~1100 K) annealing process formed SB in them due to dislocation climb. (3) The <span class="hlt">olivine</span> grains were then mixed with E-chondritic materials containing at least both Si-bearing Fe- Ni metals and silica. (4) During metamorphism and/or impact heating process (T>~700 K), reduction of the <span class="hlt">olivine</span> proceeded along SB to precipitate reduction products. (5) After reduction, the ROs were comminuted to grain sizes less than ~60 micrometers. (6) Finally, the fine- grained ROs were assembled with other E-chondritic components (e.g., sulfides) to form Y-691 chondrite at temperatures lower than ~500 degrees C (Nagel, 1991). Boland J.N. and Duba A.G. (1986) Jour. Geophys. Res. 91, 4711- 4722. El Goresy A. et al. (1988) Proc. NIPR Symp. Antarct. Meteorites 13th, 65-101. Nagel H.-J. (1991) Ph.D. Thesis, Univ. of Heidelberg, 117 pp. Wood J.A. (1979) In Asteroids (ed. T. Gehrels), pp. 849-891. Univ. Arizona Press, Tucson, Arizona.</p> <div class="credits"> <p class="dwt_author">Matsunami, S.; El Goresy, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">264</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AGUFMMR22A..07C"> <span id="translatedtitle">Diffusion of highly charged cations in <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Diffusion of tungsten, titanium and phosphorus have been measured in natural iron-bearing <span class="hlt">olivine</span> (~Fo90) and synthetic forsterite. Experiments were run under buffered conditions (with iron-wustite or Ni-NiO buffers) in 1-atm furnaces. The sources of diffusant for experiments were MgWO4 for tungsten diffusion, Mg2TiO4 for Ti diffusion, and AlPO4 for P diffusion; in all cases these compounds were pre-reacted at high temperature with Mg2SiO4 or Fe-bearing <span class="hlt">olivine</span> prior to diffusion anneals. Samples were placed with the source materials in noble metal or silica capsules, which were sealed under vacuum in silica glass ampoules with solid buffers. Rutherford backscattering spectrometry (RBS) was used to measure depth profiles for all sets of experiments; measurements of P were also made with Nuclear Reaction Analysis using the 31P(?,p)34S reaction. These new data suggest marked differences among diffusivities of these cations, with titanium diffusion faster than diffusion of tungsten, but slower than diffusion of phosphorus over the conditions investigated. Diffusivities of all of these elements appear significantly slower than those of divalent cations in <span class="hlt">olivine</span>. These results will be discussed in context with extant diffusion data for major, trace and minor elements in <span class="hlt">olivine</span>. The effects of oxygen fugacity and <span class="hlt">olivine</span> composition on diffusion, and potential implications for diffusion mechanisms will also be considered.</p> <div class="credits"> <p class="dwt_author">Cherniak, D. J.; Watson, E. B.; Liang, Y.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">265</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFMGC51B0951J"> <span id="translatedtitle">Effect of a Si-rich layer on <span class="hlt">olivine</span> carbonation under in-situ conditions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Mineral carbonation, a geochemical reaction between Mg-, Fe-, and Ca-silicate minerals and dissolved carbon dioxide (CO2), results in the long-term, stable storage of CO2 as carbonate minerals. Although the reaction is thermodynamically favored and occurs naturally, the kinetics are typically slow at temperatures < 100°C and thus limit industrial applications of the process. This study presents the results of a series of batch reactions designed to further understand the kinetics and mechanism of <span class="hlt">olivine</span> carbonation in a three-phase system (water, solid, and supercritical CO2) at conditions relevant to in-situ¬ carbonation (60°C, 100 <span class="hlt">bar</span> CO2 pressure, water:solid of 20:1 to 50:1, pH 3-6 ). Twin Sisters (OR) <span class="hlt">olivine</span> ((Mg0.85 Fe0.15)2SiO4) was chosen as the reactive silicate mineral because <span class="hlt">olivines</span> are abundant and undergo carbonation in nature. The carbonation of <span class="hlt">olivine</span> in the presence of water and supercritical CO2 proceeds via dissolution of the starting mineral and CO2, followed by precipitation of secondary phases. Two secondary phases are relevant to this study. The first is Mg-carbonate (magnesite, MgCO3), the desired reaction product because it sequesters CO2 for geologic time scales. The second is amorphous silica (SiO2), a side-product that increases the total volume of solids in the system but does not interact with CO2. Because the solubility of silica is much less than that of Mg-carbonate at <100°C, silica reaches thermodynamic saturation first. The present study shows that the rate of <span class="hlt">olivine</span> dissolution depends on the saturation state of amorphous silica and decreases by up to two orders of magnitude (from 10-11 to 10-13 mol cm-2 s-1) as saturation is approached. This observed effect is likely due to formation of a Si-rich layer on <span class="hlt">olivine</span> grain surfaces after exposure to acidic solution, observed by x-ray photoelectron spectroscopy. The initial <span class="hlt">olivine</span> dissolution is incongruent over the timeframe of several hours as shown by solution compositions determined by ICP-AES, but becomes congruent over longer periods. This behavior has been noted by others. We hypothesize that when in contact with an aqueous solution at saturation with respect to silica, the Si-rich layer will significantly lower Mg diffusion as well as the dissolution rate of <span class="hlt">olivine</span>. The net effect is thus an apparent <span class="hlt">olivine</span> dissolution rate of near zero for time periods ranging from 1 to 20 days. After this period the measured <span class="hlt">olivine</span> dissolution rate increases, indicating that the Si-rich layer is no longer plays a role in passivating the surface. We hypothesize that as the surface area of secondary silica increases, there is an increasing movement of SiO2 from the <span class="hlt">olivine</span> surface layer to physically separate secondary silica particles. We conclude that the rate of <span class="hlt">olivine</span> carbonation under the conditions of our experiments depends strongly on SiO2 saturation and that this effect must be mitigated for a commercially viable Mg-silicate carbonation process.</p> <div class="credits"> <p class="dwt_author">Johnson, N. C.; Thomas, B.; Rosenbauer, R. J.; Maher, K.; Brown, G. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">266</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20030110823&hterms=Si+Al+Ca&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DSi%252C%2BAl%252C%2BO%252C%2BCa"> <span id="translatedtitle">Al-rich <span class="hlt">Chondrules</span>: Petrologic Basis for Their Diversity, and Relation to Type C CAIs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Al-rich <span class="hlt">chondrules</span> share mineralogical and chemical properties with, and are intermediate in a volatility sense between, CAIs and ferromagnesian <span class="hlt">chondrules</span>. In some way they must be petrogenetic links between the two. A recent upsurge of interest in Al-rich <span class="hlt">chondrules</span> is due to their constituent plagioclase feldspar and Al-rich glass being amenable to successful ion microprobe searches for radiogenic Mg-26, the decay product of Al-26 (t(sub 1/2) = 720,000 y). This has allowed estimates to be made of the time duration between CAI formation and the onset of Al-rich (and possibly, by extension, ferromagnesian) <span class="hlt">chondrule</span> formation, on the order of 1.5-2.5 million years.</p> <div class="credits"> <p class="dwt_author">MacPherson, G. J.; Huss, G. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">267</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20020046279&hterms=Precursor&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DPrecursor"> <span id="translatedtitle">Recycled Chondroids in LEW86018: A Petrographic Study of <span class="hlt">Chondrule</span> Precursors</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Chondroids are any kind of nebular particle that would melt to become <span class="hlt">chondrules</span>. We describe the petrography and basic chemistry of chondroids in LEW86018 (L3.1). Additional information is contained in the original extended abstract.</p> <div class="credits"> <p class="dwt_author">Nettles, J. W.; Lofgren, G. E.; McSween, H. Y., Jr.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">268</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013M%26PSA..76.5175L"> <span id="translatedtitle">Characterization of Presolar Material in Fine-Grained <span class="hlt">Chondrule</span> Rims and Matrix of CR Chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We identified abundant (~100 ppm) presolar silicates and oxides in <span class="hlt">chondrule</span> rims of three CR chondrites, indicating a nebular origin of the fine-grained material. High proportions of presolar silicates in the rims emphasize their primitive nature.</p> <div class="credits"> <p class="dwt_author">Leitner, J.; Vollmer, C.; Hoppe, P.; Zipfel, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">269</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19890045645&hterms=vitrification&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2522vitrification%2B%253F%253F%253F%253F%253F%253F%253F%2522"> <span id="translatedtitle">Raman spectra of shocked minerals. I - <span class="hlt">Olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The Raman spectra of <span class="hlt">olivine</span> contained in a chip of the Twin Sisters Peak (Washington) dunite shocked to 22.2 GPa is shown to be identical to that of unshocked <span class="hlt">olivine</span> in the same rock. The Raman spectra of powder of the rock shocked to 20.1 GPa and of chips shocked to 59.5 GPa and 60.7 GPa display strong and broad low-frequency features with crests at 475/cm, 556/cm, and 572/cm, and broad high-frequency features near 1100/cm. It is suggested that these features are due to the formation of <span class="hlt">olivine</span> glass with a considerable degree of three-dimensional Si-O-Si linkage having scattered domains of greatly variable grain size, internal structure, and chemical composition.</p> <div class="credits"> <p class="dwt_author">Heymann, D.; Celucci, T. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">270</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24735106"> <span id="translatedtitle">Enhanced <span class="hlt">olivine</span> carbonation within a basalt as compared to single-phase experiments: reevaluating the potential of CO2 mineral sequestration.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Batch experiments were conducted in water at 150 °C and PCO2 = 280 <span class="hlt">bar</span> on a Mg-rich tholeiitic basalt (9.3 wt % MgO and 12.2 wt % CaO) composed of <span class="hlt">olivine</span>, Ti-magnetite, plagioclase, and clinopyroxene. After 45 days of reaction, 56 wt % of the initial MgO had reacted with CO2 to form Fe-bearing magnesite, (Mg0.8Fe0.2)CO3, along with minor calcium carbonates. The substantial decrease in <span class="hlt">olivine</span> content upon carbonation supports the idea that ferroan magnesite formation mainly follows from <span class="hlt">olivine</span> dissolution. In contrast, in experiments performed under similar run durations and P/T conditions with a San Carlos <span class="hlt">olivine</span> separate (47.8 wt % MgO) of similar grain size, only 5 wt % of the initial MgO content reacted to form Fe-bearing magnesite. The overall carbonation kinetics of the basalt was enhanced by a factor of ca. 40. This could be explained by differences in the chemical and textural properties of the secondary silica layer that covers reacted <span class="hlt">olivine</span> grains in both types of sample. Consequently, laboratory data obtained on <span class="hlt">olivine</span> separates might yield a conservative estimate of the true carbonation potential of <span class="hlt">olivine</span>-bearing basaltic rocks. PMID:24735106</p> <div class="credits"> <p class="dwt_author">Sissmann, Olivier; Brunet, Fabrice; Martinez, Isabelle; Guyot, François; Verlaguet, Anne; Pinquier, Yves; Daval, Damien</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-20</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">271</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/14898913"> <span id="translatedtitle">Young <span class="hlt">chondrules</span> in CB chondrites from a giant impact in the early Solar System</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Chondrules</span>, which are the major constituent of chondritic meteorites, are believed to have formed during brief, localized, repetitive melting of dust (probably caused by shock waves) in the protoplanetary disk around the early Sun. The ages of primitive <span class="hlt">chondrules</span> in chondritic meteorites indicate that their formation started shortly after that of the calcium-aluminium-rich inclusions (4,567.2 +\\/- 0.7Myr ago) and lasted</p> <div class="credits"> <p class="dwt_author">Alexander N. Krot; Yuri Amelin; Patrick Cassen; Anders Meibom</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">272</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1989E%26PSL..93..170B"> <span id="translatedtitle">Al-rich <span class="hlt">chondrules</span> from the Ybbsitz H4-chondrite - Evidence for formation by collision and splashing</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A chemical and mineralogical study of three Al-rich <span class="hlt">chondrules</span> from the H4-chondrite Ybbsitz is presented. These <span class="hlt">chondrules</span> are found to have a high concentration of incompatible elements, to be fractionated, and to be enriched in light rare earths. The results indicate that the Al-rich Ybbsitz <span class="hlt">chondrules</span> formed by different processes than the Ca-Al-rich inclusions from carbonaceous chondrites. A model is proposed in which partly molten ferromagnesian <span class="hlt">chondrules</span> collided with other objects, and Al-melt fractions were ejected to form independent Al-rich <span class="hlt">chondrules</span>. It is suggested that the strong positive Eu anomaly noted may be due to diffusive exchange of Eu between the matrix and the Al-rich <span class="hlt">chondrules</span>.</p> <div class="credits"> <p class="dwt_author">Bischoff, A.; Palme, H.; Spettel, B.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">273</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930055819&hterms=PCT&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DPCT"> <span id="translatedtitle">Magnetite-sulfide <span class="hlt">chondrules</span> and nodules in CK carbonaceous chondrites - Implications for the timing of CK oxidation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">CK carbonaceous chondrites contain rare (about 0.1 vol pct) magnetite-sulfide <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> in CK chondrites. It seems likely that the magnetite-sulfide <span class="hlt">chondrules</span> constitute the subset of magnetite-sulfide nodules that escaped as immiscible droplets from their molten silicate <span class="hlt">chondrule</span> hosts during <span class="hlt">chondrule</span> formation. The intactness of the magnetite-sulfide <span class="hlt">chondrules</span> 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.</p> <div class="credits"> <p class="dwt_author">Rubin, Alan E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">274</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1993Metic..28..130R"> <span id="translatedtitle">Magnetite-sulfide <span class="hlt">chondrules</span> and nodules in CK carbonaceous chondrites - Implications for the timing of CK oxidation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">CK carbonaceous chondrites contain rare (about 0.1 vol pct) magnetite-sulfide <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> in CK chondrites. It seems likely that the magnetite-sulfide <span class="hlt">chondrules</span> constitute the subset of magnetite-sulfide nodules that escaped as immiscible droplets from their molten silicate <span class="hlt">chondrule</span> hosts during <span class="hlt">chondrule</span> formation. The intactness of the magnetite-sulfide <span class="hlt">chondrules</span> 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.</p> <div class="credits"> <p class="dwt_author">Rubin, A. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">275</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/g22m571768n77265.pdf"> <span id="translatedtitle">Zoning of phosphorus in igneous <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We describe P zoning in <span class="hlt">olivines</span> from terrestrial basalts, andesites, dacites, and komatiites and from a martian meteorite.\\u000a P2O5 contents of <span class="hlt">olivines</span> vary from below the detection limit (?0.01 wt%) to 0.2–0.4 wt% over a few microns, with no correlated\\u000a variations in Fo content. Zoning patterns include P-rich crystal cores with skeletal, hopper, or euhedral shapes; oscillatory\\u000a zoning; structures suggesting replacement of</p> <div class="credits"> <p class="dwt_author">Margaret S. Milman-Barris; John R. Beckett; Michael B. Baker; Amy E. Hofmann; Zachary Morgan; Meghan R. Crowley; Daniel Vielzeuf; Edward Stolper</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">276</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20120001957&hterms=forsterite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dforsterite"> <span id="translatedtitle">Mineralogy of Stardust Track 112 Particle: Relation to Amoeboid <span class="hlt">Olivine</span> Aggregates</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The successful analysis of comet 81P/Wild 2 particles returned by the Stardust mission has revealed that the Wild 2 dust contains abundant silicate grains that are much larger than interstellar grains and appear to have formed in the inner regions of the solar nebula [1]. Wild 2 particles include minerals which are isotopically and mineralogically similar to CAIs [e.g., 2, 3] and <span class="hlt">chondrules</span> [e.g., 4] in chondrites. In addition, particles similar to amoeboid <span class="hlt">olivine</span> aggregates (AOAs) also have been discovered [5, 6,7]. C2067,2,112,1 is a terminal particle recovered from track #112 (T112). Nakamura-Messenger et al. [7] showed that the forsterite grain in T112 has O-16 enrichment of approximately 40 0/00 (vs. SMOW) and possibly formed together with AOAs. In this study, we have examined the mineralogy of the T112 particle and compared the possible relationships between T112 and AOAs in primitive meteorites.</p> <div class="credits"> <p class="dwt_author">Komatsu, M.; Fagan, T.; Mikouchi, T.; Miyamoto, M.; Zolensky, M.; Ohsumi, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">277</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050173926&hterms=dating&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Ddating"> <span id="translatedtitle">I-Xe Dating: The Time Line of <span class="hlt">Chondrule</span> Formation and Metamorphism in LL Chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Refractory inclusions, considered to be the oldest solids formed in the solar nebula. (4567.2 0.6 Ma) [1], are common in many carbonaceous and in some ordinary and enstatite chondrites. High-precision Pb- Pb ages for CAI s and <span class="hlt">chondrules</span> (from different meteorites) suggested that <span class="hlt">chondrule</span> formation appeared to have started about 2 Ma later than that of CAIs [1]. However, recent 26Al/26Mg data suggest simultaneous formation of CAI s and <span class="hlt">chondrules</span> in Allende [2]. The I-Xe ages of CAI s in Allende are about 2 Ma younger than the I-Xe ages of Allende <span class="hlt">chondrules</span> [3] but, like all chronometers, the I-Xe system records closure time of its particular host phase. In the case of Allende CAI s, the major iodine-bearing phase is sodalite, a secondary phase presumably formed by aqueous alteration, so I-Xe reflects the post-formational processes in these objects. In <span class="hlt">chondrules</span> the iodine host phases vary and can reflect formation and/or alteration but, to put <span class="hlt">chondrule</span> ages on a quantative basis, some problems should first be addressed.</p> <div class="credits"> <p class="dwt_author">Pravdivtseva, O. V.; Hohenberg, C. M.; Meshik, A. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">278</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004M%26PS...39.1387W"> <span id="translatedtitle">I-Xe measurements of CAIs and <span class="hlt">chondrules</span> from the CV3 chondrites Mokoia and Vigarano</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">I-Xe analyses were carried out for <span class="hlt">chondrules</span> and refractory inclusions from the two CV3 carbonaceous chondrites Mokoia and Vigarano (representing the oxidized and reduced subgroups, respectively). Although some degree of disturbance to the I-Xe system is evident in all of the samples, evidence is preserved of aqueous alteration of CAIs in Mokoia 1 Myr later than the I-Xe age of the Shallowater standard and of the alteration of a <span class="hlt">chondrule</span> (V3) from Vigarano ~0.7 Myr later than Shallowater. Other <span class="hlt">chondrules</span> in Mokoia and Vigarano experienced disturbance of the I-Xe system millions of years later and, in the case of one Vigarano <span class="hlt">chondrule</span> (VS1), complete resetting of the I-Xe system after decay of essentially all 129I, corresponding to an age more than 80 Myr after Shallowater. Our interpretation is that accretion and processing to form the Mokoia and Vigarano parent bodies must have continued for at least 4 Myr and 80 Myr, respectively. The late age of a <span class="hlt">chondrule</span> that shows no evidence for any aqueous alteration or significant thermal processing after its formation leads us to postulate the existence of an energetic <span class="hlt">chondrule</span>-forming mechanism at a time when nebular processes are not expected to be important.</p> <div class="credits"> <p class="dwt_author">Whitby, J. A.; Russell, S. S.; Turner, G.; Gilmour, J. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">279</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70022620"> <span id="translatedtitle">Bleached <span class="hlt">chondrules</span>: Evidence for widespread aqueous processes on the parent asteroids of ordinary chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">We present the first detailed study of a population of texturally distinct <span class="hlt">chondrules</span> 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' <span class="hlt">chondrules</span>, which are exclusively radial pyroxene and cryptocrystalline in texture, have porous outer zones where mesostasis has been lost. Bleached <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> in a cross section of ordinary chondrites. We studied bleached <span class="hlt">chondrules</span> from Semarkona by ion microprobe for trace elements and H isotopes, and by transmission electron microscopy. <span class="hlt">Chondrule</span> 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-<span class="hlt">chondrule</span> reaction. The mineralogy of bleached <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> 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 <span class="hlt">chondrules</span> were certainly open systems in all chondrites that experienced aqueous alteration leading to bleaching.</p> <div class="credits"> <p class="dwt_author">Grossman, J. N.; Alexander, C. M. O'D.; Wang, J.; Brearley, A. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">280</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1007/BF00306412"> <span id="translatedtitle">Transmission electron microscopy of subsolidus oxidation and weathering of <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary"><span class="hlt">Olivine</span> crystals in basaltic andesites which crop out in the Abert Rim, south-central Oregon have been studied by high-resolution and analytical transmission electron microscopy. The observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of <span class="hlt">olivine</span> oxidation. The <span class="hlt">olivine</span> crystals contain rare, dense arrays of coherently intergrown Ti-free magnetite and inclusions of a phase inferred to be amorphous silica. We interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava. The second <span class="hlt">olivine</span> alteration assemblage contains complex ordered intergrowths on (001) of forsterite-rich <span class="hlt">olivine</span> and laihunite (distorted <span class="hlt">olivine</span> structure with Fe3+ charge balanced by vacancies). Based on experimental results for laihunite synthesis (Kondoh et al. 1985), these intergrowths probably formed by <span class="hlt">olivine</span> oxidation between 400 and 800??C. The third episode of alteration involves the destruction of <span class="hlt">olivine</span> by low-temperature hydrothermal alteration and weathering. Elongate etch-pits and channels in the margins of fresh <span class="hlt">olivine</span> crystals contain semi-oriented bands of smectite. <span class="hlt">Olivine</span> weathers to smectite and hematite, and subsequently to arrays of oriented hematite crystals. The textures resemble those reported by Eggleton (1984) and Smith et al. (1987). We find no evidence for a metastable phase intermediate between <span class="hlt">olivine</span> and smectite ("M" - Eggleton 1984). The presence of laihunite exerts a strong control on the geometry of <span class="hlt">olivine</span> weathering. Single laihunite layers and laihunite-forsteritic <span class="hlt">olivine</span> intergrowths increase the resistance of crystals to weathering. Preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in <span class="hlt">olivine</span>, rather than where coherency-strain is associated with laihunite-<span class="hlt">olivine</span> interfaces. ?? 1990 Springer-Verlag.</p> <div class="credits"> <p class="dwt_author">Banfield, J. F.; Veblen, D. R.; Jones, B. F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_13");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_14");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a style="font-weight: bold;">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_16");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">281</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950042145&hterms=chromite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dchromite"> <span id="translatedtitle">Nitrogen and xenon isotopic disequilibrium in Bachmut (L6) <span class="hlt">chondrule</span> J2689 and matrix. [Abstract only</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><span class="hlt">Chondrule</span> J2689, a large (8-mm) RP <span class="hlt">chondrule</span> from Bachmut (L6) was previously found to be in disequilibrium with its host in a variety of features: (1) It has a fine-grained hornfelsic texture; (2) it contains low amounts of metal with a low-Ni taenite composition not found in the matrix; (3) the Ni/Co ratio of that metal is close to the solar ratio, which is equal to the bulk Ni/Co ratio (23) of the <span class="hlt">chondrule</span>; (4) the bulk alkali content of the <span class="hlt">chondrule</span> is high and the Na/K ratio is fractionated with respect to the average L chondrite ratio of 8; (5) Cr is depleted in spite of the high pyroxene content; (6) the siderophile elements are strongly depleted but are fractionated with their abundances increasing with volatility; and (7) the O isotopes of the <span class="hlt">chondrule</span> and the host are out of equilibrium. However, the (Fe,Mg) silicates, feldspar, and chromite have chemical compositions indistinguishable from that of the host chondrite. We have studied a chip of the chondrite and of adjacent matrix by stepwise heating and by combustion in O for N and Xe isotopic abundances. (1) The <span class="hlt">chondrule</span> preserved distinct bulk, metal, and O isotopic compositional features. It is therefore unlikely that the 'equilibration' of the major silicates Fe/Mg ratios could have taken place after accretion; (2) the <span class="hlt">chondrule</span> was well equilibrated before break-up and exposure to cosmic rays; (3) two N signatures in the matrix also indicate that the matrix is not equilibrated; and (4) all data collected so far point toward the presence of unequilibrated Bachmut components. Very few reactions took place after accretion.</p> <div class="credits"> <p class="dwt_author">Kim, Y.; Marti, K.; Kurat, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">282</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.V51E1770G"> <span id="translatedtitle">Mechanisms and Timescales for Reequilibration of Water in <span class="hlt">Olivine</span>-Hosted Melt Inclusions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Water solubility in silicate melts drops substantially with decreasing pressure. A magma containing several weight % dissolved H2O in the shallow crust is left with only a few thousand ppm following eruption. <span class="hlt">Olivine</span>-hosted melt inclusions provide information on the pre-eruptive H2O contents of degassed magmas because the strength of the host crystal protects the melt inclusion from the decompression experienced by the entraining magma. The principal uncertainty involved with interpreting pre-eruptive H2O concentrations from melt inclusions is the potential for diffusive loss or gain of H+ (protons) through the host <span class="hlt">olivine</span>. It has been proposed that Fe redox reactions severely limit the proton flux, and that episodes of H2O loss/gain are easily identifiable through changes in oxidation state of the inclusion [1,2]. Results from hydration and dehydration experiments carried out on natural inclusion-bearing <span class="hlt">olivines</span> and analyzed by SIMS confirm that H2O re-equilibratrion occurs rapidly via proton diffusion through the host <span class="hlt">olivine</span>, and demonstrate that re-equilibration of oxygen fugacity within the inclusions occurs on comparable timescales via diffusion of point defects. Therefore, an <span class="hlt">olivine</span>-hosted melt inclusion only provides a reliable record for the H2O content of the external melt with which it most recently equilibrated. Hydration experiments were performed on <span class="hlt">olivines</span> from Puu Wahi, a scoria cone on the NE rift zone of Mauna Loa volcano. Melt inclusions initially containing 0.36±0.05 wt% H2O were held at 1 GPa and 1250°C in water enriched in 18O (18O/?O = 0.977) and D (2H/?H = 0.998) to map the transport of protons and oxygen during equilibration of melt inclusions with an external fluid. Dehydration experiments were carried out for 1 to 18 hrs at 1 <span class="hlt">bar</span> and 1250 °C on inclusion-bearing <span class="hlt">olivines</span> in scoria erupted from Cerro Negro volcano, Nicaragua, in 1999. The initial concentration of H2O in these melt inclusions is uniformly high (3.6±0.6 wt%). All run products were analyzed by SIMS on the Cameca 1280 ion microprobe at WHOI. Results from our experiments confirm that the mechanism for loss or gain of H2O from <span class="hlt">olivine</span>-hosted melt inclusions is lattice diffusion of protons. This process leaves behind an O2- for every 2 protons lost, and scavenges an O2- for every 2 protons gained, producing an increase or decrease, respectively, of the fugacity of oxygen within the inclusion. However, H2O loss/gain for <span class="hlt">olivine</span>-hosted melt inclusions is coupled with point defect-mediated oxygen fugacity re-equilibration. Therefore, Fe redox reactions do not limit either the amount or rate of water loss or gain by the inclusion. The H2O concentration of an <span class="hlt">olivine</span>-hosted melt inclusion can change rapidly, and that change is not recorded by the oxygen fugacity of the melt. References: [1] A. V. Sobolev, L. V. Danyushevsky, J Petrol 35, 1183 (1994); [2] L. V. Danyushevsky, A. W. McNeill, A. V. Sobolev, Chem Geol 183, 5 (2002).</p> <div class="credits"> <p class="dwt_author">Gaetani, G. A.; O'Leary, J. A.; Shimizu, N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">283</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011Icar..211..876C"> <span id="translatedtitle">Accretion of dust by <span class="hlt">chondrules</span> in a MHD-turbulent solar nebula</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Numerical magnetohydrodynamic (MHD) simulations of a turbulent solar nebula are used to study the growth of dust mantles swept up by <span class="hlt">chondrules</span>. A small neighborhood of the solar nebula is represented by an orbiting patch of gas at a radius of 3 AU, and includes vertical stratification of the gas density. The differential rotation of the nebular gas is replaced by a shear flow. Turbulence is driven by destabilization of the flow as a result of the magnetorotational instability (MRI), whereby magnetic field lines anchored to the gas are continuously stretched by the shearing motion. A passive contaminant mimics small dust grains that are aerodynamically well coupled to the gas, and <span class="hlt">chondrules</span> are modeled by Lagrangian particles that interact with the gas through drag. Whenever a <span class="hlt">chondrule</span> enters a region permeated by dust, its radius grows at a rate that depends on the local dust density and the relative velocity between itself and the dust. The local dust abundance decreases accordingly. Compaction and fragmentation of dust aggregates are not included. Different <span class="hlt">chondrule</span> volume densities ?c lead to varying depletion and rimmed-<span class="hlt">chondrule</span> size growth times. Most of the dust sweep-up occurs within ˜1 gas scale-height of the nebula midplane. <span class="hlt">Chondrules</span> can reach their asymptotic radius in 10-800 years, although short growth times due to very high ?c may not be altogether realistic. If the sticking efficiency Q of dust to <span class="hlt">chondrules</span> depends on their relative speed ?v, such that Q < 10 -2 whenever ?v > vstick ? 34 cm/s (with vstick a critical sticking velocity), then longer growth times result due to the prevalence of high MRI-turbulent relative velocities. The vertical variation of nebula turbulent intensity results in a moderate dependence of mean rimmed-<span class="hlt">chondrule</span> size with nebula height, and in a ˜20% dispersion in radius values at every height bin. The technique used here could be combined with Monte Carlo (MC) methods that include the physics of dust compaction, in a self-consistent MHD-MC model of dust rim growth around <span class="hlt">chondrules</span> in the solar nebula.</p> <div class="credits"> <p class="dwt_author">Carballido, Augusto</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">284</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2000GeCoA..64.3897G"> <span id="translatedtitle">Oxygen isotopes in R-chondrite magnetite and <span class="hlt">olivine</span>: links between R chondrites and ordinary chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Ion-microprobe studies yield ? 17O (=? 17O - 0.52 · ? 18O) values in magnetite from the Rumurti chondrite (RC) PCA91241 (which is paired with PCA91002) of +3.1 to +3.9‰, slightly higher than that in O from whole-rock R samples. Despite ? 17O values in whole-rock RCs that are much (by ca. 1.6‰) higher than in whole-rock LL chondrites, the ? 17O in R magnetite is much lower (by ca. 2‰) than the values (+4 to +7‰) from LL3 Semarkona and Ngawi (Choi et al., 1998). The ? 18O values in PCA magnetite (-15 to -10‰) are the lowest known in meteorites, well below the range in Semarkona (-4 to +9‰). On a ? 17O-? 18O diagram both magnetite data sets form linear arrays with slopes of ca. 0.7, indicating mixing of O from different isotopic reservoirs; the slopes and intercepts of the two arrays are similar enough to permit them to be segments of a single array. This suggests that, in RCs and LL chondrites, magnetite formed from the same raw materials by the same processes, probably by aqueous alteration of metal in an asteroidal setting. We observed ? 17O values in <span class="hlt">olivines</span> and pyroxene from RCs ranging from -1.2 to +2.9‰ and ? 18O from +1.4 to +9.1‰. These compositions scatter in the same general range observed in <span class="hlt">chondrules</span> from ordinary chondrites. The similarity in the O-isotopic composition of minerals that preserve a record of formation in the solar nebula supports a model in which RCs formed from nebular components similar to those in H chondrites, but with a matrix/<span class="hlt">chondrule</span> ratio several times higher in the RCs, and with more extensive aqueous alteration in the RCs than in known H chondrites. We postulate that the matrix in R chondrites has ? 17O higher than whole-rock values. We suggest that the original ? 17O value of H 2O in the RC body was similar to that incorporated into the ordinary chondrites, previously estimated by Choi et al. (1998) to be ca. +7‰ in the LL parent body.</p> <div class="credits"> <p class="dwt_author">Greenwood, James P.; Rubin, Alan E.; Wasson, John T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">285</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011NatGe...4..244B"> <span id="translatedtitle">Earliest rock fabric formed in the Solar System preserved in a <span class="hlt">chondrule</span> rim</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Rock fabrics--the preferred orientation of grains--provide a window into the history of rock formation, deformation and compaction. Chondritic meteorites are among the oldest materials in the Solar System and their fabrics should record a range of processes occurring in the nebula and in asteroids. However, owing to abundant fine-grained material, chondrites have largely resisted traditional in situ fabric analysis. Here we use high-resolution electron backscatter diffraction to map the orientation of submicrometre grains in the Allende CV carbonaceous chondrite. We look at the fine-grained rims surrounding the <span class="hlt">chondrules</span>--spherical grains cooled from molten droplets before accretion in the meteorite--as well as the matrix material between the <span class="hlt">chondrules</span>. Although the matrix exhibits a bulk uniaxial fabric indicative of a compressive event in the parent asteroid, we find that the <span class="hlt">chondrule</span> rims preserve a spherically symmetric fabric centred on the <span class="hlt">chondrule</span>. We define a method to quantitatively relate fabric intensity to net compression, and reconstruct an initial rim porosity of 70-80%. Our calculations provide meteoritic evidence that the first solids formed in the Solar System accreted with high porosity, similar to modelling and laboratory estimates. We conclude that the <span class="hlt">chondrule</span> rim textures formed in a nebula setting and may therefore represent the first rock fabric in the Solar System.</p> <div class="credits"> <p class="dwt_author">Bland, Philip A.; Howard, Lauren E.; Prior, David J.; Wheeler, John; Hough, Robert M.; Dyl, Kathryn A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">286</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/16107841"> <span id="translatedtitle">Young <span class="hlt">chondrules</span> in CB chondrites from a giant impact in the early Solar System.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><span class="hlt">Chondrules</span>, which are the major constituent of chondritic meteorites, are believed to have formed during brief, localized, repetitive melting of dust (probably caused by shock waves) in the protoplanetary disk around the early Sun. The ages of primitive <span class="hlt">chondrules</span> in chondritic meteorites indicate that their formation started shortly after that of the calcium-aluminium-rich inclusions (4,567.2 +/- 0.7 Myr ago) and lasted for about 3 Myr, which is consistent with the dissipation timescale for protoplanetary disks around young solar-mass stars. Here we report the 207Pb-206Pb ages of <span class="hlt">chondrules</span> in the metal-rich CB (Bencubbin-like) carbonaceous chondrites Gujba (4,562.7 +/- 0.5 Myr) and Hammadah al Hamra 237 (4,562.8 +/- 0.9 Myr), which formed during a single-stage, highly energetic event. Both the relatively young ages and the single-stage formation of the CB <span class="hlt">chondrules</span> are inconsistent with formation during a nebular shock wave. We conclude that <span class="hlt">chondrules</span> and metal grains in the CB chondrites formed from a vapour-melt plume produced by a giant impact between planetary embryos after dust in the protoplanetary disk had largely dissipated. These findings therefore provide evidence for planet-sized objects in the earliest asteroid belt, as required by current numerical simulations of planet formation in the inner Solar System. PMID:16107841</p> <div class="credits"> <p class="dwt_author">Krot, Alexander N; Amelin, Yuri; Cassen, Patrick; Meibom, Anders</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-08-18</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">287</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006AGUFM.V53E..02S"> <span id="translatedtitle">Trace-Element Diffusion Coefficients in <span class="hlt">Olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have undertaken chemical diffusion experiments at 1300°C to determine both crystal/melt partition coefficients and diffusion coefficients for a wide range of trace elements in forsteritic <span class="hlt">olivine</span>. Experiments were conducted at 1 atm under controlled fO2 for up to 25 days using synthetic melts made to a composition in equilibrium with <span class="hlt">olivine</span> for major elements, and doped with selected trace elements. The melt was put into a 5 mm diameter cylindrical hole in gem quality San Carlos <span class="hlt">olivine</span> crystals drilled paralell to the a axis. Diffusion profiles were obtained both for trace elements that were added to the starting material and diffuse into the <span class="hlt">olivine</span>, and also for several trace elements present at natural abundances in the <span class="hlt">olivine</span> that diffuse out. The profiles were measured across sections perpendicular to crystal/melt boundary at a variety of crystallographic orientations (confirmed by EBSD) by laser-ablation ICP-MS. A thin laser slit oriented parallel to the crystal/melt interface was traversed from the melt through the crystal. Element concentrations were fitted to the diffusion equation to obtain both diffusion coefficients and concentrations at the crystal/melt interface, and hence partition coefficients. Calculated diffusivities for many trace elements (Ca, REE, Y, Sc, V, Cr, Ni, Co, Mn, Na, Li, Be, Ti) are relatively fast (D = 10-16 to 10^{-13 m2/s at 1300°C). The diffusion of Li in <span class="hlt">olivine</span> (approx. D = 10^{-15} m2/s) is only slightly slower than REEs and similar to divalent cations, in good agreement with inferences from zoning profiles in natural <span class="hlt">olivine</span> [1]. This rate is considerably slower than for plagioclase and clinopyroxene [2], a result which has important implications for interpreting Li isotopic data from mantle-derived rocks. The fastest diffusing trace element we observe is Be. Applying our diffusion and partition coefficients to the model of Qin et al. [3], we calculate that the REEs of <span class="hlt">olivine</span>-hosted melt inclusions in the mantle will extensively re-equilibrate with external magma in weeks (heavy REEs) to a few years (light REEs). These timescales are significantly shorter than the times estimated for the production and extraction of magma from the mantle or magma residence in the lower crust, implying anomalous melt inclusions are probably not a direct result of melting of heterogeneities in the mantle. Instead, anomalous melt inclusions likely form by assimilation processes shortly before eruption [4] and so may be useful monitors of such processes. Refs: [1] Parkinson et al., Abstract, Goldschmidt Conference 2006; [2] Coogan et al., EPSL 240, 415-424 (2005); [3] Qin et al. Am. Min. 77, 565-576 (1992); [4] Danyushevsky et al., J. Petrol. 45, 2531-2553 (2004).</p> <div class="credits"> <p class="dwt_author">Spandler, C.; O'Neill, H. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">288</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/6824886"> <span id="translatedtitle">Mechanisms of electrical conductivity in <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Data on the electrical conductivity and the thermoelectric effect in single crystals indicate that the charge conduction mechanism in pure magnesium forsterite is electrons. The concentration of electrons can be varied by controlling the number of oxygen vacancies through manipulation of the oxygen pressure. For iron bearing <span class="hlt">olivine</span>, the conduction mechanism is by electron holes localized on an iron ion. Since iron strongly affects the creep process as well, oxidation of iron is probably accompanied by the production of magnesium vacancies. 15 references.</p> <div class="credits"> <p class="dwt_author">Schock, R.N.; Duba, A.G.; Shankland, T.J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">289</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48944087"> <span id="translatedtitle">Dislocation creep of fine-grained <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Deformation experiments conducted in a gas medium apparatus at temperatures from 1200 to 1350°C with a fine-grained, solution-gelation derived Fe-bearing <span class="hlt">olivine</span> show a stress dependence of the strain rate at stresses above ?150 MPa, which is much stronger than previously reported for polycrystalline samples. The data can be fit by a power law with $\\\\dot {\\\\epsilon }$$\\\\propto$?n with n ?</p> <div class="credits"> <p class="dwt_author">U. H. Faul; J. D. Fitz Gerald; R. J. M. Farla; R. Ahlefeldt; I. Jackson</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">290</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19910046580&hterms=iodine&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Diodine"> <span id="translatedtitle">Iodine-xenon studies of petrographically and chemically characterized Chainpur <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">INAA, noble gas, and petrographic studies conducted on samples of 18 <span class="hlt">chondrules</span> and matric material from the Chainpur (LL3) indicate that the I-129/I-127 ratio, R(0), varies by a factor of more than 10 among the <span class="hlt">chondrules</span>. This corresponds to a greater-than-50 Ma span in apparent I-Xe ages. Models which invoke either gas-dust mixing or nebular heterogeneity cannot satisfactorily explain these data, any more than can hypotheses which attribute the variations to differences in formation age, metamorphic rate, or time of aqueous alteration. It is alternatively suggested that the variations represent periods of low-grade shock events.</p> <div class="credits"> <p class="dwt_author">Swindle, T. D.; Caffee, M. W.; Hohenberg, C. M.; Lindstrom, M. M.; Taylor, G. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">291</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950055059&hterms=ivanova&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522ivanova%2522"> <span id="translatedtitle">The origin of chromitic <span class="hlt">chondrules</span> and the volatility of Cr under a range of nebular conditions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">We characterize ten chromatic <span class="hlt">chondrules</span>, two spinelian <span class="hlt">chondrules</span> andd one spinel-bearing <span class="hlt">chondrule</span> and summarize data for 120 chromitic inclusions discovered in an extensive survey of ordinary chondrites. Compositional and petrographic evidence suggests that chromitic <span class="hlt">chondrules</span> and inclusions are closely related. The Cr/(Cr + Al) ratios in the spinal of these objects range from 0.5 to 0.9 and bulk Al2O3 contents are uniformly high (greater than 10 wt%, except for one with 8 wt%). No other elements having comparable solar abundances are so stongly enriched, and alkali feldspar and merrillite are more common than in normal <span class="hlt">chondrules</span>. The Cr/Mg ratios in chromitic <span class="hlt">chondrules</span> are 180-750 times the ratios in the bulk chondrite. With the possible exception of magnetic clumping of chromite in the presolar cloud, mechanical processes cannot account for this enrichment. Examination of nebular equilibrium processes shows that 50%-condensation temperatures of Cr at pH2/pH2O of 1500 are several tens of degrees below those of Mg as Mg2SiO4; the condensation of Cr is primarily as MgCr2O4 dissolved in MgAl2O4 at nebular pressures of 10(exp -4) atm or below. At pH2 = 10(exp -3) atm condesation as Cr in Fe-Ni is favored. Making the nebula much more oxidizing reduces the difference in condensation temperatures but Mg remains more refractory. We conclude that nebular equilibrium processes are not responsible for the enhanced Cr/Mg ratios. We propose that both Cr and Al became enriched in residues formed by incomplete evaporation of presolar lumps. We suggest that spinals remained as solid phases when the bulk of the silicates were incorporated into the evaporating melt; vaporization of Al and Cr were inhibited by the slow kinetics of diffusion. Subsequent melting and crystallization of these residues fractionated Cr from Al. The resulting materials constituted major components in the precursors of chromitic <span class="hlt">chondrules</span>. Our model implies that chromitic <span class="hlt">chondrules</span> and inclusions preserve the Cr isotopic record of presolar sources.</p> <div class="credits"> <p class="dwt_author">Krot, Alexander; Ivanova, Marina A.; Wasson, John T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">292</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.nlm.nih.gov/medlineplus/videos/news/Sexual_Agression_030414-1.html"> <span id="translatedtitle"><span class="hlt">Bars</span> and Sexual Boundaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://medlineplus.gov/">MedlinePLUS</a></p> <p class="result-summary">... Pages Alcohol Sexual Health Women's Health Transcript Sexual aggression against young women in <span class="hlt">bars</span> is the subject ... and Experimental Research analyzed more than 1,050 aggressive incidents in <span class="hlt">bars</span> across Toronto, Canada between 2000 ...</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">293</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1114889"> <span id="translatedtitle">Water and Carbon Dioxide Adsorption at <span class="hlt">Olivine</span> Surfaces</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Plane-wave density functional theory (DFT) calculations were performed to simulate water and carbon dioxide adsorption at the (010) surface of five <span class="hlt">olivine</span> minerals, namely, forsterite (Mg2SiO4), calcio-<span class="hlt">olivine</span> (Ca2SiO4), tephroite (Mn2SiO4), fayalite (Fe2SiO4), and Co-<span class="hlt">olivine</span> (Co2SiO4). Adsorption energies per water molecule obtained from energy minimizations varied from -78 kJ mol-1 for fayalite to -128 kJ mol-1 for calcio-<span class="hlt">olivine</span> at sub-monolayer coverage and became less exothermic as coverage increased. In contrast, carbon dioxide adsorption energies at sub-monolayer coverage ranged from -20 kJ mol-1 for fayalite to -59 kJ mol-1 for calcio-<span class="hlt">olivine</span>. Therefore, the DFT calculations show a strong driving force for carbon dioxide displacement by water at the surface of all <span class="hlt">olivine</span> minerals in a competitive adsorption scenario. Additionally, adsorption energies for both water and carbon dioxide were found to be more exothermic for the alkaline-earth (AE) <span class="hlt">olivines</span> than for the transition-metal (TM) <span class="hlt">olivines</span> and to not correlate with the solvation enthalpies of the corresponding divalent cations. However, a correlation was obtained with the charge of the surface divalent cation indicating that the more ionic character of the AE cations in the <span class="hlt">olivine</span> structure relative to the TM cations leads to greater interactions with adsorbed water and carbon dioxide molecules at the surface and thus more exothermic adsorption energies for the AE <span class="hlt">olivines</span>. For calcio-<span class="hlt">olivine</span>, which exhibits the highest divalent cation charge of the five <span class="hlt">olivines</span>, ab initio molecular dynamics simulations showed that this effect leads both water and carbon dioxide to react with the surface and form hydroxyl groups and a carbonate-like species, respectively.</p> <div class="credits"> <p class="dwt_author">Kerisit, Sebastien N.; Bylaska, Eric J.; Felmy, Andrew R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-11-14</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">294</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20120002880&hterms=search&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dsearch"> <span id="translatedtitle">Search for <span class="hlt">Olivine</span> Spectral Signatures on the Surface of Vesta</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The occurrence of <span class="hlt">olivines</span> on Vesta were first postulated from traditional petrogenetic models which suggest the formation of <span class="hlt">olivine</span> as lower crustal cumulates. An indirect confirmation is given by their presence as a minor component in some samples of diogenite meteorites, the harzburgitic diogenites and the dunitic diogenites, and as <span class="hlt">olivine</span> mineral clasts in howardites. Another indication for this mineral was given by interpretations of groundbased and Hubble Space Telescope observations that suggested the presence of local <span class="hlt">olivine</span>-bearing units on the surface of Vesta. The VIR instrument onboard the DAWN mission has been mapping Vesta since July 2011. VIR acquired hyperspectral images of Vesta s surface in the wavelength range from 0.25 to 5.1 m during Approach, Survey and High Altitude Mapping (HAMO) orbits that allowed a 2/3 of the entire asteroid surface to be mapped. The VIR operative spectral interval, resolution and coverage is suitable for the detection and mapping of any <span class="hlt">olivine</span> rich regions that may occur on the Vesta surface. The abundance of <span class="hlt">olivine</span> in diogenites is typically lower than 10% but some samples richer in <span class="hlt">olivine</span> are known. However, we do not expect to have extensive exposures of <span class="hlt">olivine</span>-rich material on Vesta. Moreover, the partial overlap of <span class="hlt">olivine</span> and pyroxene spectral signatures will make <span class="hlt">olivine</span> difficult to detect. Different spectral parameters have been used to map <span class="hlt">olivine</span> on extraterrestrial bodies, and here we discuss the different approaches used, and develop new ones specifically for Vesta. Our new methods are based on combinations of the spectral parameters relative to the 1 and 2 micron bands (the most prominent spectral features of Vesta surface in the visible and the infrared), such as band center locations, band depths, band areas, band area ratios. Before the direct application to the VIR data, the efficiency of each approach is evaluated by means of analysis of laboratory spectra of HED meteorites, pyroxenes, <span class="hlt">olivines</span> and their mixtures.</p> <div class="credits"> <p class="dwt_author">Palomba, E.; De Sanctis, M. C.; Ammannito, E.; Capaccioni, F.; Capria, M. T.; Farina, M.; Frigeri, A.; Longobardo, A.; Tosi, F.; Zambon, F.; McSween, H. Y.; Mittlefehldt, D. W.; Russell, C. T.; Raymond, C. A.; Sunshine, J.; McCord, T. B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">295</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013M%26PS..tmp..410I"> <span id="translatedtitle">Experimental simulation of oxygen isotopic exchange in <span class="hlt">olivine</span> and implication for the formation of metamorphosed carbonaceous chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have conducted hydration-dehydration experiments on terrestrial <span class="hlt">olivine</span> to investigate the behavior of oxygen isotopic fractionation to test the hypothesis that multiple cycles of aqueous and thermal processing on a parent asteroid comprise a genetic relationship between CM2s and metamorphosed carbonaceous chondrites (MCCs). Two experiments were undertaken. In the first experiment, serpentine was obtained by hydrating terrestrial <span class="hlt">olivine</span> (Fo90.9) in the laboratory. During this experiment, <span class="hlt">olivine</span> was reacted with isotopically heavy water (?18O 21.5‰) at T = 300 °C, PH2O = 300 <span class="hlt">bar</span>, for 100 days. The oxygen isotopic composition of the experimental serpentine was enriched in 18O (by 10 ‰ in ?18O) due to exchange of oxygen isotopes between <span class="hlt">olivine</span> and the 18O-rich water. Dehydrated serpentine was then produced during laboratory heating experiment in vacuum, at T = 930 °C, for 1 h. The oxygen isotopic composition of the dehydrated serpentine was enriched in 18O by a further 7 ‰. The net result of the hydration-dehydration process was an enrichment of 18O in the final material by approximately 17‰. The new experimental results suggest that the oxygen isotopic compositions of MCCs of the Belgica-like group, including Dhofar 225 and Dhofar 725, could be derived from those of typical CM2 chondrites via several cycles of hydration-dehydration caused by aqueous alteration and subsequent thermal metamorphism within their parent asteroids.</p> <div class="credits"> <p class="dwt_author">Ivanova, Marina A.; Lorenz, Cyril A.; Franchi, Ian A.; Bychkov, Andrei Y.; Post, Jeffrey E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">296</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19910050068&hterms=mantle+petrology&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dmantle%2Bpetrology"> <span id="translatedtitle"><span class="hlt">Olivine</span> diogenites - The mantle of the eucrite parent body</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Two <span class="hlt">olivine</span>-rich Antarctic diogenites (ALH A77256 and ALH 84001) of the howardite-eucrite-diogenite (HED) meteorite association have <span class="hlt">olivine</span>/pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites. Based on chemical data and petrological analysis, these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body (EPB). Mineral assemblages in these <span class="hlt">olivine</span>-rich diogenites record a continuum in thermal histories from initial partial melting (1150-1200 C) to subsolidus reequilibration (795 + or - 55 C). The small number of <span class="hlt">olivine</span>-rich diogenites known hints that only the outer portion of the EPB has been sampled.</p> <div class="credits"> <p class="dwt_author">Sack, Richard O.; Azeredo, William J.; Lipschutz, Michael E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">297</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1126/science.1089647"> <span id="translatedtitle">Discovery of <span class="hlt">Olivine</span> in the Nili Fossae Region of Mars</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">We have detected a 30,000-square-kilometer area rich in <span class="hlt">olivine</span> in the Nili Fossae region of Mars. Nili Fossae has been interpreted as a complex of grabens and fractures related to the formation of the Isidis impact basin. We propose that post-impact faulting of this area has exposed subsurface layers rich in <span class="hlt">olivine</span>. Linear mixture analysis of Thermal Emission Spectrometer spectra shows surface exposures of 30% <span class="hlt">olivine</span>, where the composition of the <span class="hlt">olivine</span> ranges from Fo30 to Fo70.</p> <div class="credits"> <p class="dwt_author">Hoefen, T. M.; Clark, R. N.; Bandfield, J. L.; Smith, M. D.; Pearl, J. C.; Christensen, P. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">298</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ia.usu.edu/viewproject.php?project=ia:1700"> <span id="translatedtitle"><span class="hlt">Bar</span> Graph Mania</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">Use these activities to build and interpret data on <span class="hlt">bar</span> graphs. Catch all the bugs in the system and put them in the correct column of the <span class="hlt">bar</span> graph. Answer the questions about the bugs in the graph. Catch bugs in six rooms. Bugs in the system Do these <span class="hlt">bar</span> graphing activities. You don\\'t have to do the last question ...</p> <div class="credits"> <p class="dwt_author">Thurlow, Ms.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-10-26</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">299</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005AGUFMGP41B0874D"> <span id="translatedtitle">Anisotropic and Isotropic Effective <span class="hlt">Olivine</span> Medium Models</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">New experimental techniques are used to accurately measure the electrical conductivity (?) of single crystal San Carlos <span class="hlt">olivine</span> (Fo89.1) along each principal orientation. The temperature (1100, 1200, and 1300°C) and oxygen fugacity (10-7<fO2<101 Pa) conditions encompassed allowed us to model the separate dependences of ? on T and fO2 with an undifferentiated mixed conduction model of small polarons and Mg vacancies to obtain steady-state fO2-independent activation energies: Ea[100] = 0.32 eV, Ea[010] = 0.56 eV, Ea[001] = 0.71 eV. A nonspecific fO2-independent parameter, ?min, is necessary to fit the data and absorbs the conductivity contributions of electrons and extrinsic defects. The model is of the form ?Tot = ?0fO2e-Ea/kT + ?mine-Ea/kT, and provides an effective <span class="hlt">olivine</span> medium for each principle orientation, suitable for use over the upper mantle temperature range and a range of oxygen buffer assemblages. A [100]-lattice preferred oriented layer of dry <span class="hlt">olivine</span> would provide a maximum of ~100.5 S/m azimuthal conductivity contrast for T = 1500°C. The anisotropic results are combined to create an isotropic model with steady-state fO2-independent Ea = 0.53 eV. The inclusion of the ?min results in conductivity that is ~0.6 log units higher than the previous SO1 and SO2 models for T = 1000°C. The difference between this model and the previous SO1 and SO2 models become larger with decreasing T. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract W-7405-ENG-48 and supported specifically by Laboratory Directed Research and Development funding.</p> <div class="credits"> <p class="dwt_author">Du Frane, W. L.; Tyburczy, J. A.; Roberts, J. J.; Toffelmier, D. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">300</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2000PEPI..121...59K"> <span id="translatedtitle">Kinetics of intracrystalline <span class="hlt">olivine</span>-ringwoodite transformation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We studied the microstructural evolution and kinetics of intracrystalline <span class="hlt">olivine</span>-ringwoodite transformation in order to evaluate the importance of this mechanism in subducting lithosphere. Intracrystalline transformation occurs within single crystals of San Carlos <span class="hlt">olivine</span> (Fo 90) at T?900°C and P?18 GPa and involves four stages: (1) Formation of (100) ? stacking faults in <span class="hlt">olivine</span>, (2) coherent nucleation of thin ringwoodite platelets on these stacking faults, (3) semi-coherent growth of the platelets and (4) incoherent nucleation of ringwoodite and/or wadsleyite grains at the platelet interfaces. Because rates of incoherent growth are about two orders of magnitude faster than rates of semi-coherent growth, the final stage is most important for bulk transformation. However, the ringwoodite platelets act as essential nucleation sites for intracrystalline incoherent transformation. The growth of ringwoodite platelets proceeds by the nucleation and migration of interface ledges (1.0-1.5 nm high) and is thermally activated with an activation energy of ˜270 kJ mol -1. This is similar to the activation energy for incoherent growth, suggesting that both processes are controlled by Si?O bond breaking. The nucleation rate of platelets, as determined from the densities of platelets observed in transmission electron microscopy (TEM) sections, is also strongly temperature-dependent and has a similar activation energy. These results suggest that intracrystalline transformation is likely to be important in subducting lithosphere in addition to the grain boundary nucleation mechanism. The intracrystalline mechanism will reduce the depth interval over which the transformation occurs and may enhance rheological weakening by reducing the grain size of the reaction products.</p> <div class="credits"> <p class="dwt_author">Kerschhofer, L.; Rubie, D. C.; Sharp, T. G.; McConnell, J. D. C.; Dupas-Bruzek, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-09-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_14");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return 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Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">301</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012Icar..218..701B"> <span id="translatedtitle">Free collisions in a microgravity many-particle experiment - II: The collision dynamics of dust-coated <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The formation of planetesimals in the early Solar System is hardly understood, and in particular the growth of dust aggregates above millimeter sizes has recently turned out to be a difficult task in our understanding (Zsom, A., Ormel, C.W., Güttler, C., Blum, J., Dullemond, C.P. [2010]. Astron. Astrophys., 513, A57). Laboratory experiments have shown that dust aggregates of these sizes stick to one another only at unreasonably low velocities. However, in the protoplanetary disk, millimeter-sized particles are known to have been ubiquitous. One can find relics of them in the form of solid <span class="hlt">chondrules</span> as the main constituent of chondrites. Most of these <span class="hlt">chondrules</span> were found to feature a fine-grained rim, which is hypothesized to have formed from accreting dust grains in the solar nebula. To study the influence of these dust-coated <span class="hlt">chondrules</span> on the formation of chondrites and possibly planetesimals, we conducted collision experiments between millimeter-sized, dust-coated <span class="hlt">chondrule</span> analogs at velocities of a few cm s-1. For 2 and 3 mm diameter <span class="hlt">chondrule</span> analogs covered by dusty rims of a volume filling factor of 0.18 and 0.35-0.58, we found sticking velocities of a few cm s-1. This velocity is higher than the sticking velocity of dust aggregates of the same size. We therefore conclude that <span class="hlt">chondrules</span> may be an important step towards a deeper understanding of the collisional growth of larger bodies. Moreover, we analyzed the collision behavior in an ensemble of dust aggregates and non-coated <span class="hlt">chondrule</span> analogs. While neither the dust aggregates nor the solid <span class="hlt">chondrule</span> analogs show sticking in collisions among their species, we found an enhanced sicking efficiency in collisions between the two constituents, which leads us to the conjecture that <span class="hlt">chondrules</span> might act as "catalyzers" for the growth of larger bodies in the young Solar System.</p> <div class="credits"> <p class="dwt_author">Beitz, E.; Güttler, C.; Weidling, R.; Blum, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">302</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009CoMP..tmp..124S"> <span id="translatedtitle">Diffusion and partition coefficients of minor and trace elements in San Carlos <span class="hlt">olivine</span> at 1,300°C with some geochemical implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Lattice diffusion coefficients have been determined for 19 elements (Li, Be, Na, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Eu, Gd, Lu and Hf) in a single crystal of San Carlos <span class="hlt">olivine</span> as a function of crystallographic orientation, at 1,300°C, 1 <span class="hlt">bar</span> and fO2 = 10-8.3 <span class="hlt">bars</span>, by equilibration with a synthetic silicate melt. Results for Li, Na, V, Cr, Fe and Zn are from diffusion of these elements out of the <span class="hlt">olivine</span>, starting from their indigenous concentrations; those for all other elements are from diffusion into the <span class="hlt">olivine</span>, from the silicate melt reservoir. Our 25-day experiment produced diffusion profiles 50 to > 700 ?m in length, which are sufficiently long that precise analyses could be achieved by scanning laser ablation inductively coupled plasma mass spectrometry, even at concentration levels well below 1 ?g g-1. For the divalent cations Ca, Mn, Fe and Ni, profiles were also obtained by electron microprobe analysis. The results of the two methods agree well with each other, and are consistent with divalent cation diffusion coefficients previously determined using different experimental methodologies. <span class="hlt">Olivine</span>/melt partition coefficients retrieved from the data are also consistent with other published partitioning data, indicating that element incorporation and transport in <span class="hlt">olivine</span> in our experiment occurred via mechanisms appropriate to natural conditions. Most of the examined trace elements diffuse through <span class="hlt">olivine</span> at similar rates to the major octahedral cations Fe and Mg, showing that cation charge and radius have little direct influence on diffusion rates. Aluminium and P remain low and constant in the <span class="hlt">olivine</span>, implying negligible transport at our analytical scale, hence Al and P diffusion rates that are at least two orders of magnitude slower than the other cations studied here. All determined element diffusivities are anisotropic, with diffusion fastest along the [001] axis, except Y and the REEs, which diffuse isotropically. The results suggest that element diffusivity in <span class="hlt">olivine</span> is largely controlled by cation site preference, charge balance mechanisms and point-defect concentrations. Elements that are present on multiple cation sites in <span class="hlt">olivine</span> (e.g. Be and Ti) and trivalent elements that are charge-balanced by octahedral site vacancies tend to diffuse at relatively fast rates.</p> <div class="credits"> <p class="dwt_author">Spandler, Carl; O'Neill, Hugh St. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">303</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/44200419"> <span id="translatedtitle">Non-equilibrium concepts lead to a unified explanation of the formation of <span class="hlt">chondrules</span> and chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Calculations of the formation of seven types of <span class="hlt">chondrules</span> in Semarkona from a gas of solar composition were performed with the Fact computer program to predict the chemistries of oxides, including silicates, developed by the authors and their colleagues. The constrained equilibrium theory was used in the calculations with two nucleation constraints suggested by nucleation theory. The first constraint was</p> <div class="credits"> <p class="dwt_author">Milton Blander; Arthur D. Pelton; In-Ho Jung; Richard Weber</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">304</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22048076"> <span id="translatedtitle">INCORPORATION OF A LATE-FORMING <span class="hlt">CHONDRULE</span> INTO COMET WILD 2</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We report the petrology, O isotopic composition, and Al-Mg isotope systematics of a <span class="hlt">chondrule</span> fragment from the Jupiter-family comet Wild 2, returned to Earth by NASA's Stardust mission. This object shows characteristics of a type II <span class="hlt">chondrule</span> that formed from an evolved oxygen isotopic reservoir. No evidence for extinct {sup 26}Al was found, with ({sup 26}Al/{sup 27}Al){sub 0} < 3.0 Multiplication-Sign 10{sup -6}. Assuming homogenous distribution of {sup 26}Al in the solar nebula, this particle crystallized at least 3 Myr after the earliest solar system objects-relatively late compared to most <span class="hlt">chondrules</span> in meteorites. We interpret the presence of this object in a Kuiper Belt body as evidence of late, large-scale transport of small objects between the inner and outer solar nebula. Our observations constrain the formation of Jupiter (a barrier to outward transport if it formed further from the Sun than this cometary <span class="hlt">chondrule</span>) to be more than 3 Myr after calcium-aluminum-rich inclusions.</p> <div class="credits"> <p class="dwt_author">Ogliore, R. C.; Huss, G. R.; Nagashima, K. [Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Butterworth, A. L.; Gainsforth, Z.; Stodolna, J.; Westphal, A. J. [Space Sciences Laboratory, University of California at Berkeley, Berkeley, CA 94720 (United States); Joswiak, D. [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Tyliszczak, T. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-02-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">305</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20020046135&hterms=forsterite&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dforsterite"> <span id="translatedtitle">Forsterite from <span class="hlt">Chondrules</span> in the Mokoia (CV3) Chondrite: Cathodoluminescence, Chemistry and Oxygen Isotopes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Forsterite in Mokoia <span class="hlt">chondrules</span> shows CL zoning which can be quite complex. Oxygen isotope analyses in forsterite with different CL intensities are homogeneous, showing that refractory and melt-grown forsterites are isotopically indistinguishable. Additional information is contained in the original extended abstract.</p> <div class="credits"> <p class="dwt_author">Jones, R. H.; Carey, R.; Leshin, L. A.; Guan, Y.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">306</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013M%26PSA..76.5084S"> <span id="translatedtitle"><span class="hlt">Olivine</span> Annealing in Molten Iron-Sulfide. A Tool to Interpret the Origin of Pallasites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Annealing of <span class="hlt">olivine</span> in molten Fe-S was performed in order to decipher the origin of rounded <span class="hlt">olivine</span> group pallasite meteorites. Growth mechanism and growth rate of <span class="hlt">olivine</span> was obtained and a variety of formation models are critically discussed.</p> <div class="credits"> <p class="dwt_author">Solferino, G. F. D.; Muir, S. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">307</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013M%26PSA..76.5321V"> <span id="translatedtitle">Compositions of Partly Altered <span class="hlt">Olivine</span> and Replacement Serpentine in the CM2 Chondrite QUE 93005</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Serpentine replacing <span class="hlt">olivine</span> in QUE 93005 has a narrow range of compositions, regardless of the reactant <span class="hlt">olivine’s</span> composition. Homogeneity of replacement serpentines in QUE 93005 and other CM2s favors homogeneity of aqueous solutions on >cm scales.</p> <div class="credits"> <p class="dwt_author">Velbel, M. A.; Tonui, E. K.; Zolensky, M. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">308</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004M%26PS...39.1897B"> <span id="translatedtitle">Non-equilibrium concepts lead to a unified explanation of the formation of <span class="hlt">chondrules</span> and chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Calculations of the formation of seven types of <span class="hlt">chondrules</span> in Semarkona from a gas of solar composition were performed with the Fact computer program to predict the chemistries of oxides, including silicates, developed by the authors and their colleagues. The constrained equilibrium theory was used in the calculations with two nucleation constraints suggested by nucleation theory. The first constraint was the blocking of Fe and other metal gaseous atoms from condensing to form solids or liquids because of the very high surface free energies and high surface tensions of the solid and liquid metals, respectively. The second constraint was the blocking of the condensation of solids and the formation of metastable liquid oxides (including silicates) well below their liquidus temperatures. Our laboratory experiments suggested subcooling of type IIA <span class="hlt">chondrule</span> compositions of 400 degrees or more below the liquidus temperature. The blocking of iron leads to a supersaturation of Fe atoms, so that the partial pressure of Fe (pFe) is larger than the partial pressure at equilibrium (pFe(eq)). The supersaturation ratio S = pFe/pFe(eq) becomes larger than 1 and increases rapidly with a decrease in temperature. This drives the reaction Fe + H2O ??H2 + FeO to the right. With S = 100, the activity of FeO in the liquid droplet is 100 times as large as the value at equilibrium. The FeO activities are a function of temperature and provide relative average temperatures of the crystallization of <span class="hlt">chondrules</span>. Our calculations for the LL3.0 chondrite Semarkona and our study of some non-equilibrium effects lead to accurate representations of the compositions of <span class="hlt">chondrules</span> of types IA, IAB, IB, IIA, IIAB, IIB, and CC. Our concepts readily explain both the variety of FeO concentrations in the different <span class="hlt">chondrule</span> types and the entire process of <span class="hlt">chondrule</span> formation. Our theory is unified and could possibly explain the formation of <span class="hlt">chondrules</span> in all chondritic meteorites as well as provide a simple explanation for the complex chemistries of chondrites, especially type 3 chondrites.</p> <div class="credits"> <p class="dwt_author">Blander, Milton; Pelton, Arthur D.; Jung, In-Ho; Weber, Richard</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">309</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950031756&hterms=pyroxene&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dpyroxene"> <span id="translatedtitle">The evolution of enstatite and <span class="hlt">chondrules</span> in unequilibrated enstatite chondrites: Evidence from iron-rich pyroxene</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">FeO-rich (Fs(sub 6)-34) pyroxene lacking cathodoluminescence (CL), hereafter black pyroxene, is a major constituent of some of the <span class="hlt">chondrules</span> and fragments in unequilibrated (type 3) enstatite chondrites (UECs). It contains structurally oriented zones of Cr-, Mn-, V-rich, FeO-poor enstatite with red CL, associated with mm-sized blebs of low-Ni, Fe-metal and, in some cases, silica. These occurrences represent clear evidence of pyroxene reduction. The black pyroxene is nearly always rimmed by minor element (Cr, Mn, V)-poor enstatite having a blue CL. More commonly, red and blue enstatites, unassociated with black pyroxene, occur as larger grains in <span class="hlt">chondrules</span> and fragments, and these constitute the major silicate phases in UECs. The rare earth element (REE) abundance patterns of the black pyroxene are LREE-depleted. The blue enstatite rims, however, have a near-flat to LREE-enriched pattern, approx. 0.5-4x chondritic. The petrologic and trace element data indicate that the black pyroxene is from an earlier generation of <span class="hlt">chondrules</span> that formed in a nebular region that was more oxidizing than that of the enstatite chondrites. Following solidification, these <span class="hlt">chondrules</span> experienced a more reducing nebular environment and underwent reduction. Some, perhaps most, of the red enstatite that is common throughout the UECs may be the product of solid-state reduction of black pyroxene. The blue enstatite rims grew onto the surfaces of the black pyroxene and red enstatite as a result of condensation from a nebular gas. The evolutionary history of some of the enstatite and <span class="hlt">chondrules</span> in enstatite chondrites can be expressed in a four-stage model that includes: Stage 1. Formation of <span class="hlt">chondrules</span> in an oxidizing nebular environment. Stage 2. Solid-state reduction of the more oxidized <span class="hlt">chondrules</span> and fragments to red enstatite in a more reducing nebular environment. Stage 3. Formation of blue enstatite rims on the black pyroxene as well as on the red enstatite. Stage 4. Reprocessing, by various degrees of melting, of many of the earlier-formed materials.</p> <div class="credits"> <p class="dwt_author">Weisberg, Michael K.; Prinz, Martin; Fogel, Robert A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">310</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.P11C1238C"> <span id="translatedtitle">Growth of dust rims around <span class="hlt">chondrules</span> in MHD-turbulent protoplanetary disks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The accretion of dust onto <span class="hlt">chondrule</span>-sized particles is modeled through magnetohydrodynamic (MHD) simulations of a protoplanetary disk. The observed dust rims around <span class="hlt">chondrules</span> in meteorites, such as CM carbonaceous chondrites, have been suggested to form on the parent body by a combination of compaction and aqueous alteration of a generic enveloping matrix. However, a nebular origin of these rims seems to be favored in semi-analytical models, where turbulence drives the dynamics of dust sweep-up by <span class="hlt">chondrules</span>. To assess the feasibility of this scenario, we model a small patch of a gaseous circumstellar disk. The patch is assumed to be located at an orbital radius of 3 AU , and is represented by a Cartesian box in which the equations of ideal MHD are solved. Turbulence is self-consistently generated by the action of the so-called magnetorotational instability, which is triggered by the effect of the disk differential rotation on magnetic field lines threading the disk. Fine-grained dust is modeled as a passive contaminant, with initial densities f0 equal to the gas density, and half this value. Turbulence quickly disperses the initial dust concentration, which acquires different equilibrium values depending on f0. These values can vary by as much as a factor of ˜100. <span class="hlt">Chondrules</span> are modeled as Lagrangian particles that are subject to gas drag. An equation for the growth rate of the radius of a <span class="hlt">chondrule</span>-dust compound is integrated whenever a <span class="hlt">chondrule</span> enters a region permeated by dust, and perfect sticking is assumed. The rate of growth of the radius depends on the local dust density and on the relative velocity between the <span class="hlt">chondrule</span> and the dust component. The variation of the equilibrium dust density has an effect on the final distribution of compound radii, with most compounds growing by factors ranging from less than ˜1.5 up to ˜8. Growth times are typically of the order of 10 years, roughly consistent with previous analytical results for the level of turbulence achieved by the MHD simulations. Future calculations should take into account non-ideal MHD effects that have a direct bearing on the turbulent structure of the protoplanetary nebula, and hence on the dust accretion dynamics.</p> <div class="credits"> <p class="dwt_author">Carballido, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">311</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012E%26PSL.341..186B"> <span id="translatedtitle"><span class="hlt">Chondrule</span> fragments from Comet Wild2: Evidence for high temperature processing in the outer Solar System</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Terminal grains from C2063,1,154,1,0 (Track 154) and C2061,1,113,5 (Track 113) from the Stardust collection of Comet Wild2's coma have been studied by TEM and NanoSIMS. Terminal grain 2 of C2063,1,154,1,0 consists of an Al-rich diopside (En 97-99%, Al2O3 9-11 wt%), pigeonite (En 85% Wo 15% with TiO2 and Al2O3 contents of 0.5 and 5.2 wt%) and minor forsterite and enstatite. The mineral assemblage and Al-rich, Ti-poor composition of the grain are consistent with being a fragment of an Al-rich <span class="hlt">chondrule</span>, similar to those present in carbonaceous chondrites. The oxygen isotopic composition of the C2063,1,154,1,0 grain was determined by NanoSIMS analyses and found to be ?17O -10.6±5.7‰, ?18O -7.5±2.5‰ and ?17O +1.4±4.3‰, ?18O -6.5±1.6‰ (1? errors) for the two sections. These figures are distinct from CAIs and consistent with an origin as Al-rich <span class="hlt">chondrule</span> fragments. Terminal grain 5 of C2061,1,113,5 consists of low Ca pyroxene En 86-87% Fs 10-11% Wo 3-4% and ?2 wt% Al2O3 and in one section 5-10% of a Na-rich silicate phase. This assemblage may be a fragment of a low-Ca pyroxene-bearing <span class="hlt">chondrule</span> and mesostasis. The original <span class="hlt">chondrule</span> diameter for the C2063,1,154,1,0 and C2061,1,113,5 samples, by analogy with carbonaceous chondrite <span class="hlt">chondrules</span>, might have been in the range 0.2-1.0 mm. If they were of that size, then the presence of large grains of high temperature material (e.g. ?1500 K for such refractory assemblages) could be explained through commonly invoked models of radial drift from inner to outer Solar System, but only if the <span class="hlt">chondrules</span> were first fragmented to dust within the inner Solar System. An alternative scenario is that some <span class="hlt">chondrule</span> formation was associated with high temperature processing and planetesimals in the outer Solar System.</p> <div class="credits"> <p class="dwt_author">Bridges, J. C.; Changela, H. G.; Nayakshin, S.; Starkey, N. A.; Franchi, I. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">312</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014E%26PSL.398...90M"> <span id="translatedtitle">Fossil records of high level of 60Fe in <span class="hlt">chondrules</span> from unequilibrated chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The short-lived now-extinct nuclide (SLN) 60Fe, which decays to 60Ni with a half-life of 2.62 Ma, is uniquely of stellar origin. Hence, its Solar System initial abundance yields information about the source of SLNs and the astrophysical environment in which the Solar System was born. Only a few <span class="hlt">chondrules</span> (?19) from unequilibrated ordinary chondrites have reported resolved 60Ni excesses using in situ secondary ion mass spectrometry implying Fe60/Fe56>?0.6×10-7 in the early Solar System, and among these very few (3) have higher excesses implying Fe60/Fe56?7×10-7 (Mishra et al., 2010; Mishra and Goswami, 2014; Telus et al., 2012). At variance, multi-collector inductively coupled plasma mass spectrometer studies of bulk samples and mineral separates from differentiated meteorites, angrites, achondrites, and <span class="hlt">chondrules</span> suggest a low abundance of 60Fe/56Fe of ?1.4×10-8 which would rule out the need for an external seeding of the early Solar with stellar 60Fe (Quitté et al., 2011; Tang and Dauphas, 2012). Two Semarkona <span class="hlt">chondrules</span> and one Efremovka <span class="hlt">chondrule</span> analyzed in the present study have mass fractionation corrected excess of up to ?75 permil (‰) and give 60Fe isochrons with initial 60Fe/56Fe ratios of (7.8±3.7)×10-7, (3.8±1.6)×10-7, and (2.2±1.1)×10-7 (2?), for Efremovka Ch 1, Semarkona Ch 12, and Semarkona Ch J5 respectively. The higher values of 60Fe/56Fe ratios seen in the <span class="hlt">chondrules</span> of these least altered meteorites samples concur with and lend greater credence to the suggestion of a massive star as the source of 60Fe, and possibly of other short-lived nuclides, to the early Solar System. However, no definitive explanation (e.g. sample bias, effects of metamorphism, 60Fe heterogeneity) to the apparent disagreement with studies of bulk <span class="hlt">chondrules</span> and <span class="hlt">chondrule</span> fragments has been found.</p> <div class="credits"> <p class="dwt_author">Mishra, Ritesh Kumar; Chaussidon, Marc</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">313</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24196707"> <span id="translatedtitle"><span class="hlt">Olivine</span> in an unexpected location on Vesta's surface.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><span class="hlt">Olivine</span> is a major component of the mantle of differentiated bodies, including Earth. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta, which is the lone surviving, large, differentiated, basaltic rocky protoplanet in the Solar System. Only a few of these meteorites, the orthopyroxene-rich diogenites, contain <span class="hlt">olivine</span>, typically with a concentration of less than 25 per cent by volume. <span class="hlt">Olivine</span> was tentatively identified on Vesta, on the basis of spectral and colour data, but other observations did not confirm its presence. Here we report that <span class="hlt">olivine</span> is indeed present locally on Vesta's surface but that, unexpectedly, it has not been found within the deep, south-pole basins, which are thought to be excavated mantle rocks. Instead, it occurs as near-surface materials in the northern hemisphere. Unlike the meteorites, the <span class="hlt">olivine</span>-rich (more than 50 per cent by volume) material is not associated with diogenite but seems to be mixed with howardite, the most common surface material. <span class="hlt">Olivine</span> is exposed in crater walls and in ejecta scattered diffusely over a broad area. The size of the <span class="hlt">olivine</span> exposures and the absence of associated diogenite favour a mantle source, but the exposures are located far from the deep impact basins. The amount and distribution of observed <span class="hlt">olivine</span>-rich material suggest a complex evolutionary history for Vesta. PMID:24196707</p> <div class="credits"> <p class="dwt_author">Ammannito, E; De Sanctis, M C; Palomba, E; Longobardo, A; Mittlefehldt, D W; McSween, H Y; Marchi, S; Capria, M T; Capaccioni, F; Frigeri, A; Pieters, C M; Ruesch, O; Tosi, F; Zambon, F; Carraro, F; Fonte, S; Hiesinger, H; Magni, G; McFadden, L A; Raymond, C A; Russell, C T; Sunshine, J M</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">314</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/59737271"> <span id="translatedtitle">Dynamic recrystallization and grain growth in <span class="hlt">olivine</span> rocks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A mechanism based description of the rheology of <span class="hlt">olivine</span> is essential for modeling of upper mantle geodynamics. Previously, mantle flow has been investigated using flow laws for grain size insensitive (GSI) dislocation creep and\\/or grain size sensitive (GSS) diffusion creep of <span class="hlt">olivine</span>. Generally, flow laws have been calibrated in experiments to relatively low strains. Recenty, however, it has become apparent</p> <div class="credits"> <p class="dwt_author">A. Kellermann Slotemaker</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">315</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=524059"> <span id="translatedtitle">Ringwoodite lamellae in <span class="hlt">olivine</span>: Clues to <span class="hlt">olivine</span>-ringwoodite phase transition mechanisms in shocked meteorites and subducting slabs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">The first natural occurrence of ringwoodite lamellae was found in the <span class="hlt">olivine</span> grains inside and in areas adjacent to the shock veins of a chondritic meteorite, and these lamellae show distinct growth mechanism. Inside the veins where pressure and temperature were higher than elsewhere, ringwoodite lamellae formed parallel to the {101} planes of <span class="hlt">olivine</span>, whereas outside they lie parallel to the (100) plane of <span class="hlt">olivine</span>. The lamellae replaced the host <span class="hlt">olivine</span> from a few percent to complete. Formation of these lamellae relates to a diffusion-controlled growth of ringwoodite along shear-induced planar defects in <span class="hlt">olivine</span>. The planar defects and ringwoodite lamellae parallel to the {101} planes of <span class="hlt">olivine</span> should have been produced in higher shear stress and temperature region than that parallel to the (100) plane of <span class="hlt">olivine</span>. This study suggests that the time duration of high pressure and temperature for the growth of ringwoodite lamellae might have lasted at least for several seconds, and that an intracrystalline transformation mechanism of ringwoodite in <span class="hlt">olivine</span> could favorably operate in the subducting lithospheric slabs in the deep Earth.</p> <div class="credits"> <p class="dwt_author">Chen, Ming; Goresy, Ahmed El; Gillet, Philippe</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">316</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20020086706&hterms=Inventory+Control&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522Inventory%2BControl%2522"> <span id="translatedtitle"><span class="hlt">Bar</span> Code Labels</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">American <span class="hlt">Bar</span> Codes, Inc. developed special <span class="hlt">bar</span> code labels for inventory control of space shuttle parts and other space system components. ABC labels are made in a company-developed anodizing aluminum process and consecutively marketed with <span class="hlt">bar</span> code symbology and human readable numbers. They offer extreme abrasion resistance and indefinite resistance to ultraviolet radiation, capable of withstanding 700 degree temperatures without deterioration and up to 1400 degrees with special designs. They offer high resistance to salt spray, cleaning fluids and mild acids. ABC is now producing these <span class="hlt">bar</span> code labels commercially or industrial customers who also need labels to resist harsh environments.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1988-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">317</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54777461"> <span id="translatedtitle">Evidence in CO3.0 <span class="hlt">chondrules</span> for a drift in the O isotopic composition of the solar nebula</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Several recent studies have shown that materials such as magnetite that formed in asteroids tend to have higher D17O (-d17O - 0.52 × d18O) values than those recorded in unaltered <span class="hlt">chondrules</span>. Other recent studies have shown that, in sets of <span class="hlt">chondrules</span> from carbonaceous chondrites, D17O tends to increase as the FeO contents of the silicates increase. We report a comparison</p> <div class="credits"> <p class="dwt_author">John T. Wasson; Alan E. Rubin; Hisayoshi Yurimoto</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">318</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2000M%26PS...35..445G"> <span id="translatedtitle">The iodine-xenon system in clasts and <span class="hlt">chondrules</span> from ordinary chondrites: Implications for early solar system chronology</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have studied the iodine-xenon system in <span class="hlt">chondrules</span> and clasts from ordinary chondrites. Cristobalite bearing clasts from Parnallee (LL3.6) closed to xenon loss 1-4 Ma after Bjurböle. Feline (a feldspar and nepheline rich clast also from Parnallee) closed at 7.04 +/- 0.15 Ma. 2 out of 3 <span class="hlt">chondrules</span> from Parnallee that yielded well defined initial iodine ratios gave ages identical to Bjurböle's within error. A clast from Barwell (L5) has a well-defined initial iodine ratio corresponding to closure 3.62 +/- 0.60 Ma before Bjurböle. Partial disturbance and complete obliteration of the I-Xe system by shock are revealed in clasts from Julesburg (L3.6) and Quenggouk (H4) respectively. Partial disturbance by shock is capable of generating anomalously high initial iodine ratios. In some cases these could be misinterpreted, yielding erroneous ages. A macrochondrule from Isoulane-n-Amahar contains concentrations of iodine similar to 'ordinary' <span class="hlt">chondrules</span> but, unlike most ordinary <span class="hlt">chondrules</span>, contains no radiogenic 129Xe. This requires resetting 50 Ma or more later than most <span class="hlt">chondrules</span>. The earliest <span class="hlt">chondrule</span> ages in the I-Xe, Mn-Cr and Al-Mg systems are in reasonable agreement. This, and the frequent lack of evidence for metamorphism capable of resetting the I-Xe chronometer, leads us to conclude that (at least) the earliest <span class="hlt">chondrule</span> I-Xe ages represent formation. If so, <span class="hlt">chondrule</span> formation took place at a time when sizeable parent bodies were present in the solar system.</p> <div class="credits"> <p class="dwt_author">Gilmour, J. D.; Whitby, J. A.; Turner, G.; Bridges, J. C.; Hutchison, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">319</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1995Metic..30R.594W"> <span id="translatedtitle">Chondrites: The Compaction of Fine Matrix and Matrix-like <span class="hlt">Chondrule</span> Rims</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Primitive chondritic meteorites mainly consist of <span class="hlt">chondrules</span>, sulfide+/-metal, and fine-grained matrix. The most unequilibrated chondrites preserve in their phase compositions and, to a lesser degree, their textures, many details about processes that occurred in the solar nebula. On the other hand, much of the textural evidence records processes that occurred in or on the parent body. I suggest that the low-porosity of <span class="hlt">chondrule</span> matrix and matrix-like rims reflects compaction processes that occurred in asteroid-size bodies, and that neither matrix lumps nor compact matrix-like rims on <span class="hlt">chondrules</span> could have achieved their observed low porosities in the solar nebula. Recent theoretical studies by Donn and Meakin (1) and Chokshi et al. (2) have concluded that grain-grain sticking in the solar nebula mainly produces fluffy structures having very high porosities (probably >>50%). If these structures grow large enough, they can provide an aerogel-like matrix that can trap <span class="hlt">chondrules</span> as well as metal and sulfide grains, and thus form suitable precursors of chondritic meteorites. However, the strength of any such structure formed in the solar nebula must be a trivial fraction of that required to survive passage through the Earth's atmosphere in order to fall as a meteorite. The best evidence of accretionary structures appears to be that reported by Metzler et al. (3). They made SEM images of entire thin sections of CM chondrites, and showed that, in the best preserved chondrites, rims are present on all entitities--on <span class="hlt">chondrules</span>, <span class="hlt">chondrule</span> fragments, refractory inclusions, etc. A study by Krot and Wasson (4) shows a more complex situation in ordinary chondrites. Although matrix is common, a sizable fraction of <span class="hlt">chondrules</span> are not surrounded by matrix-like rims. As summarized by Rubin and Krot (1995), there are reports of small textural and compositional differences between matrix lumps and mean matrix-like <span class="hlt">chondrule</span> rims, but there is so much overlap in properties between these two classes that I will assume that they can be treated as parts of a single statistical population. Published SEM images of matrix lumps and matrix-like rims show them to be relatively compact. Although some porosity is surely present as indicated by broad-beam electron-probe analysis totals <100%, it never reaches values comparable to those expected from low-velocity collisions in the solar nebula. Most chondrite researchers seem to hold that the low porosities reflect efficient packing of each grain as it accreted to the assemblage (i.e., as micrometer-size grains gradually covered the surface of a <span class="hlt">chondrule</span> to form the matrix-like rim). I find this process very difficult to envision. If the velocities are low, the fluffy structures of Dodd and Meakin (1) should result; if the velocities are high, then rim erosion would seem to be more probable than growth. A possible scenario that avoids this dilemma is to form cm to m-size fluffy structures in low-turbulence regions of the nebular midplane. During accretion of these larger objects these experienced enough compaction to form tough, low-porosity (but unequilibrated) chondrites. If no <span class="hlt">chondrules</span> were in a region, matrix lumps formed; if <span class="hlt">chondrules</span> were widely separated, a matrix-like rim resulted. And, if <span class="hlt">chondrules</span> were close to other <span class="hlt">chondrules</span> or <span class="hlt">chondrule</span> fragments, only small amounts of intervening fine-grained materials now separate them from their neighbors. During the compaction event, gas and dust migration occurred, and matrix filled all interstices, as now observed in the most primitive chondrites. According to this picture there could have been more diversity in the fine-grained nebular component before compaction occurred. These differences would be best preserved in matrix-like rims and matrix lumps. Much of the interchondrule matrix should consist of homogenized dust that was mixed during compaction-induced transport. References: [1] Donn B. and Meakin P. (1989) Proc. LPSC 19th, 577-580. [2] Chokshi A. et al. (1993) Astrophys. J., 407, 806-819. [3] Metzler K. et al. (1992) GCA,</p> <div class="credits"> <p class="dwt_author">Wasson, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">320</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19860058985&hterms=magnetite+solar&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dmagnetite%2Bsolar"> <span id="translatedtitle">Mineralogy of interplanetary dust particles from the '<span class="hlt">olivine</span>' infrared class</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Analytical electron microscopy observations establish that <span class="hlt">olivine</span> is abundant and the predominant silicate phase in three interplanetary dust particles (IDPs) from the '<span class="hlt">olivine</span>' infrared spectra category. Two of the particles have microstructures resembling those of most nonhydrous chondritic IDPs, consisting of micron to submicron grains together with a matrix composed of amorphous carbonaceous material and sub-500 A grains. In addition to <span class="hlt">olivine</span> these particles respectively contain enstatite and magnetite, and pentlandite plus Ca-rich clinopyroxene. The third IDP consists mostly of <span class="hlt">olivine</span> and pyrrhotite with little or no matrix material. <span class="hlt">Olivine</span> grains in this particle contain prominent solar-flare ion tracks with densities corresponding to a space-exposure age between 1000 to 100,000 years. Although the three particles have <span class="hlt">olivine</span>-rich mineralogies in common, other aspects of their mineralogies and microstructures suggest that they experienced different formation histories. The differences between the particles indicate that the <span class="hlt">olivine</span> infrared spectral category is a diverse collection of IDPs that probably incorporates several genetic groups.</p> <div class="credits"> <p class="dwt_author">Christoffersen, R.; Buseck, P. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_15");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a style="font-weight: bold;">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_18");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">321</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFMMR33A1662A"> <span id="translatedtitle">Heterogeneous distribution of Fe in <span class="hlt">olivine</span> grains generated by serpentinization</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We investigated Fe-rich stripes developed within <span class="hlt">olivine</span> crystals composed of serpentinized peridotites which were obtained at Conical seamount in the Mariana forearc. Modal analyses of primary minerals and their serpentinized pseudomorphs indicate that the protoliths of the peridotites are harzburgite and dunite. They are composed of serpentine minerals, acicular diopside, <span class="hlt">olivine</span>, magnetite, and rare brucite as metamorphic minerals, and <span class="hlt">olivine</span>, diopside, and chromian spinel as primary minerals. Chrysotile and/or lizardite are main serpentine minerals, but antigorite is widely distributed in the samples. Forsterite composition of the <span class="hlt">olivine</span> is Fo90-92. Fe-rich stripes with ca. 5 um width are well developed within the <span class="hlt">olivine</span> crystals. The distribution of the Fe-rich stripes is restricted only at the area contacted with antigorite. TEM samples made using the Focused Ion Beam system indicate clearly that the Fe-rich stripes are created on the dislocation arrays making (100) sub-grain boundaries. Forsterite composition on the dislocation arrays measured by ATEM and EPMA is ca. 88 mol%. These facts can be explained by interdiffusion between Mg and Fe along the dislocation core during serpentinization after ceasing plastic deformation of <span class="hlt">olivines</span>. The origin of high Fe composition is probably <span class="hlt">olivine</span> itself, because the antigorite formation causes an extra Fe. This phenomenon is much important to understand the behavior of fluid and composition during serpentinization.</p> <div class="credits"> <p class="dwt_author">Ando, J.; Ohfuji, H.; Urata, Y. M.; Murata, K.; Maekawa, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">322</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/39659799"> <span id="translatedtitle">The dependence of the Fe 2+ Mg cation-partitioning between <span class="hlt">olivine</span> and basaltic liquid on pressure, temperature and composition</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The equilibrium partitioning of Fe2+ and Mg between <span class="hlt">olivine</span> and liquid along a liquid line of descent has been determined for a calc-alkaline system, ranging in composition from picritic to andesitic. Experiments were conducted between 1000–1450° C and 1 <span class="hlt">bar</span> to 30 kbar. Within the compositional range investigated \\u000a$${\\\\text{x}}_{Mg}^{liq} = 0.4 - 0.8$$\\u000a and \\u000a$$log Kd_{Fe}^{ol - liq} = 0.624</p> <div class="credits"> <p class="dwt_author">Peter Ulmer</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">323</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=PB81222648"> <span id="translatedtitle">Ring <span class="hlt">Bar</span> Grizzly.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The patent application relates to a ring <span class="hlt">bar</span> grizzly used as a materials handling device to enable the jam-free transfer of loose rocks or other materials at the discharge end of a generally horizontal conveyor. Normally, this ring <span class="hlt">bar</span> grizzly is used in ...</p> <div class="credits"> <p class="dwt_author">A. T. Fisk</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">324</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.shodor.org/interactivate/activities/MultiBarGraph/"> <span id="translatedtitle">Multi <span class="hlt">Bar</span> Graph</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">In this activity, students enter in data to be represented in a double <span class="hlt">bar</span> graph. Multi <span class="hlt">bar</span> graphs allow the student to compare multiple characteristics of different subjects like population for different continents over time. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.</p> <div class="credits"> <p class="dwt_author">Shodor</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-02</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">325</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.nsa.gov/academia/_files/collected_learning/elementary/data_analysis/data_build_bar_graphs.pdf"> <span id="translatedtitle">Building Brilliant <span class="hlt">Bar</span> Graphs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">In this series of three lesson plans, students create <span class="hlt">bar</span> graphs, double <span class="hlt">bar</span> graphs, and determine appropriate intervals for scale. Each lesson incorporates teacher modeling, student practice (students have an opportunity to label and create the scale for their own graphs), assessment (including rubrics), and reteaching or extension options.</p> <div class="credits"> <p class="dwt_author">Bower, Briana; Miller, Mary</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">326</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.shodor.org/interactivate/activities/BarGraphSorter/"> <span id="translatedtitle"><span class="hlt">Bar</span> Graph Sorter</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">In this activity, students make <span class="hlt">bar</span> graphs by sorting shapes either by shape or by color. This activity allows students to explore how to sort data to make <span class="hlt">bar</span> graphs. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">327</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012Litho.128....1M"> <span id="translatedtitle">The case for a cognate, polybaric origin for kimberlitic <span class="hlt">olivines</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Kimberlitic <span class="hlt">olivines</span> typically show a continuous range in size and texture rather than two discrete populations. The cores of small euhedral <span class="hlt">olivines</span> commonly provide the template for the final crystal shape, which in turn closely matches morphologies produced by crystallization from a moderately under-cooled magma. Cores and edges of the majority of all <span class="hlt">olivines</span> define a continuous compositional field, which can be interpreted in terms of Raleigh crystallization. Marked chemical gradients at the <span class="hlt">olivine</span> margins are linked to rapid physico-chemical changes to the magma associated with loss of volatiles during the late stages of emplacement. Thus, rapid crystallization of groundmass <span class="hlt">olivines</span> would deplete the magma in Ni, but increase Ca activity. The latter would be enhanced by decreasing pressure coupled with loss of CO 2 from the carbonate-bearing kimberlite magma. For mantle <span class="hlt">olivines</span> and the most refractory <span class="hlt">olivines</span> in kimberlites (~ Fo 94) to be in equilibrium with bulk rock compositions matching those of Mg-rich macrocrystic and aphanitic kimberlites (Mg# ~ 88) requires a mineral-melt Mg-Fe distribution coefficient of 0.47. This is well within the experimentally determined range for this distribution coefficient in carbonate-bearing systems. In southern African post-Gondwana alkaline pipe clusters, the average bulk rock Mg# and composition of the associated most Mg-rich <span class="hlt">olivine</span> both decrease sympathetically from the interior to the continental margin, which is also consistent with a cognate origin for the <span class="hlt">olivines</span>. A kimberlite magma following a plausible P-T trajectory relative to the CO 2/H 2O peridotite solidus would initially experience superheating, resulting in partial resorption of early-formed <span class="hlt">olivines</span> that crystallized on the cool conduit walls. It would become supersaturated as it crossed the carbonated peridotite "ledge", resulting in tabular and hopper growth forms typical of euhedral <span class="hlt">olivine</span> cores. With further ascent, the magma would once again become superheated, resulting in partial resorption of these cores. Thus, apparently complex textures and internal zonation patterns of kimberlitic <span class="hlt">olivines</span> are predicted by a plausible magma P-T trajectory.</p> <div class="credits"> <p class="dwt_author">Moore, Andy E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">328</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/16913142"> <span id="translatedtitle">Carbon sequestration via aqueous <span class="hlt">olivine</span> mineral carbonation: role of passivating layer formation.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">CO2 sequestration via carbonation of widely available low-cost minerals, such as <span class="hlt">olivine</span>, can permanently dispose of CO2 in an environmentally benign and a geologically stable form. We report the results of studies of the mechanisms that limit aqueous <span class="hlt">olivine</span> carbonation reactivity under the optimum sequestration reaction conditions observed to date: 1 M NaCl + 0.64 M NaHCO3 at Te 185 degrees C and P(CO2) approximately equal to 135 <span class="hlt">bar</span>. A reaction limiting silica-rich passivating layer (PL) forms on the feedstock grains, slowing carbonate formation and raising process cost. The morphology and composition of the passivating layers are investigated using scanning and transmission electron microscopy and atomic level modeling. Postreaction analysis of feedstock particles, recovered from stirred autoclave experiments at 1500 rpm, provides unequivocal evidence of local mechanical removal (chipping) of PL material, suggesting particle abrasion. This is corroborated by our observation that carbonation increases dramatically with solid particle concentration in stirred experiments. Multiphase hydrodynamic calculations are combined with experimentto better understand the associated slurry-flow effects. Large-scale atomic-level simulations of the reaction zone suggest that the PL possesses a "glassy" but highly defective SiO2 structure that can permit diffusion of key reactants. Mitigating passivating layer effectiveness is critical to enhancing carbonation and lowering sequestration process cost. PMID:16913142</p> <div class="credits"> <p class="dwt_author">Béarat, Hamdallah; McKelvy, Michael J; Chizmeshya, Andrew V G; Gormley, Deirdre; Nunez, Ryan; Carpenter, R W; Squires, Kyle; Wolf, George H</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">329</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.V11H..05S"> <span id="translatedtitle"><span class="hlt">Olivines</span> from Kimberlites and Diamonds: Problem of Origin</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Mg-rich <span class="hlt">olivine</span> Fo [100Mg/(Mg + Fe)] 85-94 is the principal mineral of kimberlites, peridotite xenoliths and diamond inclusions. It is completely altered in common kimberlites, however, it is absolutely fresh in a huge block from Udachnaya-East kimberlite in Yakutia (Russia). Pioneering studies of this unaltered kimberlite resulted in a discovery of high role of a mantle chlorine along with very low water content (Kamenetsky et al., 2004, Geology, 32: 845-848). Two <span class="hlt">olivine</span> populations are distinguished, which are represented by oval-rounded unzoned or partly zoned xenocrysts of <span class="hlt">olivine</span> I (more than 1 mm) and well defined zoned phenocrysts ( 0.05-1.0 mm) of <span class="hlt">olivine</span> II (e.g. Kamenetsky et al., 2008, J.Petrol., 49: 823-839). The cores of <span class="hlt">olivine</span> II are compositionally similar to <span class="hlt">olivine</span> I with Mg# 86-94, but rims of <span class="hlt">olivine</span> II and partly preserved rims of <span class="hlt">olivine</span> I have constant Fo values about 89-90. We report here the results of major and minor elements analyses by EPMA of more than 300 grains of <span class="hlt">olivine</span> I and <span class="hlt">olivine</span> II, both of cores and rims by high precision approach (Sobolev et al., 2007, Science, 316: 412-417) to minor elements including Ti, Al, Cr, Ca, Mn, Ni, Co using the high sample current and high counting time, which was found optimal to obtain limit of detection about 10 ppm. Several grains of analyzed <span class="hlt">olivines</span> contain clinopyroxene (cpx) and pyrope (prp) inclusions confirming their high pressure origin. One large <span class="hlt">olivine</span> I grain contains clusters of cpx ( 33 grains) and prp ( 6 grains) inclusions., having a range in Cr2O3 (1.52- 2.36 wt%) , Al2O3 (0.99-5.53 wt%) and Na2O (1.45-5.96 wt%) for cpx and Cr2O3 (3.51-4.42 wt%) and CaO (5.64-6.61 wt%) for prp, showing disequilibrium in <span class="hlt">olivine</span> I core, containing 200 ppm Ti. This is completely different from any peridotite xenoliths, confirming the uniqueness of this assemblage. The systematic high Ti ( more than 150 ppm) of all studied cores of <span class="hlt">olivine</span> grains containing low T (Ca# 43.3-48) cpx and prp inclusions confirm the listed differences from all <span class="hlt">olivines</span> from peridotites and diamonds (e.g. Sobolev et al., 2009, Lithos, 112S: 701-713.). Earlier, similar Ti abundance was reported only for <span class="hlt">olivines</span> from dunite nodules in Greenland kimberlites (e.g. Arndt et al., 2010, J. Petrol., 51: 573-602).We suggest that Ti-bearing <span class="hlt">olivine</span>, represented more that 70% of studied samples, is a part of high pressure pyrope lherzolite assemblage, which was formed and grew during the formation and early evolution of kimberlites</p> <div class="credits"> <p class="dwt_author">Sobolev, N. V.; Sobolev, A. V.; Tomilenko, A. A.; Kovyazin, S. V.; Kuzmin, D. V.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">330</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19820038764&hterms=fasano&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dfasano"> <span id="translatedtitle">Flow behavior of droplet <span class="hlt">chondrules</span> in the Manych /L-3/ chondrite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The Manych (L-3) chondrite contains <span class="hlt">chondrules</span> that have radically different thermal histories. The high-SiO2 composition cooled at about 1 K/min to a glassy state or more slowly to form a variety of fractions of crystals. The low-SiO2 composition cooled at about 3000 K/min to form a glassy coating or much more slowly to form microporphyry. The extreme range of cooling rates displayed by objects in the Manych chondrite is difficult to reconcile with a model involving droplet condensation at low pressure which provides a uniform temperature, a uniform cooling rate, and an ambient that is not necessarily cold. The experimental results presented here are interpreted to mean that the origin of the <span class="hlt">chondrules</span> is likely a result of impact melting because of the range of cooling histories represented in the chondrite.</p> <div class="credits"> <p class="dwt_author">Klein, L. C.; Fasano, B.; Hewins, R. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">331</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003EAEJA....14382R"> <span id="translatedtitle">Boron and lithium isotopic composition in <span class="hlt">chondrules</span> from the mokoia meteorite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Introduction: Large Boron isotopic variations have been reported in individual <span class="hlt">chondrules</span> from several meteorites [1, 2]. These variations were interpreted as resulting from the incomplete mixing of two isotopically distinct sources of Boron. Spallation is the only known nucleosynthetic process that can yield Boron in substantial amounts at the scale of the Universe. Therefore it has been proposed that the two sources observed in <span class="hlt">chondrules</span> correspond to two different types of spallation reactions, namely at high and low energies. Indeed, in the case of Boron, the 11B/10B ratio is sensitive to the energy at which the spallation reaction takes place. Since this report of large B isotopic variations in <span class="hlt">chondrules</span>, two observations have allowed to identify the natural conditions under which at least one of such spallation reactions may have taken place in the early solar system. First, X-ray observations of T-Tauri stars have revealed daily outbursts which mimic the present day solar activity during the emission of flares [3]. Second, the decay product (i.e. 10B) of the short lived radio-isotope 10Be was discovered in Calcium-Aluminum-rich inclusions (CAIs) [4]. This is an indication that spallation did occurr in the solar system, shortly (i.e. less than a few million years) before the formation of the CAIs. In addition the possible occurrence of 7Be in CAIs suggests that this duration can be as short as a few months [5]. Sampling and Results: In the 8 <span class="hlt">chondrules</span> from Mokoia, the ?11B values range between -39±6.8 ppm and -0.6±7.8 ppm (2 sigma). In one Boron depleted area of one <span class="hlt">chondrule</span>, the ?11B value was found to be as low as -68.5 ppm and -61.5 ppm (±29; 2 sigma). In one <span class="hlt">chondrule</span> from Mokoia the ?11B values range between -33.7±5.4 ppm and -3.8±5.4 ppm. These data confirm with a resolution of ? ±6 ppm the presence of a significant Boron isotopic heterogeneity,.The ?^7Li were also measured along with the ^delta11B. They range from -53.7±2.4 and -0.15±1.6 ppm (2 sigma) in the 8 <span class="hlt">chondrules</span> of the Mokoia meteorite. Therefore the heterogeneity in B has its counterpart for Li. Interpretation: A two end member mixing model members can be proposed : ?11B ?0 ppm and ?11B<= -70 ppm. The value of 0 ppm is still significantly different from the matrix value reported by [6] (+19.2 ppm) and thus the possible contamination of the <span class="hlt">chondrule</span> by their surrounding matrix is highly unlikely. The second end member should have ?11B and ?^7Li values le-70 ppm and le-50 ppm, respectively, resulting from Li and B produced at high energy by spallation reactions (E >= 100 MeV/nucleon, ?11B =-375 ?^7Li = -830 ppm). References: [1] Chaussidon M., Robert F. (1995) Nature 374, 337-339. [2] Chaussidon M. and Robert F. (1998) Earth Planet Sci. Lett. 164, 577-589. [3] Montmerle T. (1999) MPE Report : Astronomy with Radioactivities, 225-236. [4] McKeegan K., Chaussidon M., Robert F. (2000) Science 289, 1334-1337. [5] Chaussidon M., Robert F. McKeegan K. (2002) Abst. 33th LPSC #1563 [6] Hoppe et al., (2001) MAPS, 36, 1331-1343. [7] Zhai M et al., (1996) Geochim. Cosmochim. Acta 60, 4877-4881.</p> <div class="credits"> <p class="dwt_author">Robert, F.; Chaussidon, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">332</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27708689"> <span id="translatedtitle">Size-selective concentration of <span class="hlt">chondrules</span> and other small particles in protoplanetary nebula turbulence</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Size-selective concentration of particles in a weakly turbulent\\u000aprotoplanetary nebula may be responsible for the initial collection of\\u000achondrules and other constituents into primitive body precursors. This paper\\u000apresents the main elements of this process of turbulent concentration. In the\\u000aterrestrial planet region, both the characteristic size and size distribution\\u000aof <span class="hlt">chondrules</span> are explained. \\</p> <div class="credits"> <p class="dwt_author">Jeffrey N. Cuzzi; Robert C. Hogan; Julie M. Paque; Anthony R. Dobrovolskis</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">333</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20020045838&hterms=Vanadium&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DVanadium"> <span id="translatedtitle">Systematics of Vanadium in <span class="hlt">Olivine</span> from Planetary Basalts</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The systematics of vanadium in <span class="hlt">olivines</span> from the Earth, Moon and Mars allows for the comparison of planetary basalt origin and igneous setting and process. Additional information is contained in the original extended abstract.</p> <div class="credits"> <p class="dwt_author">Karner, J. M.; Papike, J. J.; Shearer, C. K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">334</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5668385"> <span id="translatedtitle"><span class="hlt">Olivine</span> diogenites: The mantle of the eucrite parent body</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Two <span class="hlt">olivine</span>-rich Antarctic diogenites (ALH A77256 and ALH 84001) of the howardite-eucritediogenite (HED) meteorite association have <span class="hlt">olivine</span>/pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites. Based on chemical data and petrological analysis, these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body (EPB). Mineral assemblages in these <span class="hlt">olivine</span>-rich diogenites record a continuum in thermal histories from initial partial melting (1150-1200{degree}C) to subsolidus re-equilibration (795 {plus minus} 55{degree}C). The small number of <span class="hlt">olivine</span>-rich diogenites known hints that only the outer portion of the EPB has been sampled.</p> <div class="credits"> <p class="dwt_author">Sack, R.O.; Azeredo, W.J.; Lipschutz, M.E. (Purdue Univ., IN (USA))</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">335</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20110008047&hterms=pyroxene&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dpyroxene"> <span id="translatedtitle"><span class="hlt">Olivine</span> and Pyroxene Compositions in Fine-Grained Chondritic Materials</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Our analyses of the Wild-2 samples returned by the Stardust Mission have illuminated critical gaps in our understanding of related astromaterials. There is a very large database of <span class="hlt">olivine</span> and low-calcium pyroxene compositions for coarse-grained components of chondrites, but a sparse database for anhydrous silicate matrix phases. In an accompanying figure, we present comparisons of Wild-2 <span class="hlt">olivine</span> with the available chondrite matrix <span class="hlt">olivine</span> major element data. We thus have begun a long-term project measuring minor as well as major element compositions for chondrite matrix and chondritic IDPs, and Wild 2 grains. Finally, we wish to re-investigate the changes to fine-grained <span class="hlt">olivine</span> and low-Ca pyroxene composition with progressive thermal metamorphism. We have examined the LL3-4 chondrites which because of the Hayabusa Mission have become very interesting.</p> <div class="credits"> <p class="dwt_author">Zolensky, Michael E.; Frank, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">336</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20010044526&hterms=olivine&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dolivine"> <span id="translatedtitle">Thermo-Reflectance Spectra of Eros: Unambiguous Detection of <span class="hlt">Olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><span class="hlt">Olivine</span> is readily detected on 433 Eros using the new thermo-reflectance spectral technique applied to near-IR spectra obtained at Eros by the NEAR spacecraft. Additional information is contained in the original extended abstract.</p> <div class="credits"> <p class="dwt_author">Lucey, P. G.; Hinrichs, J. L.; Urquhart-Kelly, M.; Wellnitz, D.; Bell, J. F., III; Clark, B. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">337</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20010045242&hterms=olivine&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dolivine"> <span id="translatedtitle"><span class="hlt">Olivine</span> Weathering: Abiotic Versus Biotic Processes as Possible Biosignatures</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A preliminary study to determine how abiotic versus biotic processes affect the weathering of <span class="hlt">olivine</span> crystals. Perhaps the differences between these weathering processes could be used as biosignatures. Additional information is contained in the original extended abstract.</p> <div class="credits"> <p class="dwt_author">Longazo, T. G.; Wentworth, S. J.; McKay, D. S.; Southam, G.; Clemett, S. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">338</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EGUGA..16.8517A"> <span id="translatedtitle">Aluminum speeds up the hydrothermal alteration of <span class="hlt">olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The reactivity of ultramafic rocks toward hydrothermal fluids controls chemical fluxes at the interface between the internal and external reservoirs of silicate planets. On Earth, hydration of ultramafic rocks is ubiquitous and operates from deep subduction zones to shallow lithospheric environments where it considerably affects the physical and chemical properties of rocks and can interact with the biosphere. This process also has key emerging societal implications, such as the production of hydrogen as a source of carbon-free energy. To date, the chemical model systems used to reproduce <span class="hlt">olivine</span> hydrothermal alteration lead to the formation of serpentine with sluggish reaction rates. Although aluminum is common in geological environments and in hydrothermal systems in particular, its role in serpentinization or <span class="hlt">olivine</span> dissolution has not been investigated under hydrothermal conditions. Nevertheless, abundant Al supply is expected in fluids released from dehydration of metapelites in subduction zones as well as during the hydrothermal alteration of gabbros at mid-ocean ridges. Aluminum was also abundant in primitive environments of both the Earth and Mars, stored in either Al-rich minerals like plagioclase or Al-enriched ultramafic lavas. We have investigated the role of Al on the hydrothermal alteration of <span class="hlt">olivine</span> in a series of experiments performed in a low-pressure diamond anvil cell while following the reaction progress in situ by optical imaging and Raman spectroscopy. Experiments were run for 4.5 to 7.5 days with two <span class="hlt">olivine</span> grains reacted in saline water (0.5 molal NaCl) at 200°C and 300°C, and P=200 MPa. After two days, <span class="hlt">olivine</span> crystals were fully transformed to an aluminous serpentine, also enriched in iron. The presence of Al in the hydrothermal fluid increases the rate of <span class="hlt">olivine</span> serpentinization by more than one order of magnitude by enhancing <span class="hlt">olivine</span> solubility and serpentine precipitation. The mechanism responsible for this increased solubility has to be further investigated but this result motivates a re-evaluation of the natural rates of <span class="hlt">olivine</span> serpentinization and of <span class="hlt">olivine</span> hydrolysis in general in a wide range of settings where <span class="hlt">olivines</span> or peridotites are intimately associated with Al-providers. Such a fast reaction rate may affect the contribution of reaction-enhanced processes at the micrometer-scale, such as reaction-driven cracking, already proposed for enhancing serpentinization or carbonation of <span class="hlt">olivine</span>. The effect of Al on lower crust and upper mantle metasomatism is expected to be even stronger at higher pressure in subduction zones where those reactions control the rheology and physical properties of the subducting plate and mantle wedge.</p> <div class="credits"> <p class="dwt_author">Andreani, Muriel; Daniel, Isabelle; Pollet-Villard, Marion</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">339</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70012903"> <span id="translatedtitle">Dissolution of <span class="hlt">olivine</span> in basaltic liquids: experimental observations and applications.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Rates of <span class="hlt">olivine</span> dissolution in synthetic lunar basalt 77115 and a silica-enriched 77115 composition (Sil-77115) at superliquidus temperatures have been determined. Dissolution-rate data have been applied to the problem of the thermal history of fragment-laden impact-melt rocks of the lunar highlands. Textural and chemical criteria are discussed for the recognition of <span class="hlt">olivine</span> resorption (and growth) phenomena in igneous rocks. -J.A.Z.</p> <div class="credits"> <p class="dwt_author">Thornber, C. R.; Huebner, J. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">340</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/4813863"> <span id="translatedtitle"><span class="hlt">Olivine</span> and Pyroxene Diversity in the Crust of Mars</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Data from the Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) on the Mars Express spacecraft identify the distinct mafic, rock-forming minerals <span class="hlt">olivine</span>, low-calcium pyroxene (LCP), and high-calcium pyroxene (HCP) on the surface of Mars. <span class="hlt">Olivine</span>- and HCP-rich regions are found in deposits that span the age range of geologic units. However, LCP-rich regions are found only in</p> <div class="credits"> <p class="dwt_author">J. F. Mustard; F. Poulet; A. Gendrin; J.-P. Bibring; Y. Langevin; B. Gondet; N. Mangold; G. Bellucci; F. Altieri</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_16");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_17");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a style="font-weight: bold;">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_19");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">341</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1224360"> <span id="translatedtitle">Volatile fractionation in the early solar system and <span class="hlt">chondrule</span>/matrix complementarity</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Bulk chondritic meteorites and terrestrial planets show a monotonic depletion in moderately volatile and volatile elements relative to the Sun's photosphere and CI carbonaceous chondrites. Although volatile depletion was the most fundamental chemical process affecting the inner solar nebula, debate continues as to its cause. Carbonaceous chondrites are the most primitive rocks available to us, and fine-grained, volatile-rich matrix is the most primitive component in these rocks. Several volatile depletion models posit a pristine matrix, with uniform CI-like chemistry across the different chondrite groups. To understand the nature of volatile fractionation, we studied minor and trace element abundances in fine-grained matrices of a variety of carbonaceous chondrites. We find that matrix trace element abundances are characteristic for a given chondrite group; they are depleted relative to CI chondrites, but are enriched relative to bulk compositions of their parent meteorites, particularly in volatile siderophile and chalcophile elements. This enrichment produces a highly nonmonotonic trace element pattern that requires a complementary depletion in <span class="hlt">chondrule</span> compositions to achieve a monotonic bulk. We infer that carbonaceous chondrite matrices are not pristine: they formed from a material reservoir that was already depleted in volatile and moderately volatile elements. Additional thermal processing occurred during <span class="hlt">chondrule</span> formation, with exchange of volatile siderophile and chalcophile elements between <span class="hlt">chondrules</span> and matrix. This chemical complementarity shows that these chondritic components formed in the same nebula region.</p> <div class="credits"> <p class="dwt_author">Bland, Philip A.; Alard, Olivier; Benedix, Gretchen K.; Kearsley, Anton T.; Menzies, Olwyn N.; Watt, Lauren E.; Rogers, Nick W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">342</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/16174733"> <span id="translatedtitle">Volatile fractionation in the early solar system and <span class="hlt">chondrule</span>/matrix complementarity.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Bulk chondritic meteorites and terrestrial planets show a monotonic depletion in moderately volatile and volatile elements relative to the Sun's photosphere and CI carbonaceous chondrites. Although volatile depletion was the most fundamental chemical process affecting the inner solar nebula, debate continues as to its cause. Carbonaceous chondrites are the most primitive rocks available to us, and fine-grained, volatile-rich matrix is the most primitive component in these rocks. Several volatile depletion models posit a pristine matrix, with uniform CI-like chemistry across the different chondrite groups. To understand the nature of volatile fractionation, we studied minor and trace element abundances in fine-grained matrices of a variety of carbonaceous chondrites. We find that matrix trace element abundances are characteristic for a given chondrite group; they are depleted relative to CI chondrites, but are enriched relative to bulk compositions of their parent meteorites, particularly in volatile siderophile and chalcophile elements. This enrichment produces a highly nonmonotonic trace element pattern that requires a complementary depletion in <span class="hlt">chondrule</span> compositions to achieve a monotonic bulk. We infer that carbonaceous chondrite matrices are not pristine: they formed from a material reservoir that was already depleted in volatile and moderately volatile elements. Additional thermal processing occurred during <span class="hlt">chondrule</span> formation, with exchange of volatile siderophile and chalcophile elements between <span class="hlt">chondrules</span> and matrix. This chemical complementarity shows that these chondritic components formed in the same nebula region. PMID:16174733</p> <div class="credits"> <p class="dwt_author">Bland, Philip A; Alard, Olivier; Benedix, Gretchen K; Kearsley, Anton T; Menzies, Olwyn N; Watt, Lauren E; Rogers, Nick W</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-09-27</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">343</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/543158"> <span id="translatedtitle">Minor and trace element partitioning between pyroxene and melt in rapidly cooled <span class="hlt">chondrules</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We present minor and trace element (REE, Sr, Y, and Zr) data for pyroxenes and mesostases in four porphyritic <span class="hlt">chondrules</span> from the Semarkona ordinary chondrite. Apparent partition coefficients for clinoenstatite, orthoenstatite, pigeonite, and augite are compared with experimental and petrologic data from the literature, and the effects on apparent partition coefficients of the rapid cooling rates at which <span class="hlt">chondrules</span> crystallized are evaluated. For most elements, the effects of cooling at rates of hundreds of degrees per hour cannot be distinguished from variations in equilibrium data resulting from differences in temperature or composition. However, for LREE apparent partition coefficients are significantly higher than comparable equilibrium data, and the ratio of HREE/LREE partition coefficients is lower, particularly for Ca-poor pyroxene. We attribute this flattening of REE patterns to the effect of rapid cooling. Apparent partition coefficients of all REE and Y in augite are higher than equilibrium data, particularly in one <span class="hlt">chondrule</span> with a high ALO, content. We suggest that this may be attributed to an increase in the uptake of trivalent trace element cations in the pyroxene crystal structure as a result of charge-balanced substitutions with API cations. 32 refs., 6 figs., 3 tabs.</p> <div class="credits"> <p class="dwt_author">Jones, R.H. [Univ. of New Mexico, Albuquerque, NM (United States); Layne, G.D. [Univ. of New Mexico, Albuquerque, NM (United States)]|[Woods Hole Oceanographic Institution, MA (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">344</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013M%26PS...48.2430S"> <span id="translatedtitle">81Kr-Kr cosmic ray exposure ages of individual <span class="hlt">chondrules</span> from Allegan</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">81Kr-Kr cosmic ray exposure (CRE) ages of individual <span class="hlt">chondrules</span> (6-10 mg) and adjacent matrix samples (5-10 mg) from the Allegan H5 chondrite have been measured using a new highly sensitive resonance ionization mass spectrometer. No conclusive evidence of variations among the CRE ages of individual <span class="hlt">chondrules</span> or between <span class="hlt">chondrules</span> and matrix has been observed—average CRE ages of 5.90 ± 0.42 Ma (81Kr-78Kr) and 5.04 ± 0.37 Ma (81Kr-80+82Kr) are identical within error to those determined for the matrix (7.42 ± 1.27 Myr, 81Kr-80+82Kr) and agree well with the literature value for bulk Allegan. If any accumulation of cosmogenic krypton in the early solar system took place, either it was below our detection limit in these samples (<100 atoms), or any such gas was lost during parent body metamorphism. However, this demonstration that useful 81Kr-Kr ages can be obtained from few milligram samples of chondritic material has clear relevance to the analysis of samples returned by planned missions to asteroids and to the search for a signature of pre-exposure in other, less processed meteorites.</p> <div class="credits"> <p class="dwt_author">Strashnov, I.; Gilmour, J. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">345</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012M%26PS...47.1191H"> <span id="translatedtitle"><span class="hlt">Chondrule</span> cooling rates inferred from diffusive profiles in metal lumps from the Acfer 097 CR2 chondrite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Abstract— CR chondrites contain metal lumps (>300 ?m) either attached to <span class="hlt">chondrule</span> silicates or apparently isolated in the matrix. Here, laser ablation microanalysis of six metal lumps from a polished thin section of the Acfer 097 CR2 chondrite at 15 ?m spatial resolution revealed zoning profiles for the volatile elements Cu and Ga. The mutual diffusivities of Cu and Ga were used to infer T ˜ 1473 ± 100 K from the correlation of Cu versus Ga. The cooling rates of the metal lumps were calculated to be 0.5-50 K h-1 for Tp ˜ 1473 ± 100 K, with a maximum possible range of 0.1-400 K h-1 for Tp ˜ 1200-1800 K, overlapping the range of cooling rates inferred from petrological studies of type I <span class="hlt">chondrules</span> (10-1000 K h-1). <span class="hlt">Chondrule</span> textures were established near the peak heating temperatures of <span class="hlt">chondrules</span> (approximately 1900-2000 K), while the Cu and Ga diffusive profiles were established after solidification (T ˜ 1500 K), consistent with nonlinear cooling. Furthermore, one <span class="hlt">chondrule</span> (N2) has a more complex zoning profile that is modeled as a three-stage cooling history involving initial cooling at approximately 1 K h-1, followed by mild re-heating (T ˜ 1700 K) that re-evaporated Cu and Ga from the outer approximately 100 ?m of the metal lump and then cooled again at approximately 5 K h-1. The thermal effects of parent body and other preaccretionary heating events on the Cu and Ga zoning profiles are examined. Although CR parent bodies have experienced aqueous alteration, the thermal effects of this process can neither produce nor erase the Cu and Ga diffusive profiles. Thus, metal lumps in CR chondrites record the solid-state thermal history of <span class="hlt">chondrules</span> as they travelled away from the <span class="hlt">chondrule</span>-forming region.</p> <div class="credits"> <p class="dwt_author">Humayun, Munir</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">346</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUFM.V24A..07G"> <span id="translatedtitle">Diffusion of Ca in San Carlos <span class="hlt">Olivine</span> at 800 to 1200 ° C</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Calcium is a minor constituent in magnesian <span class="hlt">olivine</span> that has potential as both a geothermobarometer [1] and a geospeedometer [2]. Fully exploiting the potential of Ca in <span class="hlt">olivine</span> requires knowledge of it's diffusivity as a function of temperature. Here we present results from new experiments in which the diffusivity of Ca in San Carlos <span class="hlt">olivine</span> has been experimentally determined over a temperature range of 400 ° C. These experiments demonstrate that a significant anisotropy develops at temperatures below 950 ° C, with diffusion parallel to the c crystallographic axis becoming significantly faster than parallel to either the a or b axes. We conclude that this anisotropy is due to the influence of low angle subgrain boundaries. Experiments were carried out on oriented pieces of gem-quality San Carlos <span class="hlt">olivine</span> at 1 <span class="hlt">bar</span> and temperatures of 800 ° to 1200 ° C using the powder-source technique. The fugacity of oxygen was controlled at the NiNiO buffer. Diffusion profiles generated at 800 ° to 1000 ° C were analyzed using Rutherford Backscattering Spectroscopy. Analyses of run products from higher temperature experiments were carried out using either Secondary Ion Mass Spectrometry or electron microprobe. At temperatures of 950 ° C or greater, our experiments show no evidence for significant anisotropy with respect to diffusion. Activation energies for diffusion parallel to the a (440±60 kJ/mol), b (457±14 kJ/mol), and c (520±90 kJ/mol) crystallographic axes are indistinguishable. However, at temperatures below 950 ° C the activation energy for diffusion parallel to the c axis decreases to only 270±40 kJ/mol. This change occurs only for diffusion parallel to c, resulting in considerable anisotropy. At 800 ° C diffusion parallel to the c axis is faster than diffusion parallel to either a or b by more than an order of magnitude. The change in diffusivity parallel to c is attributed to the presence of (100) tilt boundaries, producing a regime in which type B kinetics dominate. Diffusion is anisotropic owing to pipe diffusion along the cores of (010)[100] edge dislocations within the low angle boundaries. The cores of edge dislocations in the (010)[100] system are parallel to the c (i.e., [001]) direction. References: [1] Köhler and Brey (1990) Geochim Cosmochim Acta 54:2375-2388. [2] Pan and Batiza (2002) J Geophys Res DOI 10.1029/2000JB000435.</p> <div class="credits"> <p class="dwt_author">Gaetani, G. A.; Hirth, G.; Cherniak, D. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">347</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19990091993&hterms=thermal+emission&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dthermal%2Bemission"> <span id="translatedtitle">Thermal Emission Spectroscopy of 1 Ceres: Evidence for <span class="hlt">Olivine</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Thermal emission spectra of the largest asteroid 1 Ceres obtained from the Kuiper Airborne Observatory display features that may provide information on its surface mineralogy. A plot of the Ceres spectrum (calibrated using alpha Boo as a standard) divided by a standard thermal model (STM) is shown. Also shown is the emissivity spectrum deduced from reflectivity measurements for <span class="hlt">olivine</span> grains <5 microns in diameter. The general shape of the Ceres and the <span class="hlt">olivine</span> curves agree in essential details, such as the maxima from 8 to 12 microns, the minimum between 12 and 14 microns, the broad peak near 17.5 micron, and the slope beyond 22 micron. (Use of the 10 to 15-micron grain reflectivities provides a better match to the 12- to 14-micron dip. We used a value of unity for beta, the beaming factor associated with small-scale surface roughness in our STM. Adjustment of beta to a lower value raises the long-wavelength side of the Ceres spectrum, providing an even better match to the <span class="hlt">olivine</span> curve.) The emissivity behavior roughly matches the emission coefficients which were calculated for <span class="hlt">olivine</span> particles with a particle radius of 3 microns. Their calculations show not only the negative slope from 23 to 25 pm, but a continued decrease past 30 micron. The Ceres emissivity is thus similar to that of small <span class="hlt">olivine</span> grains from 8 to 30 micron, but <span class="hlt">olivine</span>'s emissivity is lower from 5 to 8 pm.</p> <div class="credits"> <p class="dwt_author">Witteborn, F. C.; Roush, T. L.; Cohen, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">348</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1993PCM....19..423A"> <span id="translatedtitle">Kinetics of intracrystalline cation redistribution in <span class="hlt">olivine</span> and its implication</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The rate of cation redistribution between M 1 and M 2 sites in <span class="hlt">olivine</span> is theoretically studied on the basis of elementary processes of cationic migration. Cationic migration in <span class="hlt">olivine</span> structure is assumed to be the superposition of a unit exchange of cations between closely spaced couple of sites. Such a process gives rise to both cation redistribution and also cationic interdiffusion in <span class="hlt">olivine</span> crystal. The time constant of cationic equilibration in the redistribution reaction is related to the interdiffusion coefficient along b-axis, and its numerical value is given as a function of temperature and composition in Mg-Fe <span class="hlt">olivine</span>. This time constant is very short, e.g., in the order of 10-2˜10-4 s at 1000 ° C. The temperature dependence of cation distribution in Mg-Fe <span class="hlt">olivine</span> could not be detected by heating and quenching experiments in some previous works, because of insufficient cooling rate. A skepticism is presented for the utility of cation distribution as a geothermometer or rate meter of cooling. Cation redistribution in <span class="hlt">olivine</span> in the deep upper mantle is sufficiently fast to take place almost in phase with the seismic waves of long periods.</p> <div class="credits"> <p class="dwt_author">Akamatsu, Tadashi; Kumazawa, Mineo</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">349</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=ADD004513"> <span id="translatedtitle">Repeatable Release Holdback <span class="hlt">Bar</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">A holdback <span class="hlt">bar</span> is described for restraining an aircraft temporarily prior to catapult assisted launch. It uses a ball and piston unloader valve to insure rapid, positive release of a pressurized hydraulic fluid. Compensator chambers each have a resilient ...</p> <div class="credits"> <p class="dwt_author">W. H. Hickle</p> <p class="dwt_publisher"></p> <p class="publishDate">1977-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">350</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.shodor.org/interactivate/lessons/HistogramsBarGraph/"> <span id="translatedtitle">Histograms and <span class="hlt">Bar</span> Graphs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">This lesson is designed to introduce students to histograms and <span class="hlt">bar</span> graphs as graphical representations of data. The lesson also covers the distinction between histograms and <span class="hlt">bar</span> graphs and the concepts of class intervals and scale. The lesson provides links to discussions and activities related to these topics as well as worksheets for further practice. Finally, the lesson provides links to follow-up lessons designed for use in succession with this one.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">351</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.compadre.org/Repository/document/ServeFile.cfm?ID=9414&DocID=1309"> <span id="translatedtitle">Magnetic <span class="hlt">Bar</span> Field Model</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">The EJS Magnetic <span class="hlt">Bar</span> Field Model shows the field of a <span class="hlt">bar</span> magnet and has a movable compass that reports the magnetic field values. The <span class="hlt">bar</span> magnet model is built by placing a group of magnetic dipoles along the <span class="hlt">bar</span> magnet. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Magnetic <span class="hlt">Bar</span> Field model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_Magnetic<span class="hlt">Bar</span>Field.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.</p> <div class="credits"> <p class="dwt_author">Christian, Wolfgang; Franciscouembre; Cox, Anne</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-09-18</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">352</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20000081089&hterms=ch&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3D%2522ch%2522"> <span id="translatedtitle"><span class="hlt">Chondrules</span> of the Very First Generation in Bencubbin/CH-like Meteorites QUE94411 and Hammadah Al Hamra 237: Condensation Origin at High Ambient Nebular Temperatures</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><span class="hlt">Chondrules</span> in QUE94411 and HH 237 formed at high ambient T prior to condensation of Fe,Ni-metal following a large scale thermal event that resulted in complete vaporization of a solar nebula region. These <span class="hlt">chondrules</span> escaped subsequent remelting.</p> <div class="credits"> <p class="dwt_author">Krot, Alexander N.; Meibom, Anders; Russell, Sara S.; Young, Edward; Alexander, Conel M.; McKeegan, Kevin D.; Lofgren, Gary; Cuzzi, Jeff; Zipfel, Jutta; Keil, Klaus</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">353</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050175999&hterms=chondrites&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522R%2Bchondrites%2522"> <span id="translatedtitle">Tracing Oxygen Fugacity in Asteroids and Meteorites Through <span class="hlt">Olivine</span> Composition</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><span class="hlt">Olivine</span> absorptions are known to dominate telescopic spectra of several asteroids. Among the meteorite collection, three groups (excluding Martian meteorites), the pallasites, brachinites, and R group chondrites are plausible analogs to <span class="hlt">olivine</span>-rich asteroids in that they are dominated by <span class="hlt">olivine</span>. These meteorite groups have distinct petrologic origins. The primitive achondrite brachinites (which include both depleted and undeleted subgroups) are products of relatively minor differentiation and evolved in oxidizing environments. R chondrites are also thought to have formed in high oxygen states, but are closely related to ordinary chondrites (yet with their own distinct compositions and oxygen isotopic signatures). In contrast, pallasites, widely thought to be mantle components from much more evolved bodies, formed in more reducing environments. Petrologic indicators that are identifiable in spectral data must be used in order to infer the petrologic history of asteroids from surveys of their actual population. As discussed below, <span class="hlt">olivine</span> composition (e.g. Fa#) can provide key constraints in exploring the origin and significance of <span class="hlt">olivine</span> dominated asteroids.</p> <div class="credits"> <p class="dwt_author">Sunshine, J. M.; Bus, S. J.; Burbine, T. H.; McCoy, T. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">354</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19780062717&hterms=Ni-In&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DNi-In"> <span id="translatedtitle">Minor elements in lunar <span class="hlt">olivine</span> as a petrologic indicator</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Accurate electron microprobe analyses (approximately 50 ppm) were made for Al, Ca, Ti, Cr, Mn, and Ni in Mg-rich <span class="hlt">olivines</span> which may derive from early lunar crust or deeper environments. Low-Ca contents consistently occur only in <span class="hlt">olivines</span> from dunitic and troctolitic breccia: spinel troctolite and other rock types have high-Ca <span class="hlt">olivines</span> suggesting derivation by near-surface processes. Rock 15445 has <span class="hlt">olivine</span> with distinctly low CaO (approximately 0.01 wt.%). Chromium ranges to higher values (max.0.2 oxide wt.%) than for terrestrial harzburgites and lherzolites but is similar to the range in terrestrial komatiites. Divalent chromium may be indicated over trivalent Cr because <span class="hlt">olivines</span> lack sufficient other elements for charge balance of the latter. NiO values in lunar specimens range from 0.00 to 0.07 wt.% and a weak anticorrelation with Cr2O3 suggests an oxidation state effect. Al2O3 values are mostly below 0.04-wt.% and show no obvious correlation with fragment type. TiO2 values lie below 0.13-wt.% and seem to correlate best with crystallization rate and plagioclase content of the host rock. High values of Al2O3 and TiO2 reported by other workers have not been confirmed, and are probably wrong.</p> <div class="credits"> <p class="dwt_author">Steele, I. M.; Smith, J. V.</p> <p class="dwt_publisher"></p> <p class="publishDate">1975-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">355</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014GeCoA.135..170D"> <span id="translatedtitle">Weathering of <span class="hlt">olivine</span> under CO2 atmosphere: A martian perspective</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent analyses from the Curiosity rover at Yellowknife Bay (Gale crater, Mars) show sedimentary rocks deposited in a lacustrine environment and containing smectite clays thought to derive from the alteration of <span class="hlt">olivine</span>. However, little is known about the weathering processes of <span class="hlt">olivine</span> under early martian conditions, and about the stability of smectite clays in particular. Here, we present a 3-month experiment investigating the weathering of forsteritic <span class="hlt">olivine</span> powders (Fo90) under a dense CO2 atmosphere, and under present-day terrestrial conditions for comparison. The experiment also evaluates the potential effects of hydrogen peroxide (H2O2), as a representation of the highly oxidizing compounds produced by photochemical reactions throughout martian history. The weathered samples were characterized by means of near-infrared spectroscopy (NIR), X-ray diffraction (XRD), transmission electron microscopy with energy dispersive X-ray spectrometry (TEM-EDX), Mössbauer spectroscopy and thermogravimetry. The results show that a Mg-rich smectite phase formed from the weathering of <span class="hlt">olivine</span> under CO2 conditions, although in lower abundance than under terrestrial conditions. The main secondary phase formed under CO2 turns out to be a silica-rich phase (possibly acting as a “passivating” layer) with a non-diagnostic near-infrared spectral signature. The use of H2O2 highlights the critical importance of both the redox conditions and Fe content of the initial <span class="hlt">olivine</span> on the nature of the secondary phases.</p> <div class="credits"> <p class="dwt_author">Dehouck, E.; Gaudin, A.; Mangold, N.; Lajaunie, L.; Dauzères, A.; Grauby, O.; Le Menn, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">356</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFMMR33C..06M"> <span id="translatedtitle">Grain boundary diffusion in <span class="hlt">olivine</span> (Invited)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Olivine</span> is the main constituent of Earth's upper mantle. The individual mineral grains are separated by grain boundaries that have very distinct properties compared to those of single crystals and strongly affect large-scale physical and chemical properties of rocks, e.g. viscosity, electrical conductivity and diffusivity. Knowledge on the grain boundary physical and chemical properties, their population and distribution in polycrystalline materials [1] is a prerequisite to understand and model bulk (rock) properties, including their role as pathways for element transport [2] and the potential of grain boundaries as storage sites for incompatible elements [3]. Studies on selected and well characterized single grain boundaries are needed for a detailed understanding of the influence of varying grain boundaries. For instance, the dependence of diffusion on the grain boundary structure (defined by the lattice misfit) and width in silicates is unknown [2, 4], but limited experimental studies in material sciences indicate major effects of grain boundary orientation on diffusion rates. We characterized the effect of grain boundary orientation and temperature on element diffusion in forsterite grain boundaries by transmission electron microscopy (TEM).The site specific TEM-foils were cut using the focused ion beam technique (FIB). To study diffusion we prepared amorphous thin-films of Ni2SiO4 composition perpendicular to the grain boundary using pulsed laser deposition. Annealing (800-1450°C) leads to crystallization of the thin-film and Ni-Mg inter-diffuse into the crystal volume and along the grain boundary. The inter-diffusion profiles were measured using energy dispersive x-ray spectrometry in the TEM, standardized using the Cliff-Lorimer equation and EMPA measurements. We obtain volume diffusion coefficients that are comparable to Ni-Mg inter-diffusion rates in forsterite determined in previous studies at comparable temperatures, with similar activation energies. Grain boundary diffusion perpendicular to the dislocation lines of the small angle grain boundaries proved to be about an order of magnitude faster than volume diffusion, whereas diffusion in high angle grain boundaries is several orders of magnitude faster. We will discuss the variation of element diffusion rates with grain boundary orientation and the temperature- and/or time-induced transition from one diffusion regime to the next regime. This is done using time series experiments and two-dimensional grain boundary diffusion simulations. Finally, we will debate the differences between our data and other data sets that result from different experimental setups, conditions and analyses.</p> <div class="credits"> <p class="dwt_author">Marquardt, K.; Dohmen, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">357</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1995Metic..30Q.543M"> <span id="translatedtitle">Exotic <span class="hlt">Olivine</span> in Antarctic Angrites LEW 87051 and Asuka 881371</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Angrites are basaltic meteorites with very early formation ages [e.g., 1] suggesting magrnatic activity on their parent body shortly after accretion. To constrain the nature of this magmatism, it is necessary to determine the composition of the melts parental to the angrite meteorites so that these melts can be compared with known phase relationships. Of the four known angrites, Angra dos Reis is highly differentiated and has had a complex history [e.g.,2]. LEW 86010 is probably a low-temperature partial melt containing minor accumulated plagioclase [3]. LEW 87051 (LEW 87) contains porphyritic <span class="hlt">olivine</span> in a fine-grained groundmass, and the <span class="hlt">olivine</span> crystals have variously been interpreted as phenocrysts [e.g., 4], xenocrysts [e.g., 5], and compound crystals in which exotic xenocryst cores have been overgrown by <span class="hlt">olivine</span> that crystallized from the melt [e.g 6]. Asuka 881371 (Asuka 88) contains large <span class="hlt">olivine</span> crystals in a medium-grained groundmass [7 and these large <span class="hlt">olivines</span> are unambiguously xenocrysts that are not directly related to the melt in which they now reside [9], and may shed light on the <span class="hlt">olivines</span> in LEW 87. Several lines of evidence point towards the exotic nature of the large <span class="hlt">olivines</span> in Asuka 88. Despite being internally homogeneous, these crystals show large variations in composition from one crystal to another. Such variations are shown for Ca and Mg/Mg+Fe in Fig. 1, but are also observed for Cr, Al, and Y. Moreover, the concentrations of these elements in the large <span class="hlt">olivines</span> are different from the concentrations in the cores of the groundmass <span class="hlt">olivines</span> that were obviously the first minerals to crystallize from the Asuka 88 melt (Fig 1). Thus the large <span class="hlt">olivines</span> could not have been in equilibrium with one another nor with the host melt. Furthermore, along healed fractures the the large <span class="hlt">olivines</span> have been altered towards the groundmass <span class="hlt">olivine</span> composition either through physical invasion of melt or by enhanced surface diffusion along the fractures. However, despite the clear exotic relationship to the Asuka 88 melt, the O isotopic composition of one <span class="hlt">olivine</span> xenocryst falls within the angrite group [9], so the xenocrysts are probably not completely exotic to the angrite parent body. By analogy with Asuka 88, we infer that the Mg-rich cores of some porphyritic <span class="hlt">olivines</span> in LEW 87 are xenocrysts (Fig. 1), but the main portions of these crystals surrounding the cores (labeled LEW 87 phenos in Fig. 1) grew from the LEW 87 melt. Agreement in minor elements between the main portions of LEW 87 <span class="hlt">olivines</span> and synthetic <span class="hlt">olivines</span> from LEW 87 experiments supports this interpretation (Fig. 1). We plan to use elemental mapping to locate more cores in LEW 87, to look for core-to-core variation and to measure additional profiles to test for diffusive equilibration between xenocrysts and the outer part of the <span class="hlt">olivine</span> or groundmass. Using the compositions of first <span class="hlt">olivines</span> to crystallize from the parent melts of both meteorites and K(sub)(DFe/Mg) of 0.29 from LEW 87 crystallization experiments, we calculate that the bulk compositions reported for Asuka 88 by [9] and LEW 87 by [12] have about 11% and 20% excess <span class="hlt">olivine</span> (exotic or accumulated) of Fo(sub)83 and Fo(sub)81 respectively. References: [1] Nyquist L. et al. (1994) Meteoritics, 29, 872-885. [2] Mittlefehldt D. and Lindstrom M. (1990) GCA, 54, 3209-3218. [3] McKay G. et al. (1988) LPS XIX, 762-763. [4] McKay G. et al. (1990) LPS XXI, 771-772. [5] Prinz et al. (1990) LPS XXI, 979. [6] Mikouchi T. et al. (1995) LPS XXVI, 973-974. [7] Yanai K. (1994) Proc. NIPR Symp. Antarc. Meteorites, 7, 30-41. [8] McKay G. et al. (1995) Antarc. Meteorites, XX, 155-158. [9] Warren P. et al. (1995) Antarc. Meteorites, XX, 261-264. [10] Warren P. and Kallemeyn G. (1990) LPS XXI, 1295-1296.</p> <div class="credits"> <p class="dwt_author">McKay, G.; Crozaz, G.; Mikouchi, T.; Miyamoto, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">358</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1994Metic..29R.448B"> <span id="translatedtitle">Petrographic, isotopic, and chemical studies of cristobalite- and tridymite-bearing <span class="hlt">chondrules</span> and clasts in ordinary chondrites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The cristobalite in <span class="hlt">chondrules</span> and clasts is uniquely O-16 depleted for chondritic material. Six alpha-cristobalite-bearing <span class="hlt">chondrules</span> from Parnallee (LL3.6), one alpha-cristobalite xenolith from Farmington (L5), and one tridymite-bearing clast from Parnallee have been studied. Silica polymorphs were identified by x ray diffraction (XRD). Some of these <span class="hlt">chondrules</span> have been described briefly. The tridymite-bearing clast is larger, 1.6 cm diameter, and contains clusters of needlelike tridymite grains (40 modal%) enclosed by clinoenstatite (En(88-91.5)). The clinoenstatite shows extreme compositional zonation towards its margins, to Wo20, Fs(75.6), En(4.3). Minor plagioclase (An(71-83)) is present. Bulk compositions of the tridymite-bearing clast and two alpha-cristobalite-rich <span class="hlt">chondrules</span> were obtained by averaging Electron Probe Microanalysis (EMPA) analyses of 280-300 points in arrays on polished sections. The assemblage protoenstatite or clinoenstatite enclosing cristobalite and tridymite crystallizes at cooling rates of 0.01-0.23 C/s in experimental charges of 65.1 wt% SiO2 (remainder MgO) from starting temperatures of around 1550 C. Typical <span class="hlt">chondrule</span> cooling rates also lie within this range, suggesting that these samples originated through flash melting of SiO2-rich, alkali- and Rare Earth Element (REE)-depleted solids. During or shortly after the flash heating events, the cristobalite and tridymite exchanged O with an O-16-poor gas. High degrees of O diffusion from an ambient gas may be due to the open structure of tridymite and cristobalite. The Si-isotopic ratios (P7-CONCEPT ion probe), of two alpha-cristobalite-bearing <span class="hlt">chondrules</span> lie on the terrestrial fractionation line, showing that the <span class="hlt">chondrules</span> are not derived from an exotic Si reservoir. All the silica-bearing samples analyzed so far are plotted on an O three-isotope plot with o.c <span class="hlt">chondrules</span>. A least-squares best-fit line of slope 0.76 is defined, showing a marked deviation from the equilibrate chondrite line (ECL) line of slope 1.0. The O-16-poor gas may be an end member at some extension of the cristobalite line (CRIL).</p> <div class="credits"> <p class="dwt_author">Bridges, J. C.; Franchi, I. A.; Hutchison, R.; Alexander, C. M. O'd.; Morse, A. D.; Pillinger, C. T.; Long, V. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">359</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/15800614"> <span id="translatedtitle">An <span class="hlt">olivine</span>-free mantle source of Hawaiian shield basalts.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">More than 50 per cent of the Earth's upper mantle consists of <span class="hlt">olivine</span> and it is generally thought that mantle-derived me