Science.gov

Sample records for barred olivine chondrules

  1. Barred olivine chondrules in ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Weisberg, Michael K.

    1987-01-01

    The characteristics of 125 barred olivine chondrules identified in polished thin sections of 26 H-L-LL3-6 chondrites were studied, using an electron microprobe for determining mineral abundances and a broad-beam electron microprobe for determining bulk compositions. Compared with all chondrule types in the H-L-LL3 ordinary chondrites, the barred olivine chondrules were found to be enriched in FeO, Al2O3, Na2O, and K2O and depleted in SiO2 and MgO; they were also found to be enriched in the feldspathic component. It is concluded that the precursor components of barred olivine chondrules consisted of a mixture of an olivine-rich component, a refractory-rich component containing Al2O3, TiO2, and CaO, and a volatile-rich alkalic component. This unusual combination implies high temperatures of melting for the refractory component and low temperatures for the volatile component, supporting the hypothesis of Grossman and Wasson (1983) that the alkalies condensed on the alumina already available.

  2. Barred olivine 'chondrules' in lunar spinel troctolite 62295

    NASA Technical Reports Server (NTRS)

    Roedder, E.; Weiblen, P. W.

    1977-01-01

    Several objects have been found in sections of lunar igneous spinel troctolite 62295 that resemble certain meteoritic barred olivine chondrules. Each consists of an apparently spherical single crystal of Fo90 olivine, approximately 0.6-0.8 mm in diameter, containing a set of approximately 30-40 subparallel stringers of An95 plagioclase, whereas the stringers in ordinary meteoritic chondrules consist of glass. The olivine of the 62295 chondrules is also more magnesian, and is radially zoned, having a relatively iron-rich core and rim and an iron-poor intermediate zone. Several possible origins are proposed: impact-generated melt globules solidified in flight, spherical phenocrysts, and meteoritic chondrules, but none of these seems adequate to explain the detailed observations.

  3. Multiple melting in a four-layered barred-olivine chondrule with compositionally heterogeneous glass from LL3.0 Semarkona

    NASA Astrophysics Data System (ADS)

    Rubin, Alan E.

    2013-03-01

    Chondrule K7p from LL3.0 Semarkona consists of four nested barred-olivine (BO) chondrules. The innermost BO chondrule (chondrule 1) formed by complete melting of an olivine-rich dustball. After formation, the chondrule was incorporated into another olivine-rich dustball. A second heating event caused this second dustball to melt; the mesostasis and some of the olivine in chondrule 1 were probably also melted at this time, but the chondrule 1 structure remained largely intact. At this stage, the object was an enveloping compound BO chondrule. This two-step process of melting and dustball enshrouding repeated two more times. The different proportions of olivine and glass in chondrules 1-4 suggest that the individual precursor dustballs differed in the amounts of chondrule fragments they contained and the mineral proportions in those fragments. The final dustball (which ultimately formed chondrule 4) was somewhat more ferroan; after melting, crystallizing, and quenching, chondrule 4 contained olivine and glass with higher FeO and MnO contents than those of the earlier formed chondrules. Subsequent aqueous alteration on the LL parent body transformed the abundant metal blebs and stringers at the chondrule surface into carbide, iron oxide, and minor Ni-rich metal. Portions of the mesostasis underwent dissolution, producing holes and adjacent blades of more resistant material. Much of the glass in the chondrule remained isotropic, even after minor hydration and leaching. The sharp, moderately lobate boundary between the extensively altered mesostasis and the isotropic glass represents the reaction front beyond which there was little or no glass dissolution.

  4. The origin of ferrous zoning in Allende chondrule olivines

    NASA Technical Reports Server (NTRS)

    Peck, Julia A.; Wood, John A.

    1987-01-01

    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 idendical to, and is not the precursor of, matrix olivine.

  5. Experimental Reproduction of Olivine rich Type-I Chondrules

    NASA Technical Reports Server (NTRS)

    Smith, Robert K.

    2005-01-01

    Ordinary chondritic meteorites are an abundant type of stony meteorite characterized by the presence of chondrules. Chondrules are small spheres consisting of silicate, metal, and sulfide minerals that experienced melting in the nebula before incorporation into chondritic meteorite parent bodies. Therefore, chondrules record a variety of processes that occurred in the early solar nebula. Two common types of unequilibrated chondrules with porphyritic textures include FeO-poor (type I) and FeO-rich (type II) each subdivided into an A (SiO2-poor) and B (SiO2-rich) series. Type IA chondrules include those with high proportions of olivine phenocrysts (>80% olivine) and type IB chondrules include those with high proportions of pyroxene phenocrysts (<20% olivine). An intermediate composition, type IAB chondrules include those chondrules in which the proportion of olivine phenocrysts is between 20-80%. We conducted high-temperature laboratory experiments (melting at 1550 C) to produce type I chondrules from average unequilibrated ordinary chondrite (UOC) material mixed with small amounts of additional olivine. The experiments were conducted by adding forsteritic rich olivine (San Carlos olivine, Fo 91) to UOC material (GRO 95544) in a 30/70 ratio, respectively. Results of these high temperature experiments suggest that we have replicated type IA chondrule textures and compositions with dynamic crystallization experiments in which a heterogeneous mixture of UOC (GRO 95544) and olivine (San Carlos olivine) were melted at 1550 C for 1 hr. and cooled at 5-1000 C/hr using graphite crucibles in evacuated silica tubes to provide a reducing environment.

  6. Laboratory Experiments Bearing on the Origin and Evolution of Olivine-rich Chondrules

    SciTech Connect

    Richter, Frank M.; Mendybaev, Ruslan A.; Christensen, John N.; Ebel, Denton; Gaffney, Amy

    2011-06-24

    Evaporation rates of K2O, Na2O, and FeO from chondrule-like liquids and the associated potassium isotopic fractionation of the evaporation residues were measured to help understand the processes and conditions that affected the chemical and isotopic compositions of olivine-rich Type IA and Type IIA chondrules from Semarkona. Both types of chondrules show evidence of having been significantly or totally molten. However, these chondrules do not have large or systematic potassium isotopic fractionation of the sort found in the laboratory evaporation experiments. The experimental results reported here provide new data regarding the evaporation kinetics of sodium and potassium from a chondrule-like melt and the potassium isotopic fractionation of evaporation residues run under various conditions ranging from high vacuum to pressures of one bar of H2+CO2, or H2, or helium. The lack of systematic isotopic fractionation of potassium in the Type IIA and Type IA chondrules compared with what is found in the vacuum and one-bar evaporation residues is interpreted as indicating that they evolved in a partially closed system where the residence time of the surrounding gas was sufficiently long for it to have become saturated in the evaporating species and for isotopic equilibration between the gas and the melt. A diffusion couple experiment juxtaposing chondrule-like melts with different potassium concentrations showed that the diffusivity of potassium is sufficiently fast at liquidus temperatures (DK>2-10-4cm2/s at 1650-C) that diffusion-limited evaporation cannot explain why, despite their having been molten, the Type IIA and Type IA chondrules show no systematic potassium isotopic fractionation.

  7. Chemical zoning and homogenization of olivines in ordinary chondrites and implications for thermal histories of chondrules

    NASA Technical Reports Server (NTRS)

    Miyamoto, Masamichi; Mckay, David S.; Mckay, Gordon A.; Duke, Michael B.

    1986-01-01

    The extent and degree of homogenization of chemical zoning of olivines in type 3 ordinary chondrites is studied in order to obtain some constraints on cooling histories of chondrites. Based on Mg-Fe and CaO zoning, olivines in type 3 chondrites are classified into four types. A single chondrule usually contains olivines with the same type of zoning. Microporphyritic olivines show all four zoning types. Barred olivines usually show almost homogenized chemical zoning. The cooling rates or burial depths needed to homogenize the chemical zoning are calculated by solving the diffusion equation, using the zoning profiles as an initial condition. Mg-Fe zoning of olivine may be altered during initial cooling, whereas CaO zoning is hardly changed. Barred olivines may be homogenized during initial cooling because their size is relatively small. To simulated microporphyritic olivine chondrules, cooling from just below the liquidus at moderately high rates is preferable to cooling from above the liquidus at low rates. For postaccumulation metamorphism of type 3 chondrites to keep Mg-Fe zoning unaltered, the maximum metamorphic temperature must be less than about 400 C if cooling rates based on Fe-Ni data are assumed. Calculated cooling rates for both Fa and CaO homogenization are consistent with those by Fe-Ni data for type 4 chondrites. A hot ejecta blanket several tens of meters thick on the surface of a parent body is sufficient to homogenize Mg-Fe zoning if the temperature of the blanket is 600-700 C. Burial depths for petrologic types of ordinary chondrites in a parent body heated by Al-26 are broadly consistent with those previously proposed.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Jones, Rhian H.; Lofgren, Gary E.

    1993-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2002-03-01

    Two chondrules from Mokoia contain olivine in which oxygen isotopes are extremely heterogeneous, with some grains highly enriched in 16O. These data provide an important link between CAIs and chondrules.

  12. Oxygen isotopic composition of relict olivine grains in cosmic spherules: Links to chondrules from carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Rudraswami, N. G.; Prasad, M. Shyam; Nagashima, K.; Jones, R. H.

    2015-09-01

    Most olivine relict grains in cosmic spherules selected for the present study are pristine and have not been disturbed during their atmospheric entry, thereby preserving their chemical, mineralogical and isotopic compositions. In order to understand the origin of the particles, oxygen isotope compositions of relict olivine grains in twelve cosmic spherules collected from deep sea sediments of the Indian Ocean were studied using secondary ion mass spectrometry. Most of the data lie close to the CCAM (Carbonaceous Chondrite Anhydrous Mineral) line, with ?17O ranging from -5 to 0. The data overlap oxygen isotopic compositions of chondrules from carbonaceous chondrites such as CV, CK, CR and CM, which suggests that chondrules from carbonaceous chondrites are the source of relict grains in cosmic spherules. Chemical compositions of olivine in cosmic spherules are also very similar to chondrule olivine from carbonaceous chondrites. Several olivine relict grains in three cosmic spherules are 16O-rich (?17O -21.9 to -18.7), similar to oxygen isotopic compositions observed in calcium aluminum rich inclusions (CAIs), amoeboid olivine aggregates (AOAs), and some porphyritic chondrules from carbonaceous chondrites. These grains appear to have recorded the initial oxygen isotopic composition of the inner solar nebula. Three olivine grains from two cosmic spherules have ?18O values >+20, which could be interpreted as mixing with stratospheric oxygen during atmospheric entry.

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

    NASA Astrophysics Data System (ADS)

    Tomeoka, Kazushige; Ohnishi, Ichiro

    2014-07-01

    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.

  14. Experimental Replication of Relict "Dusty" Olivine in Type 1B Chondrules

    NASA Technical Reports Server (NTRS)

    Lofgren, Gary E.; Le, L.

    2002-01-01

    Introduction: Relict "dusty" olivine is considered to be a remnants of previous chondrule forming events based on petrographic and chemical evidence. Dynamic crystallization experiments confirm that dusty olivine can be produced by reduction of FeO-rich olivine in Unequilibrated Ordinary Chondrite (UOC) material. The results of these experiments compliment those of who also produced dusty olivine, but from synthetic starting materials. Techniques: Dynamic crystallization experiments were conducted in which UOC material was reduced in presence of graphite. Starting material was coarsely ground GR095554 or WSG95300 that contained olivine of Fo 65-98. Approximately 75 mg. of UOC material was placed in a graphite crucible and sealed in an evacuated silica tube. The tube was suspended in a gas-mixing furnace operated at 1 log unit below the IW buffer. The experiments were as brief as 1.5 hrs up to 121 hrs. Results: Dusty olivine was produced readily in experiments melted at 1400 C for I hr. and cooled between 5 and 100 C/hr or melted at 1300-1400 C for 24 hours. Fe-rich olivine (dusty olivine precursors) that have been partially reduced were common in the experiments melted at 1400 C and cooled at 1000 C/hr or melted at 1200 C for 24 hrs. Relict olivine is absent in experiments melted at 1400 for 24 hrs, melted above 1400 C, or cooled more slowly than 10 C/hr. Relict olivine in the experiments has minimum Fo value of 83 . Thus even in the shortest experiments the most Fe-rich olivine has been altered significantly. The precursor olivine disappears in a few to many hours depending on temperature. The experiments show Fe-rich olivine in all stages of transition to the new dusty form. The olivine is reduced to form dusty olivine in a matter of a few hours at temperatures less than 1400 C and in minutes at higher temperatures. The reduction appears to proceed from the rim of the crystal inward with time. The reduction appears initially rectilinear as if controlled by crystallography, but with time Fe-metal blebs are randomly distributed throughout the olivine. In a given experiment, dusty olivine can be found in varying stages of development, but in the longest experiments, the Fe-metal blebs are dominant and they appear to be migrating out of the olivine. The composition of the dusty olivine ranges from Fo 94-99. The Cr, Mn, and Ca content of the newly formed, dusty olivine is slightly less on average that the precursor olivine, but is till with the range of type 1 olivine. Chadacrysts in the low Ca pyroxene are most common in the higher temperature, more slowly cooled experiments and range in composition from Fo 90-99. Application to chondrule formation: These experiments place time-temperature limits on the preservation of Fe-rich olivine and the production of dusty olivine during chondrule forming events. The reduction process proceeds in a few hours at temperatures above 1400 C and in 10's of hours at temperature between 1200 and 1300 C. This result further confirms th at chondrules form in a few hours to days as suggested earlier. The experiments also confirm that dusty olivine can form from typical Fe-rich olivine in UOC material during the recycling of such olivine in the chondrule forming process.

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

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.

    2006-01-01

    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.

  16. 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)

    Ruzicka, A.; Floss, C.

    2004-01-01

    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.

  17. An experimental study of trace element partitioning between olivine, orthopyroxene and melt in chondrules - Equilibrium values and kinetic effects

    NASA Technical Reports Server (NTRS)

    Kennedy, A. K.; Lofgren, G. E.; Wasserburg, G. J.

    1993-01-01

    Mineral/melt partition coefficients were measured using an ion microprobe for 32 elements in orthopyroxene and olivine in equilibrium and dynamic crystallization experiments on compositions corresponding to chondrules. The mineral/melt partition coefficients calculated from the measured concentrations for both olivine and orthopyroxene show very little change between equilibrium experiments and dynamic experiments with cooling rates of up to 100 C/h. The results provide a self-consistent set of partition coefficients that can be used in thermodynamic models of equilibrium and kinetic partitioning between olivine, orthopyroxene, and melt. These data can be used in models of partial melting and crystal fractionation in olivine- and orthopyroxene-rich systems, such as chondrules. The results may also be applicable to mantle peridotites, komatiitic and picritic lavas, and ultramafic intrusions.

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

    NASA Astrophysics Data System (ADS)

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

    2004-04-01

    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 (k <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.

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

    NASA Technical Reports Server (NTRS)

    Johnson, Craig A.; Prinz, Martin

    1991-01-01

    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.

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

    PubMed

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

    2008-06-24

    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

  1. Relative abundances of chondrule primary textural types in ordinary chondrites and their bearing on conditions of chondrule formation

    NASA Astrophysics Data System (ADS)

    Gooding, J. L.; Keil, K.

    1981-03-01

    A petrographic survey of > 1600 chondrules in thin-sections of 12 different mildly to highly unequilibrated H-, L-, and Li-chondrites, as well as morphological and textural study of 141 whole chondrules separated from 11 of the same chondrites, was used to determine the relative abundances of definable chondrule primary textural types. Percentage abundances of various chondrule types are remarkably similar in all chondrites studied and are 47-52 porphyritic olivine-pyroxene (POP), 15-27 porphyritic olivine (P 0), 9-11 porphyritic pyroxene (PP), 34 barred olivine (BO), 7-9 radial pyroxene (RP), 2-5 granular olivine-pyroxene (GOP), 3-5 cryptocrystalline (C), and ? 1 metallic (M). Neither chondrule size nor shape is strongly correlated with textural type. Compound and cratered chondrules, which are interpreted as products of collisions between plastic chondrules, comprise 2-28% of non-porphyritic (RP, GOP, C) but only 2-9% of porphyritic (POP, PO, PP, BO) chondrules, leading to a model-dependent implication that non-porphyritic chondrules evolved at number densities (chondrules per unit volume of space) which were 102 to 104 times greater than those which prevailed during porphyritic chondrule formation (total range of 1 to 106 m-3. Distinctive "rims" of fine-grained sulfides and/or silicates occur on both porphyritic and non-porphyritic types and appear to post-date chondrule formation. Apparently, either the same process(es) contributed chondrules to all unequilibrated ordinary chondrites or, if genetically different, the various chondrule types were well mixed before incorporation into chondrites. Melting of pre-existing materials is the mechanism favored for chondrule formation.

  2. A new estimate of the chondrule cooling rate deduced from an analysis of compositional zoning of relict olivine

    SciTech Connect

    Miura, H.; Yamamoto, T.

    2014-03-01

    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 and Rubin, we estimate the cooling rate to be ∼200-2000 K s{sup –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.

  3. The formation conditions of enstatite chondrites: Insights from trace element geochemistry of olivine-bearing chondrules in Sahara 97096 (EH3)

    NASA Astrophysics Data System (ADS)

    Jacquet, Emmanuel; Alard, Olivier; Gounelle, Matthieu

    2015-09-01

    We report in situ LA-ICP-MS trace element analyses of silicate phases in olivine-bearing chondrules in the Sahara 97096 (EH3) enstatite chondrite. Most olivine and enstatite present rare earth element (REE) patterns comparable to their counterparts in type I chondrules in ordinary chondrites. They thus likely share a similar igneous origin, likely under similar redox conditions. The mesostasis however frequently shows negative Eu and/or Yb (and more rarely Sm) anomalies, evidently out of equilibrium with olivine and enstatite. We suggest that this reflects crystallization of oldhamite during a sulfidation event, already inferred by others, during which the mesostasis was molten, where the complementary positive Eu and Yb anomalies exhibited by oldhamite would have possibly arisen due to a divalent state of these elements. Much of this igneous oldhamite would have been expelled from the chondrules, presumably by inertial acceleration or surface tension effects, and would have contributed to the high abundance of opaque nodules found outside them in EH chondrites. In two chondrules, olivine and enstatite exhibit negatively sloped REE patterns, which may be an extreme manifestation of a general phenomenon (possibly linked to near-liquidus partitioning) underlying the overabundance of light REE observed in most chondrule silicates relative to equilibrium predictions. The silicate phases in one of these two chondrules show complementary Eu, Yb, and Sm anomalies providing direct evidence for the postulated occurrence of the divalent state for these elements at some stage in the formation reservoir of enstatite chondrites. Our work supports the idea that the peculiarities of enstatite chondrites may not require a condensation sequence at high C/O ratios as has long been believed.

  4. Visualizing the Magnetic Behavior of Chondrule Dusty Olivine Using Electron Holography

    NASA Astrophysics Data System (ADS)

    Shah, J.; Muxworthy, A. R.; Almeida, T. P.; Kovcs, A.; Russell, S. S.; Genge, M. J.; Dunin-Borkowski, R. E.

    2015-07-01

    We present the first off-axis electron holography study of natural dusty olivine in Bishunpur (LL3.1) to investigate its nanoscale rock magnetic properties. We find highly magnetic, multi-vortex domain structures within the dusty olivine kamacite.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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 Shişr 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.

  6. Size-distributions of chondrule types in the Inman and Allan Hills A77011 L3 chondrites

    NASA Astrophysics Data System (ADS)

    Rubin, A. E.; Keil, K.

    1984-09-01

    The size distributions of barred-olivine (BO) and radial-pyroxene/cryptocrystalline (RPC) chondrules are investigated in a petrographic study of nine and 18 thin sections (respectively) of the L3 chondrites Inman and ALHA77011. It is found that the Inman chondrules are significantly larger than the ALHA77011 chondrules and that RPC chondrules in Inman and BO chondrules in ALHA77011 are relatively more numerous, but no significant difference in the BO and RPC size distributions is observed. A formation mechanism involving size sorting of dustball chondrule precursors by aerodynamic particle-gas interactions in a large region of the solar nebula, melting of sorted dustballs in relatively small regions, and chondrule mixing and agglomeration (from subreservoirs containing uniformly large or uniformly small chondrules of a particular compositional type) to form chondrites is proposed.

  7. 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)

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

    2012-01-01

    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.

  8. 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

    Hua, X.; Adam, J.; Palme, H.; Goresy, A. E. )

    1988-06-01

    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.

  9. Relict grains in chondrules: Evidence for chondrule recycling

    NASA Technical Reports Server (NTRS)

    Jones, R. H.

    1994-01-01

    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.

  10. Size-frequency distributions of EH3 chondrules

    NASA Astrophysics Data System (ADS)

    Rubin, Alan E.; Grossman, Jeffrey N.

    1987-09-01

    Size-frequency distributions of chondrules in three EH3 chondrites, namely Qingzhen, Kota-Kota and ALHA77156, are presently determined. Radial pyroxene chondrules are larger than cryptocrystalline chondrules, while nonporphyritic chondrules have a broader size-frequency distribution than the porphyritic, and porphyritic olivine-pyroxene chondrules are larger than porphyritic pyroxene chondrules. This last result is due to a reaction of fine-grained olivine with free silica to form pyroxene during mild thermal metamorphism of the whole-rocks.

  11. Size-frequency distributions of EH3 chondrules

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.; Grossman, Jeffrey N.

    1987-01-01

    Size-frequency distributions of chondrules in three EH3 chondrites, namely Qingzhen, Kota-Kota and ALHA77156, are presently determined. Radial pyroxene chondrules are larger than cryptocrystalline chondrules, while nonporphyritic chondrules have a broader size-frequency distribution than the porphyritic, and porphyritic olivine-pyroxene chondrules are larger than porphyritic pyroxene chondrules. This last result is due to a reaction of fine-grained olivine with free silica to form pyroxene during mild thermal metamorphism of the whole-rocks.

  12. Cooling rates of chondrules: A new approach

    NASA Technical Reports Server (NTRS)

    Weinbruch, S.; Mueller, W. F.

    1994-01-01

    Mineralogy and texture of chondrules have been reproduced experimentally and it was demonstrated that the abundance of heterogeneous nuclei is an important factor controlling chondrule textures. Cooling rates of chondrules were estimated from the zoning patterns of olivine. Low cooling rates (less than 100 C/h) yielded chemically homogeneous olivine crystals, whereas higher cooling rates, between 100 and 2000 C/h, produced olivine compositions similar to those observed in natural chondrules. We present a new approach to determining cooling rates of chondrules based on the microstructure of chondrule clinopyroxene and plagioclase. All observations were made on Allende chondrules. Two independent processes (Ca and Mg diffusion in pyroxene and Al/Si ordering in plagioclase) yield similar cooling rates on the order of 10-1 C/h for granular olivine pyroxene (GOP) chondrules in Allende. Our cooling rates are at least one order of magnitude lower than those derived from dynamic crystallization experiments.

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

    NASA Technical Reports Server (NTRS)

    Krot, Alexander N.; Rubin, Alan E.

    1993-01-01

    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.

  14. Timing of Formation of a Wassonite-bearing Chondrule

    NASA Technical Reports Server (NTRS)

    Needham, A. W.; Nakamura-Messenger, K.; Rubin, A. E.; Choi, B.-G.; Messenger, S.

    2014-01-01

    Wassonite, ideally stoichiometric TiS, is a titanium monosulfide recently discovered in the Yamato 691 EH3 enstatite chondrite. Wassonite grains were located within the mesostasis of a single barred olivine chondrule. Such chondrules likely formed in the solar nebula by melting of fine grained precursor dust. The reduced nature of enstatite chondrites, and the wassonite-bearing chondrule in particular, may suggest precursor materials included Ti-bearing troilite, metallic Fe-Ni, and possibly graphite. Under the reducing conditions present in enstatite chondrites S can partition more readily into silicate melt, leading to raised Ti content of the residual Fe-FeS melt. By the time sulfide crystallized from the melt, the Ti concentration was high enough to form small grains of pure TiS - wassonite. As a mineral not previously observed in nature wassonite and its host chondrule may provide additional constraints on physical and chemical conditions in the solar nebula at a specific time and location relevant to planetary formation. Enstatite chondrites and Earth share similar isotopic compositions of Cr, Ni, Ti, O and N. Understanding the formation conditions of enstatite chondrite chondrules may therefore have wider relevance for terrestrial planet accretion and other early inner solar system processes. Here we present preliminary results of an investigation of the Al-Mg systematics of the only known wassonite-bearing chondrule. The goal of this study is to determine whether this chondrule's formation was contemporaneous with other enstatite chondrite chondrules and to establish its place in the broader timeline of solar system events.

  15. The conditions of chondrule formation, Part II: Open system

    NASA Astrophysics Data System (ADS)

    Friend, Pia; Hezel, Dominik C.; Mucerschi, Daniel

    2016-01-01

    We studied the texture of 256 chondrules in thin sections of 16 different carbonaceous (CV, CR, CO, CM, CH) and Rumuruti chondrites. In a conservative count ∼75% of all chondrules are mineralogically zoned, i.e. these chondrules have an olivine core, surrounded by a low-Ca pyroxene rim. A realistic estimate pushes the fraction of zoned chondrules to >90% of all chondrules. Mineralogically zoned chondrules are the dominant and typical chondrule type in carbonaceous and Rumuruti chondrites. The formation of the mineralogical zonation represents a fundamentally important process of chondrule formation. The classic typification of chondrules into PO, POP and PP might in fact represent different sections through mineralogically zoned chondrules. On average, the low-Ca pyroxene rims occupy 30 vol.% of the entire chondrule. The low-Ca pyroxene most probably formed by reaction of an olivine rich chondrule with SiO from the surrounding gas. This reaction adds 3-15 wt.% of material, mainly SiO2, to the chondrule. Chondrules were open systems and interacted substantially with the surrounding gas. This is in agreement with many previous studies on chondrule formation. This open system behaviour and the exchange of material with the surrounding gas can explain bulk chondrule compositional variations in a single meteorite and supports the findings from complementarity that chondrules and matrix formed from the same chemical reservoir.

  16. Textural evidence bearing on the origin of isolated olivine crystals in C2 carbonaceous chondrites

    NASA Technical Reports Server (NTRS)

    Richardson, S. M.; Mcsween, H. Y., Jr.

    1978-01-01

    In some cases the mechanical competence of chondrules in carbonaceous chondrites has been reduced by alteration of their mesostasis glass to friable phyllosilicate, providing a mechanism by which euhedral olivines can be separated from chondrules. Morphological features of isolate olivine grains found in carbonaceous chondrites are similar to those of olivine phenocrysts in chondrules. These observations suggest that the isolated olivine grains formed in chondrules, by crystallization from a liquid, rather than by condensation from a vapor.

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

    SciTech Connect

    Simon, S.B.; Sutton, S.R.; Grossman, L.

    2008-04-28

    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.

  18. Congruent Melting Kinetics: Constraints on Chondrule Formation

    NASA Technical Reports Server (NTRS)

    Greenwood, James P.; Hess, Paul C.

    1995-01-01

    The processes and mechanisms of melting and their applications to chondrule formation are discussed A model for the kinetics of congruent melting is developed and used to place constraints on the duration and maximum temperature experienced by the interiors of relict-bearing chondrules. Specifically, chondrules containing relict forsteritic olivine or enstatitic pyroxene cannot have been heated in excess of 1901 C or 1577 C, respectively, for more than a few seconds.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

  20. Shock Effects in Olivine from Mocs Chondrite

    NASA Astrophysics Data System (ADS)

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

    1995-09-01

    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.

  1. Major element chemical compositions of chondrules in unequilibrated chondrites

    NASA Technical Reports Server (NTRS)

    Ikeda, Y.

    1984-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Fedkin, Alexei V.; Grossman, Lawrence

    2013-07-01

    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.

  3. Impact jetting as the origin of chondrules.

    PubMed

    Johnson, Brandon C; Minton, David A; Melosh, H J; Zuber, Maria T

    2015-01-15

    Chondrules are the millimetre-scale, previously molten, spherules found in most meteorites. Before chondrules formed, large differentiating planetesimals had already accreted. Volatile-rich olivine reveals that chondrules formed in extremely solid-rich environments, more like impact plumes than the solar nebula. The unique chondrules in CB chondrites probably formed in a vapour-melt plume produced by a hypervelocity impact with an impact velocity greater than 10 kilometres per second. An acceptable formation model for the overwhelming majority of chondrules, however, has not been established. Here we report that impacts can produce enough chondrules during the first five million years of planetary accretion to explain their observed abundance. Building on a previous study of impact jetting, we simulate protoplanetary impacts, finding that material is melted and ejected at high speed when the impact velocity exceeds 2.5 kilometres per second. Using a Monte Carlo accretion code, we estimate the location, timing, sizes, and velocities of chondrule-forming impacts. Ejecta size estimates indicate that jetted melt will form millimetre-scale droplets. Our radiative transfer models show that these droplets experience the expected cooling rates of ten to a thousand kelvin per hour. An impact origin for chondrules implies that meteorites are a byproduct of planet formation rather than leftover building material. PMID:25592538

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

  5. Relationships between type I and type II chondrules: Implications on chondrule formation processes

    NASA Astrophysics Data System (ADS)

    Villeneuve, Johan; Libourel, Guy; Soulié, Camille

    2015-07-01

    In unequilibrated chondrites, the ferromagnesian silicates in chondrules exhibit wide ranges of mg# = Mg/(Mg + Fe), allowing to sub-divide porphyritic chondrules into either type I (mg# > 0.9) or type II (mg# < 0.9). Although both chondrule types formed under oxidizing conditions relative to the canonical solar nebula, it is generally inferred that type II chondrules formed in more oxidizing conditions than type I. In order to check whether this redox difference was established during chondrule formation, or reflects differences in their precursors, we have undertaken a set of experiments aimed at heating type I olivine-rich (A) chondrule proxy, i.e. forsterite + Fe metal + Ca-Mg-Si-Al glass mixtures, under oxidizing conditions. We show that high temperature (isothermal) oxidation of type IA-like assemblages is a very efficient and rapid process (e.g. few tens of minutes) to form textures similar to type IIA chondrules. Due to the rapid dissolution of Fe metal blebs, a FeO increase in the melt and in combination with the dissolution of magnesian olivine allows the melt to reach ferroan olivine saturation. Crystallization of ferroan olivine occurs either as new crystal in the mesostasis or as overgrowths on the remaining unresorbed forsterite grains (relicts). Interruption of this process at any time before its completion by rapid cooling allows to reproduce the whole range of textures and chemical diversity observed in type A chondrules, i.e. from type I to type II. Several implications on chondrule formation processes can be inferred from the presented experiments. Type I chondrules or fragments of type I chondrules are very likely the main precursor material involved in the formation of most type II chondrules. Formation of porphyritic olivine type II chondrules is very likely the result of processes generating crystal growth by chemical disequilibrium at high temperature rather than processes generating crystallization only by cooling rates. This questions the reliability of chondrule thermal history (e.g. cooling rate values) hitherto inferred for producing porphyritic textures from dynamical cooling rate experiments only. Type A chondrule formation can be a very fast process. After periods of sub-isothermal heating or slow cooling (<50 K/h) as short as several tens of minutes and no longer than few hundreds of minutes at 1500-1800 °C, type A chondrules terminates their formation by a fast cooling (>103-104 K/h) in order to preserve their glassy mesostasis. Such inferred thermal history being at odds with nebular shock models, we thus advocate that impacts on planetesimals causing rapid melting and vaporization may provide the high density and highly volatile-enriched gaseous environments required to form chondrules. In this scenario, chondrules and their diversity should result from various degrees of interaction of the ejected fragments with the impact vapor plume; the most oxidizing conditions recorded in type IIA chondrules being very likely the closest to those imposed by the impact vapor plume.

  6. A CRITICAL EXAMINATION OF THE X-WIND MODEL FOR CHONDRULE AND CALCIUM-RICH, ALUMINUM-RICH INCLUSION FORMATION AND RADIONUCLIDE PRODUCTION

    SciTech Connect

    Desch, S. J.; Morris, M. A.; Connolly, H. C.; Boss, Alan P.

    2010-12-10

    Meteoritic data, especially regarding chondrules and calcium-rich, aluminum-rich inclusions (CAIs), and isotopic evidence for short-lived radionuclides (SLRs) in the solar nebula, potentially can constrain how planetary systems form. Interpretation of these data demands an astrophysical model, and the 'X-wind' model of Shu et al. and collaborators has been advanced to explain the origin of chondrules, CAIs, and SLRs. It posits that chondrules and CAIs were thermally processed <0.1 AU from the protostar, then flung by a magnetocentrifugal outflow to the 2-3 AU region to be incorporated into chondrites. Here we critically examine key assumptions and predictions of the X-wind model. We find a number of internal inconsistencies: theory and observation show no solid material exists at 0.1 AU; particles at 0.1 AU cannot escape being accreted into the star; particles at 0.1 AU will collide at speeds high enough to destroy them; thermal sputtering will prevent growth of particles; and launching of particles in magnetocentrifugal outflows is not modeled, and may not be possible. We also identify a number of incorrect predictions of the X-wind model: the oxygen fugacity where CAIs form is orders of magnitude too oxidizing, chondrule cooling rates are orders of magnitude lower than those experienced by barred olivine chondrules, chondrule-matrix complementarity is not predicted, and the SLRs are not produced in their observed proportions. We conclude that the X-wind model is not relevant to chondrule and CAI formation and SLR production. We discuss more plausible models for chondrule and CAI formation and SLR production.

  7. Oxygen isotope heterogeneity in chondrules from the Mokoia CV3 carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Jones, Rhian H.; Leshin, Laurie A.; Guan, Yunbin; Sharp, Zachary D.; Durakiewicz, Tomasz; Schilk, Alan J.

    2004-08-01

    We report a study of the oxygen isotope ratios of chondrules and their constituent mineral grains from the Mokoia, oxidized CV3 chondrite. Bulk oxygen isotope ratios of 23 individual chondrules were determined by laser ablation fluorination, and oxygen isotope ratios of individual grains, mostly olivine, were obtained in situ on polished mounts using secondary ion mass spectrometry (SIMS). Our results can be compared with data obtained previously for the oxidized CV3 chondrite, Allende. Bulk oxygen isotope ratios of Mokoia chondrules form an array on an oxygen three-isotope plot that is subparallel to, and slightly displaced from, the CCAM (carbonaceous chondrite anhydrous minerals) line. The best-fit line for all CV3 chondrite chondrules has a slope of 0.99, and is displaced significantly (by ? 17O -2.5) from the Young and Russell slope-one line for unaltered calcium-aluminum-rich inclusion (CAI) minerals. Oxygen isotope ratios of many bulk CAIs also lie on the CV-chondrule line, which is the most relevant oxygen isotope array for most CV chondrite components. Bulk oxygen isotope ratios of most chondrules in Mokoia have ? 18O values around 0, and olivine grains in these chondrules have similar oxygen isotope ratios to their bulk values. In general, it appears that chondrule mesostases have higher ? 18O values than olivines in the same chondrules. Our bulk chondrule data spread to lower ? 18O values than any ferromagnesian chondrules that have been measured previously. Two chondrules with the lowest bulk ? 18O values (-7.5 and -11.7) contain olivine grains that display an extremely wide range of oxygen isotope ratios, down to ? 17O, ? 18O around -50 in one chondrule. In these chondrules, there are no apparent relict grains, and essentially no relationships between olivine compositions, which are homogeneous, and oxygen isotopic compositions of individual grains. Heterogeneity of oxygen isotope ratios within these chondrules may be the result of incorporation of relict grains from objects such as amoeboid olivine aggregates, followed by solid-state chemical diffusion without concomitant oxygen equilibration. Alternatively, oxygen isotope exchange between an 16O-rich precursor and an 16O-poor gas may have taken place during chondrule formation, and these chondrules may represent partially equilibrated systems in which isotopic heterogeneities became frozen into the crystallizing olivine grains. If this is the case, we can infer that the earliest nebular solids from which chondrules formed had ? 17O and ? 18O values around -50, similar to those observed in refractory inclusions.

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

    NASA Astrophysics Data System (ADS)

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

    1986-02-01

    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.

  9. Oxygen isotopic constraints on the origin of magnesian chondrules and on the gaseous reservoirs in the early Solar System

    NASA Astrophysics Data System (ADS)

    Chaussidon, Marc; Libourel, Guy; Krot, Alexander N.

    2008-04-01

    We report in situ ion microprobe analyses of the oxygen isotopic composition of the major silicate phases (olivine, low-Ca pyroxene, silica, and mesostasis) of 37 magnesian porphyritic (type I) chondrules from CV (Vigarano USNM 477-2, Vigarano UH5, Mokoia, and Efremovka) and CR (EET 92042, EET 92147, EET 87770, El Djouf 001, MAC 87320, and GRA 95229) carbonaceous chondrites. In spite of significant variations of the modal proportions of major mineral phases in CR and CV chondrules, the same isotopic characteristics are observed: (i) olivines are isotopically homogeneous at the level within a chondrule although they may vary significantly from one chondrule to another, (ii) low-Ca pyroxenes are also isotopically homogeneous but systematically 16O-depleted relative to olivines of the same chondrule, and (iii) all chondrule minerals analyzed show 16O-enrichments relative to the terrestrial mass fractionation line, enrichments that decrease from olivine (spinel) to low-Ca pyroxene and to silica and mesostasis. The observation that, in most of the type I chondrules studied, the coexisting olivine and pyroxene crystals and glassy mesostasis have different oxygen isotopic compositions implies that the olivine and pyroxene grains are not co-magmatic and that the glassy mesostasis is not the parent liquid of the olivine. The ? 18O and ? 17O values of pyroxene and olivine appear to be strongly correlated for all the studied CR and CV chondrules according to:

  10. On the origin of enstatite chondrite chondrules based on their petrography and comparison with experimentally produced chondrules

    NASA Technical Reports Server (NTRS)

    Lofgren, Gary E.; Dehart, John M.; Burkett, P. J.

    1994-01-01

    The recent discovery of several types 3 and 4 enstatite chondrites (EC) in the Antarctic collection increases greatly the ability to compare unaltered, naturally-formed EC chondrules with chondrules produced experimentally from melts of enstatitic chondrule composition. Because these discoveries are so recent we have undertaken the task of characterizing these chondrules for purposes of comparison. We have looked at several new Antarctic E3 chondrites and Qingzhen. They all have numerous chondrules with well defined outlines and readily identifiable textures. All have mostly porphyritic chondrules, but there are differences in the size and kinds of textures. Radial pyroxene, barred/dendritic px, and cryptocrystalline chondrules are present in differing amounts with one exception.

  11. Fayalitic Olivine in Matrix of the Krymka LL3.1 Chondrite

    NASA Astrophysics Data System (ADS)

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

    1995-09-01

    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 olivine (as observed in the Kaidun CR chondrite), the platelet overgrowths on larger olivine crystals probably represent growth features and not a replacement of phyllosilicates. The platy morphology of fayalitic olivine could also indicate growth from a vapor consistent with hypotheses 1 and 2. The wide range in compositions of associated fayalitic olivine platelets suggests that they did not all form in the same environment and were not in contact under high enough temperatures to result in equilibrium; therefore, we conclude that the fayalitic olivine formed in a nebular environment. The fayalitic olivine platelets and associated fayalitic olivine in Krymka matrix may record vapor solid reactions under oxidizing nebular conditions or partial evaporation of a more Mg-rich olivine to produce a fayalite vapor, followed by recondensation. Formation through heating/dehydration of phyllosilicates is less likely. References. [1] Nagahara H. (1984) GCA, 48, 2581-2595. [2] Nagahara H. and Kushiro I. (1987) EPSL, 85, 537-547. [3] Hua X. and Buseck P. R. (1995) GCA, 59, 563-578. [4] Nagahara H. et al. (1994) GCA, 58, 1951-1963. [5] Alexander C. M. et al. (1989) EPSL, 95, 187-207. [6] Kojima T. and Tomeoka K. (1994) Meteoritics, 29, 484.

  12. Non-spherical lobate chondrules in CO3.0 Y-81020: General implications for the formation of low-FeO porphyritic chondrules in CO chondrites

    NASA Astrophysics Data System (ADS)

    Rubin, Alan E.; Wasson, John T.

    2005-01-01

    Non-spherical chondrules (arbitrarily defined as having aspect ratios ?1.20) in CO3.0 chondrites comprise multi-lobate, distended, and highly irregular objects with rounded margins; they constitute 70% of the type-I (low-FeO) porphyritic chondrules in Y-81020, 75% of such chondrules in ALHA77307, and 60% of those in Colony. Although the proportion of non-spherical type-I chondrules in LL3.0 Semarkona is comparable (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 10 -3 s, too little time for their 20-? m-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 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.

  13. Oxygen Isotope Systematics of Chondrules from the Least Equilibrated H Chondrite

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

    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].

  14. The lack of potassium-isotopic fractionation in Bishunpur chondrules

    USGS Publications Warehouse

    Alexander, C.M. O'D.; Grossman, J.N.; Wang, Jingyuan; Zanda, B.; Bourot-Denise, M.; Hewins, R.H.

    2000-01-01

    In a search for evidence of evaporation during chondrule formation, the mesostases of 11 Bishunpur chondrules and melt inclusions in olivine phenocrysts in 7 of them have been analyzed for their alkali element abundances and K-isotopic compositions. Except for six points, all areas of the chondrules that were analyzed had ?41K compositions that were normal within error (typically 3%, 2s?). The six anomalous points are probably all artifacts. Experiments have shown that free evaporation of K leads to large 41K enrichments in the evaporation residues, consistent with Rayleigh fractionation. Under Rayleigh conditions, a 3% enrichment in ?41K is produced by ?12% loss of K. The range of L-chondrite-normalized K/Al ratios (a measure of the K-elemental fractionation) in the areas analyzed vary by almost three orders of magnitude. If all chondrules started out with L-chondrite-like K abundances and the K loss occurred via Rayleigh fractionation, the most K-depleted chondrules would have had compositions of up to ?41K ? 200%. Clearly, K fractionation did not occur by evaporation under Rayleigh conditions. Yet experiments and modeling indicate that K should have been lost during chondrule formation under currently accepted formation conditions (peak temperature, cooling rate, etc.). Invoking precursors with variable alkali abundances to produce the range of K/Al fractionation in chondrules does not explain the K-isotopic data because any K that was present should still have experienced sufficient loss during melting for there to have been a measurable isotopic fractionation. If K loss and isotopic fractionation was inevitable during chondrule formation, the absence of K-isotopic fractionation in Bishunpur chondrules requires that they exchanged K with an isotopically normal reservoir during or after formation. There is evidence for alkali exchange between chondrules and rim-matrix in all unequilibrated ordinary chondrites. However, melt inclusions can have alkali abundances that are much lower than the mesostases of the host chondrules, which suggests that they at least remained closed since formation. If it is correct that some or all melt inclusions remained closed since formation, the absence of K-isotopic fractionation in them requires that the K-isotopic exchange took place during chondrule formation, which would probably require gas-chondrule exchange. Potassium evaporated from fine-grained dust and chondrules during chondrule formation may have produced sufficient K-vapor pressure for gas-chondrule isotopic exchange to be complete on the timescales of chondrule formation. Alternatively, our understanding of chondrule formation conditions based on synthesis experiments needs some reevaluation.

  15. A systematic for oxygen isotopic variation in meteoritic chondrules

    NASA Astrophysics Data System (ADS)

    Marrocchi, Yves; Chaussidon, Marc

    2015-11-01

    Primitive meteorites are characteristically formed from an aggregation of sub-millimeter silicate spherules called chondrules. Chondrules are known to present large three-isotope oxygen variations, much larger than shown by any planetary body. We show here that the systematic of these oxygen isotopic variations results from open-system gas-melt exchanges during the formation of chondrules, a conclusion that has not been fully assessed up to now. We have considered Mg-rich porphyritic chondrules and have modeled the oxygen isotopic effects that would result from high-temperature interactions in the disk between precursor silicate dust and a gas enriched in SiO during the partial melting and evaporation of this dust. This formation process predicts: (i) a range of oxygen isotopic composition for bulk chondrules in agreement with that observed in Mg-rich porphyritic chondrules, and (ii) variable oxygen isotopic disequilibrium between chondrule pyroxene and olivine, which can be used as a proxy of the dust enrichment in the chondrule-forming region(s). Such enrichments are expected during shock waves that produce transient evaporation of dust concentrated in the mid-plane of the accretion disk or in the impact plumes generated during collisions between planetesimals. According to the present model, gas-melt interactions under high PSiO(gas) left strong imprints on the major petrographic, chemical and isotopic characteristics of Mg-rich porphyritic chondrules.

  16. Vesicles in Experimental Chondrules as Clues to Chondrule Precursors

    NASA Astrophysics Data System (ADS)

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

    1993-07-01

    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.

  17. Young Pb-Isotopic Ages of Chondrules in CB Carbonaceous Chondrites

    NASA Technical Reports Server (NTRS)

    Amelin, Yuri; Krot, Alexander N.

    2005-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Mccoy, Timothy J.; Scott, Edward R. D.; Keil, Klaus; Taylor, G. Jeffrey; Jones, Rhian H.

    1991-01-01

    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.

  19. Hydrous and anhydrous alterations of chondrules in Kaba and Mokoia CV chondrites

    NASA Astrophysics Data System (ADS)

    Kimura, M.; Ikeda, Y.

    1998-09-01

    Chondrules in the Bali-like CV chondrite Kaba and the Allende-like portion of the Mokoia breccia have been studied to explore relationship between hydrous alteration to form phyllosilicates and anhydrous alteration resulted in secondary olivine zonation, replacement of enstatite by ferroan olivine and formation of feldspathoids (nepheline and sodalite). All Kaba chondrules experienced extensive hydrous alteration, whereas anhydrous alteration is minor and resulted only in the olivine zonation. On the other hand, all of the Mokoia chondrules experienced both extensive anhydrous and hydrous alteration. Bronzite rims formed between relic enstatite grains and phyllosilicates in both Kaba and Mokoia during the hydrous alteration. Petrographic observations indicate that phyllosilicates in Mokoia postdate formation of the secondary ferroan olivine and feldspathoids. We conclude that anhydrous alteration in Kaba and Mokoia predated hydrous alteration and took place before accretion of chondrules into the CV parent asteroid.

  20. Serpentinisation of Chondrules in the Murchison CM Carbonaceous Chondrite by Centripetal Replacement and Cementation

    NASA Astrophysics Data System (ADS)

    Lee, M. R.; Lindgren, P.

    2015-07-01

    We have found that phenocrysts in Murchison chondrules contain serpentine. Olivine-hosted veins have formed by replacement whereas polyhedral serpentine has formed by cementation of pores within clinoenstatite grains.

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

    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.

  2. Compound chondrules fused cold

    NASA Astrophysics Data System (ADS)

    Hubbard, Alexander

    2015-07-01

    About 4-5% of chondrules are compound: two separate chondrules stuck together. This is commonly believed to be the result of the two component chondrules having collided shortly after forming, while still molten. This allows high velocity impacts to result in sticking. However, at T ? 1100 K, the temperature below which chondrules collide as solids (and hence usually bounce), coalescence times for droplets of appropriate composition are measured in tens of seconds. Even at 1025 K, at which temperature theory predicts that the chondrules must have collided extremely slowly to have stuck together, the coalescence time scale is still less than an hour. These coalescence time scales are too short for the collision of molten chondrules to explain the observed frequency of compound chondrules. We suggest instead a scenario where chondrules stuck together in slow collisions while fully solid; and the resulting chondrule pair was subsequently briefly heated to a temperature in the range of 900-1025 K. In that temperature window the coalescence time is finite but long, covering a span of hours to a decade. This is particularly interesting because those temperatures are precisely the critical window for thermally ionized MRI activity, so compound chondrules provide a possible probe into that vital regime.

  3. Chondrules Formed Through Cementation of Mineral Clusters by Feldspathic Melts

    NASA Astrophysics Data System (ADS)

    Lu, J.

    1992-07-01

    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.

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

    SciTech Connect

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

    1991-02-01

    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.

  5. 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)

    Jones, Rhian H.

    1990-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  7. Chondrule magnetic properties

    NASA Technical Reports Server (NTRS)

    Wasilewski, P. J.; Obryan, M. V.

    1994-01-01

    The topics discussed include the following: chondrule magnetic properties; chondrules from the same meteorite; and REM values (the ratio for remanence initially measured to saturation remanence in 1 Tesla field). The preliminary field estimates for chondrules magnetizing environments range from minimal to a least several mT. These estimates are based on REM values and the characteristics of the remanence initially measured (natural remanence) thermal demagnetization compared to the saturation remanence in 1 Tesla field demagnetization.

  8. Oxygen Isotopes in Early Solar System Materials: A Perspective Based on Microbeam Analyses of Chondrules from CV Carbonaceous Chondrites

    NASA Astrophysics Data System (ADS)

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

    2004-03-01

    We have measured oxygen isotope ratios in olivine grains from chondrules in the Allende and Mokoia CV chondrites, using SIMS. We show how microbeam data can be used to address fundamental questions about the early solar system.

  9. Metal and Sulfide in Semarkona Chondrules and Rims: Evidence for Reduction, Evaporation, and Recondensation During Chondrule Formation

    NASA Astrophysics Data System (ADS)

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

    1993-07-01

    The fact that many chondrules in UOCs contain metal associated with sulfide has been attributed to either low temperature of formation (<680 K) and lack of subsequent heating sufficient to cause evaporation [1] or metamorphism after chondrule formation [2]. We have examined the metal and sulfide in group A and B chondrule interiors and rims in the most primitive ordinary chondrite, Semarkona, in order to further explore these options. Most group A1 chondrules contain abundant metal(3-4 wt%), which is mainly as rounded grains of kamacite (< 1 micrometer~60 micrometers) usually situated in the mesostasis near chondrule edge. For the 37 group A1 chondrules investigated, only five contain sulfide and in only one was it abundant. Usually the sulfides were found associated with metal near the chondrule surfaces, and in a few cases, the metal grains were enclosed in sulfides. The "dusty metal" [3] is common in group A1 chondrules, but is not found in group B chondrules, and the host olivine is often embayed by metal-free pyroxene, which has lower Fe/Fe+Mg ratio than the coexisting olivine. In contrast, metal in group B1 chondrules is much less abundant (generally less than 1 wt%) and occurs as both kamacite and taenite. It is often associated with sulfide, with the sulfide being more abundant than metal. Metal in group A1 chondrules is generally poorer in Ni than the metal in group B1 chondrules (Fig. 1). A similar observation was made for type IA and II chondrules [4,5], which are subsets of group A and B respectively. Additionally, metal in chondrules with Fe-poor olivine contains lower abundance of Ni and Co than metal in chondrules with Fe-rich olivine (Fig. 1) [6]. Group A1 chondrules are more frequently rimmed than group B1 chondrules (~70% by number, compared with ~30% ) and seem to have higher ratios of rim thickness to chondrule diameter (Fig. 2). Most group A1 chondrule rims contain ultra-fine-grained metal- and sulfide-rich materials, which are not observed in chondrites of higher petrographic grades. In contrast, group B1 chondrule rims, when present, contain fine-grained matrix-like materials with dispersed or massive sulfide and metal, which, in contrast to the ultra-fine sulfides/metal-rich rims in group A chondrules, are also observed in higher petrographic types [7]. These results can best be explained by reduction of ferrous olivine and loss of FeS by evaporation during group A1 chondrule formation with the recondensation of FeS and/or reactions between recondensed metal and H2S in the nebular gas at lower temperatures. Thermoluminescence, cathodoluminescence, and compositional zoning in several Semarkona group A1 chondrules has also been interpreted in terms of recondensation of major volatile elements like Na and Mn [8,9]. References: [1] Grossman J. N and Wasson J. T. (1983) In Chondrules and their Origins (E. K. King, ed.), 88-121. [2] Wood J. A. (1993) personal communication; see also Grossman J. N. (1988) In Meteorites and the Early Solar System (J. F. Kerridge and M. S. Matthews, eds.), 680-696. [3] Rambaldi E. R. and Wasson J. T. (1982) GCA, 46, 929-939. [4] Jones R. H. and Scott E. R. D. (1989) LPS XIX, 523-536. [5] Jones R. H. (1990) GCA, 54, 1785- 1802. [6] Snellenburg J. (1978) Ph.D. Thesis, State University of New York at Stony Brook. [7] Allen J. S. et al. (1980) GCA, 44, 1161-1176. [8] DeHart J. M. (1989) Ph.D. Thesis, University of Arkansas. [9] Matsunami S. et al (1992) GCA (in press). Fig. 1, which appears here in the hard copy, shows chondrule melt compositions (data from [4,6,8]). Fig. 2, which appears here in the hard copy, shows rim thickness against chondrule diameter with regression lines.

  10. Amoeboid Olivine Aggregates (AOAs) in the Efremovka (CVR) Chondrite: First SIMS Trace-Element Results

    NASA Astrophysics Data System (ADS)

    Ruzicka, A.; Floss, C.; Hutson, M.

    2008-03-01

    SIMS trace-element results for six inclusions in Efremovka imply that condensation was important in the formation of AOAs and that precursor compositions or mode of origin were different for olivine in AOAs and in chondrules.

  11. Three Unusual Chondrules in the Bovedy (L3) Chondrite

    NASA Astrophysics Data System (ADS)

    Hill, H. G. M.

    1993-07-01

    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.

  12. Terminal particle from Stardust track 130: Probable Al-rich chondrule fragment from comet Wild 2

    NASA Astrophysics Data System (ADS)

    Joswiak, D. J.; Nakashima, D.; Brownlee, D. E.; Matrajt, G.; Ushikubo, T.; Kita, N. T.; Messenger, S.; Ito, M.

    2014-11-01

    A 4 × 6 μm terminal particle from Stardust track 130, named Bidi, is composed of a refractory assemblage of Fo97 olivine, Al- and Ti-bearing clinopyroxene and anorthite feldspar (An97). Mineralogically, Bidi resembles a number of components found in primitive chondritic meteorites including Al-rich chondrules, plagioclase-bearing type I ferromagnesian chondrules and amoeboid olivine aggregates (AOAs). Measured widths of augite/pigeonite lamellae in the clinopyroxene indicate fast cooling rates suggesting that Bidi is more likely to be a chondrule fragment than an AOA. Bulk element concentrations, including an Al2O3 content of 10.2 wt%, further suggests that Bidi is more akin to Al-rich rather than ferromagnesian chondrules. This is supported by high anorthite content of the plagioclase feldspar, overall bulk composition and petrogenetic analysis using a cosmochemical Al2O3-Ca2SiO4-Mg2SiO4 phase diagram. Measured minor element abundances of individual minerals in Bidi generally support an Al-rich chondrule origin but are not definitive between any of the object types. Oxygen isotope ratios obtained from olivine (+minor high-Ca pyroxene)fall between the TF and CCAM lines and overlap similar minerals from chondrules in primitive chondrites but are generally distinct from pristine AOA minerals. Oxygen isotope ratios are similar to some minerals from both Al-rich and type I ferromagnesian chondrules in unequilibrated carbonaceous, enstatite and ordinary chondrites. Although no single piece of evidence uniquely identifies Bidi as a particular object type, the preponderance of data, including mineral assemblage, bulk composition, mineral chemistry, inferred cooling rates and oxygen isotope ratios, suggest that Bidi is more closely matched to Al-rich chondrules than AOAs or plagioclase-bearing type I ferromagnesian chondrules and likely originated in a chondrule-forming region in the inner solar system.

  13. Cosmogenic neon in grains separated from individual chondrules: Evidence of precompaction exposure in chondrules

    NASA Astrophysics Data System (ADS)

    Das, J. P.; Goswami, J. N.; Pravdivtseva, O. V.; Meshik, A. P.; Hohenberg, C. M.

    2012-11-01

    Neon was measured in 39 individual olivine (or olivine-rich) grains separated from individual chondrules from Dhajala, Bjurböle, Chainpur, Murchison, and Parsa chondrites with spallation-produced 21Ne the result of interaction of energetic particle irradiation. The apparent 21Ne cosmic ray exposure (CRE) ages of most grains are similar to those of the matrix with the exception of three grains from Dhajala and single grains from Bjurböle and Chainpur, which show excesses, reflecting exposure to energetic particles prior to final compaction of the object. Among these five grains, one from chondrule BJ2A5 of Bjurböle shows an apparent excess exposure age of approximately 20 Ma and the other four from Dhajala and Chainpur have apparent excesses, described as an "age," from 2 to 17 Ma. The precompaction irradiation effects of grains from chondrules do not appear to be different from the effects seen in olivine grains extracted from the matrix of CM chondrites. As was the case for the matrix grains, there appears to be insufficient time for this precompaction irradiation by the contemporary particle sources. The apparent variations within single chondrules appear to constrain precompaction irradiation effects to irradiation by lower energy solar particles, rather than galactic cosmic rays, supporting the conclusion derived from the precompaction irradiation effects in CM matrix grains, but for totally different reasons. This observation is consistent with Chandra X-Ray Observatory data for young low-mass stars, which suggest that our own Sun may have been 105 times more active in an early naked T-Tauri phase (Feigelson et al. 2002).

  14. Oxygen-isotope compositions of chondrule phenocrysts and matrix grains in Kakangari K-grouplet chondrite: Implication to a chondrule-matrix genetic relationship

    NASA Astrophysics Data System (ADS)

    Nagashima, Kazuhide; Krot, Alexander N.; Huss, Gary R.

    2015-02-01

    To investigate a possible relationship between chondrules and matrix, we studied mineralogy, mineral chemistry, and in situ O-isotope compositions of chondrules, clastic matrix grains, and amoeboid olivine aggregates (AOAs) in the Kakangari K-grouplet chondrite. Most olivines and low-Ca pyroxenes in the Kakangari chondrules, matrix, and AOAs have similar magnesium-rich compositions, Fo?95-97 (?0.3-0.5 wt% MnO) and En?90-96, respectively. These rather uniform chemical compositions of the different chondritic components are likely due to partial Fe-Mg-Mn equilibration during thermal metamorphism experienced by the host meteorite. Oxygen-isotope compositions of olivine and low-Ca pyroxene grains in chondrules and matrix plot along a slope-1 line on a three O-isotope diagram and show a range from 16O-enriched composition similar to that of the Sun to 16O-depleted composition similar to the terrestrial O-isotope composition. Most olivines and low-Ca pyroxenes in chondrules are 16O-poor and plot on or close to the terrestrial mass-fractionation line (mean ?17O values 2 standard deviations: 0.0 0.8 and +0.2 0.9 for olivine and pyroxene, respectively), consistent with the previously reported compositions of bulk chondrules (?17O = -0.16 0.70). In addition to these 16O-poor grains, a coarse-grained igneous rim surrounding a porphyritic chondrule contains abundant 16O-rich relict olivines (?17O ? -24). Oxygen-isotope compositions of olivines and low-Ca pyroxenes in matrix show a bimodal distribution: 12 out of 13 olivine and 4 out of 17 pyroxene grains measured are similarly 16O-rich (?17O ? -23.5 2.9), others are similarly 16O-poor (?17O ? -0.1 1.7). Due to slow oxygen self-diffusion, olivines and low-Ca pyroxenes largely retained their original oxygen-isotope compositions. The nearly identical O-isotope compositions between the chondrule phenocrysts and the 16O-poor matrix grains suggest both chondrules and matrix of Kakangari sampled isotopically the same reservoirs. In addition, the presence of abundant 16O-rich grains in matrix and the chondrule igneous rim suggests both components acquired similar precursor inventories. These observations imply that chondrules and matrix in Kakangari are genetically related in the sense that material that formed matrix was one of the precursors of chondrules and chondrules and some fraction of matrix experienced the same thermal processing event. The 16O-enriched bulk matrix value compared to the bulk chondrules reported previously is likely due to presence of abundant 16O-rich grains in the Kakangari matrix.

  15. A RELICT Spinel Grain in an Allende Ferromagnesian Chondrule

    NASA Astrophysics Data System (ADS)

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

    1993-07-01

    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.

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

    PubMed

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

    1991-01-01

    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

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

    NASA Technical Reports Server (NTRS)

    Wasson, John T.; Rubin, Alan E.

    2003-01-01

    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.

  18. Chondrule thermal history from unequilibrated H chondrites: A transmission and analytical electron microscopy study

    NASA Astrophysics Data System (ADS)

    Ferraris, C.; Folco, L.; Mellini, M.

    2002-10-01

    Sixteen texturally different (porphyritic, barred, radial, cryptocrystalline) FeO-rich chondrules from the unequilibrated ordinary chondrites Brownfield, Frontier Mountain (FRO) 90003 and FRO 90032 were characterized by optical and scanning electron microscopy and then thoroughly studied by transmission and analytical electron microscopy. Nanotextural and nanochemical data indicate similar thermal evolution for chondrules of the same textural groups; minor, yet meaningful differences occur among the different groups. Olivine is the earliest phase formed and crystallizes between 1500 and 1400 deg C. Protoenstatite crystallizes at temperatures higher than 1350-1200 deg C; it later inverts to clinoenstatite in the 1250-1200 deg C range. Enstatite is surrounded by pigeonitic or (less frequently) augitic rims; the minimal crystallization temperature for the rims is 1000 C; high pigeonite later inverts to low pigeonite, between 935 and 845 deg C. The outer pigeonitic or augitic rims are constantly exsolved, producing sigmoidal augite or enstatite precipitates; sigmoidal precipitates record exsolution temperatures between 1000 and 640 deg C. Cooling rate (determined using the speedometer based upon ortho-clinoenstatite intergrowth) was in the order of 50-3000 deg C/h at the clinoenstatite-orthoenstatite transition temperature (close to 1250-1200 deg C), but decreased to 5-10 deg C/h or slower at the exsolution temperature (between 1000 and 650 deg C), thus revealing nonlinear cooling paths. Nanoscale observations indicate that the individual chondrules formed and cooled separately from 1500 deg down to at least 650 deg C. Accretion into chondritic parent body occurred at temperatures lower than 650 deg C.

  19. Carbon, CAIs and chondrules

    NASA Technical Reports Server (NTRS)

    Ash, R. D.; Russell, S. S.

    1994-01-01

    It has been shown that C is present in CAI's and chondrules. It can be distinguished from matrix C both by its thermal stability and isotopic composition, which implies that it was not introduced after parent body accretion. It is concluded that C must have been present in the chondrule and CAI precursor material. Therefore any models of chondrule and CAI formation and inferences drawn about solar system conditions during these events must take into account the consequences of the presence of C on inclusion chemistry, mineralogy, and oxidation state.

  20. Chondrule Crystallization Experiments

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    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.

  1. EH3 matrix mineralogy with major and trace element composition compared to chondrules

    NASA Astrophysics Data System (ADS)

    Lehner, S. W.; McDonough, W. F.; NéMeth, P.

    2014-12-01

    We investigated the matrix mineralogy in primitive EH3 chondrites Sahara 97072, ALH 84170, and LAR 06252 with transmission electron microscopy; measured the trace and major element compositions of Sahara 97072 matrix and ferromagnesian chondrules with laser-ablation, inductively coupled, plasma mass spectrometry (LA-ICPMS); and analyzed the bulk composition of Sahara 97072 with LA-ICPMS, solution ICPMS, and inductively coupled plasma atomic emission spectroscopy. The fine-grained matrix of EH3 chondrites is unlike that in other chondrite groups, consisting primarily of enstatite, cristobalite, troilite, and kamacite with a notable absence of olivine. Matrix and pyroxene-rich chondrule compositions differ from one another and are distinct from the bulk meteorite. Refractory lithophile elements are enriched by a factor of 1.5-3 in chondrules relative to matrix, whereas the matrix is enriched in moderately volatile elements. The compositional relation between the chondrules and matrix is reminiscent of the difference between EH3 pyroxene-rich chondrules and EH3 Si-rich, highly sulfidized chondrules. Similar refractory element ratios between the matrix and the pyroxene-rich chondrules suggest the fine-grained material primarily consists of the shattered, sulfidized remains of the formerly pyroxene-rich chondrules with the minor addition of metal clasts. The matrix, chondrule, and metal-sulfide nodule compositions are probably complementary, suggesting all the components of the EH3 chondrites came from the same nebular reservoir.

  2. Bulk Chondrule Compositions, Constraints for Chondrule Formation

    NASA Astrophysics Data System (ADS)

    Palme, H.; Hezel, D. C.

    2013-09-01

    Chondrules in Allende and Mokoia show a continuum in total Fe and roughly chondritic ratios of Fe, Ni, Co. The highly siderophile Ir is neither correlated with Ni nor with the lithophile refractory Sc. Some Ir came with refractory metal nuggets.

  3. Condensates from vapor made by impacts between metal-, silicate-rich bodies: Comparison with metal and chondrules in CB chondrites

    NASA Astrophysics Data System (ADS)

    Fedkin, Alexei V.; Grossman, Lawrence; Humayun, Munir; Simon, Steven B.; Campbell, Andrew J.

    2015-09-01

    The impact hypothesis for the origin of CB chondrites was tested by performing equilibrium condensation calculations in systems composed of vaporized mixtures of projectile and target materials. When one of the impacting bodies is composed of the metal from CR chondrites and the other is an H chondrite, good agreement can be found between calculated and observed compositions of unzoned metal grains in CB chondrites but the path of composition variation of the silicate condensate computed for the same conditions that reproduce the metal grain compositions does not pass through the measured compositions of barred olivine (BO) or cryptocrystalline (CC) chondrules in the CBs. The discrepancy between measured chondrule compositions and those of calculated silicates is not reduced when diogenite, eucrite or howardite compositions are substituted for H chondrite as the silicate-rich impacting body. If, however, a CR chondrite body is differentiated into core, a relatively CaO-, Al2O3-poor mantle and a CaO-, Al2O3-rich crust, and later accretes significant amounts of water, a collision between it and an identical body can produce the necessary chemical conditions for condensation of CB chondrules. If the resulting impact plume is spatially heterogeneous in its proportions of crust and mantle components, the composition paths calculated for silicate condensates at the same Ptot, Ni/H and Si/H ratios and water abundance that produce good matches to the unzoned metal grain compositions pass through the fields of BO and CC chondrules, especially if high-temperature condensates are fractionated in the case of the CCs. While equilibrium evaporation of an alloy containing solar proportions of siderophiles into a dense impact plume is an equally plausible hypothesis for explaining the compositions of the unzoned metal grains, equilibrium evaporation can explain CB chondrule compositions only if an implausibly large number of starting compositions is postulated. Kinetic models applied to co-condensing metal grains and silicate droplets in a region of the plume with very similar composition, but with high cooling rate and sharply declining Ptot during condensation, produce very good matches to the zoning profiles of Ir, Ni, Co and Cr concentrations and Fe and Ni isotopic compositions observed in the zoned metal grains in CB chondrites but produce very large positive δ56Fe in the cogenetic silicate, which are not found in the chondrules.

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

    SciTech Connect

    Ruzicka, A. )

    1990-06-01

    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.

  5. Chemistry, petrology and bulk oxygen isotope compositions of chondrules from the Mokoia CV3 carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Jones, R. H.; Schilk, A. J.

    2009-10-01

    We report bulk chemical compositions and physical properties for a suite of 94 objects, mostly chondrules, separated from the Mokoia CV3 ox carbonaceous chondrite. We also describe mineralogical and petrologic information for a selected subset of the same suite of chondrules. The data are used to examine the range of chondrule bulk compositions, and to investigate the relationships between chondrule mineralogy, texture and bulk compositions, as well as oxygen isotopic properties that we reported previously. Most of the chondrules show minimal metamorphism, corresponding to petrologic subtype <3.2. In general, elemental fractionations observed in chondrule bulk compositions are reflected in the compositions of constituent minerals. For chondrules, mean bulk compositions and compositional ranges are very similar for large (>2 mg) and small (<2 mg) size fractions. Two of the objects studied are described as matrix-rich clasts. These have similar bulk compositions to the chondrule mean, and are potential chondrule precursors. One of these clasts has a similar bulk oxygen isotopic composition to Mokoia chondrules, but the other has an anomalously high value of ? 17O (+3.60). Chondrules are diverse in bulk chemical composition, with factor of 10 variations in most major element abundances that cannot be attributed to secondary processes. The chondrules examined show evidence for extensive secondary oxidation, and possible sulfidization, as expected for an oxidized CV chondrite, but minimal aqueous alteration. Some of the bulk chondrule compositional variation might be the result of chemical (e.g. volatilization or condensation) or physical (e.g. metal loss) processes during chondrule formation. However, we suggest that it is mainly the result of significant variations in the assembly of particles that constituted chondrule precursors. Precursor material likely included a refractory component, possibly inherited from disaggregated CAIs, an FeO-poor ferromagnesian component such as olivine or pyroxene, an oxidized ferromagnesian component, and a metal component. Bulk oxygen isotope ratios of chondrules can be explained if refractory and ferromagnesian precursor materials initially shared similar oxygen isotopic compositions of ? 17O, ? 18O around -50, and then significant exchange occurred between the chondrule and surrounding 16O-poor gas during melting.

  6. Chondrules and the Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    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.

  7. Mass transfer of Fe during the serpentinization of olivine by SiO2 rich fluid at 300C, 500 bars: Perspectives from mineral dissolution/precipitation rates and Fe isotope systematics

    NASA Astrophysics Data System (ADS)

    Syverson, D. D.; Tutolo, B. M.; Borrok, D. M.; Seyfried, W. E., Jr.

    2014-12-01

    High temperature (~300C) hydrothermal alteration of peridotites can produce an alteration assemblage abundant in Fe-bearing serpentine and magnetite without the presence of brucite. This is particularly so in systems with SiO2-rich fluids derived from the hydration of orthopyroxene in basaltic intrusions and gabbros [1]. Few experimental studies have investigated the effects of aSiO2(aq) on the rate of olivine serpentinization and none that have examined the Fe isotopic composition of olivine hydrolysis products. Thus, this study addresses these problems by using flexible gold cell hydrothermal equipment to react olivine (Fo90) and talc with a NaCl-bearing fluid at 300 C and 500 bars for ~90 days; providing time-series solution chemistry data coupled with Fe isotope, magnetic susceptibility, and Mssbauer measurements of reactant olivine and the serpentinization product. Talc is used to elevate the aSiO2(aq)above the serpentine-brucite buffer, effectively preventing brucite formation and allowing only the formation of Fe-bearing serpentine and magnetite from olivine alteration. Initial time series solution chemistry data indicate that the net rate of the serpentinization of olivine and talc dissolution is such that the experimental system is poised between the serpentine-brucite and serpentine-talc stability fields, with little H2 generated by the oxidation of Fe2+ upon formation of Fe-serpentine and magnetite. However, as the talc Si-source becomes effectively titrated, the continued hydration of olivine decreases the aSiO2(aq) towards the serpentine-brucite stability field concurrent with an increasing rate of H2 generation. This chemical transition likely reflects an enhanced rate of magnetite formation upon a decrease in the relative stability of Fe-serpentine. Fe isotope data indicate a slight enrichment trend in ?56Fe versus Fe3+/?Fe of the altered mineral phases, magnetite > Fe-serpentine > olivine, although the observed inter-mineral fractionations are small, <0.1 . These experimental data are consistent with observations of natural Fe isotope data derived from hydrothermally altered peridotites [2] while providing requisite quantitative constraints to understand better their origin and evolution. [1] Bach et al., 2006 (GRL) [2] Craddock et al., 2014 (EPSL)

  8. Thermoluminescence and compositional zoning in the mesostasis of a Semarkona group A1 chondrule and new insights into the chondrule-forming process

    NASA Astrophysics Data System (ADS)

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

    1993-05-01

    A large, group A1, porphyritic olivine chondrule in the Semarkona chondrite with induced thermoluminescence (TL) and compositional zoning in its mesostasis has been discovered. The chondrule has Ca-rich and Fe-poor olivine and its mesostasis is highly anorthite-normative. The chondrule shows an intense induced TL peak at about 300 C with a half-width of about 180 C. The induced TL in the 40-440 C range increases monotonically by a factor of about 6 from center to rim, while SiO2, Na2O, and MnO increase by factors of about 1.1, about 3.6, and about 6, respectively. The spectrum of the induced TL over the 200-350 C range and the Mn-TL correlation suggest Mn-activated plagioclase is an important constituent of the refractory mesostases in group A1 chondrules. The zoning may reflect fractional crystallization, Soret diffusion, transport of volatiles into the chondrule by aqueous alteration, a zoned precursor, reduction of precursor dust aggregate, or recondensation of volatiles lost during chondrule formation.

  9. 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)

    Treiman, Allan H.; Goodrich, Cyrena Anne

    2001-01-01

    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.

  10. Evidence for primitive nebular components in chondrules from the Chainpur chondrite

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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.

  12. The formation and alteration of the Renazzo-like carbonaceous chondrites III: Toward understanding the genesis of ferromagnesian chondrules

    NASA Astrophysics Data System (ADS)

    Schrader, Devin L.; Connolly, Harold C.; Lauretta, Dante S.; Zega, Thomas J.; Davidson, Jemma; Domanik, Kenneth J.

    2015-01-01

    To better understand the formation conditions of ferromagnesian chondrules from the Renazzo-like carbonaceous (CR) chondrites, a systematic study of 210 chondrules from 15 CR chondrites was conducted. The texture and composition of silicate and opaque minerals from each observed FeO-rich (type II) chondrule, and a representative number of FeO-poor (type I) chondrules, were studied to build a substantial and self-consistent data set. The average abundances and standard deviations of Cr2O3 in FeO-rich olivine phenocrysts are consistent with previous work that the CR chondrites are among the least thermally altered samples from the early solar system. Type II chondrules from the CR chondrites formed under highly variable conditions (e.g., precursor composition, redox conditions, cooling rate), with each chondrule recording a distinct igneous history. The opaque minerals within type II chondrules are consistent with formation during chondrule melting and cooling, starting as S- and Ni-rich liquids at 988-1350 °C, then cooling to form monosulfide solid solution (mss) that crystallized around olivine/pyroxene phenocrysts. During cooling, Fe,Ni-metal crystallized from the S- and Ni-rich liquid, and upon further cooling mss decomposed into pentlandite and pyrrhotite, with pentlandite exsolving from mss at 400-600 °C. The composition, texture, and inferred formation temperature of pentlandite within chondrules studied here is inconsistent with formation via aqueous alteration. However, some opaque minerals (Fe,Ni-metal versus magnetite and panethite) present in type II chondrules are a proxy for the degree of whole-rock aqueous alteration. The texture and composition of sulfide-bearing opaque minerals in Graves Nunataks 06100 and Grosvenor Mountains 03116 suggest that they are the most thermally altered CR chondrites.

  13. Origin of plagioclase-olivine inclusions in carbonaceous chondrites

    SciTech Connect

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

    1991-02-01

    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.

  14. Chondrule transport in protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Goldberg, Aaron Z.; Owen, James E.; Jacquet, Emmanuel

    2015-10-01

    Chondrule formation remains one of the most elusive early Solar system events. Here, we take the novel approach of employing numerical simulations to investigate chondrule origin beyond purely cosmochemical methods. We model the transport of generically produced chondrules and dust in a 1D viscous protoplanetary disc model in order to constrain the chondrule formation events. For a single formation event we are able to match analytical predictions of the memory they retain of each other (complementarity), finding that a large mass accretion rate (≳10-7 M⊙ yr-1) allows for delays on the order of the disc's viscous time-scale between chondrule formation and chondrite accretion. Further, we find older discs to be severely diminished of chondrules, with accretion rates ≲10-9 M⊙ yr-1 for nominal parameters. We then characterize the distribution of chondrule origins in both space and time, as functions of disc parameters and chondrule formation rates, in runs with continuous chondrule formation and both static and evolving discs. Our data suggest that these can account for the observed diversity between distinct chondrite classes, if some diversity in accretion time is allowed for.

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

    NASA Technical Reports Server (NTRS)

    Jones, Rhian H.; Rubie, David C.

    1991-01-01

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

  16. Sibling and Independent Compound Chondrules

    NASA Astrophysics Data System (ADS)

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

    1993-07-01

    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.

  17. Genetic relationship between Na-rich chondrules and Ca,Al-rich inclusions? - Formation of Na-rich chondrules by melting of refractory and volatile precursors in the solar nebula

    NASA Astrophysics Data System (ADS)

    Ebert, Samuel; Bischoff, Addi

    2016-03-01

    Al-rich objects (Ca,Al-rich inclusions (CAIs), Al-rich chondrules, Al-rich fragments) occur in all chondrite classes. These objects can be centimeter-sized in CV3 carbonaceous chondrites, but they are generally much smaller in other chondrite groups and classes. Within the ordinary chondrites, most Al-rich objects are chondrules that vary from Ca- to Na-rich. Here, we have investigated the mineralogy and major element chemistry of 32 Na-rich chondrules and 3 Na-rich fragments from 15 different chondrites. Most objects (chondrules and chondrule fragments) are from ordinary chondrites (petrologic types 3.2-3.8), but two of the chondrules are from two CO3 chondrites, and three of the chondrules are from one Rumuruti (R)-chondrite. We found that these Na-rich objects have bulk Na2O-concentrations between 4.3 and 15.2 wt%. Texturally, they typically consist of euhedral to subhedral (often skeletal) mafic minerals (olivine and pyroxenes) embedded within a nepheline-normative, glassy mesostasis, which is brownish in transmitted light. In addition, some chondrules contain euhedral to subhedral spinel. Bulk chondrule compositions show group II, group III, and ultrarefractory rare earth element (REE) patterns similar to those found in CAIs. These results clearly demonstrate that the Na-rich chondrules must have been formed by melting of precursors containing an (ultra-)refractory element-rich component and Na-rich constituents. The Na-rich chondrules showed Sm and Eu anomalies, indicating that they must have formed at low oxygen fugacities. Based on the chemical composition of the Na-rich objects, we can rule out that they were formed as a result of planetary formation due to metasomatic processes or processes related to collisions between molten planetesimals.

  18. Iodine-xenon, chemical, and petrographie studies of Semarkona chondrules: Evidence for the timing of aqueous alteration

    USGS Publications Warehouse

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

    1991-01-01

    We have performed INAA, petrographie, and noble gas analyses on seventeen chondrules from the Semarkona meteorite (LL3.0) primarily to study the relationship of the I-Xe system to other measured properties. We observe a range of ???10 Ma in apparent I-Xe ages. The three latest apparent ages fall in a cluster, suggesting the possibility of a common event. The initial 129I/127I ratio (R0) is apparently related to chondrule type and/or mineralogy, with nonporphyritic and pyroxene-rich chondrules showing evidence for lower R0'S (later apparent I-Xe ages) than porphyritic and olivine-rich chondrules. In addition, chondrules with sulfides on or near the surface have lower R0S than other chondrules. The 129Xe/132Xe ratio in the trapped Xe component anticorrelates with R0, consistent with evolution of a chronometer in a closed system or in multiple similar systems. On the basis of these correlations, we conclude that the variations in R0 represent variations in ages, and that later event(s), possibly aqueous alteration, preferentially affected chondrules with nonporphyritic textures and/or sulfide-rich exteriors about 10 Ma after the formation of the chondrules. ?? 1991.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    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.

  20. Producing chondrules by recycling and volatile loss

    NASA Technical Reports Server (NTRS)

    Alexander, C. M. O.

    1994-01-01

    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.

  1. Turbulence, Chondrules, and Planetesimals

    NASA Technical Reports Server (NTRS)

    Cuzzi, Jeffrey; Hogan, Robert C.; Dobrovolskis, Anthony R.; Paque, Julie M.

    1998-01-01

    It has been shown both numerically and experimentally that 3-D turbulence concentrates aerodynamically size-selected particles by orders of magnitude. In a previous review chapter, in "Chondrules and the protoplanetary disk" we illustrated the initial predictions of Turbulent Concentration (TC) as applied to the solar nebula. We predicted the particle size which will be most effectively concentrated by turbulence; it is the particle which has a gas drag stopping time equal to the overturn time of the smallest (Kolmogorov scale) eddy. The primary uncertainty is the level of nebula turbulence, or Reynolds number Re, which can be expressed in terms of the standard nebula eddy viscosity parameter alpha = Re(nu)(sub m)/cH, where nu(sub m) is molecular viscosity, c is sound speed, and H is vertical scale height. Several studies, and observed lifetimes of circumstellar disks, have suggested that the level of nebula turbulence can be described by alpha = 10(exp -2) - 10(exp -4). There is some recent concern about how energy is provided to maintain this turbulence, but the issue remains open. We adopt a canonical minimum mass nebula with a range of alpha > 0. We originally showed that chondrule-sized particles are selected for concentration in the terrestrial planet region if alpha = 10(exp -3) - 10(exp -4). In addition, Paque and Cuzzi found that the size distribution of chondrules is an excellent match for theoretical predictions. One then asks by what concentration factor C these particles can be concentrated; our early numerical results indicated an increase of C with alpha, and were supported by simple scaling arguments, but the extrapolation range was quite large and the predictions (C 10(exp 5) - 10(exp 6) not unlikely) uncertain. The work presented here, which makes use of our recent demonstration that the particle density field is a multifractal with flow-independent properties provides a far more secure ground for such predictions. We also indicate how fine-grained dust rims on chondrules might enter into constraining the situation.

  2. Chondrules in CK carbonaceous chondrites and thermal history of the CV-CK parent body

    NASA Astrophysics Data System (ADS)

    Chaumard, NoëL.; Devouard, Bertrand

    2016-01-01

    CK chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6. It is commonly reported than ~15 vol% of CK4-6 samples are composed of chondrules. The modal abundance of chondrules estimated here for 18 CK3-6 (including five CK3s) ranges from zero (totally recrystallized) to 50.5%. Although almost all chemically re-equilibrated with the host matrix, we recognized in CK3s and Tanezrouft (Tnz) 057 (CK4) up to 85% of chondrules as former type I chondrules. Mean diameters of chondrules range from 0.22 to 1.05 mm for Karoonda (CK4) and Tnz 057 (CK4), respectively. Up to ~60% of chondrules in CK3-4 are surrounded by igneous rims (from ~20 μm to 2 mm width). Zoned olivines were found in unequilibrated chondrules from DaG 431 (CK3-an), NWA 4724 (CK3.8), NWA 4423 (CK3.9), and Tnz 057 (CK4). We modeled Fe/Mg interdiffusion profiles measured in zoned olivines to evaluate the peak metamorphic temperatures and time scales of the CK parent body metamorphism, and proposed a two-stage diffusion process in order to account for the position of inflection points situated within chondrules. Time scales inferred from Fe/Mg interdiffusion in olivine from unequilibrated chondrules are on the order of tens to a hundred thousand years (from 50 to 70,000 years for peak metamorphic temperatures of 1140 and 920 K, respectively). These durations are longer than what is commonly accepted for shock metamorphism and shorter than what is required for nuclide decay. Using the concept of a continuous CV-CK metamorphic series, which is reinforced by this study, we estimated peak metamorphic temperatures <850 K for CV, 850-920 K for CK3, and 920-1140 K for CK4-6 chondrites considering a duration of 70,000 years.

  3. Chondrules in CK carbonaceous chondrites and thermal history of the CV-CK parent body

    NASA Astrophysics Data System (ADS)

    Chaumard, NoëL.; Devouard, Bertrand

    2016-03-01

    CK chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6. It is commonly reported than ~15 vol% of CK4-6 samples are composed of chondrules. The modal abundance of chondrules estimated here for 18 CK3-6 (including five CK3s) ranges from zero (totally recrystallized) to 50.5%. Although almost all chemically re-equilibrated with the host matrix, we recognized in CK3s and Tanezrouft (Tnz) 057 (CK4) up to 85% of chondrules as former type I chondrules. Mean diameters of chondrules range from 0.22 to 1.05 mm for Karoonda (CK4) and Tnz 057 (CK4), respectively. Up to ~60% of chondrules in CK3-4 are surrounded by igneous rims (from ~20 μm to 2 mm width). Zoned olivines were found in unequilibrated chondrules from DaG 431 (CK3-an), NWA 4724 (CK3.8), NWA 4423 (CK3.9), and Tnz 057 (CK4). We modeled Fe/Mg interdiffusion profiles measured in zoned olivines to evaluate the peak metamorphic temperatures and time scales of the CK parent body metamorphism, and proposed a two-stage diffusion process in order to account for the position of inflection points situated within chondrules. Time scales inferred from Fe/Mg interdiffusion in olivine from unequilibrated chondrules are on the order of tens to a hundred thousand years (from 50 to 70,000 years for peak metamorphic temperatures of 1140 and 920 K, respectively). These durations are longer than what is commonly accepted for shock metamorphism and shorter than what is required for nuclide decay. Using the concept of a continuous CV-CK metamorphic series, which is reinforced by this study, we estimated peak metamorphic temperatures <850 K for CV, 850-920 K for CK3, and 920-1140 K for CK4-6 chondrites considering a duration of 70,000 years.

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

    NASA Technical Reports Server (NTRS)

    Wasson, John T.; Rubin, Alan E.

    2006-01-01

    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.

  5. Indicators of parent-body processes: Hydrated chondrules and fine-grained rims in the Mokoia CV3 carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Tomeoka, Kazushige; Ohnishi, Ichiro

    2010-08-01

    A petrographic and electron microscopic study of the Mokoia CV3 carbonaceous chondrite shows that all of the chondrules and inclusions (>400 ?m in diameter) and most of their fine-grained rims studied (referred to as chondrules/rims) contain various amounts of hydrous phyllosilicates (mostly saponite) formed by aqueous alteration of anhydrous silicates. The rims mainly consist of fine-grained olivine and saponite in varying proportions and contain crosscutting veins of Fe-rich olivine. The boundaries between the chondrules and their rims are irregular and show abundant evidence of aqueous alteration interactions between them. In contrast, the host matrix contains very minor amounts of saponite and shows no evidence of such extensive aqueous alteration. The boundaries between the chondrules/rims and the matrix are sharp and show no traces of the matrix having been involved in the alteration of the chondrules/rims. These observations indicate that the aqueous alteration in the chondrules/rims did not occur in the present setting. We suggest that the chondrules/rims are actually clasts transported from a location on the meteorite parent body different from where the Mokoia meteorite was from. The aqueous alteration of the chondrules/rims probably occurred there. The veins in the rims were originally fractures produced in an interchondrule matrix by impacts; these were later filled by Fe-rich olivine during aqueous activity. This location was then involved in impact brecciation, and individual chondrules were ejected as clasts with remnants of the matrix surrounding them. During the continuing brecciation, those chondrule/rim clasts were transported, mixed with anhydrous matrix grains, and finally lithified to the present meteorite. Therefore, the rims are fragmented remnants of a former matrix. Textures characterized by fine-grained rims surrounding chondrules in chondrites have been widely thought to have formed in the solar nebula before they accreted into their parent bodies. However, our results suggest that some textures may not be explained by such an accretionary model; instead, the multi-stage parent-body process modeled for the Mokoia rim formation may be a more plausible explanation.

  6. Strain Measurements of Chondrules and Refraction Inclusion in Allende

    NASA Technical Reports Server (NTRS)

    Tait, Alastair W.; Fisher, Kent R.; Simon, Justin I.

    2013-01-01

    This study uses traditional strain measurement techniques, combined with X-ray computerized tomography (CT), to evaluate petrographic evidence in the Allende CV3 chondrite for preferred orientation and to measure strain in three dimensions. The existence of petrofabrics and lineations was first observed in carbonaceous meteorites in the 1960's. Yet, fifty years later only a few studies have reported that meteorites record such features. Impacts are often cited as the mechanism for this feature, although plastic deformation from overburden and nebular imbrication have also been proposed. Previous work conducted on the Leoville CV3 and the Parnallee LL3 chondrites, exhibited a minimum uniaxial shortening of 33% and 21%, respectively. Petrofabrics in Allende CV3 have been looked at before; previous workers using Electron Back Scatter Diffraction (EBSD) found a major-axis alignment of olivine inside dark inclusions and an "augen"-like preferred orientation of olivine grains around more competent chondrules

  7. Little Chondrules and Giant Impacts

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2005-10-01

    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.

  8. The effect of Na vapor on the Na content of chondrules

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Sugiura, N.; Miyazaki, A.

    2006-05-01

    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.

  10. Conference on Chondrules and Their Origins

    NASA Technical Reports Server (NTRS)

    Hrametz, K.

    1983-01-01

    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.

  11. Constraints on chondrule agglomeration from fine-grained chondrule rims

    NASA Technical Reports Server (NTRS)

    Metzler, K.; Bischoff, A.

    1994-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Johnson, M. C.

    1986-01-01

    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.

  13. RELICT Olivines in Micrometeorites from Greenland and Antarctica

    NASA Astrophysics Data System (ADS)

    Beckerling, W.; Klock, W.; Bischoff, A.

    1993-07-01

    Previously, [1] studied the bulk chemistry and texture of 223 micrometeorites from Greenland (size: 100-200 micrometers): 82% spherical, 6% porous, and 12% monomineralic particles or particles with unique textures and from Antarctica (size: 50-100 micrometers): 24% spheres, 62% porous, and 14% particles with unique textures. In order to obtain information about the origin of micrometeorites we have studied minerals within these particles that escaped melting during atmospheric heating. Relict olivine grains occur in 27 spheres, 3 porous particles, and 11 particles with unique textures. Relict olivines (mostly > 5 micrometers in apparent size) can be distinguished from secondary crystallized (subsequent to atmospheric melting) olivines by their grain size, morphology, composition, and/or the presence of Fe/Ni-metal inclusions in olivine. Previously, [2] studied 26 Mg-rich olivines from Antarctic micrometeorites and [3] investigated about 70 olivines in micrometeorites from Antarctica and Greenland. Within the 41 micrometeorites containing such grains, 98 relict olivines were analyzed by electron microprobe, representing a much wider range of compositions than reported by [2]. In most micrometeorites, only one or two relict olivines occur and were large enough to be analyzed. In some particles, however the Fa-contents of several relict olivines were obtained (Fig. 1). Relict olivines with Fa-contents below 5.2 mol% Fe are abundant (Fig. 1). One forsterite within a porous particle is manganese- enriched and similar in composition to LIME olivines known from IDPs and primitive meteorites [4]. Comparing olivines from chondrites with those in micrometeorites, Fa-poor olivines occur in Type I chondrules from carbonaceous chondrites [5] and as isolated olivines in the matrix of C2, C3, and unequilibrated ordinary chondrites [2]. Between Fa(sub)5.2 and Fa(sub)~12 a gap exists in the distribution of the Fa-contents (Fig. 1). Relict olivines, however, with about 12 and 30 mol% Fa occur. These Fa- contents are similar to those of equilibrated H, L, and LL chondrites and may indicate that many particles are related to ordinary chondrites. In addition, several other micrometeorites contain olivines with Fa-contents exceeding those of olivines in ordinary chondrites. Considering chondrites as potential material of their origin, they may be related to matrix olivines in Type III carbonaceous chondrites and to olivines in Type II chondrules [5]. In six micrometeorites relict olivines with highly variable compositions were analyzed, indicating that the precursor was unequilibrated prior to thermal processing during atmospheric entry. Comparing all data, it appears that the larger-sized particles from Greenland may contain a slightly higher abundance of forsteritic relict olivines than the small particles from Antarctica. However, we cannot rule out that this observation is a result of insufficient data. References: [1] Beckerling W. et al. (1992) Meteoritics, 27, 200- 201. [2] Steele I. M. (1992) GCA, 56, 2923-2929. [3] Christophe Michel-Levy M. and Bourot-Denise M.(1992) Meteoritics, 27, 73-80. [4] Klock W. et al. (1989) Nature, 339, 126-128. [5] McSween H. Y. (1977) GCA, 41, 477-491.

  14. Correlations and zoning patterns of phosphorus and chromium in olivine from H chondrites and the LL chondrite Semarkona

    NASA Astrophysics Data System (ADS)

    McCanta, M. C.; Beckett, J. R.; Stolper, E. M.

    2016-02-01

    Phosphorus zoning is observed in olivines in high-FeO (type IIA) chondrules in H chondrites over the entire range of petrologic grades: H3.1-H6. Features in P concentrations such as oscillatory and sector zoning, and high P cores are present in olivines that are otherwise unzoned in the divalent cations. Aluminum concentrations are low and not significantly associated with P zoning in chondrule olivines. In highly unequilibrated H chondrites, phosphorus zoning is generally positively correlated with Cr. Atomic Cr:P in olivine is roughly 1:1 (3:1 for one zone in one olivine in RC 075), consistent with Cr3+ charge-balancing P5+ substituting for Si4+. Normal igneous zonation involving the dominant chrome species Cr2+ was observed only in the LL3.0 chondrite Semarkona. In more equilibrated chondrites (H3.5-H3.8), Cr spatially correlated with P is occasionally observed but it is diffuse relative to the P zones. In H4-H6 chondrites, P-correlated Cr is absent. One signature of higher metamorphic grades (≥H3.8) is the presence of near matrix olivines that are devoid of P oscillatory zoning. The restriction to relatively high metamorphic grade and to grains near the chondrule-matrix interface suggests that this is a response to metasomatic processes. We also observed P-enriched halos near the chondrule-matrix interface in H3.3-H3.8 chondrites, likely reflecting the loss of P and Ca from mesostasis and precipitation of Ca phosphate near the chondrule surface. These halos are absent in equilibrated chondrites due to coarsening of the phosphate and in unequilibrated chondrites due to low degrees of metasomatism. Olivines in type IA chondrules show none of the P-zoning ubiquitous in type IIA chondrules or terrestrial igneous olivines, likely reflecting sequestration of P in reduced form within metallic alloys and sulfides during melting of type IA chondrules.

  15. Correlations and zoning patterns of phosphorus and chromium in olivine from H chondrites and the LL chondrite Semarkona

    NASA Astrophysics Data System (ADS)

    McCanta, M. C.; Beckett, J. R.; Stolper, E. M.

    2016-03-01

    Phosphorus zoning is observed in olivines in high-FeO (type IIA) chondrules in H chondrites over the entire range of petrologic grades: H3.1-H6. Features in P concentrations such as oscillatory and sector zoning, and high P cores are present in olivines that are otherwise unzoned in the divalent cations. Aluminum concentrations are low and not significantly associated with P zoning in chondrule olivines. In highly unequilibrated H chondrites, phosphorus zoning is generally positively correlated with Cr. Atomic Cr:P in olivine is roughly 1:1 (3:1 for one zone in one olivine in RC 075), consistent with Cr3+ charge-balancing P5+ substituting for Si4+. Normal igneous zonation involving the dominant chrome species Cr2+ was observed only in the LL3.0 chondrite Semarkona. In more equilibrated chondrites (H3.5-H3.8), Cr spatially correlated with P is occasionally observed but it is diffuse relative to the P zones. In H4-H6 chondrites, P-correlated Cr is absent. One signature of higher metamorphic grades (≥H3.8) is the presence of near matrix olivines that are devoid of P oscillatory zoning. The restriction to relatively high metamorphic grade and to grains near the chondrule-matrix interface suggests that this is a response to metasomatic processes. We also observed P-enriched halos near the chondrule-matrix interface in H3.3-H3.8 chondrites, likely reflecting the loss of P and Ca from mesostasis and precipitation of Ca phosphate near the chondrule surface. These halos are absent in equilibrated chondrites due to coarsening of the phosphate and in unequilibrated chondrites due to low degrees of metasomatism. Olivines in type IA chondrules show none of the P-zoning ubiquitous in type IIA chondrules or terrestrial igneous olivines, likely reflecting sequestration of P in reduced form within metallic alloys and sulfides during melting of type IA chondrules.

  16. Mineralogy and petrology of chondrules and inclusions in the Mokoia CV3 chondrite

    NASA Technical Reports Server (NTRS)

    Cohen, R. E.; Kornacki, A. S.; Wood, J. A.

    1983-01-01

    The inclusions and chondrules of the Mokoia CV3 chondrite are studied systematically and compared with those in the Allende meteorite. Five polished thin sections of Mokoia were examined by optical microscopy, backscattered scanning electron microscopy, and electronprobe microanalysis, and objects greater than about 100 microns in apparent diameter were measured and classified petrographically. Three major types of olivine chondrules are distinguished: igneous chondrules, which evidently crystallized from droplets of silicate melt; recrystallized chondrules, apparently metamorphosed at relatively high temperatures; and accretional aggregates, which are probably fragments of igneous chondrules. Refractory inclusions in Mokoia are generally similar to those found in Allende, although Mokoia inclusions include phyllosilicates rather than feldspathoids and melilite-rich Ca, Al-rich inclusions (CAIs) are more abundant in Allende. The small, fine-grained CAIs, which are more abundant than coarse-grained CAIs in both meteorites, are observed to represent aggregates of three distinct constituents: concentric objects, chaotic material and inclusion matrix. It is concluded that most of the CAIs probably formed during metamorphism, partial melting, and incomplete distillation of primitive dust aggregates heated in the solar nebula.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    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.

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

    SciTech Connect

    Olsen, Mia B.; Schiller, Martin; Krot, Alexander N.; Bizzarro, Martin

    2013-10-10

    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 (μ{sup 25}Mg), indicating that the correlated variability was imparted by a volatility-controlled process (evaporation/condensation). The mass-independent {sup 26}Mg composition (μ{sup 26}Mg*) of chondrules is consistent with single stage formation from an initially homogeneous magnesium reservoir if the observed μ{sup 25}Mg variability was generated by non-ideal Rayleigh-type evaporative fractionation characterized by a β 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 μ{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.

  19. Amoeboid olivine aggregates (AOAs) in the Efremovka, Leoville and Vigarano (CV3) chondrites: A record of condensate evolution in the solar nebula

    NASA Astrophysics Data System (ADS)

    Ruzicka, Alex; Floss, Christine; Hutson, Melinda

    2012-02-01

    Amoeboid olivine aggregates (AOAs) in the Efremovka, Leoville, and Vigarano CV3 chondrites were studied using petrographic and microanalytical techniques to evaluate the origins of these inclusions and their relationships to other chondrite components. Our data support the idea that the inclusions formed by dust growth in the solar nebula as condensates and that they preserve a record of mineralogical and chemical evolution. Spinel-rich nodules and ribbons in AOAs often show Group II trace element patterns and formed either by fractional condensation or by condensation following partial vaporization. The dominant olivine component in AOAs can be explained as a condensate produced in the same way, but with fractionation occurring at a lower temperature. Other spinel-rich material in AOAs appears to be a vaporization residue. Ca-rich pyroxene + anorthite patches in AOAs show chemical signatures similar to those observed for spinel- or melilite-bearing regions but with lower refractory element and higher Mg and Si contents, supporting the idea that the patches formed by reaction between CAI-like material and Mg-Si-rich gas. Different trace element patterns (Group II and non-Group II refractory) are sometimes found for Al-rich regions (Ca-pyroxene + anorthite, or melilite-bearing) in a given AOA, suggesting that AOAs agglomerated from materials that formed under different conditions and that they did not subsequently homogenize. AOAs appear to have originated in a system with near-canonical solar composition and a low pressure gas (˜10-6-10-4 bar) over a range of temperatures (mainly ˜1200-1384 K) under somewhat non-equilibrium conditions. Relative to predicted equilibrium condensates, most AOAs show an apparent paucity of metal, possibly reflecting differential, density-dependent sorting between olivine and metal grains during aggregate formation. Trace element data are consistent with a simple model involving melting and igneous fractionation of AOA-like olivine to produce Type I chondrule olivine, but other data suggest that open-system melting of chondrules occurred in a different gaseous environment than that which produced AOAs.

  20. Impact-Induced Chondrule Deformation and Aqueous Alteration of CM2 Murchison

    NASA Technical Reports Server (NTRS)

    Hanna, R. D.; Zolensky, M.; Ketcham, R. A.; Behr, W. M.; Martinez, J. E.

    2014-01-01

    Deformed chondrules in CM2 Murchison have been found to define a prominent foliation [1,2] and lineation [3] in 3D using X-ray computed tomography (XCT). It has been hypothesized that chondrules in foliated chondrites deform by "squeezing" into surrounding pore space [4,5], a process that also likely removes primary porosity [6]. However, shock stage classification based on olivine extinction in Murchison is consistently low (S1-S2) [4-5,7] implying that significant intracrystalline plastic deformation of olivine has not occurred. One objective of our study is therefore to determine the microstructural mechanisms and phases that are accommodating the impact stress and resulting in relative displacements within the chondrules. Another question regarding impact deformation in Murchison is whether it facilitated aqueous alteration as has been proposed for the CMs which generally show a positive correlation between degree of alteration and petrofabric strength [7,2]. As pointed out by [2], CM Murchison represents a unique counterpoint to this correlation: it has a strong petrofabric but a relatively low degree of aqueous alteration. However, Murchison may not represent an inconsistency to the proposed causal relationship between impact and alteration, if it can be established that the incipient aqueous alteration post-dated chondrule deformation. Methods: Two thin sections from Murchison sample USNM 5487 were cut approximately perpendicular to the foliation and parallel to lineation determined by XCT [1,3] and one section was additionally polished for EBSD. Using a combination of optical petrography, SEM, EDS, and EBSD several chondrules were characterized in detail to: determine phases, find microstructures indicative of strain, document the geometric relationships between grain-scale microstructures and the foliation and lineation direction, and look for textural relationships of alteration minerals (tochilinite and Mg-Fe serpentine) that indicate timing of their formation relative to deformation event(s). Preliminary Results: Deformed chondrules are dominated by forsterite and clinoenstatite with lesser amounts of Fe-Mg serpentine, sulfides, and low calcium pyroxene. Olivine grains are commonly fractured but generally show sharp optical extinction. The pyroxene, in contrast, is not only fractured but also often displays undulose extinction. In addition, the clinoenstatite is frequently twinned but it is unclear whether the twins are the result of mechanical deformation or inversion from protoenstatite [8]. EBSD work is currently ongoing to determine if areas of higher crystallographic strain can be imaged and mapped, and to determine the pyroxene twin orientations. In regards to alteration, we have found evidence for post-deformation formation of tochilinite and Mg-Fe serpentine indicating that aqueous alteration has indeed post-dated the deformation of the chondrules.

  1. Olivines and olivine coronas in mesosiderites

    NASA Technical Reports Server (NTRS)

    Nehru, C. E.; Zucker, S. M.; Harlow, G. E.; Prinz, M.

    1980-01-01

    The paper presents a study of olivines and their surrounding coronas in mesosiderites texturally and compositionally using optical and microprobe methods. Olivine composition ranges from Fo(58-92) and shows no consistent pattern of distribution within and between mesosiderites; olivine 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 olivine orthopyroxenites. Fine-grained coronas surround olivine, 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.

  2. Effect of metamorphism on isolated olivine grains in CO3 chondrites

    NASA Technical Reports Server (NTRS)

    Jones, Rhian H.

    1993-01-01

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

  3. Chondrule destruction in nebular shocks

    SciTech Connect

    Jacquet, Emmanuel; Thompson, Christopher

    2014-12-10

    Chondrules are millimeter-sized silicate spherules ubiquitous in primitive meteorites, but whose origin remains mysterious. One of the main proposed mechanisms for producing them is melting of solids in shock waves in the gaseous protoplanetary disk. However, evidence is mounting that chondrule-forming regions were enriched in solids well above solar abundances. Given the high velocities involved in shock models, destructive collisions would be expected between differently sized grains after passage of the shock front as a result of differential drag. We investigate the probability and outcome of collisions of particles behind a one-dimensional shock using analytic methods as well as a full integration of the coupled mass, momentum, energy, and radiation equations. Destruction of protochondrules seems unavoidable for solid/gas ratios ε ≳ 0.1, and possibly even for solar abundances because of 'sandblasting' by finer dust. A flow with ε ≳ 10 requires much smaller shock velocities (∼2 versus 8 km s{sup –1}) in order to achieve chondrule-melting temperatures, and radiation trapping allows slow cooling of the shocked fragments. Initial destruction would still be extensive; although re-assembly of millimeter-sized particles would naturally occur by grain sticking afterward, the compositional heterogeneity of chondrules may be difficult to reproduce. We finally note that solids passing through small-scale bow shocks around few kilometer-sized planetesimals might experience partial melting and yet escape fragmentation.

  4. Magnetite-Pentlandite Chondrules in CK Chondrites

    NASA Astrophysics Data System (ADS)

    Rubin, A. E.

    1992-07-01

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

  5. Spatially resolved NRM of the Bishunpur LL3.1 chondrite measured by scanning SQUID microscopy: implications for chondrule formation

    NASA Astrophysics Data System (ADS)

    Church, N. S.; Andrade Lima, E.; Lappe, S. L.; Russell, S.; Weiss, B. P.; Harrison, R. J.

    2012-12-01

    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 chondrules 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 chondrules 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 chondrules 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 olivineiron nanoparticle-bearing silicate that constitutes a proportion of the chondrules of Bishunpuris an stable recorder over these timescales even at temperatures approaching the Curie temperature of iron. In bulk measurements, however, the paleointensity signal from the chondrules is masked by magnetic phases on chondrule 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 chondrules 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 chondrule rim, but the sensitivity of the scanning SQUID technique allows weak signals from individual chondrules 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 olivine 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 chondrule formation and the process of accretion in the solar nebula.

  6. A Regolith Origin of ``Pre-Irradiation" of Murchison Chondrules

    NASA Astrophysics Data System (ADS)

    Riebe, M.; Huber, L.; Wieler, R.; Metzler, K.; Maden, C.; Meier, M. M. M.; Busemann, H.

    2015-07-01

    Individual chondrules from a lithic fragment in Murchison all have similar CRE ages whereas chondrules from outside the fragment have variable ages, providing evidence that additional irradiation of chondrules occurred in the parent body regolith.

  7. Petrology, mineralogy, and oxygen isotope compositions of aluminum-rich chondrules from CV3 chondrites

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Hsu, Weibiao; Li, Xianhua; Li, Qiuli; Liu, Yu; Tang, Guoqiang

    2016-01-01

    Bulk major element composition, petrography, mineralogy, and oxygen isotope compositions of twenty Al-rich chondrules (ARCs) from five CV3 chondrites (Northwest Africa [NWA] 989, NWA 2086, NWA 2140, NWA 2697, NWA 3118) and the Ningqiang carbonaceous chondrite were studied and compared with those of ferromagnesian chondrules and refractory inclusions. Most ARCs are marginally Al-richer than ferromagnesian chondrules with bulk Al2O3 of 10-15 wt%. ARCs are texturally similar to ferromagnesian chondrules, composed primarily of olivine, pyroxene, plagioclase, spinel, Al-rich glass, and metallic phases. Minerals in ARCs have intermediate compositions. Low-Ca pyroxene (Fs0.6-8.8Wo0.7-9.3) has much higher Al2O3 and TiO2 contents (up to 12.5 and 2.3 wt%, respectively) than that in ferromagnesian chondrules. High-Ca pyroxene (Fs0.3-2.0Wo33-54) contains less Al2O3 and TiO2 than that in Ca,Al-rich inclusions (CAIs). Plagioclase (An77-99Ab1-23) is much more sodic than that in CAIs. Spinel is enriched in moderately volatile element Cr (up to 6.7 wt%) compared to that in CAIs. Al-rich enstatite coexists with anorthite and spinel in a glass-free chondrule, implying that the formation of Al-enstatite was not due to kinetic reasons but is likely due to the high Al2O3/CaO ratio (7.4) of the bulk chondrule. Three ARCs contain relict CAIs. Oxygen isotope compositions of ARCs are also intermediate between those of ferromagnesian chondrules and CAIs. They vary from -39.4‰ to 13.9‰ in δ18O and yield a best fit line (slope = 0.88) close to the carbonaceous chondrite anhydrous mineral (CCAM) line. Chondrules with 5-10 wt% bulk Al2O3 have a slightly more narrow range in δ18O (-32.5 to 5.9‰) along the CCAM line. Except for the ARCs with relict phases, however, most ARCs have oxygen isotope compositions (>-20‰ in δ18O) similar to those of typical ferromagnesian chondrules. ARCs are genetically related to both ferromagnesian chondrules and CAIs, but the relationship between ARCs and ferromagnesian chondrules is closer. Most ARCs were formed during flash heating and rapid cooling processes like normal chondrules, only from chemically evolved precursors. ARCs extremely enriched in Al and those with relict phases could have had a hybrid origin (Krot et al. 2002) which incorporated refractory inclusions as part of the precursors in addition to ferromagnesian materials. The occurrence of melilite in ARCs indicates that melilite-rich CAIs might be present in the precursor materials of ARCs. The absence of melilite in most ARCs is possibly due to high-temperature interactions between a chondrule melt and the solar nebula.

  8. Petrology, mineralogy, and oxygen isotope compositions of aluminum-rich chondrules from CV3 chondrites

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Hsu, Weibiao; Li, Xianhua; Li, Qiuli; Liu, Yu; Tang, Guoqiang

    2015-12-01

    Bulk major element composition, petrography, mineralogy, and oxygen isotope compositions of twenty Al-rich chondrules (ARCs) from five CV3 chondrites (Northwest Africa [NWA] 989, NWA 2086, NWA 2140, NWA 2697, NWA 3118) and the Ningqiang carbonaceous chondrite were studied and compared with those of ferromagnesian chondrules and refractory inclusions. Most ARCs are marginally Al-richer than ferromagnesian chondrules with bulk Al2O3 of 10-15 wt%. ARCs are texturally similar to ferromagnesian chondrules, composed primarily of olivine, pyroxene, plagioclase, spinel, Al-rich glass, and metallic phases. Minerals in ARCs have intermediate compositions. Low-Ca pyroxene (Fs0.6-8.8Wo0.7-9.3) has much higher Al2O3 and TiO2 contents (up to 12.5 and 2.3 wt%, respectively) than that in ferromagnesian chondrules. High-Ca pyroxene (Fs0.3-2.0Wo33-54) contains less Al2O3 and TiO2 than that in Ca,Al-rich inclusions (CAIs). Plagioclase (An77-99Ab1-23) is much more sodic than that in CAIs. Spinel is enriched in moderately volatile element Cr (up to 6.7 wt%) compared to that in CAIs. Al-rich enstatite coexists with anorthite and spinel in a glass-free chondrule, implying that the formation of Al-enstatite was not due to kinetic reasons but is likely due to the high Al2O3/CaO ratio (7.4) of the bulk chondrule. Three ARCs contain relict CAIs. Oxygen isotope compositions of ARCs are also intermediate between those of ferromagnesian chondrules and CAIs. They vary from -39.4 to 13.9 in ?18O and yield a best fit line (slope = 0.88) close to the carbonaceous chondrite anhydrous mineral (CCAM) line. Chondrules with 5-10 wt% bulk Al2O3 have a slightly more narrow range in ?18O (-32.5 to 5.9) along the CCAM line. Except for the ARCs with relict phases, however, most ARCs have oxygen isotope compositions (>-20 in ?18O) similar to those of typical ferromagnesian chondrules. ARCs are genetically related to both ferromagnesian chondrules and CAIs, but the relationship between ARCs and ferromagnesian chondrules is closer. Most ARCs were formed during flash heating and rapid cooling processes like normal chondrules, only from chemically evolved precursors. ARCs extremely enriched in Al and those with relict phases could have had a hybrid origin (Krot et al. 2002) which incorporated refractory inclusions as part of the precursors in addition to ferromagnesian materials. The occurrence of melilite in ARCs indicates that melilite-rich CAIs might be present in the precursor materials of ARCs. The absence of melilite in most ARCs is possibly due to high-temperature interactions between a chondrule melt and the solar nebula.

  9. Stardust to Planetesimals: A Chondrule Connection?

    NASA Technical Reports Server (NTRS)

    Paque, Julie; Bunch, Ted

    1997-01-01

    The unique nature of chondrules has been known for nearly two centuries. Modern techniques of analysis have shown that these millimeter sized silicate objects are among the oldest objects in our solar system. Researchers have devised textural and chemical classification systems for chondrules in an effort to determine their origins. It is agreed that most chondrules were molten at some point in their history, and experimental analogs suggest that the majority of chondrules formed from temperatures below 1600 C at cooling rates in the range of hundreds of degrees per hour. Although interstellar grains are present in chondrite matrices, their contribution as precursors to chondrule formation is unknown. Models for chondrule formation focus on the pre-planetary solar nebula conditions, although planetary impact models have had proponents.

  10. Conditions of formation of pyroxene excentroradial chondrules

    NASA Astrophysics Data System (ADS)

    Hewins, R. H.; Klein, L. C.; Fasano, B. V.

    Understanding the exact mechanism of origin of chondrules 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 chondrules. Chondrule-like spherules were formed in dynamic crystallization experiments, using gas-mixing facilities. It is found that textures in pyroxene-rich chondrules are well reproduced in the laboratory by cooling melts of chondrule composition from just above the liquidus. The range of pyroxene dendrite widths is slightly greater for natural chondrules 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.

  11. Spinel-bearing, Al-rich chondrules in two chondrite finds from Roosevelt County, New Mexico - Indicators of nebular and parent body processes

    NASA Technical Reports Server (NTRS)

    Mccoy, Timothy J.; Pun, Aurora; Keil, Klaus

    1991-01-01

    Two rare spinel-bearing Al-rich chondrules are identified in chondrite finds from Roosevelt County, New Mexico-RC 071 (L4) and RC 072 (L5). These chondrules 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 olivine and spinel during parent-body metamorphism can explain the asymmetric zoning of these elements. The bulk compositions of the chondrules suggest affinities with the Na-Al-Cr-rich chondrules, as would be expected from the abundance of Al-Cr-rich spinels. The most important factors are the temperature to which the molten chondrule was heated and the cooling rate during crystallization. These two chondrules cooled rapidly from near the liquidus, as indicated by the zoning, occurrence and sizes of spinels, radiating chondrule textures and localized chromite depletions.

  12. Mineralogy, Petrography, and Oxygen-Isotope Compositions of Carbonates and Olivines in Sutter"s Mill, CM Chondrite Breccia

    NASA Astrophysics Data System (ADS)

    Nagashima, K.; Yin, Q.-Z.; Krot, A. N.; Ogliore, R. C.

    2012-09-01

    Sutter's Mill sample we studied has two CM-like lithologies, CM2.0 and CM2.1. O-isotope compositions of chondrule and AOA olivines plot along CCAM line. Dolomites and calcites plot below TF line. Calcites show a spread in ?18O values, +13 to +39.

  13. I-Xe studies of individual chondrules: What can they tell us about chondrule formation?

    NASA Technical Reports Server (NTRS)

    Swindle, T. D.; Hohenberg, C. M.

    1994-01-01

    In the past 14 years, I-Xe studies have been performed on nearly 100 individual chondrules from five different meteorites. More than half the studied chondrules come from the unequilibrated ordinary chondrites (UOC's) Chainpur, Semarkona, and Tieschitz. However, 'unequilibrated' does not necessarily mean 'unaltered,' and the I-Xe studies of chondrules from UOC's have ultimately been interpreted in terms of postformation alteration. Two types of constraints on chondrule formation are discussed: (1) the duration, location, and timing of postformation alteration (in solids over a 50-m.y. span); and (2) the ages of the earliest formed chondrules (a few million years after the earliest solids).

  14. Cosmogenic and trapped noble gases in individual chondrules: Clues to chondrule formation

    NASA Astrophysics Data System (ADS)

    Das, J. P.; Murty, S. V. S.

    2009-12-01

    We studied the elemental and isotopic abundances of noble gases (He, Ne, Ar in most cases, and Kr, Xe also in some cases) in individual chondrules separated from six ordinary, two enstatite, and two carbonaceous chondrites. Most chondrules show detectable amounts of trapped 20Ne and 36Ar, and the ratio (36Ar/20Ne)t (from ordinary and carbonaceous chondrites) suggests that HL and Q are the two major trapped components. A different trend between (36Ar/20Ne)t and trapped 36Ar is observed for chondrules in enstatite chondrites indicating a different environment and/or mechanism for their formation compared to chondrules in ordinary and carbonaceous chondrites. We found that a chondrule from Dhajala chondrite (DH-11) shows the presence of solar-type noble gases, as suggested by the (36Ar/20Ne)t ratio, Ne-isotopic composition, and excess of 4He. Cosmic-ray exposure (CRE) ages of most chondrules are similar to their host chondrites. A few chondrules show higher CRE age compared to their host, suggesting that some chondrules and/or precursors of chondrules have received cosmic ray irradiation before accreting to their parent body. Among these chondrules, DH-11 (with solar trapped gases) and a chondrule from Murray chondrite (MRY-1) also have lower values of (21Ne/22Ne)c, indicative of SCR contribution. However, such evidences are sporadic and indicate that chondrule formation event may have erased such excess irradiation records by solar wind and SCR in most chondrules. These results support the nebular environment for chondrule formation.

  15. The Collisions of Chondrules Behind Shock Waves

    NASA Technical Reports Server (NTRS)

    Ciesla, F. J.; Hood, L. L.

    2004-01-01

    One of the reasons that the mechanism(s) responsible for the formation of chondrules has remained so elusive is that each proposed mechanism must be able to explain a large number of features observed in chondrules. Most models of chondrule formation focus on matching the expected thermal histories of chondrules: 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 chondrules can be explained in the context of this model. One area of interest is understanding the collisional evolution of chondrules 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 chondrule formation and chondrule destruction by collisions behind a shock wave.

  16. Petrology and Origin of Ferromagnesian Silicate Chondrules

    NASA Astrophysics Data System (ADS)

    Lauretta, D. S.; Nagahara, H.; Alexander, C. M. O'd.

    Ferromagnesian silicate chondrules are major components of most primitive meteorites. The shapes, textures, and mineral compositions of these chondrules are consistent with crystallization of a molten droplet that was floating freely in space in the presence of a gas. The texture and mineralogy of a chondrule reflects the nature and composition of its precursor material as well as its thermal history. There is an enduring debate about the degree to which chondrules interacted with the ambient gas during formation. In particular, it is uncertain whether or not chondrules experienced evaporation during heating and recondensation during cooling. The extent to which these processes took place in chondrule melts varied as a function of the duration of heating as well as the environmental conditions such as pressure, temperature, composition, and size. Thus, locked in chondrule bulk compositions, mineralogy, and textures are clues to the ambient conditions of the solar nebula and the nature of material processing in the inner solar system at the early stages of planet formation. Here we survey what is known about the properties of ferromagnesian chondrules in primitive meteorites and use this information to place constraints on these important parameters.

  17. A Microanalytical (TEM) Study of Fine-grained Chondrule Rims in NWA 5717

    NASA Technical Reports Server (NTRS)

    Bigolski, J. N.; Frank, D. R.; Zolensky, Michael E.; Weisberg, M. K.; Ebel, D. S.; Rahman, Z.

    2013-01-01

    Northwest Africa (NWA) 5717 is a highly primitive ordinary chondrite of petrologic type 3.05 with ubiquitous fine-grained chondrule rims [1, 2]. Rims appear around approximately 60% of chondrules 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 olivine. 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.

  18. Experimental Constraints on Alkali Volatilization during Chondrule Formation: Implications for Early Solar System Heterogeneity

    NASA Astrophysics Data System (ADS)

    Ustunisik, G. K.; Ebel, D. S.; Nekvasil, H.

    2014-12-01

    The chemical variability of chondrule volatile element contents provide a wealth of information on the processes that shaped the early solar system and its compositional heterogeneity. An essential observation is that chondrule melts contain very low alkalies and other volatile elements (e.g., Cl). The reason for this depletion is the combined effects of cooling rates (10 to 1000K/h), the small size of chondrules, and their high melting temperatures (~1700 to 2100 K) resulting in extensive loss of volatiles at canonical pressures (e.g., 10-4bar). However, we observe some chondrules with significant concentrations of volatiles (Na, Cl), that differ markedly from chondrules dominated by refractory elements. Could such heterogeneity arise from loss of alkalis and Cl to a gas phase that itself later condenses, thereby yielding variations in volatile enrichments in chondrules? Does Cl enhance volatility of the alkalis to varying extents? Experiments on Cl-bearing and Cl-free melts of equivalent composition for 10 min, 4 h, and 6 h reveal systematic effects of Cl on alkali volatility. Cl-bearing melts lose 48% of initial Na2O, 66% of K2O, 96% of Cl within the first 10 minutes of degassing. Then the amount of alkali loss decreases due to the absence of Cl. Cl-free melts loses only 15% of initial Na2O and 33% K2O. After 4 hours, melts lose 1/3 of initial Na2O and 1/2 of K2O. For both systems, Na2O is more compatible in the melt relative to K2O. Therefore, the vapor given off has a K/Na ratio higher than the melt through time in spite of the much higher initial Na abundance in the melt. Enhanced vaporization of alkalis from Cl-bearing melt suggests that Na and K evaporate more readily as volatile chlorides than as monatomic gases. Cl-free initial melts with normative plagioclase of An50Ab44Or6 evolved into slightly normal zoned ones (An49Ab50Or1) while Cl-bearing initial melts normative to albitic plagioclase (An46Ab50Or4) evolved to reverse zoned ones (An54Ab45Or1). The vapor phase over Cl-bearing chondrule melts may have a bimodal character over time. The heteregeneous volatile contents of chondrules may result from quenching of melt droplets at different stages of repeated heating, chondrule fragment recycling, and recondensation of exsolved volatiles.

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

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.

    2006-01-01

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

  20. Olivine-rich asteroids, pallasitic olivine and olivine-metal mixtures: Comparisons of reflectance spectra

    NASA Technical Reports Server (NTRS)

    Cloutis, E. A.

    1993-01-01

    The recent acquisition of high resolution 0.3 - 2.6 micron reflectance spectra for a number of olivine-rich asteroids permits the analysis of their surface compositions to be made on the basis of new and existing laboratory spectral data for pallasitic olivines and olivine-metal mixtures. Analysis of the spectral data for the latter has revealed a number of spectral parameters which can be used to constrain olivine and metal abundances, grain sizes, and olivine compositions. The following topics are discussed in greater detail: pallasite olivine spectra, olivine-metal mixture spectra, and olivine-rich asteroid spectra.

  1. The compositions of chondrules in unequilibrated chondrites An evaluation of models for the formation of chondrules and their precursor materials

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    Recent progress toward the resolution of the problem of chondrule composition is reviewed. Special attention is given to studies of both the chemical and textural properties of chondrules. The characteristic variations of the composition of carbonaceous chondrite chrondules are discussed within the framework of current theories of chondrule evolution. Consideration is also given to the possible mechanisms for chondrule melts, and the relationship between chondrules and other chondrite components.

  2. Flash melting of chondrule precursors in excess of 1600 C. Series 1: Type 2 (B1) chondrule composition experiments

    NASA Technical Reports Server (NTRS)

    Connolly, Harold C., Jr.; Hewins, Roger H.; Lofgren, Gary E.

    1993-01-01

    Several questions in chondrule production remain an enigma despite years of experiments. What were the melting temperatures experienced by chondrules? What were the physical characteristics of chondrule precursors? How and why did volatile elements (i.e. Na) found within chondrules 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 chondrule formation.

  3. Titanium diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, Daniele J.; Liang, Yan

    2014-12-01

    Diffusion of Ti has been characterized in natural olivine and synthetic forsterite. Experiments on the natural olivines were run under buffered conditions (IW and NNO), and those on synthetic forsterite were run in air. Titanium diffusion appears relatively insensitive to crystallographic orientation and oxygen fugacity under the range of investigated conditions, and diffusivities are similar for Fe-bearing olivine and forsterite. For Ti diffusion in synthetic forsterite, we obtain the following Arrhenius relation for diffusion over the temperature range 900-1400 °C:

  4. Photophoretic strength on chondrules. 1. Modeling

    SciTech Connect

    Loesche, Christoph; Wurm, Gerhard; Teiser, Jens; Friedrich, Jon M.; Bischoff, Addi

    2013-12-01

    Photophoresis is a physical process that transports particles in optically thin parts of protoplanetary disks, especially at the inner edge and at the optical surface. To model the transport and resulting effects in detail, it is necessary to quantify the strength of photophoresis for different particle classes as a fundamental input. Here, we explore photophoresis for a set of chondrules. The composition and surface morphology of these chondrules were measured by X-ray tomography. Based on the three-dimensional models, heat transfer through illuminated chondrules was calculated. The resulting surface temperature map was then used to calculate the photophoretic strength. We found that irregularities in particle shape and variations in composition induce variations in the photophoretic force. These depend on the orientation of a particle with respect to the light source. The variation of the absolute value of the photophoretic force on average over all chondrules is 4.17%. The deviation between the direction of the photophoretic force and illumination is 3.0 1.5. The average photophoretic force can be well approximated and calculated analytically assuming a homogeneous sphere with a volume equivalent mean radius and an effective thermal conductivity. We found an analytic expression for the effective thermal conductivity. The expression depends on the two main phases of a chondrule and decreases with the amount of fine-grained devitrified, plagioclase-normative mesostasis up to factor of three. For the chondrule sample studied (Bjurble chondrite), we found a dependence of the photophoretic force on chondrule size.

  5. Genetic Relationships Between Chondrules, Rims and Matrix

    NASA Technical Reports Server (NTRS)

    Huss, G. R.; Alexander, C. M. OD.; Palme, H.; Bland, P. A.; Wasson, J. T.

    2004-01-01

    The most primitive chondrites are composed of chondrules and chondrule fragments, various types of inclusions, discrete mineral grains, metal, sulfides, and fine-grained materials that occur as interchondrule matrix and as chondrule/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 chondrules formed by melting of matrix or matrix precursors? Did chondrule formation result in appreciable transfer of chondrule 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, chondrule 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.

  6. I-Xe studies of individual Allende chondrules

    NASA Technical Reports Server (NTRS)

    Swindle, T. D.; Caffee, M. W.; Hohenberg, C. M.; Lindstrom, M. M.

    1983-01-01

    Nine Allende chondrules and a sample of oxidized Allende matrix material are subjected to iodine-xenon studies, and the model compositions derived are compared with those of the Bjurbole chondrules. Chondrule 6 yields a well-defined isochron, with an apparent age that is later than Bjurbole whole rock. Elemental abundances suggest that all the chondrules except 6 may be pyroxene- or mesostasis-rich. The oxidized matrix sample gives a well defined isochron with an initial I-129/I-127 ratio higher than any plateaus seen in the chondrules, suggesting that the matrix predates the chondrules.

  7. Textural variability of ordinary chondrite chondrules: Implications of their formation

    NASA Technical Reports Server (NTRS)

    Zinovieva, N. G.; Mitreikina, O. B.; Granovsky, L. B.

    1994-01-01

    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 chondrules depends on the chemical composition of the chondrules. The comparison of bulk-rock chemistries of the chondrules 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 chondrules of the intermediate, peridotitic type. The effect is vividly demonstrated by the 'chondrule-in-chondrule' structure.

  8. Metal Precursors and Reduction in Renazzo Chondrules

    NASA Astrophysics Data System (ADS)

    Zanda, B.; Hewins, R. H.; Bourot-Denise, M.

    1993-07-01

    The positive Co-Ni correlation and Cr, P contents of metal in CR chondrites have generally been taken to indicate their primitive nature, probably inherited from condensation [1,2]. Si in the metal of primitive chondrites has also been reported and interpreted as a condensation heritage [3,4]. However, Cr, P, and Si (dissolved or in the form of inclusions) in metal of any CR chondrule generally fall within a +-10% range, though large interchondrule variations exist [5]. We have shown that Cr and Si in metal are in equilibrium with Fo and En in silicates, due to the reducing conditions that prevailed during chondrule formation [6]. In the present paper, we show that the Co-Ni trend was also established during chondrule formation out of heterogeneous precursor material with a variable Co/Ni ratio. Chondrules in Renazzo are classified as highly molten (HM), in which metal has been expelled to form a mantle outside the chondrule, medium molten (MM), with metal inside and at the periphery, and with evidence for grain coalescence, and little melted (LM), in which metal is only present in the form of small blebs dispersed among the silicates. In HM chondrules, Ni and Co concentrations are extremely homogeneous, comparatively low and in the cosmic ratio. In LM chondrules, quite the opposite: Ni and Co spread over a large range and the amount of scatter increases with decreasing degree of melting of the chondrule. In addition, they do not correlate along the cosmic ratio, but show a negative correlation if any. This heterogeneity is present not only from grain to grain in these chondrules, but also in individual metal grains. Such a heterogeneity is also exhibited in Cr and P abundances that span a much larger range than the +-10% found in the other chondrules. These results indicate that chondrule formation is responsible for the homogenization of Co and Ni contents of metal grains through coalescence and mixing. The less melted objects give an idea of the nature of metal in chondrule precursors, extremely heterogeneous and fine grained (each small heterogeneous metal bleb might be the result of partial melting of one or of coalescence and imperfect mixing of a few such grains). Co and Ni in these individual grains were not in the cosmic ratio, but wide sampling of dust in each chondrule precursor insured that this ratio was attained after mixing and homogenization, as seen in HM chondrule metal grains and from mean values of Co and Ni in LM chondrules. In MM chondrules, scatter of Ni and Co data are, as expected, intermediate between those of HM and LM chondrules, but Co and Ni are close to the cosmic ratio. The scatter is mostly due to addition of variable quantities of iron in the reduction during chondrule formation, which is responsible for Cr and Si integration into metal. Further evidence of such a process can be found in the less molten of these objects, in which metal grain coalescence is limited and peripheral grains are still different from inside grains. In these cases, Co and Ni distributions are clearly bimodal, high in inside grains, low in peripheral grains. Co/Ni in these two populations are somewhat scattered around the cosmic ratio, but their means (Ni: 7.75 = +- 0.24, Co: 0.36 +- 0.04, and Ni: 4.39 +- 0.34, Co: 0.23 +- 0.02, e.g., in the case of chondrule AL1) are very close to the cosmic ratio. This is in good agreement with the low values found in the homogeneous mantle grains of HM chondrules and, as noted by Lee et al. [7], indicates that the reducing agent was external to the chondrule. Cr abundances of these peripheral metal grains, however, match Cr abundances of the interior ones in these chondrules. This indicates that the redox state of all these grains was attained simultaneously and controlled by equilibrium with chondrule silicates. Slightly more extensive reduction of the latter close to the chondrule surface that added more Fe to peripheral metal grains resulted in only a minor variation of the Cr partition coefficient: it consequently also induced Cr addition, the Cr/Fe ratio varying only marg

  9. Heating during solar nebula formation and Mg isotopic fractionation in precursor grains of CAIs and chondrules

    NASA Technical Reports Server (NTRS)

    Sasaki, S.; Nagahara, H.; Kitagami, K.; Nakagawa, Y.

    1994-01-01

    In some Ca-Al-rich inclusion (CAI) grains, mass-dependent isotopic fractionations of Mg, Si, and O are observed and large Mg isotopic fractionation is interpreted to have been produced by cosmochemical processes such as evaporation and condensation. Mass-dependent Mg isotopic fractionation was found in olivine chondrules of Allende meteorites. Presented is an approximate formula for the temperature of the solar nebula that depends on heliocentric distance and the initial gas distribution. Shock heating during solar nebula formation can cause evaporative fractionation within interstellar grains involved in a gas at the inner zone (a less than 3 AU) of the disk. Alternatively collision of late-accreting gas blobs might cause similar heating if Sigma(sub s) and Sigma are large enough. Since the grain size is small, the solid/gas mass ratio is low and solar (low P(sub O2)), and the ambient gas pressure is low, this heating event could not produce chondrules themselves. Chondrule formation should proceed around the disk midplane after dust grains would grow and sediment to increase the solid/gas ratio there. The heating source there is uncertain, but transient rapid accretion through the disk could release a large amount of heat, which would be observed as FU Orionis events.

  10. Detection of new olivine-rich locations on Vesta

    NASA Astrophysics Data System (ADS)

    Palomba, Ernesto; Longobardo, Andrea; De Sanctis, Maria Cristina; Zinzi, Angelo; Ammannito, Eleonora; Marchi, Simone; Tosi, Federico; Zambon, Francesca; Capria, Maria Teresa; Russell, Christopher T.; Raymond, Carol A.; Cloutis, Edward A.

    2015-09-01

    The discovery of olivine on Vesta's surface by the VIR imaging spectrometer onboard the Dawn space mission has forced us to reconsider our views of Vestan petrogenetic models. Olivines were expected to be present in the interior of Vesta: in the mantle of a vertically layered body as invoked by the magma ocean models, or at the base (or within) the mantle-crust boundary as proposed by fractionation models. Olivines have been detected by VIR-Dawn in two wide areas near Arruntia and Bellicia, regions located in the northern hemisphere. Interestingly, these olivine-rich terrains are far from the Rheasilvia and the more ancient Veneneia basins, which are expected to have excavated the crust down to reach the mantle. In this work we present our attempts to identify other undetected olivine rich areas on Vesta by using spectral parameters sensitive to olivine such as the Band Area Ratio (BAR) and other specific parameters created for the detection of olivines on Mars (forsterite, fayalite and a generic olivine index). As a preliminary step we calibrated these parameters by means of VIS-IR spectra of different HED meteorite samples: behaviors versus sample grain size and albedo were analyzed and discussed. We selected the BAR and the Forsterite Index as the best parameters that can be used on Vesta. A cross-correlation analysis has been applied in order to detect olivine signature on the VIR hyperspectral cubes. These detections have then been confirmed by an anti-correlation analysis between the BAR and one of the olivine parameters, independent of the first method applied. In agreement with the recent discovery, Arruntia and Bellicia were found to be as the most olivine-rich areas, i.e. where the parameter values are strongest. In addition we detected 6 new regions, all but one located in the Vesta north hemisphere. This result confirms again that the old petrogenetic models cannot be straightforwardly applied to Vesta and should be reshaped in the view of these new detections. An alternative and very recent option can be represented by the model according to which surface "eruption" of material from the mantle, including olivine can reach the surface of Vesta.

  11. On the Lower Limit of Chondrule Cooling Rates: The Significance of Iron Loss in Dynamic Crystallization Experiments

    NASA Technical Reports Server (NTRS)

    Paque, Julie M.; Connolly, Harold C., Jr.; Lofgren, Gary E.

    1998-01-01

    It is unlikely that the presence of chondrules, and thus their formation, within the protoplanetary nebula would be predicted if it were not for their ubiquitous presence in most chondritic meteorites. The study of these enigmatic, igneous objects has a direct influence on how meteoritic and solar system researchers model the processes operating and the materials present within our protoplanetary nebula. Key to understanding chondrule formation is a determination of constraints on their thermal histories. The three important variables in this history are their peak melting temperatures, the duration of their melting at peak temperatures, and the rate at which these object cool. Although these three variables are interdependent, it is cooling rate that provides the most powerful constraint. Cooling rate has a direct affect on the development of both crystal morphology and the elemental distributions within these grains. To date, experiments have indicated that chondrule cooling rates are in the range of 10's to 100's of degrees per hour for porphyritic chondrules (the most abundant type). The cooling rate for radial and barred chondrules is thought to be more rapid. To generate these cooling rates (rapid relative to the cooling of the nebula as a whole, but slow compared to simple black body radiation) the environment of chondrule formation must have been localized, and the abundance of solid materials must have been greatly enhanced above a gas of solar composition. Thus accurate determinations of chondrule cooling rates is critical in understanding both their formation and the nebular environment in which they formed. In a quest to more accurately determine the lower limit on cooling rates and to determine in more detail the effects of Fe loss from a molten sample to Pt wire loops, Weinbruch et al. have explored this issue experimentally and reevaluated the findings of Radomsky and Hewins in light of their new results. The basic conclusions of their paper are an important contribution to our understanding of how experimental techniques can affect established constraints on chondrule formation and are thus of interest to a wide audience. We do believe, however, that their methodology produces results that provide inappropriate impressions of the applicability of their study to chondrule formation and nebular processes. Furthermore, the extensive body of previous experimental work on chondrule bulk compositions cannot be invalidated, as they suggest, by the results of Weinbruch et al. It is for these reasons that within this comment we address to applicability of the results presented by Weinbruch et al. to previous studies, and illustrate how the experimental conditions chosen for their series of experiments introduced a significant bias in their results.

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

    NASA Astrophysics Data System (ADS)

    Béjina, Frédéric; Sautter, Violaine; Jaoul, Olivier

    2009-01-01

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

  13. Chondrule formation in the radiative accretional shock

    NASA Technical Reports Server (NTRS)

    Ruzmaikina, T. V.; Ip, W.

    1994-01-01

    The physical, mineralogical, and isotopic properties of chondrules strongly indicate that they were formed by the rapid melting and resolidification of preexisting solids composed of primitive material. The chondrule 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 chondrule precursors to such a temperature and melt them. Lightning discharges and flares in the solar nebula, and heating of the chondrule 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 chondrule formation. One advantage of chondrule 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 chondrule formation in the accretional shock by heating of chondrule 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 chondrule 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 chondrule 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.

  14. Lunar and Planetary Science XXXV: Chondrules and CAIs

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The session "Chondrules and CAI's" included the following reports:Metallic Chondrules in NWA 1390 (H3-6): Clues to Their History from Metallic Cu; Relationship Between Bulk Chemical Composition and Formation Age of Chondrules in Bishunpur and Krymka; Relict Forsterite in Chondrules: Implications for Cooling Rates; An Evaluation of Quantitative Methods of Determining the Degree of Melting Experienced by a Chondrule; Rare Earth Element Fractionation in Chondrules; Mineralogy and Petrology of Chondrules in Carbonaceous Chondrite NWA 770; Isotopic Cosmobarometry: A Synthesis of Concepts and Implications for Chondrule 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 .

  15. Chemistry and Petrology of Chondrules from the Mokoia CV Chondrite

    NASA Technical Reports Server (NTRS)

    Jones, R. H.; Schilk, A. J.

    2000-01-01

    Bulk chemical compositions of 94 chondrules from Mokoia have been obtained by INAA. Elemental abundances are correlated with petrology. Chemical and petrological properties are very similar to chondrules from Allende and do not show strong alteration signatures.

  16. Chondrules - An origin by impacts between dust grains

    NASA Technical Reports Server (NTRS)

    Lange, D. E.; Larimer, J. W.

    1973-01-01

    Modern theories regarding the origin of chondrules may be divided into two broad categories. According to primary theories, chondrules are thought to condense directly from the cooling nebular gas as stable or metastable liquid droplets. According to secondary theories, chondrules are thought to be produced by the flash heating and remelting of the original dust-like condensate. A collisional mechanism of chondrule formation is discussed.

  17. Detection of new olivine-rich locations on Vesta

    NASA Astrophysics Data System (ADS)

    Palomba, E.; Longobardo, A.; De Sanctis, M.; Tosi, F.; Capria, M.; Capaccioni, F.; Ammannito, E.; Raymond, C.; Russell, C.

    2014-07-01

    The recent discovery of olivines on Vesta by the VIR imaging spectrometer onboard the Dawn space mission changed dramatically the vision about the Vestan petrogenetic models [1]. Before that, olivines were expected to be present in the Vesta interior: in the mantle of a vertically layered body as invoked by the magma ocean models [2] or at the base of (or within) the mantle-crust boundary as claimed by fractionation models [3]. Olivines were detected by VIR-Dawn in two wide areas near the Arruntia and Bellicia regions. These are located in the northern hemisphere and not in the south, where the Rheasilvia and the more ancient Veneneia huge basins should have excavated the crust down to reach the mantle. In this work, we present our attempts to retrieve other undetected olivine-rich areas on Vesta by using spectral parameters sensitive to olivine such as the Band Area Ratio (BAR) and other specific parameters created for the detection of olivines on Mars (forsterite, fayalite, and a generic olivine index [4,5]). As a preliminary step, we calibrated these parameters by means of VIS-IR spectra of different HED meteorite samples: their behaviors as a function of sample grain size and albedo were retrieved and discussed. We selected the BAR and the forsterite index as the best parameters that can be used on Vesta and applied two independent methods to detect olivine signatures on the VIR hyperspectral cubes: a cross-correlation and an anti-correlation analysis between the BAR and one of the olivine parameters. In agreement with the recent discovery, Arruntia and Bellicia were the most olivine rich areas. In addition, we detected 6 new regions, all but one located in Vesta's northern hemisphere. This result confirms again that the old petrogenetic models cannot be applied, in a straightforward way, to Vesta and should be reshaped in the view of these new detections. An alternative and very recent option can be represented by the model described in [4], in which surface ''eruption'' of material from the mantle, including olivine, can reach the surface of Vesta.

  18. Exogenous Olivine on Vesta

    NASA Astrophysics Data System (ADS)

    Hoffmann, Martin; Nathues, Andreas; Schäfer, Michael; Thangjam, Guneshwar; Le Corre, Lucille; Vishnu, Reddy; Christensen, Ulrich; Mengel, Kurt; Sierks, Holger; Vincent, Jean-Baptist; Cloutis, Edward A.; Russell, Christopher T.; Schäfer, Tanja; Gutierrez-Marques, Pablo; Hall, Ian; Ripken, Joachim; Büttner, Irene

    2014-11-01

    Vesta has conserved an early status of planetary evolution, demonstrated by the global coverage of HED lithology on its surface. Being sufficiently large to retain some material from slow projectiles, but small enough to prevent its complete evaporation during the impacts, this unique environment is ideal for distinction and identification of exogenous material. In particular, the distribution, concentration, and geological context of olivine exposures are poorly consistent with a Vestan mantle origin. Similar arguments are valid for the areas of dark carbonaceous chondrite-like lithology, and a few other features with unusual visual spectral slopes. Most olivine is found close to the large impact craters Bellicia, Arruntia, and Pomponia in the northern hemisphere, whose ejecta sheet is characterized by a mixing trend from an HED lithology to S- or A-type asteroid material. The olivine has diagnostic significance for the extent and duration of differentiation during the early accretion of parent bodies in the asteroid region. Sources for exogenous olivine are available in Vesta’s environment among A- and S-type asteroids. It is not clear, however, if it is derived mainly from achondritic or chondritic sources. On the other hand, the lack of evidence for Vesta’s mantle material implies constraints on its inner structure, e.g. the depth of the crust.

  19. Microbial Weathering of Olivine

    NASA Technical Reports Server (NTRS)

    McKay, D. S.; Longazo, T. G.; Wentworth, S. J.; Southam, G.

    2002-01-01

    Controlled microbial weathering of olivine experiments displays a unique style of nanoetching caused by biofilm attachment to mineral surfaces. We are investigating whether the morphology of biotic nanoetching can be used as a biosignature. Additional information is contained in the original extended abstract.

  20. On the origin of porphyritic chondrules

    SciTech Connect

    Blander, M.; Unger, L.; Pelton, A.; Ericksson, G.

    1994-05-01

    A computer program for the complex equilibria in a cooling nebular gas was used to explore a possible origin of porphyritic chondrules, the major class of chondrules in chondritic meteorites. It uses a method of accurately calculating the thermodynamic properties of molten multicomponent aluminosilicates, which deduces the silicate condensates vs temperature and pressure of a nebular gas. This program is coupled with a chemical equilibrium algorithm for systems with at least 1000 chemical species; it has a data base of over 5000 solid, liquid, and gaseous species. Results are metastable subcooled liquid aluminoscilicates with compositions resembling types IA and II porphyritic chondrules at two different temperatures at any pressure between 10{sup {minus}2} and 1 (or possibly 10{sup {minus}3} to 5) atm. The different types of chondrules (types I, II, III) could have been produced from the same gas and do not need a different gas for each apparent oxidation state; thus, the difficulty of current models for making porphyritic chondrules by reheating different solids to just below their liquidus temperatures in different locations is not necessary. Initiation of a stage of crystallization just below liquidus is part of the natural crystallization (recalescence) process from metastable subcooled liquidus and does not require an improbably heating mechanism. 2 tabs.

  1. Petrology and geochemistry of chondrules and metal in NWA 5492 and GRO 95551: A new type of metal-rich chondrite

    NASA Astrophysics Data System (ADS)

    Weisberg, Michael K.; Ebel, Denton S.; Nakashima, Daisuke; Kita, Noriko T.; Humayun, Munir

    2015-10-01

    Northwest Africa (NWA) 5492 and Grosvenor Mountains (GRO) 95551 are metal-rich chondrites having silicate (olivine and pyroxene) compositions that are more reduced than those in other metal-rich chondrites, such as the CH and CB chondrites. Additionally, sulfides in NWA 5492 and GRO 95551 are more abundant and not related to the metal, as in the CB chondrites. Average metal compositions in NWA 5492 and GRO 95551 are close to H chondrite metal. Oxygen isotope ratios of NWA 5492 and GRO 95551 components (chondrules and fragments) show a range of compositions with most having ?17O values >0. Since there is no matrix component, their average chondrule + fragment oxygen isotopic compositions are considered to be representative of whole rock and (?17O values) are sandwiched between the values for enstatite (E) and ordinary (O) chondrites. These data argue for a close relationship between NWA 5492 and GRO 95551 and suggest that they are the first examples of a new type of metal-rich chondrite. Oxygen isotope ratios of chondrules in NWA 5492 and GRO 95551 show considerable overlap with chondrules in O, E and R chondrites, with average compositions indistinguishable from LL3 chondrules, suggesting considerable mixing between these Solar System materials during chondrule formation and/or that their precursors experienced similar formation environments and/or processes. Another characteristic shared between NWA 5492 and GRO 95551 and O, E and R chondrites is that they are all relatively dry (low abundances of hydrated minerals), compared to many C chondrites and have fewer, smaller CAIs than many C chondrites. (No CAIs were found in NWA 5492 or GRO 95551 but they contain rare Al-rich chondrules.) We suggest that O, E, R and the NWA 5492 and GRO 95551 chondrites are closely related Solar System materials.

  2. Constraints on chondrule origin from petrology of isotopically characterized chondrules in the Allende meteorite

    NASA Astrophysics Data System (ADS)

    McSween, H. Y., Jr.

    1985-09-01

    The petrologic and chemical properties of the ferromagnesian chondrules 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 chondrules by exchanges between isotopically heavy nebular gases and O-16 enriched solids. Different rates of gaseous exchange occurred with the various types of chondrules. Factors which may have controlled the exchanges are discussed.

  3. International conference: Chondrules and the protoplanetary disk

    NASA Astrophysics Data System (ADS)

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

    1996-06-01

    This book is the first comprehensive review of chondrules and their origins since a consensus developed that they were made in the disk of gas and solids that formed the Sun and planets 4.5 billion years ago. Fifty scientists from assorted disciplines have collaborated to review how chondrules could have formed in the protoplanetary disk. When and where in the disk did they form? What were they made from and how fast were they heated and cooled? What provided the energy to melt chondrules--nebular shock waves, lightning discharges, protostellar jets? Following an exciting international conference in Albuquerque, New Mexico, the latest answers to these questions are presented in thirty-four articles, which will appeal to researchers in planetary science and meteoritics.

  4. Formation of chondrules by electrical discharge heating

    NASA Technical Reports Server (NTRS)

    Love, S. G.; Keil, K.; Scott, E. R. D.

    1994-01-01

    A possible mechanism for making chondrules 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 chondrule formation. Nebular discharges do not appear a viable source of heat for melting chondrule 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.

  5. Cosmochemical Studies: Meteorites, Asteroidal Processes, Chondrules

    NASA Technical Reports Server (NTRS)

    Wasson, John T.

    2002-01-01

    Our research mainly concerned the asteroidal processes involved in the formation of meteorites and meteoritic chondrules. We continued to generate large amounts of instrumental-neutron-activation analysis (INAA) data, both for irons, chondrites and primitive achondrites. Major themes of our chondrule research were: (1) the temperature and crystallization history of individual chondrules, and (2) the evolution of the solar nebula during the period within which chondrule formation occurred. Much of our chondrule research was focused on the highly primitive CO3 chondrites. We initiated a study of the cooling history of high-FeO chondrules by characterizing the overgrowth layers on relict grains.. We also continued our studies of the composition and the formation of iron meteorites and the evolution of their parent planets. The large data sets that we have generated at UCLA allows systematic comparisons of the large magmatic groups both in terms of fractional crystallization (including rough estimates of non-metal contents of the parental melts) and in terms of the effects of variable contents of trapped melt. We have completed a preliminary study of group IIIAB in which we developed a trapped-melt model and more detailed studies of group IVA and the main-group pallasites. By comparing these large groups and modeling them by a combination of crystallization and melt trapping, we are able to better define both the formation processes and the nature of the solid/liquid elemental partitioning. We helped maintain the excellent neutron-activation facilities at UCLA, a major resource for the cosmochemical community.

  6. "Black-colored olivines" in peridotites: dehydrogenation from hydrous olivines

    NASA Astrophysics Data System (ADS)

    Arai, Shoji; Hoshikawa, Chihiro; Miura, Makoto

    2015-04-01

    Fresh olivines that are black to the naked eye are found in some dunites. Peridotites are easily converted to be black in color, when serpentinized, due to production of secondary fine magnetite particles. The dunites that contain fresh but black-colored olivines are usually coarse-grained. These coarse olivine grains are sometimes very heterogeneous in color; the blackish part grades to whitish parts in single grains. The black color is due to homegeneous distribution of minute (< 10 microns) black particles in olivine. They are rod-like or plate-like in shape in thin section, sometimes being aligned under crystallographic control of the host olivine. Olivines are clear and free of these inclusions around primary chromian spinel inclusions or chromian spinel lamellae (Arai, 1978). Raman spectroscopy indicates the minute black particles are magnetite always associated with diopside. It is interesting to note that olivine in mantle peridotites accompanied by the black-colored dunites is totally free of the black inclusions, giving the ordinary colors (pale yellow to whitish) of Mg-rich olivine. It is not likely that the magnetite inclusions formed through secondary oxidation of olivine by invasion of oxygen, which is possible along cracks or grain boundaries. They most probably formed due to dehydrogenation from primary OH-bearing olivines upon cooling. Hydrogen was quickly diffused out from the olivines to leave magnetite and excess silica. The excess silica was possibly combined with a monticellite component to form diopside. The OH-bearing (hydrous) olivines can be precipitated from hydrous magmas, and the hydrous nature of the magma can promote an increase in grain size due to faster diffusion of elements. The minute inclusions of magnetite + diopside is thus an indicator of primary hydrous character of host olivine.

  7. Uranium isotopic composition and absolute ages of Allende chondrules

    NASA Astrophysics Data System (ADS)

    Brennecka, G. A.; Budde, G.; Kleine, T.

    2015-11-01

    A handful of events, such as the condensation of refractory inclusions and the formation of chondrules, represent important stages in the formation and evolution of the early solar system and thus are critical to understanding its development. Compared to the refractory inclusions, chondrules appear to have a protracted period of formation that spans millions of years. As such, understanding chondrule formation requires a catalog of reliable ages, free from as many assumptions as possible. The Pb-Pb chronometer has this potential; however, because common individual chondrules have extremely low uranium contents, obtaining U-corrected Pb-Pb ages of individual chondrules is unrealistic in the vast majority of cases at this time. Thus, in order to obtain the most accurate 238U/235U ratio possible for chondrules, we separated and pooled thousands of individual chondrules from the Allende meteorite. In this work, we demonstrate that no discernible differences exist in the 238U/235U compositions between chondrule groups when separated by size and magnetic susceptibility, suggesting that no systematic U-isotope variation exists between groups of chondrules. Consequently, chondrules are likely to have a common 238U/235U ratio for any given meteorite. A weighted average of the six groups of chondrule separates from Allende results in a 238U/235U ratio of 137.786 ± 0.004 (±0.016 including propagated uncertainty on the U standard [Richter et al. 2010]). Although it is still possible that individual chondrules have significant U isotope variation within a given meteorite, this value represents our best estimate of the 238U/235U ratio for Allende chondrules and should be used for absolute dating of these objects, unless such chondrules can be measured individually.

  8. Nonporphyritic chondrules and chondrule fragments in enstatite chondrites: Insights into their origin and secondary processing

    NASA Astrophysics Data System (ADS)

    Varela, M. E.; Sylvester, P.; BrandstäTter, F.; Engler, A.

    2015-08-01

    Sixteen nonporphyritic chondrules and chondrule fragments were studied in polished thin and thick sections in two enstatite chondrites (ECs): twelve objects from unequilibrated EH3 Sahara 97158 and four objects from equilibrated EH4 Indarch. Bulk major element analyses, obtained with electron microprobe analysis (EMPA) and analytical scanning electron microscopy (ASEM), as well as bulk lithophile trace element analyses, determined by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), show that volatile components (K2O + Na2O versus Al2O3) scatter roughly around the CI line, indicating equilibration with the chondritic reservoir. All lithophile trace element abundances in the chondrules from Sahara 97158 and Indarch are within the range of previous analyses of nonporphyritic chondrules in unequilibrated ordinary chondrites (UOCs). The unfractionated (solar-like) Yb/Ce ratio of the studied objects and the mostly unfractionated refractory lithophile trace element (RLTE) abundance patterns indicate an origin by direct condensation. However, the objects possess subchondritic CaO/Al2O3 ratios; superchondritic (Sahara 97158) and subchondritic (Indarch) Yb/Sc ratios; and chondritic-normalized deficits in Nb, Ti, V, and Mn relative to RLTEs. This suggests a unique nebular process for the origin of these ECs, involving elemental fractionation of the solar gas by the removal of oldhamite, niningerite, and/or another phase prior to chondrule condensation. A layered chondrule in Sahara 97158 is strongly depleted in Nb in the core compared to the rim, suggesting that the solar gas was heterogeneous on the time scales of chondrule formation. Late stage metasomatic events produced the compositional diversity of the studied objects by addition of moderately volatile and volatile elements. In the equilibrated Indarch chondrules, this late process has been further disturbed, possibly by a postaccretional process (diffusion?) that preferentially mobilized Rb with respect to Cs in the studied objects.

  9. Partitioning of Moderately Siderophile Elements Among Olivine, Silicate Melt, and Sulfide Melt: Constraints on Core Formation in the Earth and Mars

    NASA Technical Reports Server (NTRS)

    Gaetani, Glenn A.; Grove, Timothy L.

    1997-01-01

    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 olivine. 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 barred olivine chondrule 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 olivine/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 olivine/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.

  10. Applicability of Henry's Law to helium solubility in olivine

    NASA Astrophysics Data System (ADS)

    Jackson, C.; Parman, S. W.; Kelley, S. P.; Cooper, R. F.

    2013-12-01

    Applicability of Henry's Law to helium solubility in olivine We have experimentally determined helium solubility in San Carlos olivine across a range of helium partial pressures (PHe) with the goal of quantifying how noble gases behave during partial melting of peridotite. Helium solubility in olivine correlates linearly with PHe between 55 and 1680 bar. This linear relationship suggests Henry's Law is applicable to helium dissolution into olivine up to 1680 bar PHe, providing a basis for extrapolation of solubility relationships determined at high PHe to natural systems. This is the first demonstration of Henry's Law for helium dissolution into olivine. Averaging all the data of the PHe series yields a Henry's coefficient of 3.8(×3.1)×10-12 mol g-1 bar-1. However, the population of Henry's coefficients shows a positive skew (skewness = 1.17), i.e. the data are skewed to higher values. This skew is reflected in the large standard deviation of the population of Henry's coefficients. Averaging the median values from each experiment yields a lower Henry's coefficient and standard deviation: 3.2(× 2.3)×10-12 mol g-1 bar-1. Combining the presently determined helium Henry's coefficient for olivine with previous determinations of helium Henry's coefficients for basaltic melts (e.g. 1) yields a partition coefficient of ~10-4. This value is similar to previous determinations obtained at higher PHe (2). The applicability of Henry's Law here suggests helium is incorporated onto relatively abundant sites within olivine that are not saturated by 1680 bar PHe or ~5×10-9 mol g-1. Large radius vacancies, i.e. oxygen vacancies, are energetically favorable sites for noble gas dissolution (3). However, oxygen vacancies are not abundant enough in San Carlos olivine to account for this solubility (e.g. 4), suggesting the 3x10-12 mol g-1 bar-1 Henry's coefficient is associated with interstitial dissolution of helium. Helium was dissolved into olivine using an externally heated pressure vessel (Brown University). The starting materials were prepared by cutting gem-quality San Carlos olivine (~Fo90) into small blocks (~4×2×1 mm) using a diamond wafering blade saw and polishing with alumina slurries and colloidal silica. Analysis was completed by laser ablation-mass spectrometry using a 193 nm excimer laser and a MAP 215-50 specifically tuned for He (Open University, UK). Laser ablation pit depth varied from 2 to 40 μm, and no correlation between pit depth and [He] is observed after accounting for variations PHe across the different experiments. This lack of correlation indicates a close approach to equilibrium was achieved over the experimental durations. Two analyses yielded spuriously high [He] (>3 std. dev. from the population mean, n = 85), and these analyses were not used to calculate Henry's coefficients. The two spuriously high analyses, in combination with the right skew of Henry's coefficients calculated from individual data points, suggests gem-quality San Carlos olivine contains volumes with anomalously high helium solubility. The nature of these volumes is currently under investigation. However, despite their presence, helium is still highly incompatible in olivine during partial melting. [1] Lux GCA 1987 [2] Heber et al. GCA 2007 [3] Shcheka & Keppler Nature 2012 [4] Walker et al. PEPI 2009

  11. Growth of Asteroids by Chondrule Accretion

    NASA Astrophysics Data System (ADS)

    Johansen, Anders; Mac Low, Mordecai-Mark; Lacerda, Pedro; Bizzarro, Martin

    2015-08-01

    Planetesimals can form from solid objects constrained by the meter-size barrier through concentration by sedimentation and streaming instabilities, followed by gravitational instability. We have performed the highest-resolution numerical simulations of this scenario to date. We find that the resulting size distribution displays significant discrepancies with the currently observed size distribution that cannot be ameliorated by collisional evolution over the lifetime of the Solar System. We then examine accretion of thick layers of chondrules (or similarly-sized grains) by gas drag onto the population of planetesimals predicted from the streaming instability models as they undergo orbital and collisional evolution during the lifetime of the protoplanetary gas disk. These models yield a size distribution far more consistent with the observations. The gas drag mechanism for accretion further leads to size-sorting of the accreted chondrules consistent with the chondrule size distributions observed in ordinary chondrites. We find that the contribution of direct collisional growth of asteroids is minor in comparison to accretion of chondrules.

  12. Experimental Reproduction of Type 1B Chondrules

    NASA Technical Reports Server (NTRS)

    Lofgren, G. E.; Le, L.

    2002-01-01

    We have replicated type 1B chondrule 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.

  13. REVISITING JOVIAN-RESONANCE INDUCED CHONDRULE FORMATION

    SciTech Connect

    Nagasawa, M.; Tanaka, K. K.; Tanaka, H.; Nakamoto, T.; Miura, H.; Yamamoto, T.

    2014-10-10

    It is proposed that planetesimals perturbed by Jovian mean-motion resonances are the source of shock waves that form chondrules. It is considered that this shock-induced chondrule formation requires the velocity of the planetesimal relative to the gas disk to be on the order of ≳ 7 km s{sup –1} at 1 AU. In previous studies on planetesimal excitation, the effects of Jovian mean-motion resonance together with the gas drag were investigated, but the velocities obtained were at most 8 km s{sup –1} in the asteroid belt, which is insufficient to account for the ubiquitous existence of chondrules. In this paper, we reexamine the effect of Jovian resonances and take into account the secular resonance in the asteroid belt caused by the gravity of the gas disk. We find that the velocities relative to the gas disk of planetesimals a few hundred kilometers in size exceed 12 km s{sup –1}, and that this is achieved around the 3:1 mean-motion resonance. The heating region is restricted to a relatively narrowband between 1.5 AU and 3.5 AU. Our results suggest that chondrules were produced effectively in the asteroid region after Jovian formation. We also find that many planetesimals are scattered far beyond Neptune. Our findings can explain the presence of crystalline silicate in comets if the scattered planetesimals include silicate dust processed by shock heating.

  14. Silica-merrihueite/roedderite-bearing chondrules and clasts in ordinary chondrites: New occurrences and possible origin

    NASA Technical Reports Server (NTRS)

    Krot, Alexander N.; Wasson, John T.

    1994-01-01

    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 chondrules 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 chondrule in L3 Mezo-Madaras, and a silica-merrihueite-bearing chondrule 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 chondrules 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 chondrules, (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 olivine 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.

  15. Evaporation of nebular fines during chondrule formation

    NASA Astrophysics Data System (ADS)

    Wasson, John T.

    2008-06-01

    Studies of matrix in primitive chondrites provide our only detailed information about the fine fraction (diameter <2 ?m) of solids in the solar nebula. A minor fraction of the fines, the presolar grains, offers information about the kinds of materials present in the molecular cloud that spawned the Solar System. Although some researchers have argued that chondritic matrix is relatively unaltered presolar matter, meteoritic chondrules bear witness to multiple high-temperature events each of which would have evaporated those fines that were inside the high-temperature fluid. Because heat is mainly transferred into the interior of chondrules by conduction, the surface temperatures of chondrules were probably at or above 2000 K. In contrast, the evaporation of mafic silicates in a canonical solar nebula occurs at around 1300 K and FeO-rich, amorphous, fine matrix evaporates at still lower temperatures, perhaps near 1200 K. Thus, during chondrule formation, the temperature of the placental bath was probably >700 K higher than the evaporation temperatures of nebular fines. The scale of chondrule forming events is not known. The currently popular shock models have typical scales of about 10 km. The scale of nebular lightning is less well defined, but is certainly much smaller, perhaps in the range 1 to 1000 m. In both cases the temperature pulses were long enough to evaporate submicrometer nebular fines. This interpretation disagrees with common views that meteoritic matrix is largely presolar in character and CI-chondrite-like in composition. It is inevitable that presolar grains (both those recognized by their anomalous isotopic compositions and those having solar-like compositions) that were within the hot fluid would also have evaporated. Chondrule formation appears to have continued down to the temperatures at which planetesimals formed, possibly around 250 K. At temperatures >600 K, the main form of C is gaseous CO. Although the conversion of CO to CH 4 at lower temperatures is kinetically inhibited, radiation associated with chondrule formation would have accelerated the conversion. There is now evidence that an appreciable fraction of the nanodiamonds previously held to be presolar were actually formed in the solar nebula. Industrial condensation of diamonds from mixtures of CH 4 and H 2 implies that high nebular CH 4/CO ratios favored nanodiamond formation. A large fraction of chondritic insoluble organic matter may have formed in related processes. At low nebular temperatures appreciable water should have been incorporated into the smoke that condensed following dust (and some chondrule) evaporation. If chondrule formation continued down to temperatures as low as 250 K this process could account for the water concentration observed in primitive chondrites such as LL3.0 and CO3.0 chondrites. Higher H 2O contents in CM and CI chondrites may reflect asteroidal redistribution. In some chondrite groups (e.g., CR) the Mg/Si ratio of matrix material is appreciably (30%) lower than that of chondrules but the bulk Mg/Si ratio is roughly similar to the CI or solar ratio. This has been interpreted as a kind of closed-system behavior sometimes called "complementarity." This leads to the conclusion that nebular fines were efficiently agglomerated. Its importance, however is obscured by the observation that bulk Mg/Si ratios in ordinary and enstatite chondrites are much lower than those in carbonaceous chondrites, and thus that complementarity did not hold throughout the solar nebula.

  16. Alkali elemental and potassium isotopic compositions of Semarkona chondrules

    USGS Publications Warehouse

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

    2005-01-01

    We report measurements of K isotope ratios in 28 Semarkona chondrules with a wide range of petrologic types and bulk compositions as well as the compositions of CPX-mesostasis pairs in 17 type I Semarkona chondrules, including two chondrules with radial alkali zonation and 19 type II chondrules. Despite the wide range in K/Al ratios, no systematic variations in K isotopic compositions were found. Semarkona chondrules do not record a simple history of Rayleigh-type loss of K. Experimentally determined evaporation rates suggest that considerable alkali evaporation would have occurred during chondrule formation. Nevertheless, based on Na CPX-mesostasis distribution coefficients, the alkali contents of the cores of most chondrules in Semarkona were probably established at the time of final crystallization. However, Na CPX-mesostasis distribution coefficients also show that alkali zonation in type I Semarkona chondrules was produced by entry of alkalis after solidification, probably during parent body alteration. This alkali metasomatism may have gone to completion in some chondrules. Our preferred explanation for the lack of systematic isotopic enrichments, even in alkali depleted type I chondrule cores, is that they exchanged with the ambient gas as they cooled. ?? The Meteoritical Society, 2005.

  17. Distribution of some highly volatile elements in chondrules

    NASA Astrophysics Data System (ADS)

    Kim, J. S.; Marti, K.

    1994-07-01

    As chondrule apparently were melted before accretion into chondritic parent bodies, we carried out a N and Xe isotopic study to obtain information on the partitioning of some of the most volatile as well as incompatible elements: noble gases, N, I, REE, and Pu. In separated silicates in Forest Vale, consisting of mostly broken chondrules, we observed rather large Xe concentrations, and since noble gases in chondrites are associated with C-rich phases, we decided to study the core portion of a suite of chondrules after removing the chondrule rim portion and adhering matrix. We selected sets of rounded chondrules from four meteorites: Allende (CV3), Dhajala (H3.8), Forest Vale (H4), and Bjurbole (L4). We compare measured N and Xe concentrations and isotopic abundances in cores of chondrules to those obtained from unetched chondrules. We discuss results obtained from melting steps, because N and Xe in the silicate lattice are mostly released at T greater than 1000 C. All cores of chondrules contain less than 1% of the Xe in the respective bulk samples. Moreover, they released much less trapped Xe in the melting step than did untreated bulk chondrites. However, the radiogenic Xer-129 and fissiogenic Xef is not or is only slightly depleted, and spallogenic Xe is a major component, particularly in Forest Vale. We can not deduce the signature of trapped Xe in the chondrules. The release systematics are completely different from those observed in primitive achondrites, which contain noble gas in the 'dusty' silicate inclusions. Allende chondrules differ from those of ordinary chondrite in the N release pattern. This represents possibly a signature of the local environment during chondrule formation, since N may exist in chondrule minerals in chemically bound forms. In contrast, all three sets of ordinary chondrite chondrules released less than 0.6 ppm N in the melting step, and these signatures reveal substantial components of cosmic-ray-produced N.

  18. Unfired olivine bricks for TES

    NASA Astrophysics Data System (ADS)

    Whittemore, O. J.

    1982-12-01

    Olivine is particularly useful for TES because of its low cost, high heat storage capacity, no crystallographic inversions, and refractoriness. Olivine TES brick are being produced by adding small amounts of clay, compacting into bricks and firing at 1200 C or higher. An olivine composition which could be compacted into dense bricks, and simply dried or cured at low temperatures to obviate the expensive firing process was developed.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  20. Relict Forsterite in Chondrules: Implications for Cooling Rates

    NASA Technical Reports Server (NTRS)

    Greeney, S.; Ruzicka, A.

    2004-01-01

    Forsterite (Fo(sub 99-100)) is often present in chondrules as relict grains that did not crystallize in situ and as isolated grains outside of chondrules; both are surrounded by ferrous overgrowths which clearly formed at a later time, probably during chondrule formation. We performed microprobe analyses across forsterite-overgrowth interfaces in 12 chondrules and 4 isolated grains in the Sahara-97210 LL3.2 (Sahara), Wells LL3.3, and Chainpur LL3.4 chondrites and modelled diffusional exchange between forsterite and overgrowths, with the goal of constraining the thermal histories during chondrule formation. The cooling rates experienced by chondrules provide an important constraint on the origin and setting of these objects.

  1. Magnetic characteristics of CV chondrules with paleointensity implications

    NASA Astrophysics Data System (ADS)

    Emmerton, Stacey; Muxworthy, Adrian R.; Hezel, Dominik C.; Bland, Philip A.

    2011-12-01

    We have conducted a detailed magnetic study on 45 chondrules 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 chondrules. The Mokoia chondrules displayed more single domain-like behavior than the Allende chondrules, suggesting smaller grain sizes and higher magnetic stability. The Mokoia chondrules also had higher average concentrations of magnetic minerals and a larger range of magnetic characteristics than the Allende chondrules. IRM acquisition analysis found that both sets of chondrules have the same dominant magnetic mineral, likely to be a FeNi phase (taenite, kamacite, and/or awaruite) contributing to 48% of the Mokoia chondrules and 42% of the Allende chondrule characteristics. FORC analysis revealed that generally the Allende chondrules displayed low-field coercivity distributions with little interactions, and the Mokoia chondrules 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 chondrules 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.

  2. Formation of chondrules and CAIs by nebular processes

    NASA Technical Reports Server (NTRS)

    Palme, H.

    1994-01-01

    Chondrules are essential components of most chondritic meteorites. Carbonaceous chondrites, with the exception of CI chondrites, contain 30-50% chondrules, ordinary and enstatite chondrites even more. A better understanding of chondrule formation will therefore lead to an improved understanding of the origin of meteorites. Most studies of chondrules are, however, concerned with their texture and mineralogy. As chondrules, 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 chondrule formation is contained in their chemical and isotopic composition. The two most important observations relevant to the chemistry of the chondrules are their generally low Fe content and the large compositional variability of chondrules 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 chondrules.

  3. An unusual layered mineral in chondrules and aggregates of the Allende carbonaceous chondrite

    NASA Technical Reports Server (NTRS)

    Tomeoka, K.; Buseck, P. R.

    1982-01-01

    Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X ray (EDS) and electron energy loss (EELS) spectroscopy examinations of the microstructures and phase relationships of minerals in opaque spherules in the Allende chondrules and aggregates are reported. The studies were carried out on petrographic thin sections which were ion-thinned. A significant metasomatic effect was observed in a highly oxidizing condition of a later cooled stage. An unusually layered Fe-, Ni-, and O-rich mineral related to serpentine was found to occur in the opaque specimen, and was judged to occur by alteration of olivine. It is noted that low temperature and a hydrous condition would have been required for the formation of the serpentine in the spherules, the first observed in Allende. It is suggested that the aqueous conditions occurred before the final stage of the meteorite formation, and proceeded in a nonterrestrial manner.

  4. Constraints on chondrule origin from petrology of isotopically characterized chondrules in the Allende meteorite

    SciTech Connect

    Mcsween, H.Y. Jr.

    1985-09-01

    The petrologic and chemical properties of the ferromagnesian chondrules 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 chondrules by exchanges between isotopically heavy nebular gases and O-16 enriched solids. Different rates of gaseous exchange occurred with the various types of chondrules. Factors which may have controlled the exchanges are discussed. 21 references.

  5. Size distributions and aerodynamic equivalence of metal chondrules and silicate chondrules in Acfer 059

    NASA Technical Reports Server (NTRS)

    Skinner, William R.; Leenhouts, James M.

    1993-01-01

    The CR2 chondrite Acfer 059 is unusual in that the original droplet shapes of metal chondrules are well preserved. We determined separate size distributions for metal chondrules and silicate chondrules; the two types are well sorted and have similar size distributions about their respective mean diameters of 0.74 mm and 1.44 mm. These mean values are aerodynamically equivalent for the contrasting densities, as shown by calculated terminal settling velocities in a model solar nebula. Aerodynamic equivalence and similarity of size distributions suggest that metal and silicate fractions experienced the same sorting process before they were accreted onto the parent body. These characteristics, together with depletion of iron in Acfer 059 and essentially all other chondrites relative to primitive CI compositions, strongly suggest that sorting in the solar nebula involved a radial aerodynamic component and that sorting and siderophile depletion in chondrites are closely related.

  6. Oxygen isotope and chemical compositions of magnetite and olivine in the anomalous CK3 Watson 002 and ungrouped Asuka-881595 carbonaceous chondrites: Effects of parent body metamorphism

    NASA Astrophysics Data System (ADS)

    Davidson, Jemma; Krot, Alexander N.; Nagashima, Kazuhide; Hellebrand, Eric; Lauretta, Dante S.

    2014-08-01

    We report in situ O isotope and chemical compositions of magnetite and olivine in chondrules of the carbonaceous chondrites Watson-002 (anomalous CK3) and Asuka (A)-881595 (ungrouped C3). Magnetite in Watson-002 occurs as inclusion-free subhedral grains and rounded inclusion-bearing porous grains replacing Fe,Ni-metal. In A-881595, magnetite is almost entirely inclusion-free and coexists with Ni-rich sulfide and less abundant Ni-poor metal. Oxygen isotope compositions of chondrule olivine in both meteorites plot along carbonaceous chondrite anhydrous mineral (CCAM) line with a slope of approximately 1 and show a range of ?17O values (from approximately -3 to -6). One chondrule from each sample was found to contain O isotopically heterogeneous olivine, probably relict grains. Oxygen isotope compositions of magnetite in A-881595 plot along a mass-dependent fractionation line with a slope of 0.5 and show a range of ?17O values from -2.4 to -1.1. Oxygen isotope compositions of magnetite in Watson-002 cluster near the CCAM line and a ?17O value of -4.0 to -2.9. These observations indicate that magnetite and chondrule olivine are in O isotope disequilibrium, and, therefore, not cogenetic. We infer that magnetite in CK chondrites formed by the oxidation of pre-existing metal grains by an aqueous fluid during parent body alteration, in agreement with previous studies. The differences in ?17O values of magnetite between Watson-002 and A-881595 can be attributed to their different thermal histories: the former experienced a higher degree of thermal metamorphism that led to the O isotope exchange between magnetite and adjacent silicates.

  7. Titanium isotopic anomalies in chondrules from carbonaceous chondrites

    SciTech Connect

    Niemeyer, S.

    1988-02-01

    Isotopic analyses of Ti from chondrules of carbonaceous chondrites reveal that Ti anomalies are present; anomalies are detected only at /sup 50/Ti. For a suite of eight Allende chondrules, four give well-resolved anomalies which range from a /sup 50/Ti deficit of two epsilon-units to a /sup 50/Ti excess of nine epsilon-units. No clear link is evident between the structure or composition of the chondrules and the Ti anomalies. However, the chondrule with by far the largest Ti isotopic anomaly is also Al-rich. Yet the absence of a strict correlation between the Ca, Al, and Ti contents and the Ti anomalies, together with the similarity of the /sup 50/Ti excess for the one chondrule to that of most Ca-Al-rich inclusions (CAIs), indicate that the relation between degree of refractory enrichment and the magnitude of Ti isotopic anomalies is not a simple one. Single chondrules from Murchison, Kaidun, and Kakangari all fail to exhibit a well-resolved anomaly, although in the latter two the single analysis of each precludes resolving anomalies of less than three epsilon-units. These observations support the view that the Ti isotopic diversity in chondrules in an inherited feature from their precursor assemblages of dust. Models which envision similar precursors for both chondrules and matrix are consistent with the Ti isotopic data. But at least two distinct solid-matter reservoirs are required for the Allende chondrules alone, which underscores the diversity in the nebular dust. These Ti anomalies also caution that more than one dust isotopic component may be necessary to account fully for the oxygen isotopic variations in chondrules. The Ti anomalies in chondrules argue strongly against models which ascribe the Ti anomalies in CAIs to unique features of their evolution; instead, heterogeneities were more common in the nebular dust.

  8. An American on Paris: Extent of aqueous alteration of a CM chondrite and the petrography of its refractory and amoeboid olivine inclusions

    NASA Astrophysics Data System (ADS)

    Rubin, Alan E.

    2015-09-01

    Paris is the least aqueously altered CM chondrite identified to date, classified as subtype 2.7; however, literature data indicate that some regions of this apparently brecciated meteorite may be subtype 2.9. The suite of CAIs in Paris includes 19% spinel-pyroxene inclusions, 19% spinel inclusions, 8% spinel-pyroxene-olivine inclusions, 43% pyroxene inclusions, 8% pyroxene-olivine inclusions, and 3% hibonite-bearing inclusions. Both simple and complex inclusions are present; some have nodular, banded, or distended structures. No melilite was identified in any of the inclusions in the present suite, but other recent studies have found a few rare occurrences of melilite in Paris CAIs. Because melilite is highly susceptible to aqueous alteration, it is likely that it was mostly destroyed during early-stage parent-body alteration. Two of the CAIs in this study are part of compound CAI-chondrule objects. Their presence suggests that there were transient heating events (probably associated with chondrule formation) in the nebula after chondrules and CAIs were admixed. Also present in Paris are a few amoeboid olivine inclusions (AOI) consisting of relatively coarse forsterite rims surrounding fine-grained, porous zones containing diopside and anorthite. The interior regions of the AOIs may represent fine-grained rimless CAIs that were incorporated into highly porous forsterite-rich dustballs. These assemblages were heated by an energy pulse that collapsed and coarsened their rims, but failed to melt their interiors.

  9. Titanium isotopic anomalies in chondrules from carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Niemeyer, S.

    1988-02-01

    Isotopic analyses of Ti from a suite of eight Allende chondrules were conducted to determine whether any relationship exists between the composition and structure of a chondrule and the Ti isotopic patterns. Four of the eight chondrules displayed well-resolved anomalies with respect to Ti-50/Ti-46 ratio, which ranged from a Ti-50 deficit of two epsilon-units to a T-50 excess of nine epsilon-units. No clear link was found between the structure of the chondrules and the Ti anomalies (although the chondrule with by far the largest Ti isotopic anomaly was also Al-rich, suggesting that there might exist a complicated relationship between the degree of refractory enrichment and the magnitude of Ti isotopic anomalies.

  10. Compositional evidence regarding the origins of rims on Semarkona chondrules

    NASA Astrophysics Data System (ADS)

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

    1987-11-01

    This paper presents results on neutron activation analyses of the interiors and the abraded surfaces of seven chondrules from Semarkona chondrite. The results showed that six of seven chondrule rims have enhanced contents of siderophiles and chalcophiles relative to chondrule interiors, indicating that, during chondrule formation, metal/sulfide melts migrated to the exterior of the chondrule; 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.

  11. The effect of oxygen fugacity on the partitioning of nickel and cobalt between olivine, silicate melt, and metal

    NASA Technical Reports Server (NTRS)

    Ehlers, Karin; Grove, Timothy L.; Sisson, Thomas W.; Recca, Steven I.; Zervas, Deborah A.

    1992-01-01

    The effect of oxygen fugacity, f(O2), on the partitioning behavior of Ni and Co between olivine, silicate melt, and metal was investigated in the CaO-MgO-Al2O3-SiO2-FeO-Na2O system, an analogue of a chondrule 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 chondrule analogue composition.

  12. CHONDRULE FORMATION IN BOW SHOCKS AROUND ECCENTRIC PLANETARY EMBRYOS

    SciTech Connect

    Morris, Melissa A.; Desch, Steven J.; Athanassiadou, Themis; Boley, Aaron C.

    2012-06-10

    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 chondrules-millimeter-sized igneous inclusions found in meteorites-were forming. We model the formation of chondrules 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 chondrules 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, chondrules are accreted onto smaller planetesimals. We calculate the thermal histories of chondrules 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 chondrules, assuming a modest enhancement above the likely solar nebula average value of chondrule densities (by a factor of 10), attributable to settling of chondrule 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 chondrules. In principle, a small number (1-10) of eccentric planetary embryos can melt the observed mass of chondrules in a manner consistent with all known constraints.

  13. Rock magnetic properties of dusty olivine: comparison and calibration of non-heating paleointensity methods

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The mechanism of chondrule formation is an important outstanding question in cosmochemistry. Magnetic signals recorded by Fe-Ni nanoparticles in chondrules could carry clues to their origin. Recently, research in this area has focused on 'dusty olivine' in ordinary chondrites as potential carriers of pre-accretionary remanence. Dusty olivine is characterised by the presence of sub-micron Fe-Ni inclusions within the olivine host. These metal particles form via subsolidus reduction of the olivine during chondrule formation and are thought to be protected from subsequent chemical and thermal alteration by the host olivine. Three sets of synthetic dusty olivines have been produced, using natural olivine (average Ni-content of 0.3 wt%), synthetic Ni-containing olivine (0.1wt% Ni) and synthetic Ni-free olivine as starting materials. The starting materials were ground to powders, packed into a 8-27 mm3 graphite crucible, heated up to 1350C under a pure CO gas flow and kept at this temperature for 10 minutes. After this the samples were held in fixed orientation and quenched into water in a range of known magnetic fields from 0.2 mT to 1.5 mT. We present a comparison of all non-heating methods commonly used for paleointensity determination of extraterrestrial material. All samples showed uni-directional, single-component demagnetization behaviour. Saturation REM ratio (NRM/SIRM) and REMc ratio show non-linear behaviour as function of applied field and a saturation value < 1. Using the REM' method the samples showed approximately constant REM' between 100 and 150 mT AF-field. Plotting the average values for this field range again shows non-linear behaviour and a saturation value < 1. Another approach we examined to obtain calibration curves for paleointensity determination is based on ARM measurents. We also present an analysis of a new FORC-based method of paleointensity determination applied to metallic Fe-bearing samples [1, 2]. The method uses a first-order reversal curve (FORC) diagram to generate a Preisach distribution of coercivities and interaction fields within the sample and then physically models the acquisition of TRM as function of magnetic field, temperature and time using thermal relaxation theory. The comparison of observed and calculated NRM demagnetisation spectra is adversely effected by a large population of particles in the single-vortex state. Comparison of observed and calculated REM' curves, however, yields much closer agreement in the high-coercivity SD-dominated range. Calculated values of the average REM' ratio show excellent agreement with the experimental values - including the observed non-linearity of the remanence acquisition curve - suggesting that this method has the potential to reduce the uncertainties in non-heating paleointensity methods for extraterrestrial samples. [1] AR Muxworthy and D Heslop(2011) A Preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements: 1. Theoretical framework. Journal of Geophysical Research, 116, B04102, doi:10.1029/2010JB007843. [2] AR Muxworthy, D Heslop, GA Paterson, and D Michalk. A Preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements: 2. Experimental testing. Journal of Geophysical Research, 116, B04103, doi:10.1029/2010JB007844.

  14. Reinvestigation of the olivine-spinel transformation in Ni2SiO4 and the incongruent melting of Ni2SiO4 olivine

    NASA Technical Reports Server (NTRS)

    Ma, C.-B.

    1974-01-01

    The olivine-spinel transformation and the melting behavior of Ni2SiO4 were investigated over the PT ranges of 20-40 kbar, 650-1200 C, and 5-13 kbar, 1600-1700 C, respectively. It was confirmed that Ni2SiO4 olivine melts incongruently at high pressures and that it is a stable phase until melting occurs. The PT slope of the incongruent melting curve is approximately 105 bars/deg. The olivine-spinel transformation curve was shown to be a reversible univariant curve, and could be expressed by the linear equation P(bars) equals 23,300 + 11.8 x T(deg C). The transformation curve determined by Akimoto et al. (1965) is nearly parallel to that of the present work, but lies at pressures about 12% lower.

  15. Origin of olivine at Copernicus

    NASA Technical Reports Server (NTRS)

    Pieters, C. M.; Wilhelms, D. E.

    1985-01-01

    The central peaks of Copernicus are among the few lunar areas where near-infrared telescopic reflectance spectra indicate extensive exposures of olivine. Other parts of Copernicus crater and ejecta, which were derived from highland units in the upper parts of the target site, contain only low-Ca pyroxene as a mafic mineral. The exposure of compositionally distinct layers including the presence of extensive olivine may result from penetration to an anomalously deep layer of the crust or to the lunar mantle. It is suggested that the Procellarum basin and the younger, superposed Insularum basin have provided access to these normally deep-seated crustal or mantle materials by thinning the upper crustal material early in lunar history. The occurrences of olivine in portions of the compositionally heterogeneous Aristarchus Region, in a related geologic setting, may be due to the same sequence of early events.

  16. Origin of olivine at Copernicus

    NASA Astrophysics Data System (ADS)

    Pieters, Carle M.; Wilhelms, Don E.

    1985-02-01

    The central peaks of Copernicus are among the few lunar areas where near-infrared telescopic reflectance spectra indicate extensive exposures of olivine. Other parts of Copernicus crater and ejecta, which were derived from highland units in the upper parts Of the target site, contain only low-Ca pyroxene as a mafic mineral. The exposure of compositionally distinct layers including the presence of extensive olivine may result from penetration to an anomalously deep layer of the crust or to the lunar mantle. We suggest that the Procellarum basin and the younger, superposed Insularum basin have provided access to these normally deep-seated crustal or mantle materials by thinning the upper crustal material early in lunar history. The occurrences of olivine in portions of the compositionally heterogeneous Aristarchus Region, in a related geologic setting, may be due to the same sequence of early events.

  17. Origin of olivine at Copernicus

    NASA Astrophysics Data System (ADS)

    Pieters, C. M.; Wilhelms, D. E.

    1985-02-01

    The central peaks of Copernicus are among the few lunar areas where near-infrared telescopic reflectance spectra indicate extensive exposures of olivine. Other parts of Copernicus crater and ejecta, which were derived from highland units in the upper parts of the target site, contain only low-Ca pyroxene as a mafic mineral. The exposure of compositionally distinct layers including the presence of extensive olivine may result from penetration to an anomalously deep layer of the crust or to the lunar mantle. It is suggested that the Procellarum basin and the younger, superposed Insularum basin have provided access to these normally deep-seated crustal or mantle materials by thinning the upper crustal material early in lunar history. The occurrences of olivine in portions of the compositionally heterogeneous Aristarchus Region, in a related geologic setting, may be due to the same sequence of early events.

  18. Mineralogy and Petrology of Amoeboid Olivine Inclusions in CO3 Chondrites: Relationship to Parent-Body Aqueous Alteration

    NASA Technical Reports Server (NTRS)

    Chizmadia, Lysa J.; Rubin, Alan E.; Wasson, John T.

    2003-01-01

    Petrographic and mineralogic studies of amoeboid olivine 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 olivine (Fa(sub 0-1)) is systematically converted into ferroan olivine (Fa(sub 60-75)). We infer that the Fe, Si and O entered the assemblage along grain boundaries, forming ferroan olivine that filled fractures and voids. As temperatures increased, Fe(+2) from the new olivine 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 olivine compositional distributions can be used to refine the classification of CO3 chondrites into subtypes. In subtype 3.0, olivine occurs as small forsterite grains (Fa(sub 0-1)), free of ferroan olivine. In petrologic subtype 3.2, narrow veins of FeO-rich olivine have formed at forsterite grain boundaries. With increasing alteration, these veins thicken to form zones of ferroan olivine at the outside AOI margin and within the AOI interior. By subtype 3.7, there is a fairly broad olivine 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 olivine grains in Isna (CO3.8) chondrules 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.

  19. Enhanced olivine carbonation within a basalt as compared to single-phase experiments: the impact of redox and bulk composition on the dissolution kinetics of olivine

    NASA Astrophysics Data System (ADS)

    Sissmann, O.; Brunet, F.; Martinez, I.; Guyot, F. J.; Verlaguet, A.; Pinquier, Y.; Garcia, B.; Chardin, M.; Kohler, E.; Daval, D.

    2014-12-01

    Olivine (Mg,Fe)2SiO4, which is one of the major mineral constituents of mafic and ultramafic rocks, has an attractive potential for CO2 mineral sequestration, as it possesses a high content of carbonate-forming divalent cations and exhibits one of the highest dissolution rate amongst rock-forming minerals. This study reports drastic differences in carbonation yields between experiments performed on olivine-rich basalt samples and on olivine separates (a more restricted chemical system). Batch experiments were conducted in water at 150C and pCO2 = 280 bars on a Mg-rich tholeiitic basalt (9.3 wt.% MgO and 12.2 wt.% CaO), composed of olivine, Ti-magnetite, plagioclase and clinopyroxene. After 45 days of reaction, 56 wt.% of the initial MgO has reacted with CO2 to form Fe-bearing magnesite (Mg0.8Fe0.2)CO3 along with minor calcium carbonates. The substantial decrease of olivine content upon carbonation supports the idea that ferroan magnesite formation mainly follows from olivine dissolution. In contrast, in experiments performed under similar run durations and P/T conditions with a San Carlos olivine 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 is enhanced by a factor of 40. It could be accounted for by differences in chemical and textural properties of the secondary-silica layer which covers reacted olivine grains in both types of sample. A TEM inspection of mineral surfaces shows that the thin amorphous silica layer (~100 nm) is porous in the case of the basalt sample and that it contains significant amounts of iron and aluminum. Thus, we propose that the composition of the olivine environment itself can strongly influence the olivine dissolution-carbonation process. Consequently, laboratory data obtained on olivine separates might yield a conservative estimate of the true carbonation potential of olivine-bearing basaltic rocks. More generally, this study questions the approach which consists in evaluating the carbonation potential of a rock based on experiments on separate minerals. It also emphasizes the impact of fO2 and potential co-injected gases on the olivine dissolution-carbonation process.

  20. The circumplanetary nebular environment: A possible source region for chondrules

    NASA Technical Reports Server (NTRS)

    Sanders, I. S.

    1994-01-01

    Hypotheses for the origin of chondrules fall into two broad groups: nebular and planetary. Arguments against the latter have prevailed in recent years such that, by default, the less testable nebular setting for chondrule formation is now generally favored. However, the recognition in ordinary chondrites of igneous clasts that probably formed on, or in, small planetoids hints that some parent bodies were still accreting after others had evolved magmatically and lost material to space, presumably by impact. If melting of planetoids can predate accretion, could the same early melting even be related to chondrule production? My affirmative response to this interesting question is expanded here in a chondrule-forming scenario, which incorporates both planetary and nebular features.

  1. Isotopic Mass Fractionation of Iron in Chondrules, Evaporation or Reduction?

    NASA Astrophysics Data System (ADS)

    Cohen, B. A.; Levasseur, S.; Zanda, B.; Hewins, R. H.; Halliday, A. N.

    2005-03-01

    The nature of Fe-isotopic mass fractionation measured in chondrules is controversial. Reduction experiments of fayalite yielded a strongly fractionated glass along side metal lacking mass fractionation. We argue for a diffusion-controlled fractionation to explain the data.

  2. Chondrule Formation: Nebular Gas Confinement of Impact Splashes

    NASA Astrophysics Data System (ADS)

    Dullemond, Cornelis Petrus; Johansen, Anders

    2013-07-01

    We show that the impact debris from a high-speed collision between two planetesimals during the first few million years would sweep up the nebular gas as a snow plow, leading to deceleration and compression of the debris into a thin shell. This shell breaks up into dense bullets through the Rayleigh-Taylor instability. As a result of the compression by the gas, these bullets will have super-Roche densities and thus will gravitationally collapse to form new planetesimals. Chondrules that may have formed from impact melting would thus rapidly be reaccreted into planetesimals. These dense environments are ideal for forming compound chondrules. The hydrodynamic interaction with the nebular gas could lead to mixing between the newly formed chondrules and surviving pre-impact material. Volatiles can be exchanged between these components in the dense bullets, allowing for chemical complementarity. We believe that this scenario may have some advantages over earlier impact scenarios for chondrule formation.

  3. Relation Between Silicate Chondrules and Metal-Sulfide Nodules in EH3 Chondrites

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

    We compare the composition of sulfides in MSN and chondrules, report spheroidal aggregates of silicates, silica, metal, and sulfides, and the variation in the abundance of opaque and non-opaque minerals comprising MSN and silicate chondrules.

  4. Petrology of Chondrules and a Diopside-Rich Inclusion in the MAC 88136 EL3 Chondrite

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

    MAC 88136 (EL3) contains densely-packed enstatite-rich chondrules, metal-rich nodules intergrown with silicate and an unusual large, diopside-rich chondrule-like object. Petrologic and chemical features suggest hot accretion for its components.

  5. Chondrule Formation via Impact Jetting Triggered by Planetary Accretion

    NASA Astrophysics Data System (ADS)

    Hasegawa, Yasuhiro; Wakita, Shigeru; Matsumoto, Yuji; Oshino, Shoichi

    2016-01-01

    Chondrules are one of the most primitive elements that can serve as a fundamental clue to the origin of our solar system. We investigate a formation scenario of chondrules that involves planetesimal collisions and the resultant impact jetting. Planetesimal collisions are the main agent to regulate planetary accretion that leads to the formation of terrestrial planets and cores of gas giants. The key component of this scenario is that ejected materials can melt when the impact velocity between colliding planetesimals exceeds about 2.5 km s-1. Previous simulations have shown that the process is efficient enough to reproduce the primordial abundance of chondrules. We examine this scenario carefully by performing semi-analytical calculations that are developed based on the results of direct N-body simulations. As found in the previous work, we confirm that planetesimal collisions that occur during planetary accretion can play an important role in forming chondrules. This arises because protoplanet-planetesimal collisions can achieve an impact velocity of about 2.5 km s-1 or higher, as protoplanets approach the isolation mass (Mp,iso). Assuming that the ejected mass is a fraction (Fch) of the colliding planetesimals’ mass, we show that the resultant abundance of chondrules is expressed well by FchMp,iso, as long as the formation of protoplanets is completed within a given disk lifetime. We perform a parameter study and examine how the abundance of chondrules and the timing of their formation change. We find that the impact jetting scenario generally works reasonably well for a certain range of parameters, while more dedicated work would be needed to include other physical processes that are neglected in this work and to examine their effects on chondrule formation.

  6. 26Al in plagioclase-rich chondrules in carbonaceous chondrites: Evidence for an extended duration of chondrule formation

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

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

  7. On the possible role of elemental carbon in the formation of reduced chondrules

    NASA Technical Reports Server (NTRS)

    Connolly, Harold C., Jr.; Hewins, Roger H.; Ash, Richard D.; Lofgren, Gary E.; Zanda, Brigitte

    1994-01-01

    Recent experiments have been designed to produce chondrule textures via flash melting while simultaneously studying the nature of chondrule 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 chondrules produced by flash melting.

  8. Trace Element Distribution in an Al-rich Chondrule from the Mokoia CV3 Chondrite

    NASA Technical Reports Server (NTRS)

    Jones, R. H.; Shearer, C. K.; Schilk, A. J.

    2001-01-01

    We have studied an Al-rich chondrule from Mokoia. SIMS analyses of plagioclase and pyroxene show that the bulk chondrule REE pattern was originally like group II CAIs. The chondrule must have had precursor material that was a condensation product. Additional information is contained in the original extended abstract.

  9. Trace Element Distribution in an Al-rich Chondrule from the Mokoia CV3 Chondrite

    NASA Astrophysics Data System (ADS)

    Jones, R. H.; Shearer, C. K.; Schilk, A. J.

    2001-03-01

    We have studied an Al-rich chondrule from Mokoia. SIMS analyses of plagioclase and pyroxene show that the bulk chondrule REE pattern was originally like group II CAIs. The chondrule must have had precursor material that was a condensation product.

  10. Trace Elements in Aluminum-rich Chondrules from the Mokoia CV Chondrite

    NASA Astrophysics Data System (ADS)

    Jones, R. H.; Norman, M. D.

    2008-03-01

    Two Al-rich chondrules have fractionated, group II REE abundance patterns. CAI-like precursor material was completely melted during chondrule formation. One chondrule has a high Th/U ratio, comparable to the highest Th/U ratios measured in CAIs.

  11. Forming chondrules in impact splashes. I. Radiative cooling model

    SciTech Connect

    Dullemond, Cornelis Petrus; Stammler, Sebastian Markus; Johansen, Anders

    2014-10-10

    The formation of chondrules is one of the oldest unsolved mysteries in meteoritics and planet formation. Recently an old idea has been revived: the idea that chondrules form as a result of collisions between planetesimals in which the ejected molten material forms small droplets that solidify to become chondrules. Pre-melting of the planetesimals by radioactive decay of {sup 26}Al would help produce sprays of melt even at relatively low impact velocity. In this paper we study the radiative cooling of a ballistically expanding spherical cloud of chondrule droplets ejected from the impact site. We present results from numerical radiative transfer models as well as analytic approximate solutions. We find that the temperature after the start of the expansion of the cloud remains constant for a time t {sub cool} and then drops with time t approximately as T ≅ T {sub 0}[(3/5)t/t {sub cool} + 2/5]{sup –5/3} for t > t {sub cool}. The time at which this temperature drop starts t {sub cool} depends via an analytical formula on the mass of the cloud, the expansion velocity, and the size of the chondrule. During the early isothermal expansion phase the density is still so high that we expect the vapor of volatile elements to saturate so that no large volatile losses are expected.

  12. Forming Chondrules in Impact Splashes. I. Radiative Cooling Model

    NASA Astrophysics Data System (ADS)

    Dullemond, Cornelis Petrus; Stammler, Sebastian Markus; Johansen, Anders

    2014-10-01

    The formation of chondrules is one of the oldest unsolved mysteries in meteoritics and planet formation. Recently an old idea has been revived: the idea that chondrules form as a result of collisions between planetesimals in which the ejected molten material forms small droplets that solidify to become chondrules. Pre-melting of the planetesimals by radioactive decay of 26Al would help produce sprays of melt even at relatively low impact velocity. In this paper we study the radiative cooling of a ballistically expanding spherical cloud of chondrule droplets ejected from the impact site. We present results from numerical radiative transfer models as well as analytic approximate solutions. We find that the temperature after the start of the expansion of the cloud remains constant for a time t cool and then drops with time t approximately as T ~= T 0[(3/5)t/t cool + 2/5]-5/3 for t > t cool. The time at which this temperature drop starts t cool depends via an analytical formula on the mass of the cloud, the expansion velocity, and the size of the chondrule. During the early isothermal expansion phase the density is still so high that we expect the vapor of volatile elements to saturate so that no large volatile losses are expected.

  13. Noble-gas-rich chondrules in an enstatite meteorite.

    PubMed

    Okazaki, R; Takaoka, N; Nagao, K; Sekiya, M; Nakamura, T

    2001-08-23

    Chondrules are silicate spherules that are found in abundance in the most primitive class of meteorites, the chondrites. Chondrules are believed to have formed by rapid cooling of silicate melt early in the history of the Solar System, and their properties should reflect the composition of (and physical conditions in) the solar nebula at the time when the Sun and planets were forming. It is usually believed that chondrules lost all their noble gases at the time of melting. Here we report the discovery of significant amounts of trapped noble gases in chondrules in the enstatite chondrite Yamato-791790, which consists of highly reduced minerals. The elemental ratios 36Ar/132Xe and 84Kr/132Xe are similar to those of 'subsolar' gas, which has the highest 36Ar/132Xe ratio after that of solar-type noble gases. The most plausible explanation for the high noble-gas concentration and the characteristic elemental ratios is that solar gases were implanted into the chondrule precursor material, followed by incomplete loss of the implanted gases through diffusion over time. PMID:11518959

  14. Chondrule Glass Alteration in Type IIA Chondrules in the CR2 Chondrites EET 87770 and EET 92105: Insights into Elemental Exchange Between Chondrules and Matrices

    NASA Technical Reports Server (NTRS)

    Burger, Paul V.; Brearley, Adrian J.

    2004-01-01

    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 chondrules (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 chondrule rims have been partially altered and chondrule 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 chondrule 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].

  15. Amoeboid olivine aggregates from CH carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    Amoeboid olivine aggregates (AOAs) in CH carbonaceous chondrites are texturally and mineralogically similar to those in other carbonaceous chondrite groups. They show no evidence for alteration and thermal metamorphism in an asteroidal setting and consist of nearly pure forsterite (Fa<3; in wt%, CaO = 0.1-0.8, Cr2O3 = 0.04-0.48; MnO < 0.5), anorthite, Al-diopside (in wt%, Al2O3 = 0.7-8.1; TiO2 < 1), Fe,Ni-metal, spinel, and, occasionally, low-Ca pyroxene (Fs1Wo2-3), and calcium-aluminum-rich inclusions (CAIs). The CAIs inside AOAs are composed of hibonite, grossite, melilite (k13-44), spinel, perovskite, Al,Ti-diopside (in wt%, Al2O3 up to 19.6; TiO2 up to 13.9), and anorthite. The CH AOAs, including CAIs within AOAs, have isotopically uniform 16O-rich compositions (average ?17O = -23.4 2.3, 2SD) and on a three-isotope oxygen diagram plot along ?slope-1 line. The only exception is a low-Ca pyroxene-bearing AOA 1-103 that shows a range of ?17O values, from -24 to -13. Melilite, grossite, and hibonite in four CAIs within AOAs show no evidence for radiogenic 26Mg excess (?26Mg). In contrast, anorthite in five out of six AOAs measured has ?26Mg corresponding to the inferred initial 26Al/27Al ratio of (4.3 0.7) 10-5, (4.2 0.6) 10-5, (4.0 0.3) 10-5, (1.7 0.2) 10-5, and (3.0 2.6) 10-6. Anorthite in another AOA shows no resolvable ?26Mg excess; an upper limit on the initial 26Al/27Al ratio is 5 10-6. We infer that CH AOAs formed by gas-solid condensation and aggregation of the solar nebula condensates (forsterite and Fe,Ni-metal) mixed with the previously formed CAIs. Subsequently they experienced thermal annealing and possibly melting to a small degree in a 16O-rich gaseous reservoir during a brief epoch of CAI formation. The low-Ca pyroxene-bearing AOA 1-103 may have experienced incomplete melting and isotope exchange in an 16O-poor gaseous reservoir. The lack of resolvable ?26Mg excess in melilite, grossite, and hibonite in CAIs within AOAs reflects heterogeneous distribution of 26Al in the solar nebula during this epoch. The observed variations of the inferred initial 26Al/27Al ratios in anorthite of the mineralogically pristine and uniformly 16O-rich CH AOAs could have recorded (i) admixing of 26Al in the protoplanetary disk during the earliest stages of its evolution and/or (ii) closed-system Mg-isotope exchange between anorthite and Mg-rich minerals (spinel, forsterite, and Al-diopside) during subsequent prolonged (days-to-weeks) thermal annealing at high temperature (?1100 C) and slow cooling rates (?0.01 K h-1) that has not affected their O-isotope systematics. The proposed thermal annealing may have occurred in an impact-generated plume invoked for the origin of non-porphyritic magnesian chondrules and Fe,Ni-metal grains in CH and CB carbonaceous chondrites about 5 Myr after formation of CV CAIs.

  16. Dynamic crystallization experiments on chondrule melts in reduced gravity

    NASA Technical Reports Server (NTRS)

    Lofgren, Gary; Williams, R. J.

    1987-01-01

    Chondrules crystallized during the earliest formational history of the solar system; and, if crystal settling and flotation are indicators of crystallization in the presence of gravity, they formed without the influence of gravity. In fact, attempts to duplicate the crystallization history of chondrules in the laboratory have met with limited success, because of the difficulty of comparing objects formed under the influence of gravity with objects that did not. These comparisons are difficult because there are several recognized features introduced by the presence of gravity and no doubt some which are not yet recognized. As a result there are several microscale and macroscale aspects of chondrule petrology which are difficult to understand quantitatively. Most of the features relate to the settling or flotation of early formed crystals. The proposed experiments are briefly described.

  17. Implications of a phase-transition thermostat for chondrule melting

    NASA Technical Reports Server (NTRS)

    Love, S. G.

    1994-01-01

    It is widely accepted that chondrules were formed in brief, localized nebular heating episodes. Given the apparent (at least local) high efficiency of chondrule 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 chondrule-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.

  18. The legacy of crystal-plastic deformation in olivine: high-diffusivity pathways during serpentinization

    NASA Astrophysics Data System (ADS)

    Plmper, Oliver; King, Helen E.; Vollmer, Christian; Ramasse, Quentin; Jung, Haemyeong; Austrheim, Hkon

    2012-04-01

    Crystal-plastic olivine 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 ( bar{X}_{text{Fe}} = 0.24 0.02 (zones); 0.12 0.02 (bulk)) or Fe-depleted ( bar{X}_{text{Fe}} = 0.10 0.01 (zones); 0.13 0.01 (bulk)) zoning in partly serpentinized olivine 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 olivine 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 olivine/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 olivine subgrain boundaries suggest that water was able to ingress along them. Crystallographic orientation relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations support the hypothesis that serpentinization was initiated along olivine subgrain boundaries.

  19. Shape, metal abundance, chemistry, and origin of chondrules in the Renazzo (CR) chondrite

    SciTech Connect

    Ebel, D.S.; Weisberg, M.K.; Hertz, J.; Campbell, A.J.

    2009-03-31

    We used synchrotron X-ray microtomography to image in 3-dimensions (3D) eight whole chondrules 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 chondrules and quantify indices of chondrule sphericity. Volumetric metal abundances in whole chondrules range from 1 to 37 volume % in 8 measured chondrules and by inspection in tomography data. We show that metal abundances and metal grain locations in individual chondrules cannot be reliably obtained from single random 2D sections. Samples were physically cut to intersect representative chondrules multiple times and to verify 3D data. Detailed 2D chemical analysis combined with 3D data yield highly variable whole-chondrule Mg/Si ratios with a supra-chondritic mean value, yet the chemically diverse, independently formed chondrules are mutually complementary in preserving chondritic (solar) Fe/Si ratios in the aggregate CR chondrite. These results are consistent with localized chondrule formation and rapid accretion resulting in chondrule + matrix aggregates (meteorite parent bodies) that preserve the bulk chondritic composition of source regions.

  20. A nebula setting as the origin for bulk chondrule Fe isotope variations in CV chondrites

    NASA Astrophysics Data System (ADS)

    Hezel, Dominik C.; Needham, Andrew W.; Armytage, Ros; Georg, Bastian; Abel, Richard L.; Kurahashi, Erika; Coles, Barry J.; Rehkmper, Mark; Russell, Sara S.

    2010-08-01

    We combined micro computer tomography with Fe and Si isotope measurements of Mokoia, Allende and Grosnaja chondrules. Ten Mokoia chondrules contain 0.9 to 11.8 vol.% opaque phases (metal + sulfide), and 6 Allende chondrules contain 0.0 to 6.6 vol.% opaque phases. Hence, the Fe isotope composition of many chondrules is dominated by the Fe isotope composition of their opaque phases. We studied Fe isotopes of 35 bulk chondrules. The range is different for each of the three meteorites studied and largest for Allende with ?56Fe ranging from - 0.82 to + 0.37. Six out of seven chondrules analysed for their Si isotope composition in Mokoia and Grosnaja have similar ?29Si of around - 0.12. One anomalous chondrule in Mokoia has a ?29Si of + 0.58. We exclude isotopically heterogeneous chondrule precursors and different isotopic chondrule reservoirs as the source of the observed Fe isotope variation among bulk chondrules. We conclude that the observed bulk chondrule Fe isotope variation is the result of evaporation and re-condensation processes in a nebula setting with high dust densities, required to explain the comparatively low isotope fractionations. Subsequent parent body alteration slightly overprinted this pre-accretionary Fe isotope variation.

  1. Papers presented to the Conference on Chondrules and the Protoplanetary Disk

    NASA Technical Reports Server (NTRS)

    1994-01-01

    The following topics are covered in the presented papers: (1) producing chondrules; (2) carbons, CAI's, and chondrules; (3) large scale processes in the solar nebula; (4) chondrule-matrix relationships in chondritic meteorites; (5) overview of nebula models; (6) constraints placed on the nature of chondrule precursors; (7) turbulent diffusion and concentration of chondrules 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 chondrules in nebular fractionations of volatiles and other elements; (12) astronomical observations of phenomena in disks; (13) experimental constraints on models for origins of chondrules, and various other topics.

  2. Multiple origins for olivine at Copernicus crater

    NASA Astrophysics Data System (ADS)

    Dhingra, Deepak; Pieters, Carle M.; Head, James W.

    2015-06-01

    Multiple origins for olivine-bearing lithologies at Copernicus crater are recognized based on integrated analysis of data from Chandrayaan-1 Moon Mineralogy Mapper (M3), Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) and Kaguya Terrain Camera (TC). We report the diverse morphological and spectral character of previously known olivine-bearing exposures as well as the new olivine occurrences identified in this study. Prominent albedo differences exist between olivine-bearing exposures in the central peaks and a northern wall unit (the latter being ?40% darker). The low-albedo wall unit occurs as a linear mantling deposit and is interpreted to be of impact melt origin, in contrast with the largely unmodified nature of olivine-bearing peaks. Small and localized occurrences of olivine-bearing lithology have also been identified on the impact melt-rich floor, representing a third geologic setting (apart from crater wall and peaks). Recent remote sensing missions have identified olivine-bearing exposures around lunar basins (e.g. Yamamoto et al., 2010; Pieters et al., 2011; Kramer et al., 2013) and at other craters (e.g. Sun and Li, 2014), renewing strong interest in its origin and provenance. A direct mantle exposure has commonly been suggested in this regard. Our detailed observations of the morphological and spectral diversity in the olivine-bearing exposures at Copernicus have provided critical constraints on their origin and source regions, emphasizing multiple formation mechanisms. These findings directly impact the interpretation of olivine exposures elsewhere on the Moon. Olivine can occur in diverse environments including an impact melt origin, and therefore it is unlikely for all olivine exposures to be direct mantle occurrences as has generally been suggested.

  3. How to form planetesimals from mm-sized chondrules and chondrule aggregates

    NASA Astrophysics Data System (ADS)

    Carrera, Daniel; Johansen, Anders; Davies, Melvyn B.

    2015-07-01

    The size distribution of asteroids and Kuiper belt objects in the solar system is difficult to reconcile with a bottom-up formation scenario due to the observed scarcity of objects smaller than ~100 km in size. Instead, planetesimals appear to form top-down, with large 100-1000 km bodies forming from the rapid gravitational collapse of dense clumps of small solid particles. In this paper we investigate the conditions under which solid particles can form dense clumps in a protoplanetary disk. We used a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from submillimeter-sized chondrules to meter-sized rocks. We found that particles down to millimeter sizes can form dense particle clouds through the run-away convergence of radial drift known as the streaming instability. We made a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) that are prone to producing dense particle clumps. Finally, we estimate the distribution of collision speeds between mm-sized particles. We calculated the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of ~105 years. This means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale (~106-107 years). Our results suggest a pathway from the mm-sized grains found in primitive meteorites to fully formed asteroids. We speculate that asteroids may form from a positive feedback loop in which coagualation leads to particle clumping driven by the streaming instability. This clumping, in turn, reduces collision speeds and enhances coagulation. Future simulations should model coagulation and the streaming instability together to explore this feedback loop further. Appendices are available in electronic form at http://www.aanda.org

  4. Sulfur Isotope Composition of Putative Primary Troilite in Chondrules

    NASA Technical Reports Server (NTRS)

    Tachibana, Shogo; Huss, Gary R.

    2002-01-01

    Sulfur isotope compositions of putative primary troilites in chondrules 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.

  5. The ascent of kimberlite: Insights from olivine

    NASA Astrophysics Data System (ADS)

    Brett, R. C.; Russell, J. K.; Andrews, G. D. M.; Jones, T. J.

    2015-08-01

    Olivine xenocrysts are ubiquitous in kimberlite deposits worldwide and derive from the disaggregation of mantle-derived peridotitic xenoliths. Here, we provide descriptions of textural features in xenocrystic olivine from kimberlite deposits at the Diavik Diamond Mine, Canada and at Igwisi Hills volcano, Tanzania. We establish a relative sequence of textural events recorded by olivine during magma ascent through the cratonic mantle lithosphere, including: xenolith disaggregation, decompression fracturing expressed as mineral- and fluid-inclusion-rich sealed and healed cracks, grain size and shape modification by chemical dissolution and abrasion, late-stage crystallization of overgrowths on olivine xenocrysts, and lastly, mechanical milling and rounding of the olivine cargo prior to emplacement. Ascent through the lithosphere operates as a "kimberlite factory" wherein progressive upward dyke propagation of the initial carbonatitic melt fractures the overlying mantle to entrain and disaggregate mantle xenoliths. Preferential assimilation of orthopyroxene (Opx) xenocrysts by the silica-undersaturated carbonatitic melt leads to deep-seated exsolution of CO2-rich fluid generating buoyancy and supporting rapid ascent. Concomitant dissolution of olivine produces irregular-shaped relict grains preserved as cores to most kimberlitic olivine. Multiple generations of decompression cracks in olivine provide evidence for a progression in ambient fluid compositions (e.g., from carbonatitic to silicic) during ascent. Numerical modelling predicts tensile failure of xenoliths (disaggregation) and olivine (cracks) over ascent distances of 2-7 km and 15-25 km, respectively, at velocities of 0.1 to >4 m s-1. Efficient assimilation of Opx during ascent results in a silica-enriched, olivine-saturated kimberlitic melt (i.e. SiO2 >20 wt.%) that crystallizes overgrowths on partially digested and abraded olivine xenocrysts. Olivine saturation is constrained to occur at pressures <1 GPa; an absence of decompression cracks within olivine overgrowths suggests depths <25 km. Late stage (<25 km) resurfacing and reshaping of olivine by particle-particle milling is indicative of turbulent flow conditions within a fully fluidized, gas-charged, crystal-rich magma.

  6. An amoeboid olivine inclusion (AOI) in CK3 NWA 1559, comparison to AOIs in CV3 Allende, and the origin of AOIs in CK and CV chondrites

    NASA Astrophysics Data System (ADS)

    Rubin, Alan E.

    2013-03-01

    An amoeboid olivine inclusion in CK3 NWA 1559 (0.54 1.3 mm) consists of a diopside-rich interior (approximately 35 vol%) and an olivine-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 olivine grains, some with 120 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 olivine 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 olivine rims as well as portions of the underlying interiors. In AOI-1, coarse plagioclase grains with diopside rinds crystallized immediately below the olivine rim. Secondary parent-body alteration transformed forsterite in the rims of CV and CK AOIs into more-ferroan olivine. 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 chondrules 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.

  7. Experimental Study of Olivine-rich Troctolites

    NASA Astrophysics Data System (ADS)

    Mu, S.; Faul, U.

    2014-12-01

    This experimental study is designed to complement field observations of olivine-rich troctolites in ophiolites and from mid-ocean ridges. The olivine-rich troctolites are characterized by high volume proportion of olivine with interstitial plagioclase and clinopyroxene. Typically the clinopyroxene occurs in the form of few large, poikilitic grains. The primary purpose of this study is to investigate the effects of cooling process on the geometry of the interstitial phases (clinopyroxene and plagioclase). Experiments are conducted in a piston cylinder apparatus by first annealing olivine plus a basaltic melt with a composition designed to be in equilibrium with four phases at ~ 1 GPa and 1250C. Initially, we anneal the olivine-basalt aggregates at 1350 C and 0.7 GPa for one week to produce a steady state microstructure. At this temperature only olivine and minor opx are present as crystalline phases. We then cool the samples over two weeks below their solidus temperature, following different protocols. The post-run samples are sectioned, polished, and imaged at high resolution and analyzed by using a field emission SEM. Initial observations show that under certain conditions clinopyroxene nucleates distributed throughout the aggregate at many sites, forming relatively small, rounded to near euhedral grains. Under certain conditions few cpx grains nucleate and grow with a poikilitic shape, partially or fully enclosing olivine grains, as is observed in natural samples. As for partially molten aggregates quenched form the annealing temperature, the microstructure will be characterized by tracing phase boundaries on screen by using ImageJ software. The geometry of the interstitial phases will be quantified by determining the grain boundary wetness, in this case the ratio of the length of polyphase to single phase (olivine-olivine) boundaries. Compositional data will also be used to study the change in major element compositions before and after the cooling process.

  8. Olivine-dominated asteroids: Mineralogy and origin

    NASA Astrophysics Data System (ADS)

    Sanchez, Juan A.; Reddy, Vishnu; Kelley, Michael S.; Cloutis, Edward A.; Bottke, William F.; Nesvorn, David; Lucas, Michael P.; Hardersen, Paul S.; Gaffey, Michael J.; Abell, Paul A.; Corre, Lucille Le

    2014-01-01

    Olivine-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 olivine-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 olivine-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 olivine-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-olivine asteroids, which are those whose spectra only exhibit the 1 ?m feature, and another referred to as olivine-rich asteroids, whose spectra exhibit the 1 ?m feature and a weak (Band II depth 4%) 2 ?m feature. For the monomineralic-olivine asteroids the olivine chemistry was found to range from Fo49 to Fo70, consistent with the values measured for brachinites and R chondrites. In the case of the olivine-rich asteroids we determined their olivine and low-Ca pyroxene abundance using a new set of spectral calibrations derived from the analysis of R chondrites spectra. We found that the olivine 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 olivine-dominated asteroids and asteroid families found no genetic link (of the type core-mantel-crust) between these objects.

  9. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

    PubMed Central

    Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

    2015-01-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag–assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars’s size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts. PMID:26601169

  10. Electromagnetic heating in the early solar nebula and the formation of chondrules.

    PubMed

    Eisenhour, D D; Daulton, T L; Buseck, P R

    1994-08-19

    Certain opaque inclusions within primitive meteorites exhibit textures that suggest chondrules formed during intense, short-duration radiative heating episodes in the early solar system. Experimental support for this interpretation is provided by the textures produced when chondrule-like assemblages are heated with visible laser light. Computer simulations of radiative heating provide additional evidence for the role of electromagnetic energy in heating nebular solids by offering an explanation for the size distributions of chondrules and the presence of dusty chondrule rims. Nebular lightning and magnetic reconnection flares are possible sources of electromagnetic energy for these transient heating events. PMID:17832896

  11. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

    NASA Astrophysics Data System (ADS)

    Johansen, Anders; Mac Low, Mordecai-Mark; Lacerda, Pedro; Bizzarro, Martin

    2015-04-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts.

  12. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion.

    PubMed

    Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

    2015-04-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts. PMID:26601169

  13. Magnetocentrifugal jets and chondrule formation in protostellar disks

    NASA Astrophysics Data System (ADS)

    Salmeron, Raquel; Ireland, Trevor

    2014-01-01

    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 (chondrules 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 chondrule-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.

  14. Turbulent Concentration of Chondrules: Size Distribution and Multifractal Scaling

    NASA Technical Reports Server (NTRS)

    Cuzzi, Jeffrey N.; Hogan, Robert C.; Paque, Julie M.; Dobrovolskis, Anthony R.

    1999-01-01

    Size-selective concentration of particles in 3D turbulence may be related to collection of chondrules 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 chondrules 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.

  15. First-Order Reversal Curve (FORC) analysis of chondrule magnetism

    NASA Astrophysics Data System (ADS)

    Emmerton, S.; Muxworthy, A. R.

    2009-12-01

    We report a rock magnetic study of the magnetic properties of chondrules from the Allende and Mokoia carbonaceous chondritic meteorites. To characterise the magnetic carriers, we have made detailed magnetic hysteresis analysis including FORC measurements. We have also conducted isothermal acquisition unmixing analysis. We have determined the ancient magnetic field intensities (paleointensities) recorded by the two meteorites. As these chondrules are highly susceptible to chemical alteration on heating, we have employed two non-heating methods of determining the ancient field intensity: (1) the calibrated REM method and (2) the newly developed Preisach-based approach that determines absolute paleointensities. Allende has been extensively studied but this is the first paleointensity estimate for the Mokoia meteorite.

  16. Electrical discharge heating of chondrules in the solar nebula

    NASA Technical Reports Server (NTRS)

    Love, Stanley G.; Keil, Klaus; Scott, Edward R. D.

    1995-01-01

    We present a rudimentary theoretical assessment of electrical discharge heating as a candidate mechanism for the formation of chondrules 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 chondrules. Despite our difficulties, we believe the topic worthy of further investigation and suggest some experiments which could improve our understanding of nebular discharges.

  17. Assessing the Degree of Secondary Alteration in Chondrules from One of the Least Altered CR Chondrites, EET 92042

    NASA Astrophysics Data System (ADS)

    Jones, R. H.; Brearley, A. J.; Henkel, T.; Lyon, I.

    2015-07-01

    Most chondrules in EET 92042 are close to pristine. Observed alteration effects at the edges of chondrules, including smooth phyllosilicate rims, are heterogeneous because they are dependent on local mineralogy.

  18. Glassy Chondrule Mesostasis in EET 96029: A CM3 Component of a Minimally Altered CM2 Carbonaceous Chondrite

    NASA Astrophysics Data System (ADS)

    Lindgren, P.; Lee, M. R.

    2014-09-01

    The CM2 carbonaceous chondrite EET 96029 contains a chondrule that has only been minimally altered so it has a mesostasis that retains glass. This provides an opportunity to study pristine CM chondrules and the earliest stages of aqueous alteration.

  19. Olivine in Almahata Sitta - Curiouser and Curiouser

    NASA Technical Reports Server (NTRS)

    Zolensky, M. E.; Herrin, J.; Mikouchi, T.; Satake, W.; Kurihara, T.; Sandford, S. A.; Milam, S. N.; Hagiya, K.; Ohsumi, K.; Friedrich, J. M.; Jeniskens, P.; Shaddad, M. H.; Le, L.; Robinson, G. A.

    2010-01-01

    Almahata Sitta (hereafter Alma) is an anomalous, polymict ureilite. Anomalous features include low abundance of olivine, large compositional range of silicates, high abundance and large size of pores, crystalline pore wall linings, and overall finegrained texture. Tomography suggests the presence of foliation, which is known from other ureilites. Alma pyroxenes and their interpretation are discussed in two companion abstracts. In this abstract we discuss the composition of olivine in Alma, which is indicative of the complexity of this meteorite.

  20. An Amoeboid Olivine Aggregate in LEW 85300

    NASA Technical Reports Server (NTRS)

    Komatsu, M. D.; Yamaguchi, A.; Fagan, T. J.; Zolensky, M. E.; Shiran, N.; Mikouchi, T.

    2016-01-01

    Amoeboid Olivine aggregates (AOAs) are irregularly shaped objects commonly observed in carbonaceous chondrites. Because they are composed of fine-grained olivine and Ca-Al-rich minerals, they are sensitive indicators for nebular process and parent body alteration of their parent bodies. Recently an AOA was found in a carbonaceous clast in polymict eucrite LEW 85300. The bulk major element composition of the clast matrix in LEW 85300 suggests a relation to CM, CO and CV chondrites, whereas bulk clast trace and major element compositions do not match any carbonaceous chondrite, suggesting they have a unique origin. Here we characterize the mineralogy of AOA in LEW 85300 and discuss the origin of the carbonaceous clasts. Results and Discussion: The AOA is located in an impact melt vein. Half of the aggregate shows recrystallization textures (euhedral pyroxene and molten metal/FeS) due to impact melting, but the remaining part preserves the original texture. The AOA is composed of olivine, FeS and Mg,Al-phyllosilicate. Individual olivine grains measure 1-8 microns, with Fe-rich rims, probably due to impact heating. Olivines in the AOA are highly forsteritic (Fo95-99), indicating that the AOA escaped thermal metamorphism [4]. Although no LIME (Low-Fe, Mn-Enriched) olivine is observed, forsterite composition and the coexistence of Mg,Al-phyllosilicate suggest that the AOA is similar to those in the Bali-type oxidized CV (CVoxB) and CR chondrites. However, it should be noted that fayalitic olivine, which commonly occurs in CVoxB AOA, is not observed in this AOA. Also, the smaller grain size (<8 microns) of olivine suggests they may be related to CM or CO chondrites. Therefore, we cannot exclude the possibility that the AOA originated from a unique carbonaceous chondrite.

  1. Planetary Embryo Bow Shocks as a Mechanism for Chondrule Formation

    NASA Astrophysics Data System (ADS)

    Mann, Christopher R.; Boley, Aaron C.; Morris, Melissa A.

    2016-02-01

    We use radiation hydrodynamics with direct particle integration to explore the feasibility of chondrule formation in planetary embryo bow shocks. The calculations presented here are used to explore the consequences of a Mars-size planetary embryo traveling on a moderately excited orbit through the dusty, early environment of the solar system. The embryo’s eccentric orbit produces a range of supersonic relative velocities between the embryo and the circularly orbiting gas and dust, prompting the formation of bow shocks. Temporary atmospheres around these embryos, which can be created via volatile outgassing and gas capture from the surrounding nebula, can non-trivially affect thermal profiles of solids entering the shock. We explore the thermal environment of solids that traverse the bow shock at different impact radii, the effects that planetoid atmospheres have on shock morphologies, and the stripping efficiency of planetoidal atmospheres in the presence of high relative winds. Simulations are run using adiabatic and radiative conditions, with multiple treatments for the local opacities. Shock speeds of 5, 6, and 7 km s‑1 are explored. We find that a high-mass atmosphere and inefficient radiative conditions can produce peak temperatures and cooling rates that are consistent with the constraints set by chondrule furnace studies. For most conditions, the derived cooling rates are potentially too high to be consistent with chondrule formation.

  2. Unambiguous voids in Allende chondrules and refractory inclusions

    SciTech Connect

    Murray, J.; Boesenberg, J.S.; Ebel, D.S.

    2003-03-26

    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 chondrules 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 chondrules and refractory inclusions in many meteorites. Voids remain ambiguous, however, because their structure and appearance vary between chondrules 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.

  3. Exsolved Ferromagnesian Olivine: Why Only in Divnoe?

    NASA Astrophysics Data System (ADS)

    Petaev, M. I.

    1995-09-01

    Recently Petaev and Brearley [1] showed that lamellar structure in olivine grains in the Divnoe meteorite was produced by the low-temperature exsolution of primary homogeneous grains. Exsolved olivine in Divnoe is in accordance with the thermodynamic model of olivine solid solution of [2], which predicts a miscibility gap in ferromagnesian olivines below ~340 degrees C within a compositional range that widens with decreasing temperature. Experiments on the coexistence of olivines having a range of compositions with aqueous solutions of (Fe,Mg)Cl2 [3] suggest that exsolution in ferromagnesian olivines could occur even at temperatures as high as ~400 - 450 degrees C. However, [1] remains the only observation of exsolution in natural olivines so far. This means either that (1) the exsolution in Divnoe olivine is unique, or (2) olivine grains in other slowly cooled coarse-grained rocks has not been studied closely enough to detect them. This work attempts to clarify the issue. Olivine grains from selected meteorites (Springwater pallasite, Lowitz mesosiderite, ALHA 84025 brachinite, Gorlovka H3-4 chondrite and Krymka L3 chondrite, and the Calcalong Creek lunar meteorite) and terrestrial rocks (San Carlos forsterite and Rockport fayalite) were studied by EPMA using the same equipment and technique as in [1]. Among meteorites, pallasites and mesosiderites are known to have slowest cooling rates at low temperatures. Olivines in the Springwater pallasite (Fa18) [4] and the Lowitz mesosiderite (Fa15-37) [5] are compositionally comparable with that of Divnoe (Fa23-29) [1], and it was expected that exsolved olivine grains would be found there. Olivines from other samples were studied for comparison. No lamellar structure was observed in BSE images of the olivine grains studied. The variations of Fa contents in olivine grains from all samples but Springwater and Lowitz meteorites display no regular pattern, and are basically within the 2sigma uncertainty range (+/-0.2 mole % Fa). As expected, olivines from the Lowitz mesosiderite and, especially, from the Springwater pallasite display somewhat larger variations, within the ranges of 20.1 - 21.0 and 15.8 -17.7 mole % Fa, respectively. The olivine in Springwater shows a surprisingly regular pattern of minima spaced at ~ 16 micrometers. For reasons that are unclear all 'minima' analyses have low totals (90.47-94.31 wt.%), whereas most other analyses have totals > 97%. However, stoichiometry of all analyses is perfect; cation totals per 4 oxygens are 3.00+/-0.01, with very minor excess of Si over Mg+Fe in the 'minima' analyses. The results obtained so far suggest that lamellar structure of olivine grains in the Divnoe meteorite is unique. While chemical variability is found in the Springwater and Lowitz olivines, there is no lamellar structure, and the magnitude of the variations is 1.5 - 2 times smaller than it is in Divnoe olivines. Since olivine compositions in Divnoe, Lowitz and Springwater are similar, the structural differences among them must be due to different thermal histories. The lack of lamellar structure in the Lowitz olivine implies that even the slowest cooling down to 250 degrees C recorded in mesosiderites [6] does not result in olivine exsolution. It is possible that Divnoe experienced secondary reheating followed by prolonged low-temperature annealing. This would also account for the lack of shock features in the Divnoe opaque minerals [7] and the difference in distributions of cosmic-ray track lengths and densities between olivine and pyroxene [8]. References: [1] Petaev M. I. and Brearley A. J. (1994) Science, 266, 1545-1547. [2] Sack R. O. and Ghiorso M. S. (1989) Contrib. Mineral. Petrol., 102, 41-68. [3] Schulien S. (1980) Contrib. Mineral. Petrol., 74, 85-91. [4] Buseck P. R. (1977) GCA, 41, 711-740. [5] Delaney J. S. et al. (1980) Proc. LPSC 11th, 1073-1087. [6] Ganguly J. et al. (1994) GCA, 58, 2711-2723. [7] Petaev M. I. et al. (1994) Meteoritics, 29, 182-199. [8] Petaev M. I. et al. (1990) LPS XXI, 950-951.

  4. Aligned Olivine in the Springwater Pallasite

    NASA Astrophysics Data System (ADS)

    Fowler-Gerace, N.; Tait, K.; Moser, D.; Barker, I.; Tian, B. Y.

    2014-12-01

    The mechanism by which olivine grains became embedded within iron-nickel alloy in pallasite meteorites continues to be a matter of scientific debate. Geochemical and textural observations have failed to fully elucidate the origin and history of the olivine crystals; however, little research attention has been devoted to their crystallographic orientations within the metal matrix. Klosterman and Buseck [1] found no crystallographic preferred orientation of olivine in nine pallasites, but the Leitz five-axis universal stage method imposed limitations on precision (estimated within ˜4◦) and sample size (only 10 crystals were measured in the Springwater pallasite, for instance). Using Electron Backscatter Diffraction, we have collected crystallographic orientation data (accurate to ±0.5◦ [2]) for 343 crystals within ˜65 cm2 sample surface from Springwater. Though no global crystallographic preferred orientation exists, very low misorientations are observed among [100] axes of olivine crystals within specific texturally-defined domains. Combined with our thorough characterization of large-scale Springwater textures, the definitively non-random spatial distribution of olivine orientations reveals the nature of the olivine's initial formation environment as well as the sequence of events subsequent to metal incorporation. [1] Klosterman and Buseck. 1973. J Geophys Res 78(32):7581-7588. [2] Oxford Instruments. 2013. http://www.ebsd.com/.

  5. Extremely NA and CL Rich Chondrule AL3509 from the Allende Meteorite

    SciTech Connect

    Wasserburg, G J; Hutcheon, I D; Aleon, J; Ramon, E C; Krot, A N; Nagashima, K; Brearley, A J

    2011-04-07

    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 chondrule 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 olivine, 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.

  6. Clear Evidence for Fe-60 in Silicate from a Semarkona Chondrule

    NASA Technical Reports Server (NTRS)

    Huss, G. R.; Tachibana, S.

    2004-01-01

    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 olivine 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 chondrule in Semarkona (LL3.0) with a very high Fe/Ni ratio that gives clear evidence of Fe-60.

  7. Atom Probe Tomography of Olivine

    NASA Astrophysics Data System (ADS)

    Parman, S. W.; Gorman, B.; Jackson, C.; Cooper, R. F.; Jaeger, D.

    2010-12-01

    Here we present atom probe tomographic (APT) analyses of natural olivine. 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. Olivine 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.

  8. Fe-Isotopic Composition of Chondrules, CAIs, Matrix and Bulk Meteorite in Mokoia and Grosnaja CV-Chondrites

    NASA Astrophysics Data System (ADS)

    Hezel, D. C.; Needham, A. W.; Russell, S. S.

    2008-03-01

    Chondrules and CAIs in CV chondrites range from -1.40 to +0.21 delta 56Fe. Average chondrule delta 56Fe must be close to matrix and bulk chondrite. Modeling shows that a combination of nebula and parent body processes explain the isotopic spread of chondrules.

  9. Chondrule size and related physical properties: A compilation and evaluation of current data across all meteorite groups

    NASA Astrophysics Data System (ADS)

    Friedrich, Jon M.; Weisberg, Michael K.; Ebel, Denton S.; Biltz, Alison E.; Corbett, Bernadette M.; Iotzov, Ivan V.; Khan, Wajiha S.; Wolman, Matthew D.

    2015-12-01

    The examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. Among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. Knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. To examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data. We include all chondrite chemical groups as well as the acapulcoite primitive achondrites, some of which contain relict chondrules. We also compile and review current literature data for other astrophysically-relevant physical properties (chondrule mass and density). Finally, we briefly examine some additional physical aspects of chondrules such as the frequencies of compound and 'cratered' chondrules. A purpose of this compilation is to provide a useful resource for meteoriticists and astrophysicists alike.

  10. Iodine-Xenon dating of chondrules from the Qingzhen and Kota Kota enstatite chondrites

    NASA Astrophysics Data System (ADS)

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

    2002-01-01

    Initial 129I/ 127I values (I-Xe ages) have been obtained for individual mineralogically characterized chondrules and interchondrule matrix from the enstatite chondrites Qingzhen (EH3) and Kota Kota (EH3). In view of the absence of aqueous alteration and the low-peak metamorphic temperatures experienced by these meteorites, we suggest that the I-Xe ages for the chondrules record the event in which they were formed. These ages are within the range recorded for chondrules from ordinary chondrites, demonstrating that chondrules formed during the same time interval in the source regions of both ordinary chondrites and enstatite chondrites. The timing of this chondrule-forming episode or episodes brackets the I-Xe closure age of planetesimal bodies such as the Shallowater aubrite parent body. Although chondrule formation need not have occurred close to planetesimals, the existence of planetesimals at the same time as chondrule formation provides constraints on models of this process. Whichever mechanisms are proposed to form and transport chondrules, they must be compatible with models of the protosolar nebula which predict the formation of differentiated bodies on the same timescale at the same heliocentric distance.

  11. Petrology and Oxygen Isotopes of Chondrules in the Kota Kota EH3 Chondrite

    NASA Astrophysics Data System (ADS)

    Weisberg, M. K.; Ebel, D. S.; Kimura, M.; Kita, N. T.; Nakashima, D.

    2010-03-01

    Oxygen isotopes of most Kota Kota chondrules plot along the TF line and some overlap the OC field on a 3-isotope plot. 16O-rich values in EH3s form a new mixing line. EH3 chondrules formed from a distinct oxygen reservoir and show mixing behavior.

  12. 26Al-26Mg Systematics in Chondrules from Kaba and Yamato 980145 CV3 Chondrites

    NASA Astrophysics Data System (ADS)

    Nagashima, K.; Krot, A. N.; Komatsu, M.

    2015-07-01

    We measured Al-Mg systematics of plagioclase in chondrules from two of the least metamorphosed CV chondrites, Kaba and Y-980145. Kaba chondrules show resolvable excesses of ?26Mg*, corresponding to initial (26Al/27Al) ratios of ~5 10^-6.

  13. Chemical and petrographic constraints on the origin of chondrules and inclusions in carbonaceous chondrites

    NASA Technical Reports Server (NTRS)

    Mcsween, H. Y., Jr.

    1977-01-01

    Bulk chemical compositions of the various petrographic types of chondrules 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. Chondrules 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 chondrules. Impact-melting models require sampling of complex target rocks which are unknown as components of meteorites; this mechanism also demands efficient mechanical processing of chondrules before accretion. A genetic relationship between chondrules 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 chondrules. Textural relationships between intergrown chondrules and inclusions support such a sequence. This model suggests that the assembled components (inclusions and chondrules) of carbonaceous chondrites are related by a common process.

  14. Metamorphism of the H-group chondrites - Implications from compositional and textural trends in chondrules

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

    The paper discusses element bulk compositions of 373 chondrules from 18 H3 to H6 chondrites determined by broad-beam electron probe analysis. Bulk chondrule 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. Chondrule diameters correlate with phenocryst sizes in porphyritic chondrules of type 3 chondrites, but this correlation is diminished in the higher petrologic types. The compositional trends in chondrules through the petrologic sequence are attributed to diffusion and equilibration among chondrules, and between chondrules and matrix in response to increasing degrees of thermal metamorphism. It is suggested that H-group chondrites are formed by accretion of high-temperature (chondrules) 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.

  15. Evaporative Loss and Degree of Melting in Semarkona Type I Chondrules

    NASA Astrophysics Data System (ADS)

    Hewins, R. H.; Zanda, B.; Bourot-Denise, M.

    1996-03-01

    Bulk compositions have been determined by broad beam techniques for Semarkona type I (FeO-poor) chondrules. The finest grained (least melted) approach CI in composition, and abundances of moderately volatile elements (K, Na, Fe, Ni, P, S) decrease as grain size (degree of melting) increases. This is unequivocal evidence of evaporative loss during chondrule formation.

  16. Pre-Accretionary Distribution of Ca and Al Between Matrix and Chondrules in CV Chondrites

    NASA Astrophysics Data System (ADS)

    Hezel, D. C.; Palme, H.

    2007-03-01

    Ca/Al-ratios in Y-86751 (CV) chondrules are super- and in matrix sub-chondritic. The opposite is true for Allende and Efremovka. Incorporation of spinel in Allende and Efremovka chondrule precursors in a nebular setting can explain this observation.

  17. Cosmogenic Neon in Individual Chondrule Fragments: Records of Pre-Compaction Exposure

    NASA Astrophysics Data System (ADS)

    Das, J. P.; Goswami, J. N.; Pravdivtseva, O. V.; Meshik, A. P.; Hohenberg, C. M.

    2010-03-01

    This first ever study on 41 splits of chondrules show that 21Ne CRE ages in 11 splits are high compared to that of host, ranging from 5-35 Ma. Splits from same chondrule show different CRE ages. We conclude that the excess is due to early active Sun.

  18. Pb-Pb Isotopic and X-ray Tomographic Constraints on the Origin of Chondrules

    NASA Astrophysics Data System (ADS)

    Charles, Christopher R. J.

    207Pb*/206Pb* chronometry was used to obtain the ages of Ca,Al-rich inclusions (CAIs) and chondrules found in ancient meteorites. Assuming a 238U/235U=137.88, Pb/Pb ages of chondrules in NWA801 (a CR2 meteorite) are 4564.6+/-1.0 Ma, chondrules in Mokoia (a CV3 chondrite) are 4564.2+/-1.1Ma, and CAIs in Mokoia are 4567.9+/-5.4 Ma. The Pb/Pb age of NWA801 chondrules is concordant with 26Al/ 26Mg ages of CR chondrules. However if a 238U/ 235U<137.88 is used, the age for NWA801 chondrules becomes younger by 1Ma and discordant with26Al/26Mg ages of CR chondrules. This suggests either a discrepancy with the U compositions or the initial Mg isotopic compositions of NWA801 chondrules. The shapes of NWA801 chondrules, and blebs of FeNi metal in the meteorite matrix, were further studied by 3D X-ray micro-computed tomography (CT). Most chondrules (92%) were 'armoured' with one discontinuous layer of FeNi metal. Two layers of FeNi metal (one on the exterior and one concentric through the interior separated by silicate) were rare <8%. Chondrules and matrix blebs occur as oblates, prolate, spheres and triaxial spheroids. It is proposed that the shapes were made free-floating in the nebula likely by ash-melting precursors into molten droplets that were vibrating as harmonic oscillators that 'froze-in' their shapes during cooling. Parent-body metamorphism and shock are not likely processes affecting the matrix-bleb and chondrule shapes. Chondrules with?2 FeNi metal layers were likely formed by mergers and not by successive deposition and annealing of metal in multiple ash-melting events. Attempts to obtain 207Pb*/206Pb* ages from chondrules and CAIs by thermal extraction (TE)-TIMS were unsuccessful. However LA-ICP-MS was shown to be useful for rapidly determining Pb isotopic trends in meteorites and unknown objects. In particular, it was shown that 137La (T1/2=60ky) should be detectable in recently fallen meteorites using LaF-4 to suppress the 137Ba isobar during tandem accelerator mass spectrometry combined with a novel instrumental technique for isobar separation.

  19. Amoeboid olivine aggregates in the Allende meteorite

    NASA Technical Reports Server (NTRS)

    Grossman, L.; Steele, I. M.

    1976-01-01

    Greyish-brown irregularly-shaped aggregates composed predominantly of olivine make up nearly 2% of the Allende meteorite by volume. Many of the aggregates are constructed of subspherical lumps of micron-sized crystals of olivine, pyroxene, nepheline and sodalite surrounded by coarser-grained olivine. Rarely, anorthite, spinel and perovskite are also present. The olivine ranges in composition from Fo64 to Fo99. Pyroxenes range from aluminous diopside to hedenbergite to very Al-rich and Ti-Al-rich varieties. The nepheline contains 1.6-2.4% K2O and 1.6-5.2% CaO but the sodalite is significantly poorer in these elements. The spinel contains 2.1-13.4% FeO. Textural information and oxygen isotopic data suggest that the aggregates are composed of primary, solid condensates from the solar nebula. The perovskite, spinel and Ti-Al-rich pyroxenes are the remains of high-temperature condensates, but the olivine compositions and the presence of feldspathoids indicate that some of the grains continued to react with the solar nebular vapor in the temperature range 500-900 K.

  20. Redistribution of chondrules in a carbonaceous chondrite parent body: A model

    NASA Astrophysics Data System (ADS)

    Tomeoka, Kazushige; Ohnishi, Ichiro

    2015-09-01

    Carbonaceous chondrites mainly consist of chondrules and inclusions embedded in a fine-grained matrix. This texture is widely believed to have formed primarily by direct accretion of solar nebular materials, although it may have been modified to various extents by subsequent parent-body processes. Recently, we studied all chondrules and inclusions larger than 400 ?m in diameter and their rims (referred to as chondrules/rims) in the Mokoia CV3 carbonaceous chondrite using a scanning electron microscope, and found that the chondrules/rims experienced various degrees of aqueous alteration and that some also exhibit evidence of thermal metamorphism. The mineralogical and petrographic characteristics of the chondrules/rims suggest that the alteration and metamorphism occurred within the meteorite parent body. In contrast, however, the surrounding matrix does not show evidence of such alteration and metamorphism. These findings indicate that the alteration and metamorphism of the chondrules/rims did not occur in situ. Based on these results, we proposed a model that the chondrules/rims are actually clasts transported from regions in the parent body different from the location where the host meteorite was finally lithified. If it can be assumed that the chondrules and inclusions studied are representative of all chondrules and inclusions in Mokoia, the results and interpretation pose a fundamental challenge regarding the formation of the whole Mokoia lithology; that is, it cannot be explained by either direct accretion of the solar nebula or conventional parent-body brecciation. We propose a model for the development of the Mokoia lithology through formation of chondrules/rims and fine matrix grains by fragmentation in different regions in the parent body, followed by transportation, mixing, and accumulation in a fluid state, and finally lithification of those objects. These processes may have been repeated, cyclically, within the parent body.

  1. Shock-produced olivine glass - First observation

    NASA Technical Reports Server (NTRS)

    Jeanloz, R.; Ahrens, T. J.; Lally, J. S.; Nord, G. L., Jr.; Christie, J. M.; Heuer, A. H.

    1977-01-01

    Transmission electron microscope (TEM) observations of an experimentally shock-deformed single crystal of natural peridot, /Mg(0.88)Fe(0.12)/2SiO4, recovered from peak pressures of about 56 billion pascals revealed the presence of amorphous zones located within crystalline regions with a high density of tangled dislocations. This is the first reported observation of olivine glass. The shocked sample exhibits a wide variation in the degree of shock deformation on a small scale, and the glass appears to be intimately associated with the highest density of dislocations. This study suggests that olivine glass may be formed as a result of shock at pressures above about 50 to 55 billion pascals and that further TEM observations of naturally shocked olivines may demonstrate the presence of glass.

  2. A search for olivine activation volume

    NASA Astrophysics Data System (ADS)

    Li, L.; Weidner, D.; Mei, S.; Raterron, P.; Chen, J.; Durham, W.

    2003-04-01

    Knowledge of the rheological properties of mantle materials is critical in modeling the dynamics of the Earth. The flow law of olivine defined at mantle pressure and temperature is especially important since the pressure dependence of rheology may affect our estimation for the strength of olivine in the Earth's interior. Conventional deformation methods in defining the flow law of olivine have to face factors of large uncertainties of differential stress measurements and/or limited confining pressure for deformation. In this study, high-temperature (up to 1473 K) deformation experiments of polycrystalline olivine (average grain size < 5 micron) at pressure up to 6.5(0.2) GPa were conducted in-situ using large-volume high-pressure apparatus (Deformation DIA) and synchrotron x-ray radiation. More than 30% strain was generated during the uniaxial compression. The sample lengths during the deformation process were monitored by x-ray radiography. The strain rate was derived with precision up to 10-6. Macroscopic differential stress was measured at constant strain rate ( 10-5 s-1) using a multi-element solid-state detector combined with a conical slit. The new data, measured at 1473 and 1273K at 6.5 and 3GPa, fits well an empirical power-law creep flow law under the condition that the activation energy is 520(20) kJ/mol and the activation volume is less than 3 cm^3/mol. Consistent with TEM observations on recovered samples, tests for grain size dependence of flow, and the empirical power law exponent, we conclude that power-law creep is the dominant flow mechanism for dry olivine at upper mantle conditions. The success of defining the flow law for olivine in this study also symbolizes a huge opening for defining the rheological flow law for other materials in the Earth's interior.

  3. The Origin of Chondrules and Refractory Inclusions in Chondritic Meteorites

    NASA Astrophysics Data System (ADS)

    Shu, Frank H.; Shang, Hsien; Gounelle, Matthieu; Glassgold, Alfred E.; Lee, Typhoon

    2001-02-01

    Examples of calcium-aluminum-rich inclusions (CAIs) surrounded by thick chondrule mantles have been found in chondritic meteorites and cast doubt on the conventional belief that CAIs and chondrules possessed different spacetime origins in the primitive solar nebula. We study specific processes by which such objects, and the more common ordinary CAIs and chondrules, might have formed by flare heating of primitive rocks interior to the inner edge of a gaseous accretion disk that has been truncated by magnetized funnel flow onto the central proto-Sun. Motivated by the appearance of the chains of Herbig-Haro knots that define collimated optical jets from many young stellar objects (YSOs), we adopt the model of a fluctuating X-wind, where the inner edge of the solar nebula undergoes periodic radial excursions on a timescale of ~30 yr, perhaps in response to protosolar magnetic cycles. Flares induced by the stressing of magnetic fields threading both the star and the inner edge of the fluctuating disk melt or partially melt solids in the transition zone between the base of the funnel flow and the reconnection ring, and in the reconnection ring itself. The rock melts stick when they collide at low velocities. Surface tension pulls the melt aggregate into a quasi-spherical core/mantle structure, where the core consists mainly of refractories and the mantle mainly of moderate volatiles. Orbital drift of rocks past the inner edge of the disk or infall of large objects from the funnel flow replaces the steady loss of material by the plasma drag of the coronal gas that corotates with the stellar magnetosphere. In quasi-steady state, agglomeration of molten or heat-softened rocks leads to a differential size-distribution in radius R proportional to R-3e-Lt/tLR, where tL~20 yr is the drift time of an object of fiducial radius L?1 cm and t is the time since the last inward excursion of the base of the funnel flow and X-wind. Thus, during the ~30 yr interval between successive flushing of the reconnection ring, flash-heated and irradiated rocks have a chance to grow to millimeter and centimeter sizes. The evaporation of the moderately volatile mantles above large refractory cores, or the dissolving of small refractory cores inside thick ferromagnesian mantles before launch, plus extended heating in the X-wind produce the CAIs or chondrules that end up at planetary distances in the parent bodies of chondritic meteorites.

  4. Constraints to the Formation of Matrix Reduced Olivine in Yamato-691 (EH3) Chondrite: Implications for the Evolution of EH Chondrites

    NASA Astrophysics Data System (ADS)

    Matsunami, S.; El Goresy, A.

    1992-07-01

    In order to understand the origin of oxidized components in enstatite chondrites, matrix reduced olivine (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 olivine," which is a mixture of forsterite, metallic Fe, and probably unreacted olivine (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 olivine took place along SB (Boland and Duba, 1986). The presence of RO with bended SB is also suggestive of plastic deformation of the olivine before reduction. We estimated the rate of reduction of (Mg,Fe)-olivine as a function of temperature, composition of olivine (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 chondrule olivines crystallized in chondrule 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 olivine 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 olivine 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.

  5. Chondrule formation in particle-rich nebular regions at least hundreds of kilometres across.

    PubMed

    Cuzzi, Jeffrey N; Alexander, Conel M O'D

    2006-05-25

    Chondrules are millimetre-sized spherules (mostly silicate) that dominate the texture of primitive meteorites. Their formation mechanism is debated, but their sheer abundance suggests that the mechanism was both energetic and ubiquitous in the early inner Solar System. The processes suggested--such as shock waves, solar flares or nebula lightning--operate on different length scales that have been hard to relate directly to chondrule properties. Chondrules are depleted in volatile elements, but surprisingly they show little evidence for the associated loss of lighter isotopes one would expect. Here we report a model in which molten chondrules come to equilibrium with the gas that was evaporated from other chondrules, and which explains the observations in a natural way. The regions within which the chondrules formed must have been larger than 150-6,000 km in radius, and must have had a precursor number density of at least 10 m(-3). These constraints probably exclude nebula lightning, and also make formation far from the nebula midplane problematic. The wide range of chondrule compositions may be the result of different combinations of the local concentrations of precursors and the local abundance of water ice or vapour. PMID:16724060

  6. Mineralogy of Stardust Track 112 Particle: Relation to Amoeboid Olivine Aggregates

    NASA Technical Reports Server (NTRS)

    Komatsu, M.; Fagan, T.; Mikouchi, T.; Miyamoto, M.; Zolensky, M.; Ohsumi, K.

    2012-01-01

    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 chondrules [e.g., 4] in chondrites. In addition, particles similar to amoeboid olivine 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.

  7. Iron isotope signatures within chondrules from Allende and Chainpur as indicators of thermal history.

    NASA Astrophysics Data System (ADS)

    Mullane, E.; Russell, S. S.; Gounelle, M.; Mason, T. F. D.

    2003-04-01

    Introduction: We have studied the petrography and Fe-isotope composition of seven chondrules, four from Allende (CV3) and three from Chainpur (LL3.4). A range of textural-chemical chondrule types are represented, allowing us to examine the Fe-isotope signature in material with different thermal histories, with a view to constraing the chondrule forming process and elucidating the nature of chondrule precursor material. Analytical procedures are detailed elsewhere [1,2,3] Fe-isotope Fractionation: The overall variation in ?56Fe is 1.98 ppm and in ?57Fe is 2.87 ppm. EM-1 (non-porphyritic) is most isotopically heavy and EM-3 (porphyritic) is most isotopically light, with all other chondrules falling in a mass fractionation line between these two end-members. This line is defined by the equation ?57Fe = (1.4500.050)?56Fe - (0.0090.016) (R^2 = 0.9995). Discussion: The Fe-fractionation exhibited here is less than would be expected during open system evaporation. This suggests that Rayleigh conditions were not fulfilled during chondrule melting. Chainpur chondrules exhibit less fractionation than Allende chondrules, a total of 0.46 ppm (?56Fe) in contrast to 1.98 ppm (?56Fe), respectively, suggesting that Chainpur may be more equilibrated than Allende. Chainpur Fe-isotopes may have been increasingly homogenised by later addition of Fe, either from the nebular reservoir or parent body alteration. Porphyritic and nonporphyritic chondrules have differing thermal histories. The former are a product of incomplete melting, whereas the latter derive from almost total/complete melting of precursor material. However, Fe-isotope fractionation does not appear to vary systematically with texture. We conclude that chondrule Fe-isotopic signatures represent that of the precursor material, with later equilibration of the Chainpur chondrules. Melting history may also influence the Fe-isotopic signature. The isotopically heaviest chondrules (e.g. EM-1 &EC-3) may derive from a melt which attained liquidus temperatures more than once. The precursor to EM-2 (isotopically lightest), may not have been subject to as many aggressive heating events. References: [1] Mullane et al. (2001) LPS XXXII, Abs. #1545. [2] Mullane et al. (2002) In: Plasma Source Mass Spec. Royal Soc. Chem. (in press). [3] Mullane et al. (2002) Met. Plan. Sci. 37, 105 Abs. [4] Alexander C.M.O'D. &Wang J. (2001) Met. Plan. Sci. 36, 419--428.

  8. Enhanced olivine carbonation within a basalt as compared to single-phase experiments: reevaluating the potential of CO2 mineral sequestration.

    PubMed

    Sissmann, Olivier; Brunet, Fabrice; Martinez, Isabelle; Guyot, François; Verlaguet, Anne; Pinquier, Yves; Daval, Damien

    2014-05-20

    Batch experiments were conducted in water at 150 °C and PCO2 = 280 bar on a Mg-rich tholeiitic basalt (9.3 wt % MgO and 12.2 wt % CaO) composed of olivine, 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 olivine content upon carbonation supports the idea that ferroan magnesite formation mainly follows from olivine dissolution. In contrast, in experiments performed under similar run durations and P/T conditions with a San Carlos olivine 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 olivine grains in both types of sample. Consequently, laboratory data obtained on olivine separates might yield a conservative estimate of the true carbonation potential of olivine-bearing basaltic rocks. PMID:24735106

  9. Transmission electron microscopy of subsolidus oxidation and weathering of olivine

    USGS Publications Warehouse

    Banfield, J.F.; Veblen, D.R.; Jones, B.F.

    1990-01-01

    Olivine 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 olivine oxidation. The olivine 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 olivine alteration assemblage contains complex ordered intergrowths on (001) of forsterite-rich olivine and laihunite (distorted olivine structure with Fe3+ charge balanced by vacancies). Based on experimental results for laihunite synthesis (Kondoh et al. 1985), these intergrowths probably formed by olivine oxidation between 400 and 800??C. The third episode of alteration involves the destruction of olivine by low-temperature hydrothermal alteration and weathering. Elongate etch-pits and channels in the margins of fresh olivine crystals contain semi-oriented bands of smectite. Olivine 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 olivine and smectite ("M" - Eggleton 1984). The presence of laihunite exerts a strong control on the geometry of olivine weathering. Single laihunite layers and laihunite-forsteritic olivine intergrowths increase the resistance of crystals to weathering. Preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine, rather than where coherency-strain is associated with laihunite-olivine interfaces. ?? 1990 Springer-Verlag.

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  11. Al-rich Chondrules: Petrologic Basis for Their Diversity, and Relation to Type C CAIs

    NASA Technical Reports Server (NTRS)

    MacPherson, G. J.; Huss, G. R.

    2003-01-01

    Al-rich chondrules share mineralogical and chemical properties with, and are intermediate in a volatility sense between, CAIs and ferromagnesian chondrules. In some way they must be petrogenetic links between the two. A recent upsurge of interest in Al-rich chondrules 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) chondrule formation, on the order of 1.5-2.5 million years.

  12. Contrasting Size Distributions of Chondrules and Inclusions in Allende CV3

    NASA Technical Reports Server (NTRS)

    Fisher, Kent R.; Tait, Alastair W.; Simon, Jusin I.; Cuzzi, Jeff N.

    2014-01-01

    There are several leading theories on the processes that led to the formation of chondrites, e.g., sorting by mass, by X-winds, turbulent concentration, and by photophoresis. The juxtaposition of refractory inclusions (CAIs) and less refractory chondrules is central to these theories and there is much to be learned from their relative size distributions. There have been a number of studies into size distributions of particles in chondrites but only on relatively small scales primarily for chondrules, and rarely for both Calcium Aluminum-rich Inclusions (CAIs) and chondrules in the same sample. We have implemented macro-scale (25 cm diameter sample) and high-resolution microscale sampling of the Allende CV3 chondrite to create a complete data set of size frequencies for CAIs and chondrules.

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

    NASA Astrophysics Data System (ADS)

    Kornacki, A. S.; Fegley, B.

    1984-02-01

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

  14. Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions.

    PubMed

    Amelin, Yuri; Krot, Alexander N; Hutcheon, Ian D; Ulyanov, Alexander A

    2002-09-01

    The lead-lead isochron age of chondrules in the CR chondrite Acfer 059 is 4564.7 +/- 0.6 million years ago (Ma), whereas the lead isotopic age of calcium-aluminum-rich inclusions (CAIs) in the CV chondrite Efremovka is 4567.2 +/- 0.6 Ma. This gives an interval of 2.5 +/- 1.2 million years (My) between formation of the CV CAIs and the CR chondrules and indicates that CAI- and chondrule-forming events lasted for at least 1.3 My. This time interval is consistent with a 2- to 3-My age difference between CR CAIs and chondrules inferred from the differences in their initial 26Al/27Al ratios and supports the chronological significance of the 26Al-26Mg systematics. PMID:12215641

  15. Redistribution of Chondrules and Matrix Grains in the Mokoia Chondrite Parent Body: A Model

    NASA Astrophysics Data System (ADS)

    Tomeoka, K.; Ohnishi, I.

    2015-07-01

    Based on our recent studies of the Mokoia CV3 chondrite, we propose a model that the lithology of this meteorite formed through redistribution of chondrules and matrix grains in the meteorite parent body.

  16. Forsterite from Chondrules in the Mokoia (CV3) Chondrite: Cathodoluminescence, Chemistry and Oxygen Isotopes

    NASA Astrophysics Data System (ADS)

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

    2002-03-01

    Forsterite in Mokoia chondrules 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.

  17. Recycled Chondroids in LEW86018: A Petrographic Study of Chondrule Precursors

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    Chondroids are any kind of nebular particle that would melt to become chondrules. We describe the petrography and basic chemistry of chondroids in LEW86018 (L3.1). Additional information is contained in the original extended abstract.

  18. Different radiation and metamorphic history of the Kainsaz CO 3.2 chondrules

    NASA Technical Reports Server (NTRS)

    Kashkarov, L. L.; Kalinina, G. V.

    1993-01-01

    Track and thermoluminescence parameters in chondrules from the Kainsaz CO 3.2 chondrite have been studied. Obtained results elucidate their individual shock-thermal history and the early pre-accretion stage of the meteorite parent body formation.

  19. A new mechanism for chondrule formation: Radiative heating by hot planetesimals

    NASA Astrophysics Data System (ADS)

    Herbst, William; Greenwood, James P.

    2016-03-01

    We propose that chondrules are formed by radiative heating of pre-existing dust clumps during close fly-bys of planetesimals with incandescent lava at their surfaces. We show that the required temperatures and cooling rates are easily achieved in this scenario and discuss how it is consistent with bulk aspects of chondritic meteorites, including complementarity and the co-mingling of FeO-poor and FeO-rich chondrules.

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

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.

    1993-01-01

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

  1. Trace-Element Diffusion Coefficients in Olivine

    NASA Astrophysics Data System (ADS)

    Spandler, C.; O'Neill, H. S.

    2006-12-01

    We have undertaken chemical diffusion experiments at 1300C to determine both crystal/melt partition coefficients and diffusion coefficients for a wide range of trace elements in forsteritic olivine. Experiments were conducted at 1 atm under controlled fO2 for up to 25 days using synthetic melts made to a composition in equilibrium with olivine 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 olivine 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 olivine, and also for several trace elements present at natural abundances in the olivine 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 1300C). The diffusion of Li in olivine (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 olivine [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 olivine-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).

  2. Dislocation Microstructures in Experimentally Deformed wet Olivine

    NASA Astrophysics Data System (ADS)

    Sharp, T. G.; Jung, H.; Karato, S.

    2002-12-01

    Seismic anisotropy in the upper mantle is generally considered to be the result of lattice preferred orientations (LPOs) of olivine as a result of mantle flow. Therefore seismic anisotropy in the upper mantle can be used to probe fabrics and therefore flow directions. Jung and Karato (2001) have demonstrated that fabrics developed in experimentally deformed olivine are dependent on H2O fugacity and stress. Fabric type C, which develops at moderate experimental stresses and high H2O fugacities, has [001] subparallel to the slip direction and (100) subparallel to the shear plane. Fabric type B, which develops at high stresses and high H2O fugacities has [001] subparallel to the slip direction and (010) subparallel to the shear plane. To investigate the role of H2O in olivine fabric transitions, we are using high-resolution and conventional transmission electron microscopy (HRTEM and TEM) to characterize the dislocation microstructures and core structures in experimentally deformed samples of Fabric types B and C. Initial results for Fabric type C (sample JK11 of Jung and Karato, 2001) show a dominance of mixed-character and screw dislocations with Burgers vectors b = [001]. This Burgers vector, combined with the (100) being subparallel to the shear plane, is consistent with the (100)[001] slip system being dominant in the C-type fabric. This slip system, which is of minor importance in dry olivine, may be favored in wet samples by changes in the dislocation core structure. We are currently using HRTEM imaging to characterize the dislocation core structures in deformed samples with type C and type B fabrics.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  4. I-Xe measurements of CAIs and chondrules from the CV3 chondrites Mokoia and Vigarano

    NASA Astrophysics Data System (ADS)

    Whitby, J. A.; Russell, S. S.; Turner, G.; Gilmour, J. D.

    2004-08-01

    I-Xe analyses were carried out for chondrules 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 chondrule (V3) from Vigarano ~0.7 Myr later than Shallowater. Other chondrules in Mokoia and Vigarano experienced disturbance of the I-Xe system millions of years later and, in the case of one Vigarano chondrule (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 chondrule that shows no evidence for any aqueous alteration or significant thermal processing after its formation leads us to postulate the existence of an energetic chondrule-forming mechanism at a time when nebular processes are not expected to be important.

  5. Constraints on the Origin of Chondrules and CAIs from Short-Lived and Long-Lived Radionuclides

    SciTech Connect

    Kita, N T; Huss, G R; Tachibana, S; Amelin, Y; Nyquist, L E; Hutcheon, I D

    2005-10-24

    The high time resolution Pb-Pb ages and short-lived nuclide based relative ages for CAIs and chondrules are reviewed. The solar system started at 4567.2 {+-} 0.6Ma inferred from the high precision Pb-Pb ages of CAIs. Time scales of CAIs ({le}0.1Myr), chondrules (1-3Myr), and early asteroidal differentiation ({ge}3Myr) inferred from {sup 26}Al relative ages are comparable to the time scale estimated from astronomical observations of young star; proto star, classical T Tauri star and week-lined T Tauri star, respectively. Pb-Pb ages of chondrules also indicate chondrule formation occur within 1-3 Myr after CAIs. Mn-Cr isochron ages of chondrules are similar to or within 2 Myr after CAI formation. Chondrules from different classes of chondrites show the same range of {sup 26}Al ages in spite of their different oxygen isotopes, indicating that chondrule formed in the localized environment. The {sup 26}Al ages of chondrules in each chondrite class show a hint of correlation with their chemical compositions, which implies the process of elemental fractionation during chondrule formation events.

  6. Exploring exogenic sources for the olivine on Asteroid (4) Vesta

    NASA Astrophysics Data System (ADS)

    Le Corre, Lucille; Reddy, Vishnu; Sanchez, Juan A.; Dunn, Tasha; Cloutis, Edward A.; Izawa, Matthew R. M.; Mann, Paul; Nathues, Andreas

    2015-09-01

    The detection of olivine on Vesta is interesting because it may provide critical insights into planetary differentiation early in our Solar System's history. Ground-based and Hubble Space Telescope (HST) observations of Asteroid (4) Vesta have suggested the presence of olivine on the surface. These observations were reinforced by the discovery of olivine-rich HED meteorites from Vesta in recent years. However, analysis of data from NASA's Dawn spacecraft has shown that this "olivine-bearing unit" is actually impact melt in the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed during the formation of the 19 km deep Rheasilvia basin on Vesta's South Pole, further complicated this picture. Ammannito et al. (Ammannito, E. et al. [2013a]. Nature 504, 122-125) reported the discovery of local scale olivine-rich units in the form of excavated material from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. These sites are concentrated in the walls and ejecta of craters Arruntia (10.5 km in diameter) and Bellicia (41.7 km in diameter), located in the northern hemisphere, 350-430 km from Rheasilvia basin's rim. Here we explore alternative sources for the olivine in the northern hemisphere of Vesta by reanalyzing the data from the VIR instrument using laboratory spectral measurements of meteorites. Our rationale for using the published dataset was to bypass calibration issues and ensure a consistent dataset between the two studies. Our analysis of the VIR data shows that while the interpretation of their spectra as an olivine-rich unit is correct, the nature and origin of that olivine could be more complicated. We suggest that these olivine exposures could also be explained by the delivery of olivine-rich exogenic material. This hypothesis is supported by meteoritical evidence in the form of exogenic xenoliths containing significant amount of olivine in some of the HED meteorites from Vesta. Previous laboratory work on HEDs show that potential sources of olivine on Vesta could be different types of olivine-rich meteorites, either primitive achondrites (acapulcoites, lodranites, ureilites), ordinary chondrites (H, L, LL), pallasites, or carbonaceous chondrites (e.g., CV). Based on our spectral band parameters analysis, the lack of correlation between the location of these olivine-rich terrains and possible mantle-excavating events, and supported by observations of HED meteorites, we propose that a probable source for the olivine seen in the northern hemisphere corresponds to remnants of impactors made of olivine-rich meteorites. The best curve-matching results with laboratory spectra suggest these units are HED material mixed with either ordinary chondrites, or with some olivine-dominated meteorites such as R-chondrites.

  7. Mineralogy and petrography of amoeboid olivine aggregates from the reduced CV3 chondrites Efremovka, Leoville and Vigarano: Products of nebular condensation, accretion and annealing

    NASA Astrophysics Data System (ADS)

    Komatsu, Mutsumi; Krot, Alexander N.; Petaev, Mikhail I.; Ulyanov, Alexander A.; Keil, Klaus; Miyamoto, Masamichi

    2001-05-01

    Amoeboid olivine aggregates (AOAs) from the reduced CV chondrites Efremovka, Leoville and Vigarano are irregularly-shaped objects, up to 5 mm in size, composed of forsteritic olivine (Fa<10) and a refractory, Ca,Al-rich component. The AOAs are depleted in moderately volatile elements (Mn, Cr, Na, K), Fe,Ni-metal and sulfides and contain no low-Ca pyroxene. The refractory component consists of fine-grained Ca,Al-rich inclusions (CAIs) composed of Al-diopside, anorthite (An100), and magnesium-rich spinel (~1 wt% FeO) or fine-grained intergrowths of these minerals; secondary nepheline and sodalite are very minor. This indicates that AOAs from the reduced CV chondrites are more pristine than those from the oxidized CV chondrites Allende and Mokoia. Although AOAs from the reduced CV chondrites show evidence for high temperature nebular annealing (e.g., forsterite grain boundaries form 120 deg triple junctions) and possibly a minor degree of melting of Al-diopside-anorthite materials, none of the AOAs studied appear to have experienced extensive (>50%) melting. We infer that AOAs are aggregates of high temperature nebular condensates, which formed in CAI-forming regions, and that they were absent from chondrule-forming regions at the time of chondrule formation. The absence of low-Ca pyroxene and depletion in moderately volatile elements (Mn, Cr, Na, K) suggest that AOAs were either removed from CAI-forming regions prior to condensation of these elements and low-Ca pyroxene or gas-solid condensation of low-Ca-pyroxene was kinetically inhibited.

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

    NASA Astrophysics Data System (ADS)

    Grossman, Jeffrey N.; Alexander, Conel M. O'd.; Wang, Jianhua; Brearley, Adrian J.

    2000-05-01

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

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

    USGS Publications Warehouse

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

    2000-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

  11. Nitrogen and xenon isotopic disequilibrium in Bachmut (L6) chondrule J2689 and matrix

    NASA Astrophysics Data System (ADS)

    Kim, Y.; Marti, K.; Kurat, G.

    1994-07-01

    Chondrule J2689, a large (8-mm) RP chondrule 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 chondrule; (4) the bulk alkali content of the chondrule 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 chondrule 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 chondrule 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 chondrule 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.

  12. Search for Olivine Spectral Signatures on the Surface of Vesta

    NASA Technical Reports Server (NTRS)

    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.

    2012-01-01

    The occurrence of olivines on Vesta were first postulated from traditional petrogenetic models which suggest the formation of olivine 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 olivine 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 olivine-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 olivine rich regions that may occur on the Vesta surface. The abundance of olivine in diogenites is typically lower than 10% but some samples richer in olivine are known. However, we do not expect to have extensive exposures of olivine-rich material on Vesta. Moreover, the partial overlap of olivine and pyroxene spectral signatures will make olivine difficult to detect. Different spectral parameters have been used to map olivine 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, olivines and their mixtures.

  13. Shock effects in olivine and implications for Hugoniot data

    NASA Technical Reports Server (NTRS)

    Jeanloz, R.

    1980-01-01

    New observations of shock deformation in single-crystal olivine are presented for the range in peak pressures from about 16 to 75 GPa. A nonequilibrium model is suggested for the behavior of olivine under shock which explains the densification associated with a mixed-phase region and which is consistent with all available observations, yet which bears little similarity to the equilibrium behavior of olivine at high pressure.

  14. Water and Carbon Dioxide Adsorption at Olivine Surfaces

    SciTech Connect

    Kerisit, Sebastien N.; Bylaska, Eric J.; Felmy, Andrew R.

    2013-11-14

    Plane-wave density functional theory (DFT) calculations were performed to simulate water and carbon dioxide adsorption at the (010) surface of five olivine minerals, namely, forsterite (Mg2SiO4), calcio-olivine (Ca2SiO4), tephroite (Mn2SiO4), fayalite (Fe2SiO4), and Co-olivine (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-olivine 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-olivine. Therefore, the DFT calculations show a strong driving force for carbon dioxide displacement by water at the surface of all olivine 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) olivines than for the transition-metal (TM) olivines 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 olivine 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 olivines. For calcio-olivine, which exhibits the highest divalent cation charge of the five olivines, 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.

  15. Diffusive Fractionation of Lithium Isotopes in Olivine

    NASA Astrophysics Data System (ADS)

    Homolova, V.; Richter, F. M.; Watson, E. B.; Chaussidon, M.

    2014-12-01

    Systematic lithium isotope variations along concentration gradients found in olivine and pyroxene grains from terrestrial, lunar and martian rocks have been attributed to diffusive isotopic fractionation [Beck et al., 2006; Tang et al., 2007]. In some cases, these isotopic excursions are so large that a single grain may display isotopic variability that spans almost the entire range of documented terrestrial values [Jeffcoate et al., 2007]. In this study, we present the results of experiments to examine diffusive isotopic fractionation of lithium in olivine. The experiments comprised crystallographically oriented slabs of San Carlos olivine juxtaposed with either spodumene powder or a lithium rich pyroxene crystal. Experiments were conducted at 1 GPa and 0.1MPa over a temperature range of 1000 to 1125?C. Oxygen fugacity in the 0.1MPa experiments was controlled using the wustite-magnetite and nickel-nickel oxide solid buffer assemblages. Lithium concentrations generally decrease smoothly away from the edges of the grains; however, experiments involving diffusion parallel to the a-axis consistently show peculiar wavy or segmented concentration profiles. Lithium diffusivity parallel to the c-axis is on the order of 1E-14m2/s at 1100?C. The diffusivity parallel to the c-axis is more than an order of magnitude faster than diffusion parallel to the b-axis and correlates positively with oxygen fugacity. The lithium isotopic composition, ?7Li = 1000 * ((?7Lisample- ?7Ligrain center)/ ?7Ligrain center), shows a decrease away from the edge of the grain to a minimum value (up to 70 lighter) and then an abrupt increase back to the initial isotopic composition of the olivine grain. This isotopic profile is similar to those found in natural grains and an experimental study on diffusive fractionation of lithium isotopes in pyroxene [Richter et al., 2014]. Results from the present study are modeled using the approach of Dohmen et al. [2010], which assumes lithium diffusion occurs on both a metal and interstitial site and that lithium is able to jump between these two sites. The best fits to the results show that diffusive isotopic fractionation may occur on both the interstitial and metal site but the degree of diffusive isotopic fractionation is always greater on the interstitial site.

  16. Discovery of Olivine in the Nili Fossae Region of Mars

    USGS Publications Warehouse

    Hoefen, T.M.; Clark, R.N.; Bandfield, J.L.; Smith, M.D.; Pearl, J.C.; Christensen, P.R.

    2003-01-01

    We have detected a 30,000-square-kilometer area rich in olivine 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 olivine. Linear mixture analysis of Thermal Emission Spectrometer spectra shows surface exposures of 30% olivine, where the composition of the olivine ranges from Fo30 to Fo70.

  17. Vaporization Studies of Olivine via Knudsen Effusion Mass Spectrometry

    NASA Technical Reports Server (NTRS)

    Costa, G. C. C.; Jacobson, N. S.

    2014-01-01

    Olivine is the major mineral in the Earth's upper mantle occurring predominantly in igneous rocks and has been identified in meteorites, asteroids, the Moon and Mars. Among many other important applications in planetary and materials sciences, the thermodynamic properties of vapor species from olivine are crucial as input parameters in computational modelling of the atmospheres of hot, rocky exoplanets (lava planets). There are several weight loss studies of olivine vaporization in the literature and one Knudsen Effusion Mass Spectrometry (KEMS) study. In this study, we examine a forsterite-rich olivine (93% forsterite and 7% fayalite, Fo93Fa7) with KEMS to further understand its vaporization and thermodynamic properties.

  18. Turbulent Size Selection and Concentration of Chondrule-Sized Objects: Reynolds Number Invariance and Implications

    NASA Technical Reports Server (NTRS)

    Cuzzi, J. N.; Hogan, R.; Dobrovolskis, A.; Paque, J.

    2006-01-01

    It is generally agreed that individual chondrules formed as entities in a gaseous nebula prior to being accumulated into a meteorite parent body, within which they incur various forms of modification before arriving in our labs. While there are major unanswered questions about the properties of the nebula environment in which chondrules formed, the process by which the most primitive meteorites are formed overwhelmingly from chondrules must then be an aspect of "nebula processing". Textures in certain fragments of primitive meteorites might be summarized as being primarily chondrules and clastic, chondrule-sized, fragments of other minerals, each covered with a rim of fine dust with physical and chemical properties which are essentially independent of the composition and mineralogy of the underlying chondrule. This (unfortunately rather rare) texture was called "primary accretionary texture" to reflect their belief that it precedes subsequent stages in which fragmentation, comminution, mixing, heating, and other forms of alteration occur on the parent body(-ies). The size distribution of these chondrules and fragments, and the properties of their dusty rims, are key clues regarding the primary nebula accretion process. Even in the much more abundant meteorites which have clearly suffered internal mixing, abrasion, grinding, and even mineralogical alteration or replacement (due presumably to the collisional growth and heating process itself), key chondrule properties such as mean size and density remain relatively well defined, and well defined rims persist in many cases. It has been our goal to infer the key nebula processes indirectly from the properties of these very earliest primitive meteorites by making use of a theoretical framework in which the nebula possesses a plausible level of isotropic turbulence. We have shown that turbulence has the property of concentrating one particular particle size by orders of magnitude, where the preferentially concentrated size depends primarily on the intensity of the turbulent kinetic energy (represented by the Reynolds number of the nebula). Specifically, the preferentially concentrated particle is that which has a stopping time equal to the turnover time of the smallest eddy. The intensity level of turbulence implied by chondrule sizes can be maintained by even a small fraction of the energy released by the radially evolving disk (it must be noted that the details of how this transfer of energy actually occurs remain obscure, however).

  19. Accretion of dust by chondrules in a MHD-turbulent solar nebula

    NASA Astrophysics Data System (ADS)

    Carballido, Augusto

    2011-01-01

    Numerical magnetohydrodynamic (MHD) simulations of a turbulent solar nebula are used to study the growth of dust mantles swept up by chondrules. 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 chondrules are modeled by Lagrangian particles that interact with the gas through drag. Whenever a chondrule 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 chondrule volume densities ?c lead to varying depletion and rimmed-chondrule size growth times. Most of the dust sweep-up occurs within 1 gas scale-height of the nebula midplane. Chondrules 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 chondrules 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-chondrule 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 chondrules in the solar nebula.

  20. Oxygen-Isotope Compositions of Chondrules and Matrix Grains in the LEW 87232, Kakangari-Like Chondrite

    NASA Astrophysics Data System (ADS)

    Nagashima, K.; Krot, A. N.; Huss, G. R.

    2012-03-01

    In LEW 87232 K-chondrite, most chondrule grains have ?^71^7O ~ 0 while matrix is isotopically heterogeneous, with the ^1^6O-poor grains having ?1^1^7O ~ -2. The chondrules and ^1^6O-poor matrix grains appear to have sampled different O-isotope reservoirs.

  1. 2D Size Distribution of Chondrules and Chondritic Fragments of an Ordinary Chondrite from Lut Desert (Iran)

    NASA Astrophysics Data System (ADS)

    Pourkhorsandi, H.; Mirnejad, H.

    2014-09-01

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

  2. Formation of Na-Rich Chondrules by Melting of Na-Rich and Condensed (Ultra)-Refractory Precursors

    NASA Astrophysics Data System (ADS)

    Ebert, S.; Bischoff, A.

    2015-07-01

    We analyzed 33 Na-rich chondrules (Na2O >4.0 wt%) from 15 different chondrites. These chondrules must have formed by melting of precursors including Na-rich materials (like nepheline) as well as condensed (ultra)-refractory components.

  3. Mineralogical Comparison of Olivine in Shergottites and A Shocked L Chondrite: Implications for Shock Histories of Brown Olivine

    NASA Technical Reports Server (NTRS)

    Takenouchi, A.; Mikouchi, T.; Yamaguchi, A.; Zolensky, M. E.

    2015-01-01

    Most Martian meteorites are heavily shocked, exhibiting numerous shock features, for example undulatory extinction of olivine and pyroxene, the presence of diaplectic glass ("maskelynite") and the formation of shock melt. Among these shock features, olivine darkening ("brown" olivine) is unique in Martian meteorites because no other meteorite group shows such a feature. Although the presence of brown olivine in shergottites was reported thirty years ago, detailed observation by TEM has not been performed until the NWA 2737 chassignite was discovered, whose olivine is darkened, being completely black in hand specimen. Fe metal nano-particles were found in NWA 2737 olivine which are considered to have been formed by olivine reduction during heavy shock. Subsequently, magnetite nano-particles were also found in other Martian meteorites and the coexistence of Fe metal and magnetite nano-particles was reported in the NWA 1950 shergottite and some Fe metal nano-particles were mantled by magnetite. Therefore, the formation process of nano-particles seems to be complex. Because "brown" olivine is unique to Martian meteorites, they have a potential to constrain their shock conditions. In order to better understand the shock history of Martian meteorites, we compared olivine in several shergottites with that in a highly-shocked L chondrite which contains ringwoodite.

  4. Geobarometry of ultramafic xenoliths from Loihi Seamount, Hawaii, on the basis of CO2 inclusions in olivine

    USGS Publications Warehouse

    Roedder, E.

    1983-01-01

    Abundant fluid inclusions in olivine of dunite xenoliths (???1-3 cm) in basalt dredged from the young Loihi Seamount, 30 km southeast of Hawaii, are evidence for three coexisting immiscible fluid phases-silicate melt (now glass), sulfide melt (now solid), and dense supercritical CO2 (now liquid + gas)-during growth and later fracturing of some of these olivine crystals. Some olivine xenocrysts, probably from disaggregation of xenoliths, contain similar inclusions. Most of the inclusions (2-10 ??m) are on secondary planes, trapped during healing of fractures after the original crystal growth. Some such planes end abruptly within single crystals and are termed pseudosecondary, because they formed during the growth of the host olivine crystals. The "vapor" bubble in a few large (20-60 ??m), isolated, and hence primary, silicate melt inclusions is too large to be the result of simple differential shrinkage. Under correct viewing conditions, these bubbles are seen to consist of CO2 liquid and gas, with an aggregate ??{variant} = ??? 0.5-0.75 g cm-3, and represent trapped globules of dense supercritical CO2 (i.e., incipient "vesiculation" at depth). Some spinel crystals enclosed within olivine have attached CO2 blebs. Spherical sulfide blebs having widely variable volume ratios to CO2 and silicate glass are found in both primary and pseudosecondary inclusions, demonstrating that an immiscible sulfide melt was also present. Assuming olivine growth at ??? 1200??C and hydrostatic pressure from a liquid lava column, extrapolation of CO2 P-V-T data indicates that the primary inclusions were trapped at ??? 220-470 MPa (2200-4700 bars), or ??? 8-17 km depth in basalt magma of ??{variant} = 2.7 g cm-3. Because the temperature cannot change much during the rise to eruption, the range of CO2 densities reveals the change in pressure from that during original olivine growth to later deformation and rise to eruption on the sea floor. The presence of numerous decrepitated inclusions indicates that the inclusion sample studied is biased by the loss of higher-density inclusions and suggests that some part of these olivine xenoliths formed at greater depths. ?? 1983.

  5. Olivine in an unexpected location on Vesta's surface.

    PubMed

    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

    2013-12-01

    Olivine 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 olivine, typically with a concentration of less than 25 per cent by volume. Olivine 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 olivine 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 olivine-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. Olivine is exposed in crater walls and in ejecta scattered diffusely over a broad area. The size of the olivine 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 olivine-rich material suggest a complex evolutionary history for Vesta. PMID:24196707

  6. Fast grain growth of olivine in liquid Fe-S and the formation of pallasites with rounded olivine grains

    NASA Astrophysics Data System (ADS)

    Solferino, Giulio F. D.; Golabek, Gregor J.; Nimmo, Francis; Schmidt, Max W.

    2015-08-01

    Despite their relatively simple mineralogical composition (olivine + Fe-Ni metal + FeS ± pyroxene), the origin of pallasite meteorites remains debated. It has been suggested that catastrophic mixing of olivine fragments with Fe-(Ni)-S followed by various degrees of annealing could explain pallasites bearing solely or prevalently fragmented or rounded olivines. In order to verify this hypothesis, and to quantify the grain growth rate of olivine in a liquid metal matrix, we performed a series of annealing experiments on natural olivine plus synthetic Fe-S mixtures. The best explanation for the observed olivine grain size distributions (GSD) of the experiments are dominant Ostwald ripening for small grains followed by random grain boundary migration for larger grains. Our results indicate that olivine grain growth in molten Fe-S is significantly faster than in solid, sulphur-free metal. We used the experimentally determined grain growth law to model the coarsening of olivine surrounded by Fe-S melt in a 100-600 km radius planetesimal. In this model, an impact is responsible for the mixing of olivine and Fe-(Ni)-S. Numerical models suggest that annealing at depths of up to 50 km allow for (i) average grain sizes consistent with the observed rounded olivine in pallasites, (ii) a remnant magnetisation of Fe-Ni olivine inclusions as measured in natural pallasites and (iii) for the metallographic cooling rates derived from Fe-Ni in pallasites. This conclusion is valid even if the impact occurs several millions of years after the differentiation of the target body was completed.

  7. Olivine in the Southern Isidis Basin

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) took this observation of the transition region between Libya Montes and the Isidis Basin on Mars at 17:16 UTC (12:16 p.m. EST) on January 2, 2007, near 3.6 degrees north latitude, 84.1 degrees east longitude. The image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 18 meters (60 feet) across. The image is about 11 kilometers (7 miles) wide at its narrowest point.

    The Isidis Basin resulted from of a gigantic impact on the surface of Mars early in the planet's history. The southern rim, where this target is located, is a region of complex geology and part of the planetary dichotomy boundary that separates the older southern highlands from the lower, younger northern plains. The image on the left was constructed from three visible wavelengths (RGB: 0.71, 0.60, 0.53 microns) and is a close approximation of how the surface would appear to the human eye. The image on the right was constructed from three infrared wavelengths (RGB: 2.49, 1.52, 1.08 microns) chosen to highlight variations in the mineralogy of the area. Of interest is that features in this image not only differ in color, but also in texture and morphology. The gray areas absorb similarly at all wavelengths used in this image, but display absorptions at other wavelengths related to the iron- and magesium-rich mineral pyroxene. The reddest areas absorb strongly at the wavelengths used for green and blue, which is attributable to another iron- and magesium-rich mineral, olivine. The brownish areas show subdued mineral absorptions and could represent some type of mixture between the other two materials. The presence of the mineral olivine is particularly interesting because olivine easily weathers to other minerals; thus, its presence indicates either the lack of weathering in this region or relatively recent exposure.

    CRISM's mission: Find the spectral fingerprints of aqueous and hydrothermal deposits and map the geology, composition and stratigraphy of surface features. The instrument will also watch the seasonal variations in Martian dust and ice aerosols, and water content in surface materials -- leading to new understanding of the climate.

    The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad.

  8. Fe and O isotope composition of meteorite fusion crusts: Possible natural analogues to chondrule formation?

    NASA Astrophysics Data System (ADS)

    Hezel, Dominik C.; Poole, Graeme M.; Hoyes, Jack; Coles, Barry J.; Unsworth, Catherine; Albrecht, Nina; Smith, Caroline; RehkMper, Mark; Pack, Andreas; Genge, Matthew; Russell, Sara S.

    2015-02-01

    Meteorite fusion crust formation is a brief event in a high-temperature (2000-12,000 K) and high-pressure (2-5 MPa) regime. We studied fusion crusts and bulk samples of 10 ordinary chondrite falls and 10 ordinary chondrite finds. The fusion crusts show a typical layering and most contain vesicles. All fusion crusts are enriched in heavy Fe isotopes, with ?56Fe values up to +0.35 relative to the solar system mean. On average, the ?56Fe of fusion crusts from finds is +0.23, which is 0.08 higher than the average from falls (+0.15). Higher ?56Fe in fusion crusts of finds correlate with bulk chondrite enrichments in mobile elements such as Ba and Sr. The ?56Fe signature of meteorite fusion crusts was produced by two processes (1) evaporation during atmospheric entry and (2) terrestrial weathering. Fusion crusts have either the same or higher ?18O (0.9-1.5) than their host chondrites, and the same is true for ?17O. The differences in bulk chondrite and fusion crust oxygen isotope composition are explained by exchange of oxygen between the molten surface of the meteorites with the atmosphere and weathering. Meteorite fusion crust formation is qualitatively similar to conditions of chondrule formation. Therefore, fusion crusts may, at least to some extent, serve as a natural analogue to chondrule formation processes. Meteorite fusion crust and chondrules exhibit a similar extent of Fe isotope fractionation, supporting the idea that the Fe isotope signature of chondrules was established in a high-pressure environment that prevented large isotope fractionations. The exchange of O between a chondrule melt and an 16O-poor nebula as the cause for the observed nonmass dependent O isotope compositions in chondrules is supported by the same process, although to a much lower extent, in meteorite fusion crusts.

  9. Early cosmic ray irradiation of chondrules and prolonged accretion of primitive meteorites

    NASA Astrophysics Data System (ADS)

    Beyersdorf-Kuis, Uta; Ott, Ulrich; Trieloff, Mario

    2015-08-01

    Chondrules, together with Ca-Al-rich inclusions (CAIs) and matrix, are the major constituents of primitive meteorites. It is clear that chondrules formed as molten objects and the conditions under which this happened seem well constrained. Partially overlapping in age, but mostly ?2-3 million years younger than the CAIs, they appear to have formed over an extended period of time (e.g., Kita et al., 2013). We have analyzed chondrules in two highly primitive CR3 meteorites, QUE 99177 and MET 00426, and find that they contain highly variable amounts of noble gases produced by irradiation with cosmic rays. The lack of implanted solar wind and the composition of the cosmogenic component in QUE 99177 chondrules argue against irradiation in a parent body regolith, which leaves irradiation in the early solar system as the most likely explanation. The cosmogenic composition also points to irradiation primarily by galactic cosmic rays (GCR), not solar cosmic rays (SCR), i.e. not by an active early sun. To allow effective production of cosmogenic isotopes by GCR, but not SCR, this should have happened rather "late" in a largely, but not completely, dust-free environment. Our results support the suggestion that chondrules formed as free-floating objects in the solar nebula; also consistent with the noble gas data is pre-irradiation in small (?dm-size) aggregates that broke up before or during accretion to the CR parent body. In both cases, chondrules spent an extended period of time before incorporation into the most primitive meteorite parent bodies, which puts constraints on accretion time scales.

  10. Possible melting produced chondrule destruction in NWA 6604 CK4 chondrite

    NASA Astrophysics Data System (ADS)

    Kereszturi, A.; Ormandi, S.; Jozsa, S.

    2015-07-01

    In analyzing a thin section of the NWA 6604 CK4 meteorite, only altered chondrules and various components that are probably left behind the destruction of former chondrules can be observed. We suggest that melting, grain size decrease, resorption of the original chondrules, and crystallization of opaque minerals were the main processes that destroyed the chondrules. Four different events could be identified as having occurred during this alteration. First, opaques crystallized along former fractures producing chains of separated grains. Later, opaques and Ca-rich minerals crystallized together in veins and large melt pockets; this was the strongest recrystallization phase involving the largest volume of melt. This occurred along different fractures than the first phase above. During the third phase, only Ca-rich plagioclase crystallized along thin veins, and in a fourth phase, fractures formed again, partly along those formed during the second phases but without substantial mineral infill. Two simple possible case models should be considered for this meteorite: alteration by purely impact-driven processes or mainly by melt-driven processes. Although for CK4 chondrites, the shock-produced alteration driven by impact is the more accepted and widespread approach, melting is also compatible with the observed textural characteristics of chondrule destruction. During melting, recrystallization took place producing iron-rich minerals earlier and Ca-Si-rich ones later. The penetration of melts into veins contributed in the chondrule destruction. The stress directions also changed during these alterations, and minerals that formed later filled differently oriented fractures than the earlier ones. From our observations, we favor a view where heat-driven melting and recrystallization produced the destruction and uniform mineralogy in the sample.

  11. Chemical dispersion among Apollo 15 olivine-normative mare basalts

    NASA Technical Reports Server (NTRS)

    Ryder, Graham; Steele, Alison

    1988-01-01

    Analysis of Apollo 15 olivine-normative mare basalts for major and minor elements suggests that the hypothesis that the coarser-grained varieties (olivine microgabbros) consist of two chemical groups is incorrect. Instead, it is found that there is a single group including vesicular, coarse-grained, and fine-grained basalts. For the entire suite, the dispersion of compositions along the olivine trend is too great to be explained by short-range unmixing of an unfractionated flow. It is suggested that the general trend for the suite is olivine separation, probably through crystal settling. The textures, mineralogical characteristics, and chemical variation of the olivine-normative basalts are shown to be consistent with a sequence of thin fractionating flows, all from a common parent.

  12. Did Ordinary Chondrite Impactors Deliver Olivine to Vesta?

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  13. A secondary origin of chondrule magnetization in the Allende CV carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Carporzen, L.; Fu, R.; Andrade Lima, E.; Weiss, B. P.

    2011-12-01

    Magnetic fields in the solar nebula may have played a key role in the radial transport of angular momentum and mass during the early accretional phase of the solar system. Chondrules and many calcium aluminum inclusions (CAIs), millimeter sized silicate objects found in most chondritic meteorites, were heated to high temperatures and cooled in the nebula and therefore may have recorded a thermoremanent magnetization (TRM) from the nebula field. Additionally, primitive magnetization in chondrules and CAIs may yield constraints about their mode of formation. However, any such primary magnetization may have been significantly altered during subsequent metamorphism and aqueous alteration on the parent asteroid. We performed two tests to determine the nebular origins of remanent magnetization in chondrules and refractory inclusions in the Allende CV3 carbonaceous chondrite: 1) a classic paleomagnetic conglomerate test to identify post-accretional remagnetization events and 2) a unidirectionality test of subsamples taken from individual chondrules and CAIs. We conducted individual measurements of mutually oriented chondrules, CAIs, and matrix as well as SQUID microscope maps of the magnetic fields of 30 ?m thin sections. All samples and thin sections were mutually oriented to within 5. Our results confirm previous findings that all subsamples of the meteorite carry a unidirectional overprint blocked up to 260-290C (MT component). Chondrules and CAIs also carry a higher temperature (HT) remanence oriented in scattered directions unrelated to the direction of the MT overprint. We have confirmed that this HT magnetization is not an artifact of the demagnetization procedure but is a preterrestrial component. Measurements of subsamples of single chondrules and CAIs show that the HT magnetization is not unidirectional within each inclusion. Petrographic data suggests that most magnetic minerals in Allende were the product of parent body alteration. These facts suggest that the magnetization in Allende chondrules and CAIs is not a preaccretional TRM and is unlikely to record the nebular field. We suggest that preaccretional remanence in Allende material was destroyed by aqueous alteration and metasomatism, which was followed or coincident with metamorphism that introduced the MT overprint. The HT component we detect may represent a chemical remanent magnetization (CRM) acquired during aqueous alteration.

  14. The origin of chromitic chondrules and the volatility of Cr under a range of nebular conditions

    NASA Technical Reports Server (NTRS)

    Krot, Alexander; Ivanova, Marina A.; Wasson, John T.

    1993-01-01

    We characterize ten chromatic chondrules, two spinelian chondrules andd one spinel-bearing chondrule and summarize data for 120 chromitic inclusions discovered in an extensive survey of ordinary chondrites. Compositional and petrographic evidence suggests that chromitic chondrules 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 chondrules. The Cr/Mg ratios in chromitic chondrules 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 chondrules. Our model implies that chromitic chondrules and inclusions preserve the Cr isotopic record of presolar sources.

  15. Chondrules with peculiar REE patterns: implications for solar nebular condensation at high C/O.

    PubMed

    Pack, Andreas; Shelley, J Michael G; Palme, Herbert

    2004-02-13

    Rare earth element (REE) data from two ordinary chondrite chondrules show distinct negative chondrite-normalized concentration anomalies of samarium, europium, and ytterbium. The peculiar patterns may be the result of REE gas/solid fractionation at an oxygen fugacity lower than has been assumed for the canonical solar nebula. We suggest that the two ordinary chondrite chondrules acquired the fractionated REE patterns by incorporation of highly reduced, ultrarefractory condensates in their precursors. This interpretation implies that high-temperature condensation processes occurred in nebular environments with a strong deficit in oxygen, such as regions with an enhanced carbon/oxygen ratio. PMID:14963326

  16. Iodine-xenon studies of petrographically and chemically characterized Chainpur chondrules

    NASA Technical Reports Server (NTRS)

    Swindle, T. D.; Caffee, M. W.; Hohenberg, C. M.; Lindstrom, M. M.; Taylor, G. J.

    1991-01-01

    INAA, noble gas, and petrographic studies conducted on samples of 18 chondrules 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 chondrules. 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.

  17. Cotectic proportions of olivine and spinel in olivine-tholeiitic basalt and evaluation of pre-eruptive processes

    USGS Publications Warehouse

    Roeder, P.; Gofton, E.; Thornber, C.

    2006-01-01

    The volume %, distribution, texture and composition of coexisting olivine, Cr-spinel and glass has been determined in quenched lava samples from Hawaii, Iceland and mid-oceanic ridges. The volume ratio of olivine to spinel varies from 60 to 2800 and samples with >0.02% spinel have a volume ratio of olivine to spinel of approximately 100. A plot of wt % MgO vs ppm Cr for natural and experimental basaltic glasses suggests that the general trend of the glasses can be explained by the crystallization of a cotectic ratio of olivine to spinel of about 100. One group of samples has an olivine to spinel ratio of approximately 100, with skeletal olivine phenocrysts and small (100 ??m) spinel crystals that show evidence of two stages of growth, and a volume ratio of olivine to spinel of 100 to well over 1000. The olivine and spinel in this group have crystallized more slowly with little physical interaction, and show evidence that they have accumulated in a magma chamber. ?? 2006 Oxford University Press.

  18. Boron, beryllium, and lithium, partitioning in olivine

    SciTech Connect

    Neroda, Elizabeth

    1996-05-01

    A one atmosphere experimental study was performed to determine the mineral/melt partition coefficients for B, Be, and Li in forsteritic olivine. Two compositions were chosen along the 1350{degrees}C isotherm, 1b (Fo{sub 17.3} Ab{sub 82.7} An{sub 0} by weight) and 8c (Fo{sub 30} Ab{sub 23.3} An{sub 47.8}, by weight) were then combined in equal amounts to form a composition was doped with 25ppm Li, B, Yb, Nb, Zr, Sr, and Hf, 50ppm Sm, and 100ppm Be, Nd, Ce, and Rb. Electron and ion microprobe analyses showed that the olivine crystals and surrounding glasses were homogeneous with respect to major and trace elements. Partition coefficients calculated from these analyses are as follows: 1b: D{sub B} = 4.41 ({+-} 2.3) E-03, D{sub Be} = 2.86 ({+-} 0.45) E-03, D{sub Li} = 1.54 ({+-} 0.21) E-01, 50/50: D{sub B} = 2.86 ({+-} 0.5) E-03, D{sub Be} = 2.07 ({+-} 0.09) E-03, D{sub Li} = 1.51 ({+-} 0.18) E-01, 8c: D{sub B} = 6.05 ({+-} 1.5) E-03, D{sub Be} = 1.81 ({+-} 0.03) E-03, D{sub Li} = 1.31 ({+-} 0.09) E-01. The results of this study will combined with similar data for other minerals as part of a larger study to understand the partitioning behavior of B, Be, and Li in melting of the upper mantle at subduction zones.

  19. Remote Compositional Analyses of Lunar Olivine-Bearing Lithologies

    NASA Astrophysics Data System (ADS)

    Isaacson, P.; Clark, R. N.; Head, J. W.; Klima, R.; Petro, N. E.; Pieters, C. M.; Staid, M.; Sunshine, J. M.; Taylor, L. A.; Thaisen, K. G.; Tompkins, S.

    2009-12-01

    The Moon Mineralogy Mapper (M3) is a guest instrument on Chandrayaan-1, Indias first mission to the Moon. M3 is an imaging spectrometer covering the wavelength range of 430 nm - 3000 nm, and was designed to map the mineralogy of the lunar surface. The high spectral resolution of M3 enables the diagnostic absorption features of lunar minerals to be identified clearly, while the high spatial resolution of M3 allows the identification and mapping of distinct lithologic units. Olivine is an important mineral with which to interpret the petrologic evolution of igneous rocks. The composition of olivine (Mg#) is used to indicate the degree of evolution of the source magma from which a sample crystallized. Visible to near-infrared reflectance spectroscopy is sensitive to the Mg# of olivine, as the diagnostic olivine absorption features shift in response to changing major element abundances (Mg and Fe) content. These changes in diagnostic absorption features can be detected by modeling the individual absorption bands with the Modified Gaussian Model (MGM). Spectra of lunar olivines differ from spectra of their terrestrial and synthetic counterparts due to the inclusions of Cr-spinel common to lunar olivines; however, analysis of lunar olivine mineral separates in terrestrial laboratories and modeling of the resulting reflectance spectra have been able to unravel the chromite effects on the olivine spectrum. Previous efforts at remote compositional analysis of lunar olivine have been limited by spectral resolution and coverage or by spatial resolution. However, the spatial and spectral resolution provided by M3 enable olivine composition to be determined remotely in a spatial context. We are in the process of identifying olivine-bearing lithologies on the lunar farside and analyzing the olivine composition with the modified MGM approach. Initial compositional analyses have been completed for a crater on the rim of the Moscoviense basin that appears to be largely dominated by olivine and relatively free from other optically active mafic phases such as pyroxene. Significant occurrences of other rocks dominated optically by olivine (e.g., troctolites) have been identified elsewhere around the basin. Olivine-dominated rocks in the lunar sample collection almost certainly formed through secondary magmatic processes following crystallization of the lunar magma ocean (the so-called Mg-suite). It is possible that similar processes produced the olivine-dominated lithologies around Moscoviense, although the scale of the intrusion required would likely be quite large. It is also possible that the Moscoviense impact event scattered locally-occurring olivine-rich rocks over the broad area observed. Preliminary compositional analysis results range from ~Fo50 to ~Fo75, broadly consistent with olivine compositions found in analyses of feldspathic lunar meteorites (likely to originate from the Feldspathic Highlands Terrane on the farside), as well as with olivines found in Apollo 16 troctolites.

  20. Replacement of olivine by serpentine in the Queen Alexandra Range 93005 carbonaceous chondrite (CM2): Reactant-product compositional relations, and isovolumetric constraints on reaction stoichiometry and elemental mobility during aqueous alteration

    NASA Astrophysics Data System (ADS)

    Velbel, Michael A.; Tonui, Eric K.; Zolensky, Michael E.

    2015-01-01

    Isovolumetric replacement of euhedral and anhedral olivine by serpentine produced both centripetal and meshwork textures in the CM2 chondrites ALH 81002 and Nogoya. The compositions of these textural varieties of serpentine are uniform within narrow limits within each previously studied meteorite, independent of the composition of olivine being replaced, and different between the two meteorites. In QUE 93005 (CM2), coarse olivines of widely varying compositions (Fo<76-99) are replaced in a texturally similar manner by compositionally uniform serpentine (Mg0.73±0.05Fe0.27±0.05)3Si2O5(OH)4. The narrow compositional range of serpentine replacing coarse olivine indicates that the aqueous solution from which the serpentine formed was compositionally uniform on scales at least as large as the meteorite (∼2.5 cm in longest dimension). Isovolumetric textures and compositional observations constrain elemental redistribution from coarse olivine to serpentine and to surrounding phases during serpentinization. Regardless of olivine's composition, isovolumetric replacement of coarse olivines by serpentine of the observed composition released more Mg and Si from olivine than was required to form the serpentine. Excess Mg and Si released by olivine destruction and not retained in serpentine were exported from the replaced volume. Olivines with different Fa/Fo proportions contributed different amounts of Fe and Mg to the serpentine. Ferroan olivines released more Fe than required to form the serpentines replacing them, so some of the Fe released from ferroan olivine was exported from the replaced volumes. Forsteritic olivines released less Fe than required to form the serpentines replacing them, so some Fe was imported into the replaced volumes augmenting the small amount of Fe released from forsteritic olivine. In QUE 93005 Fo83.8 is the threshold composition between Fe-exporting and Fe-importing behavior in individual olivine-serpentine pairs, which released exactly the amount of Fe required to form serpentine of the observed uniform composition. Compositions of serpentines isovolumetrically replacing olivines, and threshold olivine compositions, in QUE 93005 differ from the corresponding values in Nogoya. Solvent and solute species diffused through the serpentine between the olivine-serpentine interface and the aqueous solution outside the isovolumetrically replaced volume. In QUE 93005, some of the Fe released from ferroan olivine in excess of the amount required to form serpentine reacted with S sourced from outside the pseudomorphs to form Fe-sulfide decorating the margins of the pseudomorphs of serpentine after fayalitic olivine. Such Fe-sulfide-decorated outlines after fayalitic olivine do not occur in ALH 81002 or Nogoya, indicating different Fe and S mass transfer regimes in different CM2 chondrites. Mg, Fe, Si, and S in the aqueous solution, including the excess Mg and Si exported from all serpentine pseudomorphs after olivine of any composition, were available to be incorporated into other phases spatially separate from the pseudomorphs after olivine, including regularly interstratified serpentine-tochilinite. Serpentines that replaced coarse olivines in QUE 93005 and ALH 81002 are less magnesian than those in Nogoya, indicating that the Nogoya aqueous-alteration environment was more evolved toward Mg-rich solutions. This easily located and characterized phase assemblage may be potentially useful for characterizing clasts of varying degrees of alteration in brecciated and heterogeneous CM chondrites, and future returned samples from mineralogically similar asteroids. partial and complete pseudomorphic and alteromorphic replacement (after euhedral and anhedral primary minerals, respectively; the terminology of Delvigne, 1998, is used sensu stricto where the distinction is important in this paper, and the more familiar term pseudomorph is used elsewhere sensu lato in the interest of brevity), meshwork serpentinization textures (Wicks and Whittaker, 1977), and "centripetal replacement" in which entire grains or fracture-bounded remnants are replaced from the margin inward (e.g., Velbel, 1984, 1993). More papers reported alteromorphic replacement of (anhedral) coarse anhydrous chondritic silicates (subhedral/anhedral silicates in chondrules; isolated monocrystalline olivine in matrix) than pseudomorphic replacement of euhedral olivine (Fuchs et al., 1973; McSween, 1979a,b; Bunch and Chang, 1980; Zolensky and McSween, 1988; Browning et al., 1996, 2000; Zolensky et al., 1997; Hanowski and Brearley, 2001; Zolensky and Ivanov, 2003; Rubin et al., 2007; MacPherson et al., 2009; Velbel et al., 2012). Centripetal replacement of olivine by serpentine during terrestrial serpentinization has been elegantly described by Boudier et al. (2010). Simple centripetal replacement of olivine by serpentine in CM chondrites has been observed and illustrated by Hanowski and Brearley (2001) and Rubin et al. (2007). Meshwork serpentines mark the former distribution of grain boundaries and intragranular fractures, and separate remnants of unreplaced primary mineral (e.g., Wicks and Whittaker, 1977; Delvigne, 1998).Bunch and Chang (1980), Hanowski and Brearley (2001), Zolensky and Ivanov (2003), and Velbel et al. (2012) describe serpentine occurring both as meshwork and pseudomorphic after olivine in altered CM2 chondrites. Velbel et al. (2012) found meshwork serpentinization textures in near end-member forsteritic olivine to be both common and similar to their terrestrial counterparts, to a much greater degree than in ferroan olivine. In both meshwork and centripetal replacement, olivine and pyroxene remnants, with maximum dimensions of tens of micrometers and rarely up to 250 μm, survive in the centers of some pseudomorphs and alteromorphs (including meshworks) of phyllosilicate after the anhydrous primary silicate (Hanowski and Brearley, 2001; Velbel et al., 2012).Serpentinization of coarse-grained olivine (and pyroxene) appears to represent an advanced intermediate stage of aqueous alteration (Hanowski and Brearley, 2001; Velbel et al., 2012; Velbel, 2014); it occurs abundantly only in CM chondrites in which essentially all other primary silicate phases in matrix, rims, and mesostasis are already extensively altered to increasingly Mg-rich serpentine (Browning and other, 1996; Hanowski and Brearley, 2001; Brearley, 2003, 2006; Rubin et al., 2007; Chizmadia and Brearley, 2008; Howard et al., 2009, 2011). Hanowski and Brearley (2001) proposed a four-stage model relating the textures and compositions of phyllosilicates replacing coarse CM2 olivine, the extent and degree of olivine alteration to serpentine, and the chemical evolution of the co-existing aqueous solutions, culminating in the observed properties of ALH 81002. Following on their four-stage model, Velbel et al. (2012) added observations and inferences from Nogoya, extending the model of Hanowski and Brearley (2001) to an even more altered, fifth stage. The expanded version as presented by Velbel et al. (2012) and Velbel (2014) is shown in Table 1. Velbel et al. (2012) summarized the initial conditions and Stages 1-3 of the Hanowski and Brearley (2001) model. Stages 4 and 5 are most relevant to the work presented in the present paper, and a brief updated summary of these stages is presented here.

  1. The pattern of Ni and Co abundances in lunar olivines

    NASA Astrophysics Data System (ADS)

    Longhi, John; Durand, Sedelia R.; Walker, David

    2010-01-01

    Near liquidus experiments on peridotite and other olivine normative compositions from 1.7 to 6 GPa confirm the applicability of exchange-based empirical models of Ni and Co partitioning between olivine and silicate liquids with compositions close to the liquidus of peridotite. Given that most estimates of lunar bulk composition are peridotitic, the partitioning models thus lend themselves to calculation of olivine compositions produced during the early stages of magma ocean crystallization. Calculation of olivine compositions produced by fractional crystallization of a model lunar magma ocean, initially 700 km deep, reveals a prominent maximum in Ni concentration versus fraction crystallized or Mg' (molar MgO/(MgO + FeO)), but a pattern of monotonically increasing Co concentration. These patterns qualitatively match the puzzling patterns of Ni and Co concentrations observed in lunar rocks in which forsteritic olivines in magnesian suite cumulates have lower Ni and Co abundances than do less magnesian olivines from low-Ti mare basalts, and olivines from the ferroan anorthosite suite (FAS) have lower Ni, but similar Co to mare basalt olivines. The Ni and Co abundances in olivines from the magnesian suite cumulates can be reconciled in terms of fractional crystallization of a deep magma ocean which initially produces a basal dunite comprised of the hottest and most magnesian olivine overlain by an olivine-orthopyroxene (harzburgite) layer that is in turn overlain by an upper zone of plagioclase-bearing cumulates. The ultramafic portion of the cumulate pile overturns sending the denser harzburgite layer, which later becomes a portion of the green glass source region, to the bottom of the cumulate pile with Ni- and Co-rich olivine. Meanwhile, the less dense, but hottest, most magnesian olivines with much lower Ni and Co abundances are transported upward to the base of the plagioclase-bearing cumulates where subsequent heat transfer leads to melting of mixtures of primary dunite, norite, and gabbronorite with KREEP (a K-REE-P enriched component widely believed to be derived from the very latest stage magma ocean liquid). These hybrid melts have Al 2O 3, Ni, and Co abundances and Mg' appropriate for parent magmas of the magnesian suite. Ni and Co abundances in the FAS are consistent with either direct crystallization from the magma ocean or crystallization of melts of primary dunite-norite mixtures without KREEP.

  2. The Bar Revue.

    ERIC Educational Resources Information Center

    Student Lawyer, 1980

    1980-01-01

    Listed are six organizations that offer bar review courses, and the addresses of state bar examiners and other pertinent information (application filing, exam dates and locations, and fees and residency requirements) for taking examinations. Available Law Student Division, American Bar Association, 1155 E. 60th St., Chicago, IL 60637; $1.00. (MSE)

  3. Microchondrules in two unequilibrated ordinary chondrites: Evidence for formation by splattering from chondrules during stochastic collisions in the solar nebula

    NASA Astrophysics Data System (ADS)

    Dobricǎ, E.; Brearley, A. J.

    2016-03-01

    The diversity of silicate, glassy spherules analogous to chondrules, called microchondrules, and the implications for their presence in unequilibrated ordinary chondrites (UOCs) were investigated using different electron microscope techniques. Our observations show that the abundance of microchondrules in UOCs is much larger than the values proposed by previous studies. We identified two different types of microchondrules, porous and nonporous, embedded within fine-grained matrices and type I chondrule rims. The porous microchondrules are characterized by distinctive textures and chemical compositions that have not been recognized previously. Additionally, we show detailed textures and chemical compositions of protuberances of silicate materials, connected to the chondrules and ending with microchondrules. We suggest that microchondrules and protuberances formed from materials splattered from the chondrules during stochastic collisions when they were still either completely or partially molten. The occurrence and distinct morphologies of microchondrules and protuberances suggest that rather than just a passive flash melting of chondrules, an additional event perturbed the molten chondrules before they underwent cooling. The bulk chemical compositions suggest that (1) nonporous microchondrules and protuberances were formed by splattering of materials that are compositionally similar to the bulk silicate composition of type I chondrules, and (2) the porous microchondrules could represent the splattered melt products of a less evolved, fine-grained dust composition. The preservation of protuberances and microchondrules in the rims suggests that the cooling and accretion rates were exceptionally fast and that they represent the last objects that were formed before the accretion of the parent bodies of OCs.

  4. Mineralogy of interplanetary dust particles from the 'olivine' infrared class

    NASA Technical Reports Server (NTRS)

    Christoffersen, R.; Buseck, P. R.

    1986-01-01

    Analytical electron microscopy observations establish that olivine is abundant and the predominant silicate phase in three interplanetary dust particles (IDPs) from the 'olivine' 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 olivine these particles respectively contain enstatite and magnetite, and pentlandite plus Ca-rich clinopyroxene. The third IDP consists mostly of olivine and pyrrhotite with little or no matrix material. Olivine 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 olivine-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 olivine infrared spectral category is a diverse collection of IDPs that probably incorporates several genetic groups.

  5. The olivine macrocryst problem: New insights from minor and trace element compositions of olivine from Lac de Gras kimberlites, Canada

    NASA Astrophysics Data System (ADS)

    Bussweiler, Yannick; Foley, Stephen F.; Prelević, Dejan; Jacob, Dorrit E.

    2015-04-01

    This study presents detailed petrographical and geochemical investigations on remarkably fresh olivines in kimberlites from the EKATI Diamond Mine™ located in the Tertiary/Cretaceous Lac de Gras kimberlite field within the Slave craton of Canada. Olivine, constituting about 42 vol.% of the analyzed samples, can be divided into two textural groups: (i) macrocrystic olivines, > 100 μm sub-rounded crystals and (ii) groundmass olivines, < 100 μm subhedral crystals. Olivines from both populations define two distinct chemical trends; a "mantle trend" with angular cores, showing low Ca (< 0.1 wt.% CaO) and high Ni (0.3-0.4 wt.% NiO) at varying Mg# (0.86-0.93), contrasts with a "melt trend" typified by thin (< 100 μm) rims with increasing Ca (up to 1.0 wt.% CaO) and decreasing Ni (down to 0.1 wt.% NiO) contents at constant Mg# (~ 0.915). These findings are in agreement with recent studies suggesting that virtually all olivine is composed of xenocrystic (i.e. mantle-related) cores with phenocrystic (i.e. melt-related) overgrowths, thereby challenging the traditional view that the origin of kimberlitic olivine can be distinguished based on size and morphology. The two main trends can be further resolved into sub-groups refining the crystallization history of olivine; the mantle trend indicates a multi-source origin that samples the layered lithosphere below the Slave craton, whereas the melt trend represents multi-stage crystallization comprising a differentiation trend starting at mantle conditions and a second trend controlled by the crystallization of additional phases (e.g. chromite) and changing magma conditions (e.g. oxidation). These trends are also seen in the concentrations of trace elements not routinely measured in olivine (e.g. Na, P, Ti, Co, Sc, Zr). Trace element mapping with LA-ICP-MS reveals the distribution of these elements within olivine grains. The trace element distribution between the two trends appears to be consistent with phenocrystic olivine overgrowths mainly originating from dissolved orthopyroxene, showing enrichment in Zr, Ga, Nb, Sc, V, P, Al, Ti, Cr, Ca and Mn in the melt trend. In a sample of magmatic kimberlite from the Leslie pipe, the amount of xenocrystic and phenocrystic olivine is estimated to be around 23 vol.% and 19 vol.%, respectively. Subtraction of this xenocrystic olivine from the Leslie bulk composition, aimed at estimating the parental kimberlite melt, results in a minor decrease of Mg# (by about 0.01) and SiO2 content (by about 3 wt.%), whereas CaO increases (by about 3 wt.%).

  6. The case for a cognate, polybaric origin for kimberlitic olivines

    NASA Astrophysics Data System (ADS)

    Moore, Andy E.

    2012-01-01

    Kimberlitic olivines typically show a continuous range in size and texture rather than two discrete populations. The cores of small euhedral olivines 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 olivines define a continuous compositional field, which can be interpreted in terms of Raleigh crystallization. Marked chemical gradients at the olivine 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 olivines 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 olivines and the most refractory olivines 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 olivine both decrease sympathetically from the interior to the continental margin, which is also consistent with a cognate origin for the olivines. 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 olivines 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 olivine 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 olivines are predicted by a plausible magma P-T trajectory.

  7. Fluorine in Olivines from Plutonic, Extrusive, and Hypabyssal Suites

    NASA Astrophysics Data System (ADS)

    Guggino, S. N.; Hervig, R. L.; Bell, D. R.

    2007-12-01

    Fluorine contents in a wide range of naturally-occurring olivine grains were determined by secondary ion mass spectrometry (SIMS) using a Cs+ primary beam, detection of negative secondary ions and an auxiliary electron gun for charge neutralization. A range of minerals and glasses containing 3 to 1300 ppm F were used to calibrate the secondary ion signal. Matrix effects appear to be small, and because fluorine has a high electron affinity, sensitivity is high (sub-ppm). Olivines from the study by Simkin and Smith (J. Geol., 1970) were analyzed for their F contents and span a range of suites that include upper mantle xenoliths and kimberlites, plutonic intrusives, ophiolites, shallow hypabyssal picrites and teschenites, and extrusive alkaline and tholeiitic basalts. Overall, the olivines in this study show a range of F concentrations from 0.5 to 32 ppm. Olivines from high- pressure environments show the highest individual and average F values, however large variations are also observed in this suite. Mantle xenoliths from this sample collection show a maximum and average F value of 14 and 4.1 ppm, respectively, and one olivine from kimberlite contains 32 ppm F. Earlier analyses from our laboratory (Hervig and Bell, 2005 Fall AGU) show a larger range in F from mantle-derived olivines. Plutonic intrusives and ophiolites, including layered intrusives and cumulates, show a range of F contents from 0.5 to 15 ppm, with an average value of 4 ppm. Olivines from the Kiglapait layered intrusion, Labrador show F content increasing with degree of fractional crystallization until the P2O5 content of the rock begins to increase. At this point, F in olivine decreases, presumably indicating partitioning of F into apatite. In the Hawaiian suites studied, F in olivine was high (8-12 ppm) in evolved andesites and lower (1-8 ppm) in more primitive basalts. Hypabyssal suites include a peridotite dike from Skye, (F < 1 ppm), a chilled olivine dolerite from Bornaskitaig (F = 2 ppm), a picrite from Igdlorsuit, Greenland (F = 4 ppm), and a teschenite from Black Jack Sill, Australia (F = 1.5 ppm). Fluorine measurements on the Simkin and Smith olivines are consistent with earlier observations that F is highest in OH-rich olivines (i.e., upper mantle xenoliths in kimberlites; Hervig & Bell, AGU Fall Mtg 2005).

  8. Forsterite from Chondrules in the Mokoia (CV3) Chondrite: Cathodoluminescence, Chemistry and Oxygen Isotopes

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    Forsterite in Mokoia chondrules 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.

  9. INCORPORATION OF A LATE-FORMING CHONDRULE INTO COMET WILD 2

    SciTech Connect

    Ogliore, R. C.; Huss, G. R.; Nagashima, K.; Butterworth, A. L.; Gainsforth, Z.; Stodolna, J.; Westphal, A. J.; Joswiak, D.; Tyliszczak, T.

    2012-02-15

    We report the petrology, O isotopic composition, and Al-Mg isotope systematics of a chondrule fragment from the Jupiter-family comet Wild 2, returned to Earth by NASA's Stardust mission. This object shows characteristics of a type II chondrule 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 chondrules 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 chondrule) to be more than 3 Myr after calcium-aluminum-rich inclusions.

  10. Olivines from Kimberlites and Diamonds: Problem of Origin

    NASA Astrophysics Data System (ADS)

    Sobolev, N. V.; Sobolev, A. V.; Tomilenko, A. A.; Kovyazin, S. V.; Kuzmin, D. V.

    2011-12-01

    Mg-rich olivine 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 olivine populations are distinguished, which are represented by oval-rounded unzoned or partly zoned xenocrysts of olivine I (more than 1 mm) and well defined zoned phenocrysts ( 0.05-1.0 mm) of olivine II (e.g. Kamenetsky et al., 2008, J.Petrol., 49: 823-839). The cores of olivine II are compositionally similar to olivine I with Mg# 86-94, but rims of olivine II and partly preserved rims of olivine 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 olivine I and olivine 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 olivines contain clinopyroxene (cpx) and pyrope (prp) inclusions confirming their high pressure origin. One large olivine 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 olivine 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 olivine grains containing low T (Ca# 43.3-48) cpx and prp inclusions confirm the listed differences from all olivines from peridotites and diamonds (e.g. Sobolev et al., 2009, Lithos, 112S: 701-713.). Earlier, similar Ti abundance was reported only for olivines from dunite nodules in Greenland kimberlites (e.g. Arndt et al., 2010, J. Petrol., 51: 573-602).We suggest that Ti-bearing olivine, 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

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Mishra, Ritesh Kumar; Chaussidon, Marc

    2014-07-01

    The short-lived now-extinct nuclide (SLN) 60Fe, which decays to 60Ni with a half-life of 2.62 Ma, is uniquely of stellar origin. Hence, its Solar System initial abundance yields information about the source of SLNs and the astrophysical environment in which the Solar System was born. Only a few chondrules (?19) from unequilibrated ordinary chondrites have reported resolved 60Ni excesses using in situ secondary ion mass spectrometry implying Fe60/Fe56>?0.610-7 in the early Solar System, and among these very few (3) have higher excesses implying Fe60/Fe56?710-7 (Mishra et al., 2010; Mishra and Goswami, 2014; Telus et al., 2012). At variance, multi-collector inductively coupled plasma mass spectrometer studies of bulk samples and mineral separates from differentiated meteorites, angrites, achondrites, and chondrules suggest a low abundance of 60Fe/56Fe of ?1.410-8 which would rule out the need for an external seeding of the early Solar with stellar 60Fe (Quitt et al., 2011; Tang and Dauphas, 2012). Two Semarkona chondrules and one Efremovka chondrule analyzed in the present study have mass fractionation corrected excess of up to ?75 permil () and give 60Fe isochrons with initial 60Fe/56Fe ratios of (7.83.7)10-7, (3.81.6)10-7, and (2.21.1)10-7 (2?), for Efremovka Ch 1, Semarkona Ch 12, and Semarkona Ch J5 respectively. The higher values of 60Fe/56Fe ratios seen in the chondrules of these least altered meteorites samples concur with and lend greater credence to the suggestion of a massive star as the source of 60Fe, and possibly of other short-lived nuclides, to the early Solar System. However, no definitive explanation (e.g. sample bias, effects of metamorphism, 60Fe heterogeneity) to the apparent disagreement with studies of bulk chondrules and chondrule fragments has been found.

  13. The effect of multiple particle sizes on cooling rates of chondrules produced in large-scale shocks in the solar nebula

    NASA Astrophysics Data System (ADS)

    Morris, Melissa A.; Weidenschilling, Stuart J.; Desch, Steven J.

    2016-03-01

    Chondrules represent one of the best probes of the physical conditions and processes acting in the early solar nebula. Proposed chondrule formation models are assessed based on their ability to match the meteoritic evidence, especially experimental constraints on their thermal histories. The model most consistent with chondrule thermal histories is passage through shock waves in the solar nebula. Existing models of heating by shocks generally yield a good first-order approximation to inferred chondrule cooling rates. However, they predict prolonged heating in the preshock region, which would cause volatile loss and isotopic fractionation, which are not observed. These models have typically included particles of a single (large) size, i.e., chondrule precursors, or at most, large particles accompanied by micron-sized grains. The size distribution of solids present during chondrule formation controls the opacity of the affected region, and significantly affects the thermal histories of chondrules. Micron-sized grains evaporate too quickly to prevent excessive heating of chondrule precursors. However, isolated grains in chondrule-forming regions would rapidly coagulate into fractal aggregates. Preshock heating by infrared radiation from the shock front would cause these aggregates to melt and collapse into intermediate-sized (tens of microns) particles. We show that inclusion of such particles yields chondrule cooling rates consistent with petrologic and isotopic constraints.

  14. Carbon sequestration via aqueous olivine mineral carbonation: role of passivating layer formation

    SciTech Connect

    Hamdallah Bearat; Michael J. McKelvy; Andrew V.G. Chizmeshya; Deirdre Gormley; Ryan Nunez; R.W. Carpenter; Kyle Squires; George H. Wolf

    2006-08-01

    CO{sub 2} sequestration via carbonation of widely available low-cost minerals, such as olivine, can permanently dispose of CO{sub 2} in an environmentally benign and a geologically stable form. The paper reports the results of studies of the mechanisms that limit aqueous olivine carbonation reactivity under the optimum sequestration reaction conditions observed to date: 1 M NaCl + 0.64 M NaHCO{sub 3} at T {approx} 185{sup o}C and P{sub CO{sub 2}} {approx} 135 bar. 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 the observation that carbonation increases dramatically with solid particle concentration in stirred experiments. Multiphase hydrodynamic calculations are combined with experiment to 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 SiO{sub 2} structure that can permit diffusion of key reactants. Mitigating passivating layer effectiveness is critical to enhancing carbonation and lowering sequestration process cost. 30 refs., 7 figs.

  15. Olivine and Pyroxene Compositions in Fine-Grained Chondritic Materials

    NASA Technical Reports Server (NTRS)

    Zolensky, Michael E.; Frank, D.

    2011-01-01

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

  16. Trace elements in the Allende meteorite. IV - Amoeboid olivine aggregates

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    INAA data for Ca, Sc, Hf, La, Ce, Sm, Eu, Tb, Yb, Lu, Os, Ir, Ru, Na, Cl, Br, Fe, Mn, Cr, Co, Au, As, and Sb are presented for ten amoeboid aggregates from the Allende meteorite. Only one lacks olivine. Seven of the remainder, as a group, have cosmic proportions of refractory lithophile and siderophile elements and appear to have formed when coarse-grained Allende inclusion material underwent partial reaction with a low-temperature nebular gas and mixture with FeO-rich olivine. The other two have highly fractionated abundances of refractory elements relative to one another compared to Cl chondrites, including Group II REE patterns, and probably formed by the mixing of fine-grained Allende inclusion material with FeO-rich olivine. Non-refractory siderophile components are also different in composition in each type of amoeboid olivine aggregate.

  17. The Microstructure of a Micrometeorite Impact into Lunar Olivine

    NASA Astrophysics Data System (ADS)

    Noble, S. K.; Keller, L. P.; Christoffersen, R.; Rahman, Z.

    2015-11-01

    Through TEM analysis of the cross-section of a ~20 µm diameter crater into an olivine single crystal we can see first-hand the effects of a single impact, including the creation of nanophase iron in the melt.

  18. Systematics of Vanadium in Olivine from Planetary Basalts

    NASA Technical Reports Server (NTRS)

    Karner, J. M.; Papike, J. J.; Shearer, C. K.

    2002-01-01

    The systematics of vanadium in olivines 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.

  19. Olivine Weathering: Abiotic Versus Biotic Processes as Possible Biosignatures

    NASA Technical Reports Server (NTRS)

    Longazo, T. G.; Wentworth, S. J.; McKay, D. S.; Southam, G.; Clemett, S. J.

    2001-01-01

    A preliminary study to determine how abiotic versus biotic processes affect the weathering of olivine crystals. Perhaps the differences between these weathering processes could be used as biosignatures. Additional information is contained in the original extended abstract.

  20. Olivine Deposits Associated with Impact Basins and Craters on Mars

    NASA Astrophysics Data System (ADS)

    Ody, A.; Poulet, F.; Langevin, Y.; Gondet, B.; Bibring, J.; Carter, J.

    2011-12-01

    An analysis of the 1?m olivine spectral signature applied to the entire and final OMEGA dataset [1] shows numerous olivine-bearing deposits in the 3 main basins of Mars (Argyre, Isidis and Hellas). These signatures are among the strongest of Mars, which suggests compositions with higher iron content and/or larger grain size and/or larger abundance than the ones of widespread olivine-bearing deposits observed on large parts of the southern highlands [1]. A spectral modeling based on a radiative transfer model [2] indicates that their compositions are still close to the forsterite one with abundance in the range of [15,40%] and grain sizes of a few hundreds of ?m. These deposits are exclusively localized on Noachian terrains. Distribution of these deposits around Argyre basin clearly takes the form of discontinuous patches of olivine-bearing rocks on the basin terrace, which strongly suggest that their formation is related to the basin formation event. Recent numerical simulations of basin formation show that impact that formed the Argyre basin could have excavated upper mantle materials and emplaced discontinuous patches of melted mantle on the basin terraces [3]. The observed olivine deposits in Argyre are thus interpreted as olivine-bearing material excavated from the upper mantle during the impact. Olivine deposits distribution around the Hellas basin is not as clear as for Argyre because of young resurfacing processes that strongly affected its region. Olivine deposits are fewer and mainly localized on the northern terrace of Hellas. Most of them are detected in crater ejecta, while a few similar to Argyre olivine discontinuous patches are also observed suggesting that a mantle origin as for Argyre is possible. Olivine has been detected by several datasets in the Nili Fossae region and in the south of Isidis basin. The spectral modeling of OMEGA spectra indicates an olivine abundance of about 40% and megacrysts of several millimeters for the region of Nili Fossae [2]. Several plausible hypotheses has been discussed to explain this unusual concentration of olivine-rich outcrops in Nili Fossae assuming three possibilities for their emplacement relative to the formation of the Isidis basin : pre-impact [4,5], contemporaneous [6], or post-impact [7]. The pretty unique settings and compositions of these deposits in comparison to the two other major basins indicate a different origin, with the post-impact one as the preferred one. Other several localized exposures with strong olivine signature are also found throughout the southern highlands and the northern plains mostly associated with craters. Olivine-bearing material is found in craters floors but also in some crater ejecta implying the presence of an olivine-rich underlying layer. Of special interest are some craters totally filled by olivine-rich lava lakes, which could have erupted through local (impact-related) fractures. [1] A. Ody et al. (2011) LPSC XXXXII.[2] F. Poulet et al. (2009), Icarus 201, 84-101.[3] Stewart S. (2010) AGU, San Francisco, abstract #P43A-08. [4] Hoefen et al. (2003) Science,302,627-630.[5] Hamilton and Christensen (2005), Geology,33,433-436.[6]J.F. Mustard et al. (2007), JGR, 112, E08S03.[7] L.L Tornabene et al. (2008), JGR, 113, E10001.

  1. Kamacite and olivine in ordinary chondrites - Intergroup and intragroup relationships

    NASA Astrophysics Data System (ADS)

    Rubin, A. E.

    1990-05-01

    Results are presented from high-precision electron microprobe analyses of olivine and kamacite in a suite of 134 ordinary chondrites (OCs). The compositional ranges of these phases are defined for each OC group (high total Fe, low total Fe, and low total Fe/low metallic Fe). Anomalous OCs that have olivine and/or kamacite compositions that lie outside the established ranges are identified. The phases in the chondritic clasts of the Netschaevo iron meteorite are characterized to determine the relationship between Netschaevo and OCs. Intragroup variations of olivine and kamacite compositions with petrologic type are examined and OCs that contain olivine and/or kamacite grains with aberrant compositions are identified as fragmental breccias. Also, a search for new metallic Fe-Ni phases with extreme compositions is conducted. As a result of these analyses, several meteorites are reclassified.

  2. Aluminum speeds up the hydrothermal alteration of olivine

    NASA Astrophysics Data System (ADS)

    Andreani, Muriel; Daniel, Isabelle; Pollet-Villard, Marion

    2014-05-01

    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 olivine 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 olivine 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 olivine 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 olivine grains reacted in saline water (0.5 molal NaCl) at 200C and 300C, and P=200 MPa. After two days, olivine crystals were fully transformed to an aluminous serpentine, also enriched in iron. The presence of Al in the hydrothermal fluid increases the rate of olivine serpentinization by more than one order of magnitude by enhancing olivine 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 olivine serpentinization and of olivine hydrolysis in general in a wide range of settings where olivines 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 olivine. 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.

  3. Dissolution of olivine in basaltic liquids: experimental observations and applications.

    USGS Publications Warehouse

    Thornber, C.R.; Huebner, J.S.

    1985-01-01

    Rates of olivine 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 olivine resorption (and growth) phenomena in igneous rocks. -J.A.Z.

  4. Thermal Emission Spectroscopy of 1 Ceres: Evidence for Olivine

    NASA Technical Reports Server (NTRS)

    Witteborn, F. C.; Roush, T. L.; Cohen, M.

    1999-01-01

    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 olivine grains <5 microns in diameter. The general shape of the Ceres and the olivine 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 olivine curve.) The emissivity behavior roughly matches the emission coefficients which were calculated for olivine 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 olivine grains from 8 to 30 micron, but olivine's emissivity is lower from 5 to 8 pm.

  5. Evidence from Chondrule Shapes and Modes for Shock Deformation in Reduced CV3 Chondrites Leoville and Efreomovka

    NASA Astrophysics Data System (ADS)

    Fagan, T. J.; Aoki, R.

    2015-07-01

    The reduced CV3 chondrites Efremovka and Leoville are characterized by (1) more elongate chondrules, and (2) lower matrix abundances compared to the oxidized CV3 Allende. Both observations can be explained by shock deformation of reduced CV3s.

  6. Deconvolution of lunar olivine reflectance spectra: Implications for remote compositional assessment

    NASA Astrophysics Data System (ADS)

    Isaacson, Peter J.; Pieters, Carl M.

    2010-11-01

    Lunar olivines typically contain inclusions of Cr-spinel (chromite) that influence their measured optical properties. These altered optical properties complicate modeled predictions of olivine composition from reflectance spectra. Approaches developed for inclusion-free terrestrial olivine spectra must be modified to be applied to chromite-bearing lunar olivine spectra. We present a revised approach for predicting the compositions of chromite-bearing lunar olivines using the Modified Gaussian Model (MGM). The results of this revised approach for chromite-bearing lunar olivines are consistent with previous results for terrestrial olivine reflectance spectra, and successfully predict the olivine's composition. These results are an important step in compositional assessment of remotely-sensed olivine spectra, and are essential to ongoing investigations of that topic. Our results are based on a limited set of available lunar olivine separates, and would be strengthened by the inclusion of additional compositions.

  7. Composite carrier bar device

    SciTech Connect

    Felder, D.W.

    1981-09-01

    A composite carrier bar is disclosed for oil well pumping units that utilize sucker rod to operate bottom hole pumps. The bar includes a recessed cavity for receiving a hydraulic ram to operate as a polish rod jack and also a secondary carrier bar for receiving a secondary polish rod clamp for use in respacing bottom hole pumps and serve as a safety clamp during operation.

  8. Interactive WSN-Bar

    NASA Astrophysics Data System (ADS)

    Lin, Jiun-Shian; Hsu, Su-Chu; Chen, Ying-Chung

    Based on the concept of ambient intelligence, we utilized wireless sensor network (WSN) and vision-based tracking technologies to create an interactive WSN-Bar. WSN-Bar is an interactive and innovative creation which has two modules: Garden of Light and Vivacious Bushes. It refers the variety of natural environmental factors and focuses on the relationship between human and nature. WSN-Bar can also detect the changes of brightness, temperature, CO2 density outdoors and the movement of people inside the building. Besides, WSN-Bar is an interactive installation art which creates the opportunity to reduce the estranged gape among the participants.

  9. Bar Code Labels

    NASA Technical Reports Server (NTRS)

    1988-01-01

    American Bar Codes, Inc. developed special bar 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 bar 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 bar code labels commercially or industrial customers who also need labels to resist harsh environments.

  10. Determining the composition of olivine on asteroidal surfaces

    NASA Technical Reports Server (NTRS)

    Sunshine, Jessica M.; Pieters, Carle M.

    1993-01-01

    Olivine was remotely identified as a major component on many S- and A-type asteroids based on qualitative analyses of broad absorption features near 1.0 micron in their telescopic reflectance spectra. Laboratory studies showed that this diagnostic olivine absorption feature is composed of three individual absorption bands resulting from electronic transitions of Fe(+2) in distorted M1 and M2 sites. Both the overall absorption feature and each of the individual absorption bands are also known to vary systematically as a function of olivine composition. Thus, it should be possible to remotely determine the composition of olivine present on the surfaces of the various olivine-rich asteroids. However, extrapolation of laboratory studies to compositional interpretation of asteroid spectra is complicated by several factors: observational noise; lower spectral resolution; compositional heterogeneities (including the presence of other phases such as pyroxenes and/or metal); and the effects of alteration processes. In order to address such complex problems, a quantitative approach to spectral analysis, the modified Gaussian model (MGM) was developed by Sunshine et al., which deconvolves spectra into their constituent absorption bands. The MGM, a refinement of the Gaussian model, more accurately adheres to the physical processes involved in electronic transition absorptions. Under the MGM, each spectrum is modeled in log reflectance and energy as a sum of absorption bands superimposed onto a baseline or continuum. Each absorption band is described by three model parameters (center, width, and strength) which can be interpreted and used to infer composition. One of the strengths of the MGM is that it allows compositional information to be extracted directly from measured spectra and is therefore complementary to other approaches to modeling asteroid spectra which require the use of meteorites and/or terrestrial samples as spectral analogs. A quantitative understanding of the properties of olivine absorptions was established by using the MGM to analyze a laboratory suite of spectra spanning a full range of olivine compositions.

  11. Bar Codes for Libraries.

    ERIC Educational Resources Information Center

    Rahn, Erwin

    1984-01-01

    Discusses the evolution of standards for bar codes (series of printed lines and spaces that represent numbers, symbols, and/or letters of alphabet) and describes the two types most frequently adopted by libraries--Code-A-Bar and CODE 39. Format of the codes is illustrated. Six references and definitions of terminology are appended. (EJS)

  12. The Bar Revue.

    ERIC Educational Resources Information Center

    Student Lawyer, 1981

    1981-01-01

    Major companies that offer streamlined, standardized bar review courses available in various media are listed, and state bar associations and licensing procedures are outlined for each state. (Journal availability: 1155 E. 60th St., Chicago, IL 60637, $1.00.) (MSE)

  13. Vapor pressures and evaporation coefficients for melts of ferromagnesian chondrule-like compositions

    NASA Astrophysics Data System (ADS)

    Fedkin, A. V.; Grossman, L.; Ghiorso, M. S.

    2006-01-01

    To determine evaporation coefficients for the major gaseous species that evaporate from silicate melts, the Hertz-Knudsen equation was used to model the compositions of residues of chondrule analogs produced by evaporation in vacuum by Hashimoto [Hashimoto A. (1983) Evaporation metamorphism in the early solar nebula-evaporation experiments on the melt FeO-MgO-SiO 2-CaO-Al 2O 3 and chemical fractionations of primitive materials. Geochem. J. 17, 111-145] and Wang et al. [Wang J., Davis A. M., Clayton R. N., Mayeda T. K., Hashimoto A. (2001) Chemical and isotopic fractionation during the evaporation of the FeO-MgO-SiO 2-CaO-Al 2O 3-TiO 2 rare earth element melt system. Geochim. Cosmochim. Acta 65, 479-494], in vacuum and in H 2 by Yu et al. [Yu Y., Hewins R. H., Alexander C. M. O'D., Wang J. (2003) Experimental study of evaporation and isotopic mass fractionation of potassium in silicate melts. Geochim. Cosmochim. Acta 67, 773-786], and in H 2 by Cohen et al. [Cohen B. A., Hewins R. H., Alexander C. M. O'D. (2004) The formation of chondrules by open-system melting of nebular condensates. Geochim. Cosmochim. Acta 68, 1661-1675]. Vapor pressures were calculated using the thermodynamic model of Ghiorso and Sack [Ghiorso M. S., Sack R. O. (1995) Chemical mass transfer in magmatic processes IV. A revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures. Contrib. Mineral. Petrol. 119, 197-212], except for the late, FeO-free stages of the Wang et al. (2001) and Cohen et al. (2004) experiments, where the CMAS activity model of Berman [Berman R. G. (1983) A thermodynamic model for multicomponent melts, with application to the system CaO-MgO-Al 2O 3-SiO 2. Ph.D. thesis, University of British Columbia] was used. From these vapor pressures, evaporation coefficients ( α) were obtained that give the best fits to the time variation of the residue compositions. Evaporation coefficients derived for Fe (g), Mg (g), and SiO (g) from the Hashimoto (1983) experiments are similar to those found by Alexander [Alexander C. M. O'D. (2004) Erratum. Meteoritics Planet. Sci. 39, 163] in his EQR treatment of the same data and also adequately describe the FeO-bearing stages of the Wang et al. (2001) experiments. From the Yu et al. (2003) experiments at 1723 K, αNa = 0.26 ± 0.05, and αK = 0.13 ± 0.02 in vacuum, and αNa = 0.042 ± 0.020, and αK = 0.017 ± 0.002 in 9 × 10 -5 bar H 2. In the FeO-free stages of the Wang et al. (2001) experiments, αMg and αSiO are significantly different from their respective values in the FeO-bearing portions of the same experiments and from the vacuum values obtained at the same temperature by Richter [Richter F. M., Davis A. M., Ebel D. S., Hashimoto A. (2002) Elemental and isotopic fractionation of Type B calcium-, aluminum-rich inclusions: experiments, theoretical considerations, and constraints on their thermal evolution. Geochim. Cosmochim. Acta 66, 521-540] for CMAS compositions much lower in MgO. When corrected for temperature, the values of αMg and αSiO that best describe the FeO-free stages of the Wang et al. (2001) experiments also adequately describe the FeO-free stage of the Cohen et al. (2004) H 2 experiments, but αFe that best describes the FeO-bearing stage of the latter experiment differs significantly from the temperature-corrected value derived from the Hashimoto (1983) vacuum data.

  14. The origin of high hydrogen content in kimberlitic olivine: Evidence from hydroxyl zonation in olivine from kimberlites and mantle xenoliths

    NASA Astrophysics Data System (ADS)

    Hilchie, Luke; Fedortchouk, Yana; Matveev, Sergei; Kopylova, Maya G.

    2014-08-01

    Olivine macrocrysts in kimberlites are the most H-rich natural olivines known. Their xenocrystic provenance makes unclear whether H-enrichment occurred in the mantle prior to entrainment in kimberlite magma or during ascent. We present a Fourier transform infrared (FTIR) spectroscopy-based study of H zonation in kimberlite-derived olivine macrocrysts and/or olivine in xenoliths from the kimberlites Jericho (Nunavut, Canada), Beartooth (Northwest Territories, Canada), and Pipe 200 and Matsoku (Lesotho). The objective of the study was to determine whether changes in the concentration or speciation of H defects in proximity to the host kimberlite could yield insights into the origin of H-enrichment. Within the Group 1 region of the FTIR spectrum (~ 3420-3700 cm- 1), we find that olivines within xenoliths and macrocrysts show weak zonation or significant H depletions in rims. Peaks in the Group 2 region (~ 3260-3420 cm- 1) in Beartooth olivines show marked decrease in the crystal margins in comparison to Group 1 peaks. We find no preserved evidence for kimberlite-related H-enrichment in our dataset. We ascribe H depletion to diffusive H loss to infiltrating kimberlitic media. Diffusion models using coefficients previously applied to dehydrogenation of olivine and assuming a dry environment produce extremely short ascent durations incompatible with the results of other geospeedometers. This mismatch suggests that the poorly developed zonation in Jericho and Beartooth olivines indicates water-enrichment and/or faster ascent of these melts (in comparison to Pipe 200 and Matsoku), resulting in greater retention of mantle-derived H. A further significant factor in the mismatch is the differing speciation of H in most natural mantle-derived olivines in comparison to those used in diffusion experiments. We argue that the presence of presumably mantle-derived Group 2 H in olivine macrocrysts indicates rapid ascent of magma exsolving water-rich fluid, permitting preservation of these faster-diffusing defects only in particularly rapidly ascending kimberlite magmas. This interpretation explains empirical correlations between the presence of Group 2 bands, water-derived diamond resorption features, and volcaniclastic kimberlite facies.

  15. A Method for the Flux Growth of Intermediate Composition Olivine

    NASA Astrophysics Data System (ADS)

    Deangelis, M. T.; Anovitz, L. M.; Labotka, T. C.; Frederick, D. A.

    2009-05-01

    Though solid solution of iron and magnesium between forsterite (Mg2SiO4) and fayalite (Fe2SiO4) is possible in the olivine crystal structure, the high oxygen fugacity condition of the terrestrial mantle inhibits the widespread crystallization of intermediate (Fo40-Fo60) composition olivine. This limitation is not the same for some other inner solar system bodies (e.g. the Moon and Mars), where conditions are reducing and olivine compositions are wide ranging. Unfortunately, the amount of samples from the Moon and Mars is extremely limited; with only Apollo and Luna mission samples, lunar meteorites, and Martian meteorites available for direct mineralogic and petrologic characterization. These characterizations have provided a useful basis for many spectroscopic and modeling interpretations, but many fundamental questions remain and may only be answerable through either direct observation of rocks or by analog experimentation. The motivation for our work on growth of intermediate olivine crystals, therefore, is to create realistic starting material for use in Mars and Moon analog experiments. A variety of crystal growth methods have been previously used to synthesize olivine, including: the Czochralski-pulling (CZ) method, the floating-zone image furnace (FZ) method, and sol-gel processing techniques. Both the CZ and FZ methods have the advantage of producing large crystals, but the growth apparatus and regulation of reduced atmospheric conditions during growth can make these techniques both time and cost intensive. Sol-gel processing to produces olivine fibers is a useful chemical technique, but obtaining larger grain sizes can be difficult. An alternative method for crystal growth is through the use a flux, which can grow crystals relatively quickly and inexpensively. We have grown synthetic crystals of intermediate composition (Fo30-Fo70) olivine using a lithium borate (B5Li3O9) flux. The starting material was a mixture of magnesite (MgCO3), siderite (FeCO3), and quartz (SiO2) powder in a 1:1:1 ratio. The advantage of using siderite is that the iron is already present in the ferrous form. Upon heating and decarbonation, this mixture represents a bulk composition of Fo50 (FeMgSiO4) olivine. Flux was then added to the starting material mixture so that the final mixture was 50% starting material and 50% flux by weight. This final mix was then placed in a platinum crucible that was heated to 1100 °C in a vacuum furnace for three days. The use of a vacuum furnace ensured that conditions remained reducing during crystal growth. The result was growth of olivine crystals that are generally small (< 1 mm in length) and have euhedral crystal form. These crystals have been analyzed by electron microprobe, and are systematically zoned from core to rim with Mg-rich cores (˜Fo70) transitioning to Fe-rich rims (˜Fo30). This zoning represents an expected heterogeneity due to olivine growth from a finite reservoir of starting material. The flux growth of this intermediate composition olivine was primarily a 'proof of concept' experiment, and showed that olivine crystals can be grown using a flux under sub-solidus conditions. Additional crystal growth experiments would be useful to gauge the response of olivine to changes in temperature, duration, and composition of the flux + starting material mixture.

  16. Formation of a metastable olivine wedge in a descending slab

    SciTech Connect

    Devaux, J.P.; Schubert, G.; Anderson, C.

    1997-11-01

    We present a thermal model of a descending slab in which the transformation of olivine to spinel is controlled by pressure- and temperature-dependent reaction kinetics. Two different formulations of the kinetics are considered with the main discriminant being the temperature range over which olivine converts to spinel at pressures of about 15 GPa (about 500{degree}{endash}515{degree}C and 560{degree}{endash}650{degree}C). We use a finite element method to solve the coupled heat conduction (perpendicular and parallel to the dip of the slab) and kinetics equations, and we include the latent heat of the phase transformation. Latent heat release together with heat conduction parallel to the dip of the slab reduces significantly the length of the metastable olivine wedge and results in a very thin ({approx_lt}5km) two-phase region. We employ the thermal parameter v{tau}sin{delta} (v is the velocity of the descending slab, {tau} is the age of the slab, and {delta} is the dip of the slab to the horizontal) to interpret the results for the length of the metastable wedge. For values of the thermal parameter smaller than about 4000 and 7000 km, depending on the model of the kinetics, no metastable olivine wedge exists (the critical value of 7000 km for the thermal parameter corresponds to the kinetics model with the lowest transition temperature range). The length of the metastable olivine wedge is also found to be very sensitive to the model of the kinetics and to the effects of adiabatic heating. If the occurrence of deep earthquakes is related to the transformation of metastable olivine to spinel, then data on earthquake depth versus thermal parameter require that the onset of the reaction takes place at temperatures of about 550{degree}{endash}575{degree}C. In this case the slab thermal parameter must be larger than 10,000 km for the metastable olivine wedge to extend down to 660 km depth. But deep earthquakes occur near 660 km depth in slabs with thermal parameter as small as about 5000 km (South America, for example). Either some deep earthquakes are unrelated to olivine metastability or our knowledge of olivine-spinel reaction kinetics is incomplete.{copyright} 1997 American Geophysical Union

  17. Extraction of in situ cosmogenic 14C from olivine

    USGS Publications Warehouse

    Pigati, J.S.; Lifton, N.A.; Timothy, Jull A.J.; Quade, Jay

    2010-01-01

    Chemical pretreatment and extraction techniques have been developed previously to extract in situ cosmogenic radiocarbon (in situ 14C) from quartz and carbonate. These minerals can be found in most environments on Earth, but are usually absent from mafic terrains. To fill this gap, we conducted numerous experiments aimed at extracting in situ 14C from olivine ((Fe,Mg)2SiO4). We were able to extract a stable and reproducible in situ 14C component from olivine using stepped heating and a lithium metaborate (LiBO2) flux, following treatment with dilute HNO3 over a variety of experimental conditions. However, measured concentrations for samples from the Tabernacle Hill basalt flow (17.3 ?? 0.3 ka4) in central Utah and the McCarty's basalt flow (3.0 ?? 0.2 ka) in western New Mexico were significantly lower than expected based on exposure of olivine in our samples to cosmic rays at each site. The source of the discrepancy is not clear. We speculate that in situ 14C atoms may not have been released from Mg-rich crystal lattices (the olivine composition at both sites was ~Fo65Fa35). Alternatively, a portion of the 14C atoms released from the olivine grains may have become trapped in synthetic spinel-like minerals that were created in the olivine-flux mixture during the extraction process, or were simply retained in the mixture itself. Regardless, the magnitude of the discrepancy appears to be inversely proportional to the Fe/(Fe+Mg) ratio of the olivine separates. If we apply a simple correction factor based on the chemical composition of the separates, then corrected in situ 14C concentrations are similar to theoretical values at both sites. At this time, we do not know if this agreement is fortuitous or real. Future research should include measurement of in situ 14C concentrations in olivine from known-age basalt flows with different chemical compositions (i.e. more Fe-rich) to determine if this correction is robust for all olivine-bearing rocks. ?? 2010 by the Arizona Board of Regents on behalf of the University of Arizona.

  18. Tracing Oxygen Fugacity in Asteroids and Meteorites Through Olivine Composition

    NASA Technical Reports Server (NTRS)

    Sunshine, J. M.; Bus, S. J.; Burbine, T. H.; McCoy, T. J.

    2005-01-01

    Olivine 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 olivine-rich asteroids in that they are dominated by olivine. 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, olivine composition (e.g. Fa#) can provide key constraints in exploring the origin and significance of olivine dominated asteroids.

  19. Olivine Composite Cathode Materials for Improved Lithium Ion Battery Performance

    SciTech Connect

    Ward, R.M.; Vaughey, J.T.

    2006-01-01

    Composite cathode materials in lithium ion batteries have become the subject of a great amount of research recently as cost and safety issues related to LiCoO2 and other layered structures have been discovered. Alternatives to these layered materials include materials with the spinel and olivine structures, but these present different problems, e.g. spinels have low capacities and cycle poorly at elevated temperatures, and olivines exhibit extremely low intrinsic conductivity. Previous work has shown that composite structures containing spinel and layered materials have shown improved electrochemical properties. These types of composite structures have been studied in order to evaluate their performance and safety characteristics necessary for use in lithium ion batteries in portable electronic devices, particularly hybrid-electric vehicles. In this study, we extended that work to layered-olivine and spinel-olivine composites. These materials were synthesized from precursor salts using three methods: direct reaction, ball-milling, and a coreshell synthesis method. X-ray diffraction spectra and electrochemical cycling data show that the core-shell method was the most successful in forming the desired products. The electrochemical performance of the cells containing the composite cathodes varied dramatically, but the low overpotential and reasonable capacities of the spinel-olivine composites make them a promising class for the next generation of lithium ion battery cathodes.

  20. Secondary processing of chondrules and refractory inclusions (CAIs) by gasdynamic heating

    NASA Technical Reports Server (NTRS)

    Podolak, M.; Prialnik, D.; Bunch, T. E.; Cassen, P.; Reynolds, R.

    1993-01-01

    Results of calculations performed to determine the conditions necessary for producing the opaque rims on chondrules and CAI rims by high-speed entry into the transient atmosphere of an accreting meteorite parent body are presented. The sensitivity of these results to variations in critical parameters is investigated. The range of entry velocities which can produce such rims is shown to depend on the size, melting temperature, and thermal conductivity of the particles. For particles greater than 2 mm in radius, with thermal conductivities of 20,000 ergs/sm s K or lower, entry velocities of about 3 km/s suffice. For particle sizes less than 1 mm in radius, the range of encounter velocities that can produce rims is narrow or vanishing, regardless of the thermal conductivity, unless the melting temperature in the outer part of the chondrule has been reduced by compositional heterogeneity.

  1. Boron and lithium isotopic composition in chondrules from the mokoia meteorite

    NASA Astrophysics Data System (ADS)

    Robert, F.; Chaussidon, M.

    2003-04-01

    Introduction: Large Boron isotopic variations have been reported in individual chondrules 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 chondrules 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 chondrules, 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 chondrules from Mokoia, the ?11B values range between -396.8 ppm and -0.67.8 ppm (2 sigma). In one Boron depleted area of one chondrule, the ?11B value was found to be as low as -68.5 ppm and -61.5 ppm (29; 2 sigma). In one chondrule from Mokoia the ?11B values range between -33.75.4 ppm and -3.85.4 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 -53.72.4 and -0.151.6 ppm (2 sigma) in the 8 chondrules 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 chondrule 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.

  2. Chondrules and Opaque Phases in Unequilibrated R Chondrites: A Comprehensive Assessment of Their Formation

    NASA Technical Reports Server (NTRS)

    Miller, K. E.; Lauretta, D. S.; Connolly, H. C., Jr.; Berger, E. L.; Domanik, K.

    2016-01-01

    Equilibrated Rumuruti (R) chondrites record an oxygen fugacity between 0 and 3.5 log units below the fayalite-magnetite-quartz buffer, and a sulfur fugacity (fS2) 2 log units above the iron-troilite buffer. They are more than an order of magnitude more oxidized than the ordinary chondrites [1], and orders of magnitude more sulfidized than solar values. Although the R chondrites have the highest (delta)O-17 value of any meteorites, analyses of unequilibrated R chondrites indicate chondrule formation in an oxygen isotope reservoir similar to that of the ordinary chondrite chondrules. We present the relationship of the R chondrite parent body to pre-accretionary volatiles O and S based on our analyses of unequilibrated R chondrite material in two thin sections from the meteorite Mount Prestrud (PRE) 95404.

  3. Composition of chondrules, fragments and matrix in the unequilibrated ordinary chondrites tieschitz and sharps

    NASA Astrophysics Data System (ADS)

    Wlotzka, F.

    The unequilibrated ordinary chondrites Tieschitz and Sharps are studied using an electron microprobe in order to substantiate the discrepancy between the chondrites' FeO content of 13.5 and 13.6 percent and their classification with the H-group chondrites where the total iron content range is 24.5 to 30.0 percent. Different populations of chondrules and fragments contained in the two chondrites are distinguished by their average FeO content and Fe/(Fe + Mg) ratios. There is also a small population of Ca, Al, Ti-rich chondrules which are mineralogically distinct. It is suggested that the FeO source may be the black matrix material which coats the chrondrules and fragments. A relation to the H-group is indicated by the close similarity between the black matrix and the average H-group chondrite in bulk composition and the total Fe content.

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

    NASA Astrophysics Data System (ADS)

    Beitz, Eike; Gttler, Carsten; Nakamura, Akiko; Blum, Jrgen

    2013-07-01

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

  5. Nearshore oblique sand bars

    NASA Astrophysics Data System (ADS)

    Ribas, F.; FalquS, A.; Montoto, A.

    2003-04-01

    The coupling between hydrodynamics and the evolving topography in the surf zone has been theoretically examined for oblique wave incidence. It is shown that positive feedback can lead to the initial growth of several types of rhythmic systems of sand bars. The bars can be down-current oriented or up-current oriented, which means that the offshore end of the bar is shifted down-current or up-current with respect to the shore attachment. In the limit of strong current compared to wave orbital motion, very oblique down-current oriented b ars are obtained with a spacing of several times the surf zone width. When wave orbital motions are dominant, systems of up-current oriented bars and crescentic/down-current oriented bars appear with spacings of the order of the surf zone width. The latter feature consists of alternating shoals and troughs at both sides of the break line with the inner shoals being bar-shaped and oblique to the coast. The growth (e-folding) time of the bars ranges from a few hours to a few days and it is favored by constant wave conditions. The range of model parameters leading to growth corresponds to intermediate beach states in between the fully dissipative and the fully reflective situations. Preliminary comparison with field observations shows qualitative agreement.

  6. Volatile fractionation in the early solar system and chondrule/matrix complementarity

    PubMed Central

    Bland, Philip A.; Alard, Olivier; Benedix, Gretchen K.; Kearsley, Anton T.; Menzies, Olwyn N.; Watt, Lauren E.; Rogers, Nick W.

    2005-01-01

    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 chondrule 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 chondrule formation, with exchange of volatile siderophile and chalcophile elements between chondrules and matrix. This chemical complementarity shows that these chondritic components formed in the same nebula region. PMID:16174733

  7. Size-Selective Concentration of Chondrules and Other Small Particles in Protoplanetary Nebula Turbulence

    NASA Technical Reports Server (NTRS)

    Cuzzi, Jeffrey N.; Hogan, Robert C.; Paque, Julie M.; Dobrovolskis, Anthony R.; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    Size-selective concentration of particles in a weakly turbulent protoplanetary nebula may be responsible for the initial collection of chondrules and other constituents into primitive bodY precursors. This paper presents the main elements of this process of turbulent concentration. In the terrestrial planet region. both the characteristic size and size distribution of chondrules are explained. "Fluffier" particles would be concentrated in nebula regions which were at a lower density and/or more intensely turbulent. The spatial distribution of concentrated particle density obeys multifractal scaling, suggesting a close tie to the turbulent cascade process. This scaling behavior allows predictions of the probability distributions for concentration in the protoplanetary nebula to be made. Large concentration factors (less than 10(exp 5)) are readily obtained, implying that numerous zones of particle density significantly exceeding the gas density could exist. If most of the available solids were actually in chondrule sized particles, the ensuing particle mass density would become so large that the feedback effects on gas turbulence due to mass loading could no longer be neglected. This paper describes the process, presenting its basic elements and some implications, without including the effects of mass loading.

  8. 81Kr-Kr cosmic ray exposure ages of individual chondrules from Allegan

    NASA Astrophysics Data System (ADS)

    Strashnov, I.; Gilmour, J. D.

    2013-12-01

    81Kr-Kr cosmic ray exposure (CRE) ages of individual chondrules (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 chondrules or between chondrules 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.

  9. Volatile fractionation in the early solar system and chondrule/matrix complementarity.

    PubMed

    Bland, Philip A; Alard, Olivier; Benedix, Gretchen K; Kearsley, Anton T; Menzies, Olwyn N; Watt, Lauren E; Rogers, Nick W

    2005-09-27

    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 chondrule 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 chondrule formation, with exchange of volatile siderophile and chalcophile elements between chondrules and matrix. This chemical complementarity shows that these chondritic components formed in the same nebula region. PMID:16174733

  10. Exogenic olivine on Vesta from Dawn Framing Camera color data

    NASA Astrophysics Data System (ADS)

    Nathues, Andreas; Hoffmann, Martin; Schäfer, Michael; Thangjam, Guneshwar; Le Corre, Lucille; Reddy, Vishnu; Christensen, Ulrich; Mengel, Kurt; Sierks, Holger; Vincent, Jean-Baptist; Cloutis, Edward A.; Russell, Christopher T.; Schäfer, Tanja; Gutierrez-Marques, Pablo; Hall, Ian; Ripken, Joachim; Büttner, Irene

    2015-09-01

    In this paper we present the results of a global survey of olivine-rich lithologies on (4) Vesta. We investigated Dawn Framing Camera (FC) High Altitude Mapping Orbit (HAMO) color cubes (∼60 m/pixel resolution) by using a method described in Thangjam et al. (Thangjam, G., Nathues, A., Mengel, K., Hoffmann, M., Schäfer, M., Reddy, V., Cloutis, E.A., Christensen, U., Sierks, H., Le Corre, L., Vincent, J.-B, Russell, C.T. [2014b]. Meteorit. Planet. Sci. arXiv:1408.4687 [astro-ph.EP]). In total we identified 15 impact craters exhibiting olivine-rich (>40 wt.% ol) outcrops on their inner walls, some showing olivine-rich material also in their ejecta and floors. Olivine-rich sites are concentrated in the Bellicia, Arruntia and Pomponia region on Vesta's northern hemisphere. From our multi-color and stratigraphic analysis, we conclude that most, if not all, of the olivine-rich material identified is of exogenic origin, i.e. remnants of A- or/and S-type projectiles. The olivine-rich lithologies in the north are possibly ejecta of the ∼90 km diameter Albana crater. We cannot draw a final conclusion on their relative stratigraphic succession, but it seems that the dark material (Nathues, A., Hoffmann, M., Cloutis, E.A., Schäfer, M., Reddy, V., Christensen, U., Sierks, H., Thangjam, G.S., Le Corre, L., Mengel, K., Vincent, J.-B., Russell, C.T., Prettyman, T., Schmedemann, N., Kneissl, T., Raymond, C., Gutierrez-Marques, P., Hall, I. Büttner, I. [2014b]. Icarus (239, 222--237)) and the olivine-rich lithologies are of a similar age. The origin of some potential olivine-rich sites in the Rheasilvia basin and at crater Portia are ambiguous, i.e. these are either of endogenic or exogenic origin. However, the small number and size of these sites led us to conclude that olivine-rich mantle material, containing more than 40 wt.% of olivine, is basically absent on the present surface of Vesta. In combination with recent impact models of Veneneia and Rheasilvia (Clenet, H., Jutzi, M., Barrat, J.-A., Gillet, Ph. [2014]. Lunar Planet Sci. 45, #1349; Jutzi, M., Asphaug, E., Gillet, P., Barrat, J.-A., Benz, W. [2013]. Nature 494, 207-210), which predict an excavation depth of up to 80 km, we are confident that the crust-mantle depth is significantly deeper than predicted by most evolution models (30 km; Mittlefehldt, D.W. [2014]. Asteroid 4 Vesta: A Fully Differentiated Dwarf Planet. NASA Technical Reports Server (20140004857.pdf)) or, alternatively, the olivine-content of the (upper) mantle is lower than our detection limit, which would lead to the conclusion that Vesta's parent material was already depleted in olivine compared to CI meteorites.

  11. An olivine-free mantle source of Hawaiian shield basalts.

    PubMed

    Sobolev, Alexander V; Hofmann, Albrecht W; Sobolev, Stephan V; Nikogosian, Igor K

    2005-03-31

    More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both nickel and silicon at lower levels. This can be resolved if the olivine of the mantle peridotite is consumed by reaction with melts derived from recycled oceanic crust, to form a secondary pyroxenitic source. Our modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from this source. In addition, we estimate that the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plume edge. These results are also consistent with volcano volumes, magma volume flux and seismological observations. PMID:15800614

  12. Reversibility of Lpo in Olivine during Deformation at High Pressure

    NASA Astrophysics Data System (ADS)

    Li, L.; Weidner, D. J.

    2014-12-01

    Olivine texture has been reported as an important contributor to the seismic anisotropy in the upper mantle. Experimental studies of deformation of olivine have also shown flow-driven lattice preferred orientation. In this study, we focus on in situ control and monitoring of LPO formation of olivine using synchrotron X-ray radiation coupled with DDIA multi-anvil deformation device. Using an energy-dispersive X-ray coupled a 10-element SSD detector; we apply a sinusoidal stress on the sample, which allows identification of growth of LPO in the specimen with relative robust signal even with small strain fields. Our data show palpable correlations among stress, strain and LPO as well as the variations among sub-grains marked by individual (hkl). This study is to demonstrate the versatile functions of X-ray for characterizing the deformation study of minerals.

  13. Iddingzitized olivine in mantle xenoliths: evidence for (really) early alteration

    NASA Astrophysics Data System (ADS)

    Low, P. C.; Schultz, L.; Stier, N.

    2011-12-01

    Iddingsite is an alteration product of olivine (or pyroxene) that contains goethite and some combination of maghemite, hematite, orthopyroxene, Mg-rich phyllosilicates, amorphous silica, and a temperature and a pressure-appropriate SiO2 polymorph and lacks the definite structure or chemical composition requisite of classification as a mineral. The process of iddingsitization is most commonly discussed as a low-temperature, near-surface phenomenon involving the oxidation and inorganic hydroxylation of olivine during weathering. High-temperature iddingsite (sometimes referred to as magmatic iddingsite) is also discussed in the literature and is generally attributed to reactions that occur at low pressure in response unusually high water content and/or high oxygen fugacity in pre-eruptive mafic magmas or during the process of extrusion and cooling or to hydrothermal metasomatism. Xenoliths from the Ponderosa flow of the Uinkaret Volcanic Field located along the Colorado River just downstream from Lava Falls in the Western Grand Canyon include spinel-bearing dunite, harzburgite, and olivine-rich lherzolite samples that exhibit geochemical characteristics that are consistent with residues of 5-17% partial melting. Olivine from xenoliths collected from this flow contain olivine that is either entirely fresh (no evidence of alteration) or olivine that has been ubiquitously partially iddingzitized with some samples containing both the green-colored fresh samples and the red-colored altered samples mere centimeters apart. Preliminary in situ FTIR mapping of water peaks in the region of 3700-3000 cm-1 indicate notable peak near 3680 cm-1 (a region of the spectrum associated with the presences of serpentine minerals) in altered samples. Iddingsite exhibits two distinct morphologies in these samples, one thicker (about 1 micrometer across) occurring mostly along fractures in the olivine grains, and the other much thinner occurring along crystallographically-oriented planes in olivine. Some of the partially altered olivine crystals exhibiting the later texture contain deformational kink bands that, given that the young eruption age of the host basalt, post-dates any crustal activity that could be responsible for such a fabric at this location, much have occurred in the lithospheric mantle. Textural evidence that the iddingzitized areas of these olivine crystals pre-date the kink banding suggests that the alteration of these olivines occurred in the mantle. Post-entrainment alteration is unlikely particularly given the close proximity of altered and unaltered samples with similar post-entrainment history and the fact that the host basalts are not particularly hydrous. The variety of alteration in xenoliths at this location suggest that the entraining flows are either sampling small regions of the mantle that contains very high gradients with regard to water content or oxygen fugacity or are sampling relatively large areas. Quantitative analysis of volatiles in altered and unaltered olivine crystals planned in order to better constrain these gradients.

  14. Thermal Emission Spectroscopy of 1 Ceres: Evidence For Olivine

    NASA Astrophysics Data System (ADS)

    Witteborn, Fred C.; Roush, Ted L.; Cohen, Martin

    2000-03-01

    Thermal emission spectra of the largest asteroid, 1 Ceres, obtained from the Kuiper Airborne Observatory display features that may provide information about its surface mineralogy. The emissivity, obtained by dividing the spectra by a standard thermal model, is compared with emissivity spectra of olivines and phyllosilicates deduced via Kirchoff's law from reflectivity measurements. The spectra provide a fairly good match to fine grained olivines (0 to 5 μm size range). The smoothness of the spectrum beyond 18 μm is an indication of particles smaller than 50 μm. While the abrupt rise in emissivity near 8 μm matches many silicates, the distinct emissivity minimum centered near 12.8 μm is consistant with iron-poor olivines, but not with phyllosilicates. It suggests the presence of opaques and does not exclude a mixture with organics and fine-grained phyllosilicates.

  15. Thermal Emission Spectroscopy of 1 Ceres: Evidence for Olivine

    NASA Astrophysics Data System (ADS)

    Witteborn, Fred. C.; Roush, Ted L.; Cohen, Martin

    1999-01-01

    Thermal emission spectra of the largest asteroid, 1 Ceres, obtained from the Kuiper Airborne Observatory display features that may provide information about its surface mineralogy. The emissivity, obtained by dividing the spectra by a standard thermal model, is compared with emissivity spectra of olivines and phyllosilicates deduced via Kirchoff's law from reflectivity measurements. The spectra provide a fairly good match to fine grained olivines (0 to 5 micrometer size range). The smoothness of the spectrum beyond 18 micrometers is an indication of particles smaller than 50 micrometers. While the abrupt rise in emissivity near 8 micrometers matches many silicates, the distinct emissivity minimum centered near 12.8 micrometers is consistant with iron-poor olivines, but not with phyllosilicates. It suggests the presence of opaques and does not exclude a mixture with organics and fine-grained phyllosilicates.

  16. The identification of crystalline olivine in cometary silicates

    NASA Astrophysics Data System (ADS)

    Campins, H.; Ryan, E. V.

    1989-06-01

    An intermediate-resolution spectrum of the 8-13 micron region in comet Halley is obtained which shows a prominent silicate emission feature with structure not observed before in other comets or in interstellar silicates. The presence of a strong 11.3 micron peak reported by Bregman and coworkers is confirmed, and evidence is found for additional structure in the band. By comparison with spectra of interplanetary dust particles and laboratory silicates, it is concluded that small crystalline olivine particles are a major component of the silicates in this comet; other silicates (e.g., amorphous or hydrated) must also be present. The identification of crystalline olivine in this part of the spectrum is supported by the observation of four peaks in 20-50 micron airborne spectra of this comet which have also been attributed to olivine.

  17. Origin of three-dimensional shapes of chondrules. I. Hydrodynamics simulations of rotating droplet exposed to high-velocity rarefied gas flow

    NASA Astrophysics Data System (ADS)

    Miura, Hitoshi; Nakamoto, Taishi; Doi, Masao

    2008-09-01

    The origin of three-dimensional shapes of chondrules is an important information to identify their formation mechanism in the early solar nebula. The measurement of their shapes by using X-ray computed topography suggested that they are usually close to perfect spheres, however, some of them have rugby-ball-like (prolate) shapes [Tsuchiyama, A., Shigeyoshi, R., Kawabata, T., Nakano, T., Uesugi, K., Shirono, S., 2003. Lunar Planet. Sci. 34, 1271-1272]. We considered that the prolate shapes reflect the deformations of chondrule precursor dust particles when they are heated and melted in the high velocity gas flow. In order to reveal the origin of chondrule shapes, we carried out the three-dimensional hydrodynamics simulations of a rotating molten chondrule exposed to the gas flow in the framework of the shock-wave heating model for chondrule formation. We adopted the gas ram pressure acting on the chondrule surface of p=10 dyncm in a typical shock wave. Considering that the chondrule precursor dust particle has an irregular shape before melting, the ram pressure causes a net torque to rotate the particle. The estimated angular velocity is ω=140 rads for the precursor radius of r=1 mm, though it has a different value depending on the irregularity of the shape. In addition, the rotation axis is likely to be perpendicular to the direction of the gas flow. Our calculations showed that the rotating molten chondrule elongates along the rotation axis, in contrast, shrinks perpendicularly to it. It is a prolate shape. The reason why the molten chondrule is deformed to a prolate shape was clearly discussed. Our study gives a complementary constraint for chondrule formation mechanisms, comparing with conventional chemical analyses and dynamic crystallization experiments that have mainly constrained the thermal evolutions of chondrules.

  18. Mobility of iron and nickel at low temperatures: Implications for 60Fe-60Ni systematics of chondrules from unequilibrated ordinary chondrites

    NASA Astrophysics Data System (ADS)

    Telus, Myriam; Huss, Gary R.; Ogliore, Ryan C.; Nagashima, Kazuhide; Howard, Daryl L.; Newville, Matthew G.; Tomkins, Andrew G.

    2016-04-01

    The Fe and Ni isotopic composition of ferromagnesian silicates in chondrules from unequilibrated ordinary chondrites (UOCs) have been used to estimate the initial abundance of the short-lived radionuclide, 60Fe, in the early Solar System. However, these estimates vary widely, and there are systematic discrepancies in initial 60Fe/56Fe ratios inferred from in situ and bulk analyses of chondrules. A possible explanation is that the Fe-Ni isotope system in UOC chondrules has not remained closed (a necessary condition for isotopic dating), and Fe and Ni have been redistributed since the chondrules formed. In order to evaluate this, we collected high-spatial-resolution X-ray fluorescence (XRF) maps of UOC chondrules to better understand the distribution and mobility of Fe and Ni at the low metamorphic temperatures of these chondrites. We used synchrotron X-ray-fluorescence microscopy to map the distribution of Fe, Ni and other elements in portions of 71 chondrules from 8 UOCs (types 3.00-3.2). The synchrotron XRF maps show clear enrichment of Fe and/or Ni in fractures ranging down to micrometer scale in chondrules from all UOCs analyzed for this study regardless of petrologic type and regardless of whether fall or find, indicating that there was significant exchange of Fe and Ni between chondrules and matrix and that the Fe-Ni system was not closed. Sixty percent of chondrules in Semarkona (LL3.00) have Fe and Ni enrichment along fractures, while 80-100% of chondrules analyzed from the other UOCs show these enrichments. Mobilization was likely a result of fluid transport of Fe and Ni during aqueous alteration on the parent body and/or during terrestrial weathering. In situ and bulk Fe-Ni analyses that incorporate extraneous Fe and Ni from chondrule fractures will result in lowering the inferred initial 60Fe/56Fe ratios.

  19. Grinding methods to enhance the reactivity of olivine

    SciTech Connect

    Summers, Cathy A.; Dahlin, David C.; Rush, Gilbert E.; O'Connor, William K.; Gerdemann, Stephen J.

    2004-01-01

    The Albany Research Center (ARC) conducted studies of mechanical activation by conventional and ultra-fine grinding techniques to enhance olivine reactivity in mineral carbonation reactions. Activated olivine is one of several solid feed materials used at ARC in reactions with carbon dioxide to form carbonate minerals. This paper compares grinding techniques via energy demand data and product characteristics, including particle size distributions, surface areas, full width at half maximum (FWHM) XRD analyses, and particle morphology by SEM analyses. Reactivity was gauged by percent conversion to carbonate in subsequent carbonation tests.

  20. Mass modeling for bars

    NASA Technical Reports Server (NTRS)

    Butler, Thomas G.

    1987-01-01

    Methods of modeling mass for bars are surveyed. A method for extending John Archer's concept of consistent mass beyond just translational inertia effects is included. Recommendations are given for various types of modeling situations.

  1. Global investigation of olivine on Mars: Insights into crust and mantle compositions

    NASA Astrophysics Data System (ADS)

    Ody, A.; Poulet, F.; Bibring, J.-P.; Loizeau, D.; Carter, J.; Gondet, B.; Langevin, Y.

    2013-02-01

    present the distribution of olivine on Mars, derived from spectral parameters based on the 1 µm olivine absorption band. The olivine can be defined with respect to two spectral end-members: type 1 corresponds to olivine with low iron content and/or small grain size and/or small abundance, and type 2, which corresponds to olivine with higher iron content and/or larger grain size and/or larger abundance. The spatial and statistical analysis of the global olivine distribution points out five major geological settings where olivine is detected: (1) Early Hesperian olivine-bearing smooth crater floors and flat intercrater plains throughout the southern highlands; (2) olivine deposits around the three main basins Argyre, Hellas, and Isidis; (3) olivine in intercrater dunes, crater ejecta, or extended deposits in the northern plains; (4) olivine associated with outcrops and sand in the floor of Valles Marineris; and (5) olivine-bearing butte outcrops in the vicinity of Hellas. The geological context, the age, and the composition of the olivine detections associated with these five major geological settings are detailed. Their origin and the implication of their occurrence on the composition of the Martian mantle and crust, as well as on the evolution of Mars volcanism are discussed.

  2. Trace Element Compositions of Pallasite Olivine Grains and Pallasite Origin

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, David W.; Herrin, J. S.

    2010-01-01

    Pallasites are mixtures of metal with magnesian olivine. Most have similar metal compositions and olivine oxygen isotopic compositions; these are the main-group pallasites (PMG). The Eagle Station grouplet of pallasites (PES) have distinctive metal and olivine compositions and oxygen isotopic compositions. Pallasites are thought to have formed at the core-mantle boundary of their parent asteroids by mixing molten metal with solid olivine of either cumulatic or restitic origin. We have continued our investigation of pallasite olivines by doing in situ trace element analyses in order to further constrain their origin. We determined Al, P, Ca, Ga and first row transition element contents of olivine grains from suite of PMG and PES by LA-ICP-MS at JSC. Included in the PMG suite are some that have anomalous metal compositions (PMG-am) and atypically ferroan olivines (PMG-as). Our EMPA work has shown that there are unanticipated variations in olivine Fe/Mn, even within those PMG that have uni-form Fe/Mg. Manganese is homologous with Fe2+, and thus can be used the same way to investigate magmatic fractionation processes. It has an advantage for pallasite studies in that it is unaffected by redox exchange with the metal. PMG can be divided into three clusters on the basis of Mn/Mg; low, medium and high that can be thought of as less, typically and more fractionated in an igneous sense. The majority of PMG have medium Mn/Mg ratios. PMG-am occur in all three clusters; there does not seem to be any relationship between putative olivine igneous fractionation and metal composition. The PMG-as and one PMG-am make up the high Mn/Mg cluster; no PMG are in this cluster. The high Mn/Mg cluster ought to be the most fractionated (equivalent to the most Fe-rich in igneous suites), yet they have among the lowest contents of incompatible lithophile elements Al and Ti and the two PMG-as in this cluster also have low Ca and Sc contents. This is inconsistent with simple igneous fractionation on a single, initially homogeneous parent asteroid. For Al and Ti, the low and high Mn/Mg clusters have generally uniform contents, while the medium cluster has wide ranges. This is also true of analyses of duplicate grains from the medium cluster pallasites which can have very different Al and Ti contents. Those from the low and high clusters do not. These observations suggest that pallasite olivines are not cumulates, but rather are restites from high degrees of melting. The moderately siderophile elements P and Ga show wide ranges in the high Mn/Mg cluster, but very uniform compositions in the medium cluster, opposite the case for Al and Ti. There is no correlation of P or Ga and Fe/Mn as might be expected if redox processes controlled the contents of moderately siderophile elements in the olivines. The lack of correlation of P could reflect equilibration with phosphates, although there is no correlation of Ca with P as might be expected

  3. Chemical zonation in olivine-hosted melt inclusions

    NASA Astrophysics Data System (ADS)

    Newcombe, M. E.; Fabbrizio, A.; Zhang, Youxue; Ma, C.; Le Voyer, M.; Guan, Y.; Eiler, J. M.; Saal, A. E.; Stolper, E. M.

    2014-07-01

    Significant zonation in major, minor, trace, and volatile elements has been documented in naturally glassy olivine-hosted melt inclusions from the Siqueiros Fracture Zone and the Galapagos Islands. Components with a higher concentration in the host olivine than in the melt (e.g., MgO, FeO, Cr2O3, and MnO) are depleted at the edges of the zoned melt inclusions relative to their centers, whereas except for CaO, H2O, and F, components with a lower concentration in the host olivine than in the melt (e.g., Al2O3, SiO2, Na2O, K2O, TiO2, S, and Cl) are enriched near the melt inclusion edges. This zonation is due to formation of an olivine-depleted boundary layer in the adjacent melt in response to cooling and crystallization of olivine on the walls of the melt inclusions, concurrent with diffusive propagation of the boundary layer toward the inclusion center. Concentration profiles of some components in the melt inclusions exhibit multicomponent diffusion effects such as uphill diffusion (CaO, FeO) or slowing of the diffusion of typically rapidly diffusing components (Na2O, K2O) by coupling to slow diffusing components such as SiO2 and Al2O3. Concentrations of H2O and F decrease toward the edges of some of the Siqueiros melt inclusions, suggesting either that these components have been lost from the inclusions into the host olivine late in their cooling histories and/or that these components are exhibiting multicomponent diffusion effects. A model has been developed of the time-dependent evolution of MgO concentration profiles in melt inclusions due to simultaneous depletion of MgO at the inclusion walls due to olivine growth and diffusion of MgO in the melt inclusions in response to this depletion. Observed concentration profiles were fit to this model to constrain their thermal histories. Cooling rates determined by a single-stage linear cooling model are 150-13,000 C h-1 from the liquidus down to ~1,000 C, consistent with previously determined cooling rates for basaltic glasses; compositional trends with melt inclusion size observed in the Siqueiros melt inclusions are described well by this simple single-stage linear cooling model. Despite the overall success of the modeling of MgO concentration profiles using a single-stage cooling history, MgO concentration profiles in some melt inclusions are better fit by a two-stage cooling history with a slower-cooling first stage followed by a faster-cooling second stage; the inferred total duration of cooling from the liquidus down to ~1,000 C ranges from 40 s to just over 1 h. Based on our observations and models, compositions of zoned melt inclusions (even if measured at the centers of the inclusions) will typically have been diffusively fractionated relative to the initially trapped melt; for such inclusions, the initial composition cannot be simply reconstructed based on olivine-addition calculations, so caution should be exercised in application of such reconstructions to correct for post-entrapment crystallization of olivine on inclusion walls. Off-center analyses of a melt inclusion can also give results significantly fractionated relative to simple olivine crystallization. All melt inclusions from the Siqueiros and Galapagos sample suites exhibit zoning profiles, and this feature may be nearly universal in glassy, olivine-hosted inclusions. If so, zoning profiles in melt inclusions could be widely useful to constrain late-stage syneruptive processes and as natural diffusion experiments.

  4. Influence of aluminum on the hydrothermal alteration rate of olivine

    NASA Astrophysics Data System (ADS)

    Andreani, M.; Daniel, I.; Pollet-Villard, M.

    2013-12-01

    The reactivity of ultramafic rocks under hydrothermal conditions 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 olivine 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 olivine 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 olivine in a series of experiments performed in a low-pressure diamond anvil cell while following the reaction progress in situ by optical imaging and by confocal Raman spectroscopy. Experiments were run for 4.5 to 7.5 days with two olivine grains reacted in saline water (0.5 molal NaCl) at 200C and 300C, and P=200 MPa. After two days, olivine crystals were fully transformed to an aluminous serpentine, also enriched in iron. The very fast precipitation of serpentine may inhibit magnetite nucleation here. However, this does not rule out an H2 production since serpentines classically incorporate non negligible amount of ferric iron in their structure. The presence of Al in the hydrothermal fluid increases the rate of olivine serpentinization by more than one order of magnitude by increasing olivine solubility and enhancing serpentine precipitation. The mechanism responsible for this increased solubility has to be investigated further but this result motivates a re-evaluation of the natural rates of olivine serpentinization and of olivine hydrolysis in general in a wide range of settings where olivines 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 olivine. 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. Finally, this study also provides a way to accelerate serpentinization reactions towards economically feasible time-scale and temperature for industrial H2 production and/or CO2 remediation.

  5. ^6^0Fe-^6^0Ni Systematics of Chainpur Chondrules and the Plutonic Angrites Northwest Africa 4590 and 4801

    NASA Astrophysics Data System (ADS)

    Spivak-Birndorf, L. J.; Wadhwa, M.; Janney, P. E.

    2012-03-01

    We present ^6^0Fe-^6^0Ni isotope systematics for bulk Chainpur chondrules and plutonic angrites. The Chainpur chondrule data are used to estimate an upper limit on the initial solar system ^6^0Fe/^5^6Fe < ~1 10^-^7.

  6. Chondrules of the Very First Generation in Bencubbin/CH-like Meteorites QUE94411 and Hammadah Al Hamra 237: Condensation Origin at High Ambient Nebular Temperatures

    NASA Technical Reports Server (NTRS)

    Krot, Alexander N.; Meibom, Anders; Russell, Sara S.; Young, Edward; Alexander, Conel M.; McKeegan, Kevin D.; Lofgren, Gary; Cuzzi, Jeff; Zipfel, Jutta; Keil, Klaus

    2000-01-01

    Chondrules 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 chondrules escaped subsequent remelting.

  7. A Study of Olivine Alteration to Iddingsite Using Raman Spectroscopy

    NASA Technical Reports Server (NTRS)

    Kuebler, K. E.; Wang, Alian; Haskin, L. A.; Jolliff, B. L.

    2003-01-01

    A crucial task of Mars surface science is to determine past environmental conditions, especially aqueous environments and their nature. Identification of mineral alteration by water is one way to do this. Recent work interprets TES spectra as indicating altered basalt on Mars. Olivine, a primary basaltic mineral, is easily altered by aqueous solutions. Alteration assemblages of olivine may be specific to deuteric, hydrothermal, surface water, or metamorphic environments. Raman spectra are produced by molecular vibrations and provide direct means for studying and identifying alteration products. Here, we present a combined study of changes in the chemical composition and Raman spectra of an olivine as it alters to iddingsite. Iddingsite is found in some SNC meteorites and is presumably present on Mars. The term 'iddingsite' has been used as a catch-all term to describe reddish alteration products of olivine, although some authors ascribe a narrower definition: an angstrom-scale intergrowth of goethite and smectite (presumably saponite) formed in an oxidizing and fluid-rich environment. Alteration conserves Fe (albeit oxidized) but requires addition of Al and H2O and removal of Mg and Si. The smectite that forms may be removed by continued alteration. Dehydration of the goethite forms hematite. Our purpose is to study the mineral assemblage, determine the structural and chemical variability of the components with respect to the degree of alteration, and to find spectral indicators of alteration that will be useful during in-situ analyses on Mars.

  8. Solar Radiation Management and Olivine Dissolution Methods in Climate Engineering

    NASA Astrophysics Data System (ADS)

    Kone, S.

    2014-12-01

    An overview of solar radiation management and olivine dissolution methods allows to discuss, comparatively, the benefits and consequences of these two geoengineering techniques. The combination of those two techniques allows to concomitantly act on the two main agents intervening in global warming: solar radiation and carbon dioxide. The earth surface temperature increases due mainly to carbon dioxide (a greenhouse gas) that keeps the solar radiation and causes the global warming. Two complementary methods to mitigate climate change are overviewed: SRM method, which uses injected aerosols, aims to reduce the amount of the inbound solar radiation in atmosphere; and olivine dissolution in water, a key chemical reaction envisaged in climate engineering , aiming to reduce the amount of the carbon dioxide in extracting it from atmosphere. The SRM method works on scenarios of solar radiation decrease and the olivine dissolution method works as a carbon dioxide sequestration method. Olivine dissolution in water impacts negatively on the pH of rivers but positively in counteracting ocean acidification and in transporting the silica in ocean, which has benefits for diatom shell formation.

  9. Near-Infrared Optical Constants of Olivine and Pyroxene

    NASA Astrophysics Data System (ADS)

    Trang, D.; Lucey, P. G.; Gillis-Davis, J.; Cahill, J. T.; Klima, R. L.; Isaacson, P.

    2012-12-01

    Producing mineral maps of planetary bodies is useful for petrological studies, future colonization, and resources. Estimating the physical and chemical properties of a surface, however, is complicated due to parameters such as, grain size and shape, mineral chemistry, space weathering, and ambient temperature. Radiative transfer modeling is one method to calculate mineral proportions and chemistry from reflectance spectra. However, radiative transfer modeling requires knowledge of the optical constants of minerals of interest. In this study, we characterized the near-infrared optical constants of two common mafic minerals, olivine and pyroxene, with a wide distribution of chemistries. Particularly, we parameterized the imaginary index of refraction, k, in the near-infrared portion of the spectrum of natural olivines as a function of foresterite content and synthetic pyroxenes as a function of wollastonite and ferrosilite content. For each k-spectrum, we modeled each absorption features and continuum using the Modified Gaussian Model (MGM) with three Gaussians and an inverse linear function respectively. We find that our fitting routine characterizes the k-spectra of olivine and pyroxene consistently. Additionally, we described each parameter of MGM and the continuum with a regression or multiple regressions as a function of mineral chemistry. Thus providing the optical parameters of olivine and pyroxene needed for radiative transfer modeling. Scatter observed between optical parameters and mineral chemistry could be the result of minor cations (e.g., Mn2+), grain size, and cation ordering. Future work will seek to characterize these effects on derived optical parameters.

  10. The search for exsolved ferromagnesian olivines: A meteoritic survey

    NASA Astrophysics Data System (ADS)

    Petaev, Michail I.

    1996-11-01

    Olivine grains from selected meteorites (the Springwater pallasite, the Lowicz mesosiderite, the ALH 84025 brachinite, the Krymka LL3 chondrite, and the Calcalong Creek lunar meteorite) and terrestrial rocks (San Carlos forsterite and Rockport fayalite) were studied by optical microscopy and high-precision electron microprobe analysis. Detailed microprobe traverses revealed regular igneous zoning in the Krymka and Calcalong Creek olivines. Traverses across the San Carlos forsterite grain are flat and display no chemical variations larger than the 2? range of counting error (0.2 mol% Fa). Traverses across olivine grains in the ALH 84025, Lowicz, and Springwater meteorites show regular patterns of periodic or wavy chemical variations well exceeding the 2? uncertainty range. However, no lamellar structure was seen in backscattered electron images. It is suggested that the periodic chemical variations may be due to spinodal decomposition of primary, more or less homogeneous grains. I conclude that the absence of earlier reports of such variations simply means that olivine grains in equilibrated meteorites have not been examined closely enough to detect them.

  11. Far-infrared continuum absorption of olivine at low temperatures

    NASA Astrophysics Data System (ADS)

    Mutschke, H.; Zeidler, S.; Chihara, H.

    2013-10-01

    The far-infrared continuum opacity of cold dust is an important quantity for the study of debris disks in planetary systems and of protoplanetary disks. Olivine is considered the most abundant crystalline dust species in such environments. We present spectroscopic absorption measurements on olivine plates of the order of a millimeter thickness at wavelengths between 60 and 400 μ m for temperatures down to 10 K. Our data reveal a strong temperature dependence of the continuum absorption coefficient, i.e. more than an order of magnitude decrease at 100 μ m for 10 K compared to room temperature. The absolute values are generally much lower than those measured with olivine powders embedded into polyethylene pellets, even if the difference between plate and powder samples is taken into account by theoretical models. In contrast to this, the room temperature data are in relatively good agreement with simulations using optical constants determined from reflection measurements. At low temperatures, the absorption coefficient of olivine was measurable with sufficient accuracy only up to 90 μ m for 10 K and up to 110 μ m for 100 K. These data reveal a drastic change in the spectral slope (from β ~ 2.0 to β > 5.0) for the continuum underlying the 69-μ m band, which is not predicted by the low-temperature optical constants determined for forsterite.

  12. Micromechanical modeling of the viscoplastic behavior of olivine

    NASA Astrophysics Data System (ADS)

    Castelnau, O.; Blackman, D. K.; Lebensohn, R. A.; Ponte CastaEda, P.

    2008-09-01

    Efforts to couple mantle flow models with rheological theories of mineral deformation typically ignore the effect of texture development on flow evolution. The fact that there are only three easy slip systems for dislocation glide in olivine crystals leads to strong mechanical interactions between the grains as the deformation proceeds, and subsequent development of large viscoplastic anisotropy in polycrystals exhibiting pronounced Lattice Preferred Orientations. Using full-field simulations for creep in dry polycrystalline olivine at high temperature and low pressure, it is shown that very large stress and strain rate intragranular heterogeneities can build up with deformation, which increase dramatically with the strength of the hard slip system (included for the purpose of enabling general deformations). Compared with earlier nonlinear extensions of the Self-Consistent mean-field theory to simulate polycrystal deformation, the "Second-Order" method is the only one capable of accurately describing the effect of intraphase stress heterogeneities on the macroscopic flow stress, as well as on the local stress- and strain rate fluctuations in the material. In particular, this approach correctly predicts that olivine polycrystals can deform with only four independent slip systems. The resistance of the fourth system (or accommodation mechanism), which is likely provided by dislocation climb or grain boundary processes as has been observed experimentally, may essentially determine the flow stress of olivine polycrystals. We further show that the "tangent" model, which had been used extensively in prior geophysical studies of the mantle, departs significantly from the full-field reference solutions.

  13. Effect of secondary phase formation on the carbonation of olivine.

    PubMed

    King, Helen E; Plmper, Oliver; Putnis, Andrew

    2010-08-15

    Large-scale olivine carbonation has been proposed as a potential method for sequestering CO(2) emissions. For in situ carbonation techniques, understanding the relationship between the formation of carbonate and other phases is important to predict the impact of possible passivating layers on the reaction. Therefore, we have conducted reactions of olivine with carbonated saline solutions in unstirred batch reactors. Altering the reaction conditions changed the Mg-carbonate morphology. We propose that this corresponded to changes in the ability of the system to precipitate hydromagnesite or magnesite. During high-temperature reactions (200 degrees C), an amorphous silica-enriched phase was precipitated that was transformed to lizardite as the reaction progressed. Hematite was also precipitated in the initial stages of these reactions but dissolved as the reaction proceeded. Comparison of the experimental observations with reaction models indicates that the reactions are governed by the interfacial fluid composition. The presence of a new Mg-silicate phase and the formation of secondary products at the olivine surface are likely to limit the extent of olivine to carbonate conversion. PMID:20704252

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  15. Olivine in kimberlites: metasomatism of the deep lithospheric mantle

    NASA Astrophysics Data System (ADS)

    Cordier, Carole; Sauzeat, Lucie; Arndt, Nicholas; Boullier, Anne-Marie

    2014-05-01

    Most kimberlites contain abundant mantle microxenoliths (nodules) and xenocrysts, mainly composed of olivine. We present here a geochemical and microstructural study of nodules from well-preserved type-I kimberlites from Kangamiut region in Greenland, the sequel of a preliminary study of Arndt et al. (2010). A striking feature of these and many other kimberlites is the wide range of olivine composition (Fo83 to Fo94) from nodule to nodule in a single kimberlite sample, contrasting with the olivine homogeneity within a single nodule (variation of less than 0.5 mol. %). We defined three chemical zones within normally zoned nodules based on Fo and Ni variations. Xenocrystic cores have high and constant Fo and Ni contents. Outer rims crystallized from the kimberlitic magma have constant Fo content (Fo88) coupled with significant decrease in Ni content (from 2500 to 500 ppm). Transition zones between cores and rims, along grain boundaries and along fluid inclusion trails have variable Fo content (Fo93 to Fo88) but roughly constant Ni content (from 3000 to 25000 ppm) and their composition mimics that defined by the nodules. Microstructural study of transition zones associated with curvilinear grain boundaries suggests these zones are produced during fluid-assisted plastic deformation. We propose that the transition zones formed during reaction of mantle peridotite with CO2-rich fluid, a process that removes the pyroxene and garnet components. The compositional variations of the transition zones monitor at the fine scale the processes that produce the chemical variability of olivine from nodule to nodule. We propose that the range of olivine composition records the position of sample relative to fluid-rich zones, grain boundaries for transition zones and larger conduits for broader scale variations registered in the nodules. This conclusion implies that metasomatic processes that produced the range of olivine composition and removed pyroxene and garnet from the initial peridotite occurred within the lithospheric mantle and not within the kimberlite magma during it ascent toward the surface. Arndt, N. T.; Guitreau, M.; Boullier, A. M.; Le Roex, A.; Tommasi, A.; Cordier, P. & Sobolev, A. V. (2010): Olivine, and the origin of kimberlite. Journal of Petrology, 51, 573-602.

  16. The effect of mineral paragenesis on Al diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Zhukova, Irina; O'Neill, Hugh; Capbell, Ian

    2014-05-01

    Al is the most abundant trivalent impurity of olivine and is particularly important because its concentration in olivine is temperature dependant, and it therefore has potential as a geothermometer (Wan, et al. 2008). Furthermore recent studies show that the incorporation of water into the olivine lattice is affected by the presents of trivalent cations such as Al3+ (Berry, et al. 2007; Hauri, et al. 2006). The Al distribution in olivines from volcanic rocks is often zoned and mantle olivines may also show an inhomogeneous distribution of Al, whereas the majority of other trace elements homogenized by diffusion (Mallmann, et al. 2009; McKibbin, et al.). However, there are no quantitative experimental data for Al diffusion in olivine, probably because the combination of low concentration rate and low diffusion rate make measurement difficult. We investigated the effect of silica activity on the diffusion rate of Al in forsterite at varying temperatures using solid-state buffer assemblages. Our study aimed to quantify the effect of major cation activities on the diffusion and concentration of Al in forsterite and also provide insights into the mechanism of Al substitution into the olivine lattice. The activities of SiO2, MgO and Al2O3 were buffered in each experiment by four different mineral associations: forsterite + periclase + spinel (fo+per+sp); forsterite + spinel + sapphirine (fo+sp+spr); forsterite + sapphirine + cordierite (fo+spr+cor); forsterite + cordierite + enstatite (fo+cor+en). Iron oxide in proportion of FeO/(FeO+MgO) = 0.1 was added to mixtures for San Carlos olivine experiments. Diffusion experiments were performed at the one-atmosphere vertical tube furnaces modified to control the fO2 by CO-CO2 gas mixing or in a box furnace in air for 10 - 28 days at temperatures from 1100 to 1500oC and logfO2 -0.7 and -5.7. The experiment with the San Carlos olivine was performed at 1300oC and at logfO2 = -5.7. In order to obtain equilibrium concentrations of the point defects we performed some experiments with pre-annealing. Diffusion profiles were measured by LA-ICP-MS in a traverse mode. The Al content of forsterite decreases with temperature dependence, increasing the potential of Al in olivine as a geothermometer. We obtain the activation energy of 379 kJ/mol for the high aSiO2 experiments, which is close within error of the value of 364 kJ/mol for the low aSiO2 experiments implying a common diffusion mechanism. The pre-exponential factor, however, increases by 5 orders of magnitude from low aSiO2 (fo+per+sp buffer) to high aSiO2 (fo+cor+en buffer). The much higher diffusivity at high aSiO2 indicates that Al diffusion occurs through octahedral cation site vacancies.

  17. The geoengineering potential of artificially enhanced silicate weathering of olivine

    NASA Astrophysics Data System (ADS)

    Khler, Peter; Hartmann, Jens; Wolf-Gladrow, Dieter A.

    2010-05-01

    Geoengineering is a proposed action to manipulate Earth's climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate in more detail the potential of a specific geoengineering technique, the carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. We here show the consequences of this technique for the chemistry of the surface ocean at rates necessary for geoengineering. We calculate that olivine dissolution has the potential to sequestrate up to one Pg C yr-1 directly, if olivine is distributed as fine powder over land areas of the humid tropics. The carbon sequestration potential is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg C yr-1. Open water dissolution of fine grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1 to 5 Pg C yr-1 for the 21st century by this technique. At maximum this technique would reduce global warming by 1 K and counteract ocean acidification by a rise in surface ocean pH by 0.1 in the year 2100.

  18. Exsolution of ferromagnesian olivine in the Divnoe meteorite

    NASA Astrophysics Data System (ADS)

    Petaev, M. I.; Brearley, A. J.

    1994-07-01

    The Divnoe meteorite is a granoblastic olivine-rich primitive achondrite whose textural and mineralogical characteristics suggest extensive recrystallization during slow cooling in the temperature range from approximately 1000 to approximately 500 C and lower. Olivine grains in this meteorite show a lamellar appearance in BSE images, caused by minor micrometer-scale chemical variations in Fe, Mg, and Mn contents between adjacent lamellae. Ten grains of lamellar olivine were studied in detail by Electron Probe Microanalysis (EPMA) and optical microscopy and two of these by Transmission Electron Microscopy (TEM). The olivine grains studied are essentially free of minor elements (Ti, Al, Cr, Ni, Ca, Na) except for Mn, and fall in the compositional range found by an earlier study. While the compositional ranges of Fe-poor and Fe-rich lamellae overlap, the differences between lamellae richest and poorest in Fe are quite similar, suggestive of their formation by an equilibrium process. Fine-scale microprobing has confirmed earlier compositional data, but has reduced lamella thicknesses to a few micrometers, which is in a good agreement with TEM observations. The structural and compositional data obtained strongly suggest that the lamellar structure in these olivine grains was produced by an exsolution process, which is in qualitative agreement with a recent thermodynamic analysis of phrase relations in the system Mg2SiO4-FeSiO2. Cracks in Fe-rich lamellae could result from expansion during the exsolution process due to the volume difference between Fe-rich and Fe-poor lamellae.

  19. Geoengineering potential of artificially enhanced silicate weathering of olivine.

    PubMed

    Khler, Peter; Hartmann, Jens; Wolf-Gladrow, Dieter A

    2010-11-23

    Geoengineering is a proposed action to manipulate Earth's climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate the potential of a specific geoengineering technique, carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. If important details of the marine chemistry are taken into consideration, a new mass ratio of CO(2) sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1 Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments, a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg of C per year, but these upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2. Open water dissolution of fine-grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1-5 Pg of C per year for the 21st century by this technique. PMID:21059941

  20. Geoengineering potential of artificially enhanced silicate weathering of olivine

    PubMed Central

    Köhler, Peter; Hartmann, Jens; Wolf-Gladrow, Dieter A.

    2010-01-01

    Geoengineering is a proposed action to manipulate Earth’s climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate the potential of a specific geoengineering technique, carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. If important details of the marine chemistry are taken into consideration, a new mass ratio of CO2 sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1 Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments, a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg of C per year, but these upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2. Open water dissolution of fine-grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1–5 Pg of C per year for the 21st century by this technique. PMID:21059941

  1. Diffusive over-hydration of olivine-hosted melt inclusions

    NASA Astrophysics Data System (ADS)

    Hartley, Margaret E.; Neave, David A.; Maclennan, John; Edmonds, Marie; Thordarson, Thor

    2015-09-01

    The pre-eruptive water content of magma is often estimated using crystal-hosted melt inclusions. However, olivine-hosted melt inclusions are prone to post-entrapment modification by H+ diffusion as they re-equilibrate with their external environment. This effect is well established for the case of H+ loss from olivine-hosted inclusions that have cooled slowly in degassed magma. Here we present evidence for the opposite effect: the addition of H+ into inclusions that are held in melts that are enriched in H2O with respect to the trapped melts. The compositional variability in a suite of 211 olivine-hosted inclusions from the Laki and Skuggafjll eruptions in Iceland's Eastern Volcanic Zone indicates that diffusive H+ gain governs the H2O content of incompatible trace element depleted inclusions. Individual eruptive units contain olivine-hosted inclusions with widely varying incompatible element concentrations but near-constant H2O. Furthermore, over 40% of the inclusions have H2 O /Ce > 380, significantly higher than the H2O/Ce expected in primary Icelandic melts or mid-ocean ridge basalts (150-280). The fact that the highest H2O/Ce ratios are found in the most incompatible element depleted inclusions indicates that hydration is a consequence of the concurrent mixing and crystallisation of compositionally diverse primary melts. Hydration occurs when olivines containing depleted inclusions with low H2O contents are juxtaposed against more hydrous melts during mixing. Melt inclusions from a single eruption may preserve evidence of both diffusive H+ loss and H+ gain. Trace element data are therefore vital for determining H2O contents of melt inclusions at the time of inclusion trapping and, ultimately, the H2O content of the mantle source regions.

  2. Olivine as a key to unlocking Kilauea's magmatic history

    NASA Astrophysics Data System (ADS)

    Garcia, M. O.; Norman, M. D.

    2011-12-01

    Olivine is a ubiquitous mineral in Hawaiian basalts. It is on the liquidus at pressures <0.5 GPa and has the potential to record numerous petrologic processes including the histories of parental magma composition changes, crystal fractionation, magma mixing and crustal contamination. These processes are recorded in olivine composition (major and trace elements, and isotopes) and by melt inclusions trapped within olivine. Here we focus on Kilauea's historical lavas (1820-present) to evaluate the magmatic history one of world's most active volcanoes. Kilauea has shown dramatic variations in it eruptive rate and style (from vigorous, quiescent effusion in 1820 to infrequent explosive activity in 1924 and then to its highest effusion during the last decade). Eruption rates correlate with whole-rock compositional and isotopic variations (P-G 1999). Most Kilauea lavas have normally zoned olivine in equilibrium with whole-rock compositions which belies complex magma chamber processes. Parental magma composition changed rapidly based on the heterogeneity of melt inclusion compositions in higher Mg olivine (>86 forsterite). Melt inclusions from single eruptions show wider variation in ratios of Ca/Al and Nb/Y than observed in lavas for the historical period. Thus, the mantle source is heterogeneous on a small scale and small batches of compositionally distinct melt are frequently delivered to the volcano. These magma batches undergo mixing, fractionation and after caldera collapses (e.g.1924), crustal contamination in the summit reservoir. This work demonstrates that an Ernstonian approach, using minerals to understand petrologic processes, is key to unlocking Kilauea's magmatic processes. Pietruszka, A.P. and Garcia, M.O., 1999, J. Petrol. 40, 1321-1342.

  3. Evidence for equilibrium conditions during the partitioning of nickel between olivine and komatiite liquids.

    USGS Publications Warehouse

    Budahn, J.R.

    1986-01-01

    Olivine-liquid partition coefficients for Ni(DNi), calculated from Ni vs MgO abundance variations in komatiite series basalts, compare favourably with experimentally determined values, if Ni variations in olivine-controlled basalts can be modelled with an equation that assumes equilibrium between the entire olivine crystal and its coexisting liquid.-J.A.Z.

  4. Characterization by EBSD of dislocations and disclinations in olivine: implications for the rheology of olivine-rich aggregates

    NASA Astrophysics Data System (ADS)

    Cordier, P.; Demouchy, S. A.; Beausir, B.; Taupin, V.; Fressengeas, C.

    2013-12-01

    The rheology of olivine-rich rocks remains poorly understood. Only intracrystalline deformation mechanisms involving dislocations are quite well known. In orthorhombic olivine only two slip directions, [100] and [001] can be activated. Most characterizations performed so far involve transmission electron microscopy studies at high magnifications or, at a larger scale, optical or scanning electron microscopy on decorated samples. In the latter case, no detailed characterization of the defects could be done. Orientation maps obtained from high-resolution electron backscattered diffraction allow recovering components of the lattice curvature tensor which in turn allow determination of components of the dislocation density tensor. The geometrically necessary dislocation content can thus be imaged. Recently Beausir & Fressengeas (2013) have shown that with this technique, components of the disclination density tensor could also be determined. Several examples have been provided in metallic alloys. In this study we show that olivine aggregates (both experimentally and naturally deformed) contain pervasive evidence of disclinations dipoles at grain boundaries. The implications on the plastic behavior of olivine rocks are discussed based on a numerical model of the response to an applied shear stress of a grain boundary made of disclinations. Beausir, B. & Fressengeas, C., Disclination densities from EBSD orientation mapping. International Journal of Solids and Structures 50 (1), 137-146 (2013).

  5. Magnetic Paleofield of Avanhandava H4 Chondrite's Matrix and Chondrules - Implications on Magnetic Fields in Early Solar System.

    NASA Astrophysics Data System (ADS)

    Kohout, T.; Pesonen, L. J.

    2005-12-01

    The Avanhandava (H4) fall occurred in 1952 in Brazil. A total of 9.33 kg had been preserved after the meteorite brake up during the impact [1]. The meteorite contains large (0.1 - 2.0 mm) chon-drules that have clearly delineated boundaries with matrix. This characteristic allows us to pick up oriented individual chondrules and study their magnetic properties. The chondrules of the Avanhandava meteorite show a low and randomly oriented NRM (10-2 - 10-1 mAm2/kg). In contrast the matrix is strongly (100 - 101 mAm2/kg) and uniformly magnet-ized [2]. Various methods for paleofield determination have been applied on matrix and individual chondrules in order to determine possi-ble magnetizing processes and paleofields in early solar systems.. The laboratory experiments reveal approximate paleofields for matrix similar to present geomagnetic field. The paleofield de-termined for chondrules is approximately one order of magnitude lower comparing to values obtained for matrix. That suggests that chondrules are not magnetically contaminated by geomagnetic or artificial fields and they acquired their NRM prior their aggregation to Avanhandava parent body (random NRM directions). The matrix shows remarkable traces of terres-trial weathering and is uniformly magnetized. The paleofield re-sult for matrix indicates possible remagnetization caused by ter-restrial weathering. The terrestrial weathering of ordinary chon-drites is observed even on falls stored in museums and can sig-nificantly influence meteorite magnetic records [3, 4]. References: [1] Paar W. et al. 1976. Revista Brasileira de Geo-ciencias 6: 201-210. [2] Kohout T. and Pesonen L. J. 2005. 68th Annual Meteoritical Society Meeting: 5202. [3] Kohout T. et al. 2004. Physics and Chemistry of the Earth 29: 885-897. [4] Lee M. R. and Bland P. A. 2004. Geochimica et Cosmochimica Acta 68: 893-916.

  6. Lattice preferred orientations of olivine in the schistosed antigorite serpentinite

    NASA Astrophysics Data System (ADS)

    Soda, Y.; Ando, J.; Mizukami, T.; Morishita, T.

    2011-12-01

    The lattice preferred orientation (LPO) of the schistosed antigorite serpentinite is considered as causes of the seismic anisotropy observed at the subduction zones (Katayama et al., 2009; Jung, 2011) and the natural examples are reported by several researchers (Bezacier et al., 2010; Hirauchi et al., 2010; Soda and Takagi, 2010). Formation process of the antigorite LPO is unclear, especially at primary serpentinized stage. To understand the development of micro-structures of antigorite serpentinite, we made structural analyses of serpentinite schist and the former peridotite fabric. Samples were taken from lenticular serpentinite bodies (< 1km) stack in Jurassic accretionary complex, Toba area, Southwest Japan. The serpentinite consist of olivine, antigorite, meta-clinopyroxene and Cr-spinel. The foliation and lineation of serpentinite is defined by parallel alignment of elongated olivine grain and antigorite blades, which make up mylonitic textures, such as a porphyroclast system and composite planar fabric. Antigorite blades show syn-kinematic growth in pressure shadows and pull-apart of olivine porphyroclast. In the less serpentinized part, antigorite blades are crystallized along the grain boundary of olivine. We measure the LPOs of coarse olivine grains in the serpentinite schist using a u-stage. The X, Y and Z directions represent directions of lineation, normal to lineation within the foliation and normal to foliation, respectively. The LPOs of olivine show point maximum or partial girdle distribution, and these concentrated crystal axes are incongruous with X, Y and Z direction. The a[100] axes of olivine are parallel to the serpentinite foliation, and form a point maximum several degrees away from the Y direction. The b[010] axes and the c[001] axes are concentrated Z and X direction forming a partial girdle normal to Y direction, respectively. Boudier et al. (2010) have reported the topotactic relationship between olivine and antigorite. They show that the (100)ol is parallel to the (001)atg or the (010)ol is parallel to the (001)atg. And, the a[100] axes of olivine are normal to serpentinite foliation with point maximum in the thin section scale. However, in the case of this study, the simple topotactic relationship does not connect the fabric in the thin section scale of serpentinite schist. Although, more detail analysis need to discuss the formation of antigorite LPO, the other mechanisms, such as crystal plastic deformation or diffusion-precipitation, might cause rearrangement of antigorite fabric. References Bezacier, L. et al., 2010, Earth and Planetary Science Letters, 289, 198-208. Boudier, F. et al., 2010, Journal of Petrology 51, 495-512. Hirauchi et al., 2010, Earth and Planetary Science Letters, 299, 196-206. Jung, H., 2011, Earth and Planetary Science Letters, 307, 535-543. Katayama, I., et al., 2009, Nature, 461, 1114-1118. Soda, Y. and Takagi, H., 2010, Journal of Structural Geology, 32, 792-802.

  7. The role of Fe and redox conditions in olivine carbonation rates: An experimental study of the rate limiting reactions at 90 and 150 C in open and closed systems

    NASA Astrophysics Data System (ADS)

    Saldi, Giuseppe D.; Daval, Damien; Morvan, Gilles; Knauss, Kevin G.

    2013-10-01

    The mechanisms and rates of olivine carbonation reactions have been the object of a number of studies, but the thermodynamic limitations and the kinetics of the elementary processes that control the overall reaction are still poorly understood and characterized. The main objective of this study is to probe the effect of Fe on the measured rates of olivine carbonation and its role in the formation of Si-rich surface layers, which can significantly inhibit olivine dissolution and limit the extent of the carbonation reaction. A series of batch and flow-through reactor experiments was conducted in pure water at 90 and 150 C and under a CO2 partial pressure of 100 and 200 bar, using both a natural sample of Fe-bearing olivine (Fo88) and a synthetic sample of pure forsterite (Fo100). Experimental results show that Fe plays an ambivalent role in the carbonation rates of olivine. On one hand, the presence of Fe favors the formation of Fe-Si-rich protective layers at the interface between olivine and aqueous solution, slowing down the dissolution reaction and limiting the extent of carbonation, whereas pure silica coatings have little to no inhibiting effect on measured carbonation rates. On the other hand, Fe enhances olivine to carbonate conversion rates at low degrees of supersaturation, by promoting the formation of fast precipitating Mg-Fe carbonate solid solutions. The passivating properties of Fe-Si-rich layers originate from the strong Fe(III)-Si interaction and are linked to the permanence of oxidizing conditions in the aqueous fluid. As a consequence, under reducing conditions, olivine carbonation rates can be significantly increased by higher extents of dissolution and by the formation of ferroan magnesites (Mg,Fe)CO3, which nucleate faster than the pure Mg end-member. Forsterite and olivine carbonation reactions can be hindered by the formation of secondary Mg sheet-silicates but, at the conditions studied, the formation of such silicate phases was observed to be transitional and not affecting significantly the rates of carbonation at the end of one-month long experimental runs. This work presents new measurements of olivine carbonation rates and delivers relevant information that suggest new reference criteria for the assessment of the sequestration potential of CO2 repositories and the optimization of the mineral carbonation process in mafic and ultramafic rocks.

  8. Gas-grain energy transfer in solar nebula shock waves: Implications for the origin of chondrules

    NASA Technical Reports Server (NTRS)

    Hood, L. L.; Horanyi, M.

    1993-01-01

    Meteoritic chondrules provide evidence for the occurrence of rapid transient heating events in the protoplanetary nebula. Astronomical evidence suggests that gas dynamic shock waves are likely to be excited in protostellar accretion disks by processes such as protosolar mass ejections, nonaxisymmetric structures in an evolving disk, and impact on the nebula surface of infalling 'clumps' of circumstellar gas. Previous detailed calculations of gas-grain energy and momentum transfer have supported the possibility that such shock waves could have melted pre-existing chondrule-sized grains. The main requirement for grains to reach melting temperatures in shock waves with plausibly low Mach numbers is that grains existed in dust-rich zones (optical depth greater than 1) where radiative cooling of a given grain can be nearly balanced by radiation from surrounding grains. Localized dust-rich zones also provide a means of explaining the apparent small spatial scale of heating events. For example, the scale size of at least some optically thick dust-rich zones must have been relatively small (less than 10 kilometers) to be consistent with petrologic evidence for accretion of hot material onto cold chondrules. The implied number density of mm-sized grains for these zones would be greater than 30 m(exp -3). In this paper, we make several improvements of our earlier calculations to include radiation self-consistently in the shock jump conditions, and we include heating of grains due to radiation from the shocked gas. In addition, we estimate the importance of momentum feedback of dust concentrations onto the shocked gas which would tend to reduce the efficiency of gas dynamic heating of grains in the center of the dust cloud.

  9. Olivine vitrophyres - A nonpristine high-Mg component in lunar breccia 14321

    NASA Technical Reports Server (NTRS)

    Shervais, John W.; Taylor, Lawrence A.; Lindstrom, Marilyn M.

    1988-01-01

    The presence of olivine vitrophyres in breccia 14321 is discussed, suggesting that olivine vitrophyres could account for the high-Mg component of soils and breccias in the lunar highlands. The olivine vitrophyre clasts from 14321 have high bulk MgO and the Mg/(Mg+Fe) ratio is 78 percent. The olivine vitrophyres are impact melt rocks and are rich in KREEP. The high MgO concentration is manifest by skeletal quench crystals of olivine that constitute about 30 percent of the mode.

  10. Chemical variation and zoning of olivine in lunar dunite 72415 - Near-surface accumulation

    NASA Technical Reports Server (NTRS)

    Ryder, Graham

    1992-01-01

    Electron microprobe remeasurements have been used to reevaluate the range of olivine compositions, including CaO, in lunar dunite sample 72415 and compare that range with olivines in established plutonic rocks. Olivines from ferroan anorthosite 62237 and samples from the Stillwater intrusion were analyzed; literature data for other lunar and terrestrial plutonic samples were used for comparisons. The analyses show that the lunar dunite 72415 contains a range of olivine compositions, that the olivines are zoned, and that they have CaO abundances that are consistent with shallow hypabyssal rather than deep plutonic accumulation.

  11. Olivine and Carbonate Globules in ALH84001: A Terrestrial Analog, and Implications for Water on Mars

    NASA Technical Reports Server (NTRS)

    Treiman, A. H.

    2005-01-01

    Carbonate globules in ALH84001 are associated with small olivine grains an unexpected finding because the olivines equilibrated at high T while the carbonate is chemically zoned and unequilibrated. A possible explanation comes from a terrestrial analog on Spitsbergen (Norway), where some carbonate globules grew in cavities left by aqueous dissolution of olivine. For ALH84001, the same process may have acted, with larger olivines dissolved out and smaller ones shielded inside orthopyroxene. Carbonate would have been deposited in holes where the olivine had been. Later shocks crushed remaining void space, and mobilized feldspathic glass around the carbonates.

  12. Real Time Pore Structure Evolution during Olivine Mineral Carbonation

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Fusseis, F.; Lisabeth, H. P.; Xiao, X.

    2014-12-01

    Aqueous carbonation of ultramafic rocks has been proposed as a promising method for long-term, secure sequestration of carbon dioxide. While chemical kinetics data indicate that carbonation reaction in olivine is one of the fastest among the mg-bearing minerals, in practice, the factors that limit the extent and rate of carbonation in ultramafic rocks are fluid supply and flux. On the one hand, reaction products could produce passivating layer that prohibits further reactions. On the other hand, the increases in solid volume during carbonation could lead to cracking and create new fluid paths. Whether carbonation in ultramafic rocks is self-limiting or self-sustaining has been hotly debated. Experimental evidence of precipitation of reaction products during olivine carbonation was reported. To date, reaction-driven cracking has not been observed. In this paper, we present the first real-time pore structure evolution data using the x-ray synchrotron microtomography. Sodium bicarbonate (NaHCO3) solution was injected into porous olivine aggregates and in-situ pore structure change during olivine carbonation at a constant confining pressure (12 MPa) and a temperature of 200oC was captured at 30 min. interval for ~160 hours. Shortly after the experiment started, filling-in of the existing pores by precipitation of reaction products was visible. The size of the in-fills kept increasing as reactions continued. After ~48 hours, cracking around the in-fill materials became visible. After ~60 hours, these cracks started to show a clear polygonal pattern, similar to the crack patterns usually seen on the surface of drying mud. After ~72 hours, some of the cracks coalesced into large fractures that cut-through the olivine aggregates. New fractures continued to develop and at the end of the experiment, the sample was completely disintegrated by these fractures. We also conducted nanotomography experiments on a sub-volume of the reacted olivine aggregate. Orthogonal sets of incipient cracks were observed, providing clear evidence that these cracks are generated by isotropic tensile stresses. This strongly indicates that the observed cracking was caused by volume expansion during mineral carbonation. The experimental results provide a mechanism for near 100% alteration of ultramafic rocks observed in nature.

  13. Evidences and consequences of slow hydrogen diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Padron-Navarta, J. A.; Hermann, J.; O'Neill, H. S.

    2014-12-01

    In the most abundant upper mantle phase, olivine, the presence of hydrogen significantly modifies the timescale of chemical diffusion, plastic deformation, electrical conductivity and the attenuation of seismic waves. Early experiments showed that hydrogen is the fastest species able to diffuse through the olivine lattice. We have found, however, experimental and natural evidence suggesting that hydrogen diffusion can also be orders of magnitude slower. In olivine there are four different hydrogen substitution mechanisms, associated with Mg vacancies, Si vacancies, trivalent cations and titanium substitution, hereafter referred to as H[Mg], H[Si], H[triv] and H[Ti] respectively. We experimentally investigated the dehydroxylation of synthetic forsterite with two contrasting hydrous defect populations: (1) dominated by H[Si], and H[Ti] with subsidiary H[Mg] and H[triv]; and (2) H[Si] exclusively. The loss rates of H[Mg] and H[triv] are in agreement with previous measurements of bulk hydrogen diffusion in forsterite, but the decrease in H[Ti] and H[Si] are ~1.5 and ~ 3 orders of magnitude slower, respectively. The activation energy and pre-exponential terms derived in these experiments are in agreement with the empirical correlation recently proposed based on the Meyer-Nedel compensation law (Jones 2014, G3, 15, 2616-2631). Natural observations attest further to slow hydrogen diffusivity in olivine dominated by H[Ti] and H[Si]. Metamorphic olivines formed after dehydration reactions in the Alpine orogeny preserve their original water contents despite long times of exhumation (2-3 Ma). Closure temperature calculations suggest that using previous fast diffusion rates, these olivines should reequilibrate down to 400C. Only slow hydrogen diffusion coefficients such as those corresponding to H[Si] are able to explain the observed preservation of water content at the peak metamorphic temperature (700-800C). These findings have implications for estimating the ascent rate of xenoliths, which are more consistent with other independent constrains, as recently noted (Hilchie et al. 2014, Lithos, 202-203, 429-441). They are also required to assess the time necessary to equilibrate experimental charges, since for the different hydrous defects this time would vary by orders of magnitudes.

  14. Toll Bar on Sea

    ERIC Educational Resources Information Center

    Hunter, Dave

    2008-01-01

    In the summer of 2007 the United Kingdom experienced some of the heaviest rainfall since records began. Toll Bar in South Yorkshire featured prominently in media coverage as the village and the homes surrounding it began to flood. Many people lost everything: their homes, their furniture, their possessions. In an effort to come to terms with what…

  15. Toll Bar on Sea

    ERIC Educational Resources Information Center

    Hunter, Dave

    2008-01-01

    In the summer of 2007 the United Kingdom experienced some of the heaviest rainfall since records began. Toll Bar in South Yorkshire featured prominently in media coverage as the village and the homes surrounding it began to flood. Many people lost everything: their homes, their furniture, their possessions. In an effort to come to terms with what

  16. Multiple bars and secular evolution

    NASA Astrophysics Data System (ADS)

    Shen, Juntai

    2015-03-01

    Bars are the most important driver of secular evolution. A significant fraction of barred galaxies also harbor small secondary bars. Secondary bars are visible even in near-infrared images, so they are not just dusty and blue, but stellar features (Erwin & Sparke 2002). Since they are quite common, secondary bars are probably long-lived stellar features. The random relative orientation of the two bars indicates that they are dynamically decoupled with different pattern speeds (Buta & Crocker 1993). Corsini et al. (2003) presented conclusive direct kinematic evidence for a decoupled secondary bar in NGC 2950. Dynamically decoupled secondary bars have long been hypothesized to be a mechanism to drive gas past the ILR of primary bars to feed active galactic nuclei (Shlosman et al. 1989). However, the dynamics of secondary bars are still not well understood, and it is still unclear what role secondary bars play in the AGN fueling process. Numerical simulations offer the best approach to understanding double-barred systems. Decoupled secondary bar in the earlier gaseous simulations only last a short time (< 1 Gyr, e.g. Friedli & Martinet 1993). Orbital studies of double-barred systems discovered a family of loop orbits that may be building blocks of long-lived nuclear stellar bars (Maciejewski & Sparke 1997, 2000). To complement orbital studies, which are not fully self-consistent, N-body simulations are preferred to further our understanding of double-barred systems. Debattista & Shen (2007) and Shen & Debattista (2009) managed to form long-lived double-barred systems with purely collisionless simulations, where a pre-existing rotating pseudo-bulge is introduced initially. The shape and size of secondary bars in the models are comparable to observed ones. They found that the rotation of the two bars is not rigid. The amplitude and pattern speed of the secondary bars oscillate as they rotate through their primary counterparts. Although the secondary bar rotates faster than the primary bar in this model, the stellar velocity field in the central region only shows a weakly twisted kinematic minor axis. Recently more simulations of double-barred galaxies with simpler initial conditions are explored (Du, Shen & Debattista 2014). We expect that the new models can be used to cross-check with the kinematic properties of double-barred galaxies from IFU observations such as SAURON and Atlas3D.

  17. Resonances in barred galaxies

    NASA Astrophysics Data System (ADS)

    Ceverino, D.; Klypin, A.

    2007-08-01

    The inner parts of many spiral galaxies are dominated by bars. These are strong non-axisymmetric features which significantly affect orbits of stars and dark matter particles. One of the main effects is the dynamical resonances between galactic material and the bar. We detect and characterize these resonances in N-body models of barred galaxies by measuring angular and radial frequencies of individual orbits. We found narrow peaks in the distribution of orbital frequencies with each peak corresponding to a specific resonance. We found five different resonances in the stellar disc and two in the dark matter. The corotation resonance (CR) and the inner and outer Lindblad resonances are the most populated. The spatial distributions of particles near resonances are wide. For example, the inner Lindblad resonance is not localized at a given radius. Particles near this resonance are mainly distributed along the bar and span a wide range of radii. On the other hand, particles near the CR are distributed in two broad areas around the two stable Lagrange points. The distribution resembles a wide ring at the corotation radius. Resonances capture disc and halo material in near-resonant orbits. Our analysis of orbits in both N-body simulations and simple analytical models indicates that resonances tend to prevent the dynamical evolution of this trapped material. Only if the bar evolves as a whole, resonances drift through the phase space. In this case particles anchored near resonant orbits track the resonance shift and evolve. The criteria to ensure a correct resonant behaviour discussed by Weinberg and Katz can be achieved with few millions particles because the regions of trapped orbits near resonances are large and evolving.

  18. The solubility of olivine in basaltic liquids - An ionic model

    NASA Technical Reports Server (NTRS)

    Herzberg, C. T.

    1979-01-01

    A model is presented which enables the temperature at which olivine is in equilibrium with any alkali-depleted basaltic compound to be calculated to within + or - 30 C. It is noted that the error increases substantially when applied to terrestrial basalts which contain several weight percent alkalis. In addition the model predicts and quantifies the reduced activity of SiO4(4-) monomers due to increasing SiO2 concentrations in the melt. It is shown that the coordination of alumina in melts which precipitate olivine only appears to be dominantly octahedral, while titanium acts as a polmerizing agent by interconnecting previously isolated SiO4(4-) monomers. It is concluded that the model is sufficiently sensitive to show that there are small repulsive forces between Mg(2+) and calcium ions which are in association with normative diopside in the melt.

  19. Helium diffusion in olivine based on first principles calculations

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Brodholt, John; Lu, Xiancai

    2015-05-01

    As a key trace element involved in mantle evolution, the transport properties of helium in the mantle are important for understanding the thermal and chemical evolution of the Earth. However, the mobility of helium in the mantle is still unclear due to the scarcity of measured diffusion data from minerals under mantle conditions. In this study, we used first principles calculations based on density functional theory to calculate the absolute diffusion coefficients of the helium in olivine. Using the climbing images nudged elastic band method, we defined the diffusion pathways, the activation energies (Ea), and the prefactors. Our results demonstrate that the diffusion of helium has moderate anisotropy. The directionally dependent diffusion of helium in olivine can be written in Arrhenius form as follows.

  20. Grinding methods to enhance the reactivity of olivine

    SciTech Connect

    Summers, Cathy A.; Dahlin, David C.; Rush, Gilbert E.; O'Connor, William K.; Gerdemann, Stephen J.

    2005-08-01

    The Albany Research Center (ARC) conducted studies of mechanical activation by conventional and ultrafine grinding techniques to enhance olivine reactivity in mineral carbonation reactions. Activated olivine is one of several solid feed materials used at ARC in reactions with carbon dioxide to form carbonate minerals. This paper compares grinding techniques via energy demand data and product characteristics, including particle size distributions, surface areas, full-width-at-half-maximum (FWHM) XRD analyses, and particle morphology by SEM analyses. Reactivity was calculated by percent conversion to carbonate in subsequent carbonation tests. Particle size reduction has the greatest impact on reactivity, and wet grinding is more energy efficient than dry grinding. Large additional inputs of energy to increase surface area or reduce crystallinity do not result in proportional improvements in reactivity.

  1. Low-temperature plastic rheology of olivine determined by nanoindentation

    NASA Astrophysics Data System (ADS)

    Kranjc, Kelly; Rouse, Zachary; Flores, Katharine M.; Skemer, Philip

    2016-01-01

    Low-temperature plasticity is a deformation mechanism that occurs mainly at high stress and low temperatures and may be important in the shallow lithosphere, at the tips of cracks, and in laboratory experiments. Previous studies investigating the low-temperature plasticity of the mineral olivine have exhibited wide variability in their extrapolations to the athermal flow strength or Peierls stress. To better constrain the rheology of olivine, nanoindentation tests were performed on samples in the temperature range of 0-175C. The indentation properties were converted to uniaxial properties using a finite element-based method. The data were fit to a standard flow law for low-temperature plasticity, and Peierls stresses between 5.32 and 6.45 GPa were obtained. These results provide increased confidence in the extrapolation of high-pressure and high-temperature laboratory experiments to low-temperature conditions and illustrate the applicability of nanoindentation methods to the study of mineral rheology.

  2. Experimental study of Mg isotope fractionation during olivine dissolution

    NASA Astrophysics Data System (ADS)

    Qiu, L.; Wang, Z.

    2012-12-01

    The dissolution of silicate minerals plays important roles in modifying the chemical composition of the ocean and earth crust. Previous studies show secondary clay minerals produced as a by-product of dissolution are enriched in heavy Mg isotopes compared with their protolith. In this study, batch olivine dissolution experiments were conducted in an autoclave to understand the evolution of Mg isotope composition in the solution as a function of controlled experimental conditions, including initial pH of the fluid (10.02 or 2.02), temperature (50, 100, or 200oC), olivine-grain size (<30?m powder or single olivine grain of ~0.2g/each), and duration of the experiments (up to ~60 hours). At the end of experiments, solid minerals were characterized by SEM and EM, and the solution was analyzed for major and trace element, and Mg isotope compositions by Element-XR and Neptune at Yale University. The Mg/Si ratio of the solution and the SEM and EM characterization of the solid phases indicate the formation of secondary mineral-talc in experiments with alkaline solutions, is consistent with the calculated saturation index. Significant Mg isotope fractionations were also observed in these experiments, which decrease with increasing temperature (e.g., up to ~ -5.8 at 50oC vs. -0.72 at 200oC), but increase with increasing the duration of the experiments. In contrast, little fractionation was observed in experiments with acidic solutions at low temperatures, or short duration of the experiments at high temperatures. These results indicate that dissolution of olivine (even in our closed system experiments) is a surface controlled process, during which Mg isotopes fractionate insignificantly, whereas secondary minerals formed during the process are strongly enriched in heavy Mg isotopes, leaving the solutions depleted in 26Mg. The fractionation factors between solution and talc have been estimated for these experiments as well.

  3. Chemical frost weathering of olivine: Experimental study and implications

    NASA Technical Reports Server (NTRS)

    Harris, S. L.; Huguenin, R. L.

    1987-01-01

    New experimental results are reported on the frost weathering of olivine. After first weathering, a decrease in Fe sup 2(+)M(2) absorption bands were noted. This decrease is related to the protonation of O(+) in the mineral. It is contented that this reaction may result in the regolith storage of 100 to 1000 m of H(sub 2) over the history of Mars.

  4. Fine-grained rims surrounding chondrules in the Tagish Lake carbonaceous chondrite: Verification of their formation through parent-body processes

    NASA Astrophysics Data System (ADS)

    Takayama, Akiko; Tomeoka, Kazushige

    2012-12-01

    A petrographic and electron microscopic study of the carbonate-poor lithology of the Tagish Lake carbonaceous chondrite reveals that most chondrules contain many pseudomorphs of opaque nodules and are surrounded by phyllosilicate-rich altered zones that were formed by replacing enstatite and opaque nodules along the chondrule peripheries. Most chondrules and other coarse-grained components are surrounded by fine-grained rims, which are commonly disaggregated and partly lacking. The altered zones and the rims are compositionally and texturally similar, although they exhibit some differences in secondary minerals. In comparison, the rims and the host matrix show more significant differences in bulk chemical composition, texture, and mineralogy. The observations suggest that the chondrules and the rims experienced aqueous alteration simultaneously, whereas the rims and the matrix experienced aqueous alteration under distinct conditions. We also found a clast that contains multiple coarse-grained components embedded in a matrix and numerous smaller matrix clasts. The coarse-grained components in the clast have no rims, and the matrices of the clasts are mineralogically identical to the rims. The results suggest that the chondrules, other coarse-grained components, and their rims (generically referred to as chondrules/rims) and the clasts originated from a common precursor region in the meteorite parent-body that was different from the location where the host meteorite was finally lithified. That is, the chondrules/rims are actually clasts produced by brecciation and later transported and incorporated into the present host matrix. The rims are, therefore, remnants of matrix material that formerly filled interspaces between the chondrules and other coarse-grained components. This model is essentially consistent with those previously proposed for the carbonate-rich lithology of Tagish Lake and the hydrated chondrules/rims in the Vigarano and Mokoia CV3 chondrites.

  5. New measurements of activation volume in olivine under anhydrous conditions

    NASA Astrophysics Data System (ADS)

    Durham, W. B.; Mei, S.; Kohlstedt, D. L.; Wang, L.; Dixon, N. A.

    2009-01-01

    A new cell assembly for the deformation-DIA (D-DIA) shows promise for limiting the water content of samples and providing a more mechanically stable environment for deformation. The 6-mm cubic cell consists of a 6-mm diameter mullite sphere cradled in a web of unfired pyrophyllite. The pyrophyllite flows during initial compression of the D-DIA to form gaskets between the six anvils while the mullite flows to become a nearly cubic-shaped pressure medium. Measurements on olivine indicate more than one order of magnitude drop in water content to <40 ppm H/Si compared with the boron-epoxy medium. Improved mechanical stability is achieved by elimination of the thermocouple from the assembly and determination of temperature from calibration curves of furnace power vs. temperature. Three samples of polycrystalline orthopyroxene-buffer San Carlos olivine have been deformed in high-temperature creep in the new cell, at pressures of 2.7-4.9 GPa and temperatures near 1473 K. Strength is consistent with that measured in the gas-apparatus at lower pressures. Over the pressure range investigated we resolve an activation volume for creep of dry olivine of V* = 9.5 ± 7 × 10 -6 m 3/mol.

  6. Creep behavior of Fe-bearing olivine under hydrous conditions

    NASA Astrophysics Data System (ADS)

    Tasaka, Miki; Zimmerman, Mark E.; Kohlstedt, David L.

    2015-09-01

    To understand the effect of iron content on the creep behavior of olivine, (MgxFe(1 - x))2SiO4, under hydrous conditions, we have conducted tri-axial compressive creep experiments on samples of polycrystalline olivine with Mg contents of x = 0.53, 0.77, 0.90, and 1. Samples were deformed at stresses of 25 to 320 MPa, temperatures of 1050 to 1200C, a confining pressure of 300 MPa, and a water fugacity of 300 MPa using a gas-medium high-pressure apparatus. Under hydrous conditions, our results yield the following expression for strain rate as a function of iron content for 0.53 ? x ? 0.90 in the dislocation creep regime: ??=??0.90((1-x/0.1))1/2exp[2261030.9-x/RT]. In this equation, the strain rate of San Carlos olivine, ??0.90, is a function of T, ?, and fH2O. As previously shown for anhydrous conditions, an increase in iron content directly increases creep rate. In addition, an increase in iron content increases hydrogen solubility and therefore indirectly increases creep rate. This flow law allows us to extrapolate our results to a wide range of mantle conditions, not only for Earth's mantle but also for the mantle of Mars.

  7. Value enhancement of olivine process dust through air classification

    NASA Astrophysics Data System (ADS)

    Kleiv, R. A.

    2012-03-01

    As a result of the production of dry olivine sand products at A/S Olivin's production plant at Åheim in western Norway, an annual quantity of some 20000-30000 t of process dust is produced. The bulk of this material is currently being sold as a slag conditioner at a relatively low price; hence, alternative uses of the process dust are now being sought. Information regarding the chemical composition of the material as a function of particle size facilitates product modifications through exclusion or mixing of individual size fractions. This paper demonstrates how such information can be obtained from air classification experiments when these are combined with chemical analysis of the produced size fractions. The classification and subsequent analysis of the olivine process dust revealed that the finer size fractions had high loss on ignition (LOI) values and were relatively low in MgO when compared with the bulk analysis. Removal of the finer fractions resulted in a remaining coarse product of significantly higher quality. The coarse material could be used as a raw material for further processing; it could be recycled or it could constitute a new product in itself.

  8. Olivine-rich asteroids in the main asteroid belt

    NASA Astrophysics Data System (ADS)

    DeMeo, Francesca E.; Polishook, David; Carry, Benoit; Moskovitz, Nick; Burt, Brian; Binzel, Rick

    2015-11-01

    Olivine-dominated asteroids, classified as A-types with near-infrared spectral measurements are largely thought to be the mantle remnants of disrupted differentiated small bodies. These A-type asteroids hold clues to asteroid differentiation and to the collisional history of those differentiated bodies. Preliminary studies of the abundance and distribution of A-type asteroids were performed by Carvano et al. (2010) and DeMeo & Carry (2013, 2014) using the Sloan Digital Sky Survey (SDSS). To confidently identify these olivine-dominated A-type asteroids, however, near-infrared spectral measurements are needed to identify the distinct broad and deep 1-micron olivine absorption feature. Using the Sloan Digital Sky Survey Moving Object Catalog to select A-type asteroid candidates, we have performed a near-infrared spectral survey of over 70 asteroids with SpeX on the IRTF. We present the abundance and distribution of A-type asteroids throughout the main asteroid belt and compare these results with similar surveys for basalt-rich V-type asteroids (e.g. Moskovitz et al. 2008). This work is supported by NASA under grant number NNX12AL26G issued through the Planetary Astronomy Program.

  9. Measurements of vertical bar Vcb vertical bar and vertical bar Vub vertical bar at BaBar

    SciTech Connect

    Rotondo, M.

    2005-10-12

    We report results from the BABAR Collaboration on the semileptonic B decays, highlighting the measurements of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix elements Vub and Vcb. We describe the techniques used to obtain the matrix element |Vcb| using the measurement of the inclusive B {yields} Xclv process and a large sample of exclusive B {yields} D*lv decays. The vertical bar Vub vertical bar matrix elements has been measured studying different kinematic variables of the B {yields} Xulv process, and also with the exclusive reconstruction of B {yields} {pi}({rho})lv decays.

  10. Blowing in the Wind: I. Velocities of Chondrule-sized Particles in a Turbulent Protoplanetary Nebula

    NASA Technical Reports Server (NTRS)

    Cuzzi, Jeffrey N.; Hogan, Robert C.; Fonda, Mark (Technical Monitor)

    2003-01-01

    Small but macroscopic particles - chondrules, higher temperature mineral inclusions, metal grains, and their like - dominate the fabric of primitive meteorites. The properties of these constituents, and their relationship to the fine dust grains which surround them, suggest that they led an extended existence in a gaseous protoplanetary nebula prior to their incorporation into their parent primitive bodies. In this paper we explore in some detail the velocities acquired by such particles in a turbulent nebula. We treat velocities in inertial space (relevant to diffusion), velocities relative to the gas and entrained microscopic dust (relevant to accretion of dust rims), and velocities relative to each other (relevant to collisions). We extend previous work by presenting explicit, closed-form solutions for the magnitude and size dependence of these velocities in this important particle size regime, and compare these expressions with new numerical calculations. The magnitude and size dependence of these velocities have immediate applications to chondrule and CAI rimming by fine dust, and to their diffusion in the nebula, which we explore separately.

  11. Ancient stardust in fine-grained chondrule dust rims from carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Leitner, Jan; Vollmer, Christian; Floss, Christine; Zipfel, Jutta; Hoppe, Peter

    2016-01-01

    Carbonaceous chondrites are fragments from primitive parent asteroids, which represent some of the most primitive meteorites accessible for laboratory analysis and offer therefore the best opportunity to explore the chemical and physical conditions in the early Solar System. Here, we report the identification of presolar grains, which are circumstellar condensates that date back from before the formation of our Solar System, in fine-grained dust rims around chondrules in carbonaceous chondrites. Average presolar grain abundances in the rims of aqueously altered chondrites (petrologic type 2) are three times higher than in the respective interchondrule matrices, while for the most pristine specimens (petrologic type 3), the opposite is observed. The presence of these grains implies a nebular origin of the rim material, and gives evidence for differing alteration pathways for different reservoirs of fine-grained material found in primitive meteorites. Moreover, our findings indicate formation of the fine-grained rims in the solar nebula prior to parent-body accretion, giving support to accretionary scenarios for parent-bodies in the presence of dust-rimmed chondrules.

  12. Formation of chondrules in magnetic winds blowing through the proto-asteroid belt

    NASA Astrophysics Data System (ADS)

    Salmeron, Raquel; Ireland, Trevor R.

    2012-04-01

    Chondrite meteorites are believed to represent the building blocks of the solar nebula, out of which our solar system formed. They are a mixture of silicate and oxide objects (chondrules and refractory inclusions) that experienced extremely high temperatures, set in a matrix that remained relatively cold. The prevalence of chondrites suggests that they formed through a very general process, related to stellar and planet formation. The nature of this mechanism, however, remains obscure as astronomical observations of star-forming regions suggest a relatively cold environment. Here we show how refractory objects could have been thermally processed in a radially-extended wind, accelerated magnetically from the surfaces of a protostellar disc. In this scenario, refractory precursor aggregates are heated while being lifted in the wind, growing through amalgamation, and eventually becoming heavy enough to drop back to the disc, where they assemble with the matrix. We show that processing at radial distances of about 1-3 AU can produce temperatures in the appropriate regime to melt chondrules and explain their basic properties, while retaining association with the colder material that provides the chondrite matrix. This mechanism is very general, as these energetic winds are commonly associated with stellar formation.

  13. Early Size Distributions of Chondrule Subgroups Overprinted by the Final Accumulation Process of Particle Components in Allende

    NASA Technical Reports Server (NTRS)

    McCain, K. A.; Simon, J. I.; Cuzzi, J. N

    2015-01-01

    Populations of compositionally distinct particles are fundamental components of undifferentiated chondritic meteorites. Many theories explain the formation of chondrites, one class of which includes mechanisms for sorting the component particles in the solar nebula prior to their accretion. Mechanisms include sorting by mass, turbulent concentration, X-winds, and photophoresis, which will produce characteristic distributions of observable properties such as particle size. Distinguishing processes that occur in specific astrophysical environments requires characterization of particle types, which include refractory Ca-Al-rich Inclusions (CAIs) and less-refractory chondrules. Previous investigations of modal abundances of CAIs and chondrules exist, but differences within and between these two groups, both of which are made up of diverse subgroups with different thermal histories and chemical compositions, remain mostly unstudied. The presence of rims, a significant event occurring after the formation of at least some chondrules, have also yet to be considered with respect to sorting. Here we present the sizes of CAIs and chondrules in Allende with attention to the smallest sizes, subgroups, and particle rims.

  14. A Chondrule from the Mokoia (CV3) Chondrite with Anomalously Low 26Mg*: Evidence for a Multi-Stage History-

    NASA Astrophysics Data System (ADS)

    Claydon, J. L.; Elliott, T.; Coath, C. D.; Chen, H. W.; Taylor, C. A.; Russell, S. S.

    2015-07-01

    MC-ICP-MS measurements of Mg isotopes in chondrule MOK13B reveal that it may have formed from low-Al/Mg material that underwent chemical fractionation to increase Al/Mg after decay of 26-Al, or it may sample a region with anomalous Al or Mg isotopes.

  15. On the Lower Limit of Chondrule Cooling Rates: The Significance of Iron Loss in Dynamic Crystallization Experiments

    NASA Technical Reports Server (NTRS)

    Paque, Julie M.; Connolly, Harold C., Jr.; Lofgren, Gary E.

    1999-01-01

    Lofgren (1989) and the further analysis of Lofgren's 1989 experiments by Jones and Lofgren (1993) established that cooling rates as slow as 5 C/hour produced analog textures and major and minor element zoning profiles in minerals, implying that a lower limit on chondrule cooling rate may be approximately 5 C/hour These results, however, are in conflict with those reported by Radomsky and Hewins (1990). In their paper, Radomsky and Hewins (1990) established a lower limit on chondrule cooling rates of I 100 C/hour a factor of 20 higher than that suggested by Jones and Lofgren (1993). The higher cooling rates suggested by Radomsky and Hewins (1990) have gained considerable favor within the meteoritic community largely because it appears more consistent with the preservation of Na in chondrules, which tends to volatilize at the slower cooling rates. In their study, however, Radomsky and Hewins (1990) did not use Pt hang wires that were coated or saturated with Fe. The lack of such techniques likely facilitated Fe loss from their experimental chondrules to the hang wire during formation (Jones and Lofgren, 1993). The effect of Fe loss could produce an inaccurate determination of cooling rates since these rates are largely determined by the Mg-Fe distributions in individual crystals.

  16. Pb-Pb dating of individual chondrules from the CBa chondrite Gujba: Assessment of the impact plume formation model

    NASA Astrophysics Data System (ADS)

    Bollard, Jean; Connelly, James N.; Bizzarro, Martin

    2015-07-01

    The CB chondrites are metal-rich meteorites with characteristics that sharply distinguish them from other chondrite groups. Their unusual chemical and petrologic features and a young formation age of bulk chondrules dated from the CBa chondrite Gujba are interpreted to reflect a single-stage impact origin. Here, we report high-precision internal isochrons for four individual chondrules of the Gujba chondrite to probe the formation history of CB chondrites and evaluate the concordancy of relevant short-lived radionuclide chronometers. All four chondrules define a brief formation interval with a weighted mean age of 4562.49 ± 0.21 Myr, consistent with its origin from the vapor-melt impact plume generated by colliding planetesimals. Formation in a debris disk mostly devoid of nebular gas and dust sets an upper limit for the solar protoplanetary disk lifetime at 4.8 ± 0.3 Myr. Finally, given the well-behaved Pb-Pb systematics of all four chondrules, a precise formation age and the concordancy of the Mn-Cr, Hf-W, and I-Xe short-lived radionuclide relative chronometers, we propose that Gujba may serve as a suitable time anchor for these systems.

  17. Why Do U-Pb Ages of Chondrules and CAIs Have More Spread than Their 26Al Ages?

    NASA Astrophysics Data System (ADS)

    Kita, N. T.; Tenner, T. J.; Ushikubo, T.; Bouvier, A.; Wadhwa, M.; Bullock, E. S.; MacPherson, G. J.

    2015-07-01

    To test 26Al homogeneity in the early solar system, we compare relative 26Al ages of chondrules and CAIs with their absolute U-Pb ages. We will summarize the relevant data and discuss possible causes of discrepancies between the two chronometers.

  18. Si-rich layer formation on olivine surfaces during reaction with water and supercritical carbon dioxide under conditions relevant for geologic carbon storage

    NASA Astrophysics Data System (ADS)

    Johnson, N. C.; Jackson, A.; Maher, K.; Bird, D. K.; Brown, G. E.

    2013-12-01

    The reaction of Mg-silicate minerals (i.e. olivine) with carbon dioxide (CO2) is a promising method for secure, long-term, geologic carbon storage. Several technical challenges must be overcome before implementing mineral carbonation technology on a large scale, one of which is slow reaction kinetics. This study probes surface reaction limitations of olivine carbonation, specifically the formation of a passivating, Si-rich layer on olivine surfaces upon exposure to water and CO2 under sequestration conditions (elevated temperature and pressure). A series of batch reactions were performed at 60C and 100 bar CO2 pressure in Dickson-style rocker bombs, varying the length of reaction and the amount of mixing (rocking). The initial aqueous phase was spiked with 29Si. Fluid samples were taken periodically and analyzed for cation content, alkalinity, and dissolved inorganic carbon. At the end of each experiment, the solid products were analyzed with a Sensitive High Resolution Ion Microprobe Reverse Geometry (SHRIMP-RG) in order to measure the amount of 29Si incorporated into the Si-rich layer on reacted olivine grains. We also cut cross sections of reacted grains from each experiment using a Focused Ion Beam (FIB) which were thinned to <100nm and imaged using Transmission Electron Microscopy (TEM). SHRIMP-RG results show incorporation of 29Si on olivine grain surfaces reacted for 19 days with no mixing, and TEM images of olivine grains from the same experiment show an amorphous, Si-rich layer that is 30nm thick. Similarly, SHRIMP-RG results for olivine grains reacted for 19 days with mixing indicate 29SiO2 precipitation and TEM images reveal a Si-rich layer 60nm thick. In both experiments, EDS (energy dispersive spectroscopy) data show a step change in composition from the bulk rock to the surface layer in addition to the sharp crystalline/amorphous interface visible in the TEM images. Olivine from the unmixed experiment also has a slow decrease in Mg relative to Si before the step change, suggesting that, at least in this experiment, a Si-rich layer precipitated on top of a Mg-depleted layer that formed via a leaching process. SHRIMP-RG data also imply the presence of a precipitated Si-rich layer on top of a leached Si-rich layer, as the 29Si penetration depth is only 25-65% of the total Si-rich layer thickness. The combination of SHRIMP-RG and FIB/TEM analysis leads us to hypothesize that a Si-rich layer forms quickly on olivine surfaces due to preferential Mg removal from the surface (the traditional 'leached' layer), and as the reaction proceeds, amorphous silica reaches saturation in the fluid and precipitates on surfaces inside the reactor (including olivine grains).

  19. Dislocations in olivine: insights from numerical modeling (Invited)

    NASA Astrophysics Data System (ADS)

    Cordier, P.; Metsue, A.; Carrez, P.; Denoual, C.; Mainprice, D.

    2009-12-01

    Olivine (Mg,Fe)2SiO4 is the main constituent of the Earths upper mantle (down to 410 km deep). The rheology of, and convection in, the upper mantle are therefore controlled by the deformation mechanisms of this mineral. Numerous experimental studies have been undertaken leading to a good description of the deformation mechanisms and rheological properties of this mineral at low pressure < 1 GPa. Based on this knowledge, crystallographic preferred orientations in olivine are commonly used to infer fossil mantle flow patterns from seismic anisotropy measurements. However, recent studies have shown that [001] glide is enhanced over [100] glide when pressure increases or when trace amounts of water are dissolved in the crystals(1). These observations have a lot of implications on our understanding of the rheology of the upper mantle and call for a more detailed description of dislocation cores and dynamics. The Peierls-Nabarro (PN) model including ?-surface energies has been used to model dislocation cores in olivine. However, the standard approach, which is restricted to the description of planar cores, which cannot be universally applied in the case of olivine. The occurrence in olivine of long straight screw [001] dislocations raise the question of the origin of lattice friction. A recent study based on full atomistic calculations (using the THB1 potential) has shown that [001] screw dislocations exhibit 3D core spreading(2). This issue must be addressed to understand the [100] to [001] glide crossover and its potential sensitivity to pressure. In this study, a novel method coupling Peierls-Nabarro and element-free Galerkin methods (called PNG) is presented. This technique expands the possibilities of previously reported calculations, in particular in permitting the modeling of 3D dislocation cores. We show that, [100] dislocations may exhibit non-collinear dissociation in the (010) plane. The PNG model confirms the occurrence of 3D core spreading of [001] screw dislocations. The lattice friction is not very sensitive to confining pressure between 0 and 10 GPa. However, [001] dislocations exhibit a complex sensitivity to the applied shear stress tensor with a significant deviation from the Schmid law under pressure. (1) Jung, Mo & Green (2009) Nature Geoscience 2, 73. (2) Carrez, Walker, Metsue & Cordier (2008) Phil. Mag. 88(16), 2477.

  20. Petrogenesis and Nd-, Pb-, Sr-isotope geochemistry of the Cenozoic olivine melilitites and olivine nephelinites (ankaratrites) in Madagascar

    NASA Astrophysics Data System (ADS)

    Melluso, Leone; le Roex, Anton P.; Morra, Vincenzo

    2011-12-01

    The Cenozoic ankaratrites of the Alaotra, Takarindoha-Vatomandry and Votovorona (NE Ankaratra) volcanic fields, Madagascar, range from olivine ( monticellite) melilitites, through olivine-melilite nephelinites to olivine ( leucite) nephelinites. The rocks show significant compositional ranges in their coexisting magmatic minerals (olivine-group minerals, melilite, clinopyroxene, nepheline, leucite, Ba-phlogopite, perovskite, ilmenite, spinels, apatite), and evidence of distinct parental magmas, often in different facies of the same vent. Primitive compositions (high Mg#, Cr and Ni concentrations) are found in each volcanic district, and a few lavas contain mantle xenoliths or xenocrysts. The rocks show enrichment in the most strongly incompatible elements (e.g., Ba and Nb up to 200 times primitive mantle, La/Ybn = 24 to 40), with troughs at K and smooth, decreasing patterns towards the least incompatible elements in mantle-normalized diagrams. The Nd-Pb-Sr isotope geochemistry indicates a marked heterogeneity of the mantle sources of the various districts (e.g., 206Pb/204Pb = 18.68-18.77, 87Sr/86Sr = 0.704011-0.704207 for the Alaotra-Votovorona districts; 206Pb/204Pb = 19.04-19.14, 87Sr/86Sr = 0.703544-0.704017 for the Takarindoha-Vatomandry districts), with significant differences to other Cenozoic mafic volcanic rocks of northern Madagascar. The genesis of the Madagascan ankaratrites is related to rifting events which triggered low-degree partial melting of a garnet peridotite enriched in dolomite and incompatible-element-rich phases, in the lowermost lithosphere. Despite marked geochemical similarities, the source of the Madagascan melilitites bears no isotopic similarity to the HIMU-related sources of melilitites of eastern and southern Africa.

  1. LA-ICP-MS mapping of olivine from the Brahin and Brenham meteorites: Complex elemental distributions in the pallasite olivine precursor

    NASA Astrophysics Data System (ADS)

    McKibbin, Seann J.; O'Neill, Hugh St. C.; Mallmann, Guilherme; Halfpenny, Angela

    2013-10-01

    To investigate the early history of olivine from the Main-Group pallasites Brahin and Brenham, we have spatially mapped their trace-element distributions using laser-ablation inductively-coupled-plasma mass spectrometry (LA-ICP-MS). Brahin olivine interiors contain ˜100-200 μm patches enriched in Cr, Al, Ti, V, Sc and Ga, separated by linear enrichments of P; these structures bear no relation to current crystal morphologies. Rather, cross-cutting relationships suggest they predate olivine-metal mixing. Brenham olivine also has internal variations for these elements. By contrast, Ni and Co concentrations in olivine from both meteorites decrease near crystal margins, as expected for freezing-in of profiles formed during diffusive re-equilibration with metal during cooling. Brenham olivine also has decreasing Al, Cr and Ti near the margin. Correlations between concentrations of Cr and Al exist for individual Brahin olivine grains, but do not hold over multiple grains, indicating a heterogeneous precursor. Al and Ti are correlated over multiple grains in Brahin, interpreted as Ti cations decorating pre-existing Al-defects. In Brenham olivine, similar geochemical trends exist, but the Cr-Al relationship probably represents both grain margin effects and pre-existing internal heterogeneity. The preservation of structure for elements which are normally fast diffusers in olivine hinges on coupled substitutions involving Al, which along with P diffuses much more slowly than most other elements under some conditions. Al concentrations in olivine are low and variable (3-33 ppm) which is inconsistent with crystallisation from a normal silicate melt; Al-in-olivine thermometers indicate that pallasite olivine was formed in a low-temperature environment. Following its delivery to the magma ocean/core-mantle boundary, Al-P systematics were not substantially modified. Assuming diffusivities for Al and P that are similar to Si (since they reside in the same crystallographic site) and temperatures of 1600-1650 K (from the melting point of the metal and the absence of orthopyroxene in pallasites) an upper limit on the residence time of pallasite olivine of ˜1 Ma can be inferred by the persistence of trace element detail over scales of 100 μm. Following the olivine-metal mixing event, homogeneous Ni and Co distributions were modified by diffusion; Cr and V were partially modified; Al and P were essentially unchanged.