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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. Petrography and olivine mineral chemistry of chondrules and inclusions in the Allende meteorite

    NASA Technical Reports Server (NTRS)

    Simon, S. B.; Haggerty, S. E.

    1979-01-01

    The examination of 19 polished-thin sections from a sample of the Allende meteorite reveals that anhedral olivine chondrules (OCs) are the most abundant chondrule type (19.7% of total chondrules + inclusions), followed by recrystallized OCs (7.5%), euhedral OCs (2.9%), glassy/skeletal OCs (2.7%), and barred OCs (2.3%). The most abundant inclusions are those comprised of many small olivine crystals with varying amounts of opaque minerals and glass (31.5%), followed by fine grained inclusions (16.1%) and single olivine crystals (15.7%). Microprobe analyses of olivines show that recrystallized and barred chondrules are the most forsteritic and exhibit relatively narrow compositional ranges, whereas single crystals have the widest range, from Fa sub 0.3 to Fa sub 49.

  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. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Relict olivine grains, chondrule recycling, and implications for the chemical, thermal, and mechanical processing

    E-print Network

    Floss, Christine

    . Louis, MO 63130, USA Received 7 March 2008; accepted in revised form 20 August 2008; available online 11 elements (Cr, Mn, P, Rb, Fe) in olivine. Redox effects are evidenced in various ways, and imply that Fe, Co conditions in the most FeO-poor melts. There is no obvious evidence for systematic variations in olivine

  1. 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 Shi?r 033. BO chondrules experienced a higher degree of melting than porphyritic chondrules, and therefore, it has been hypothesized that they more accurately recorded the O-isotope composition of the gas in chondrule-forming regions. We studied the O-isotope composition of silica as it has been hypothesized to have formed via direct condensation from the gas.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. The Vaguries of Pyroxene Nucleation and the Resulting Chondrule Textures

    NASA Technical Reports Server (NTRS)

    Lofgren, G. E.; Le, L.

    2004-01-01

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

  7. 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.

  8. 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.

  9. Glass-rich chondrules in ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Krot, Alexander N.; Rubin, Alan E.

    1994-01-01

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

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  13. 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.

  14. PETROGRAPHY AND MINERAL CHEMISTRY OF THE CHONDRULE, INCLUSION AND OLIVINE POPULATIONS IN THE TAGISH LAKE CARBONACEOUS CHONDRITE. S. B. Simon1

    E-print Network

    to cause forsterite to sink). The material that floated weighed 0.788 g, and the dense fraction weighed 0 of interest are two occur- rences of olivine with Cr-spinel, an object rich in spinel, forsterite cryptocrystalline. Forsterite aggregates are generally porous objects consisting of anhedral grains of non

  15. Wednesday, March 14, 2007 CHONDRULES AND THEIR FORMATION

    E-print Network

    Rathbun, Julie A.

    ] Isothermal and dynamic crystallization experiments show that relict olivines retain their original 18 OWednesday, March 14, 2007 CHONDRULES AND THEIR FORMATION 1:30 p.m. Crystal Ballroom B Chairs: H. C crystallization. 3:45 p.m. Wasson J. T. * Rubin A. E. Implications of Textural Distributions for Chondrule

  16. 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.

  17. 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

  18. 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.

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

    NASA Technical Reports Server (NTRS)

    2004-01-01

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

  20. Retention of sodium during chondrule melting

    SciTech Connect

    Hewins, R.H. )

    1991-04-01

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

  1. 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].

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

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.; Wasson, John T.

    2006-01-01

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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Oxygen isotope systematics of chondrules in the Allende CV3 chondrite: High precision ion microprobe studies

    E-print Network

    Meyers, Stephen R.

    Oxygen isotope systematics of chondrules in the Allende CV3 chondrite: High precision ion in revised form 21 September 2011 Abstract The oxygen three-isotope systematics of 36 chondrules from. However, most relict olivine grains show oxygen iso- tope ratios that overlap with those in homogeneous

  9. Compound Chondrules fused Cold

    E-print Network

    Hubbard, Alexander

    2015-01-01

    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 ~ 1100K, 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 1025K, 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 900-1025K. In that temperatur...

  10. 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).

  11. 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.

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

    NASA Astrophysics Data System (ADS)

    Jones, R. H.

    1990-06-01

    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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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 ?m 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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 ?56Fe in the cogenetic silicate, which are not found in the chondrules.

  3. 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.

  4. 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.

  5. Chondrule Transport in Protoplanetary Disks

    E-print Network

    Goldberg, Aaron Z; Jacquet, Emmanuel

    2015-01-01

    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 disk model, in order to constrain the chondrule formation events. For a single formation event we are able to match analytical predictions of the memory chondrule and dust populations retain of each other (complementarity), finding that a large mass accretion rate ($\\gtrsim 10^{-7}$~M$_\\odot$~yr$^{-1}$) allows for delays on the order of the disk's viscous timescale between chondrule formation and chondrite accretion. Further, we find older disks to be severely diminished of chondrules, with accretion rates $\\lesssim 10^{-9}$~M$_\\odot$~yr$^{-1}$ for nominal parameters. We then characterize the distribution of chondrule origins in both space and time, as functions of disk parameters and chondrule format...

  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. Magnesium isotopic fractionation in chondrules from the Murchison and Murray CM2 carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Bouvier, Audrey; Wadhwa, Meenakshi; Simon, Steven B.; Grossman, Lawrence

    2013-03-01

    We present high-precision measurements of the Mg isotopic compositions of a suite of types I and II chondrules separated from the Murchison and Murray CM2 carbonaceous chondrites. These chondrules are olivine- and pyroxene-rich and have low 27Al/24Mg ratios (0.012-0.316). The Mg isotopic compositions of Murray chondrules are on average lighter (?26Mg ranging from -0.95‰ to -0.15‰ relative to the DSM-3 standard) than those of Murchison (?26Mg ranging from -1.27‰ to +0.77‰). Taken together, the CM2 chondrules exhibit a narrower range of Mg isotopic compositions than those from CV and CB chondrites studied previously. The least-altered CM2 chondrules are on average lighter (average ?26Mg = -0.39 ± 0.30‰, 2SE) than the moderately to heavily altered CM2 chondrules (average ?26Mg = -0.11 ± 0.21‰, 2SE). The compositions of CM2 chondrules are consistent with isotopic fractionation toward heavy Mg being associated with the formation of secondary silicate phases on the CM2 parent body, but were also probably affected by volatilization and recondensation processes involved in their original formation. The low-Al CM2 chondrules analyzed here do not exhibit any mass-independent variations in 26Mg from the decay of 26Al, with the exception of two chondrules that show only small variations just outside of the analytical error. In the case of the chondrule with the highest Al/Mg ratio (a type IAB chondrule from Murchison), the lack of resolvable 26Mg excess suggests that it either formed >1 Ma after calcium-aluminum-rich inclusions, or that its Al-Mg isotope systematics were reset by secondary alteration processes on the CM2 chondrite parent body after the decay of 26Al.

  8. Zoned chondrules in Semarkona: Evidence for high-and low-temperature processing

    USGS Publications Warehouse

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

    2002-01-01

    At least 15% of the low-FeO chondrules in Semarkona (LL3.0) have mesostases that are concentrically zoned in Na, with enrichments near the outer margins. We have studied zoned chondrules using electron microprobe methods (x-ray mapping plus quantitative analysis), ion micropobe analysis for trace elements and hydrogen isotopes, cathodoluminescence imaging, and transmission electron microscopy in order to determine what these objects can tell us about the environment in which chondrules formed and evolved. Mesostases in these chondrules are strongly zoned in all moderately volatile elements and H (interpreted as water). Calcium is depleted in areas of volatile enrichment. Titanium and Cr generally decrease toward the chondrule surfaces, whereas Al and Si may either increase or decrease, generally in opposite directions to one another; Mn follows Na in some chondrules but not in others; Fe and Mg are unzoned. D/H ratios increase in the water-rich areas of zoned chondrules. Mesostasis shows cathodoluminescence zoning in most zoned chondrules, with the brightest yellow color near the outside. Mesostasis in zoned chondrules appears to be glassy, with no evidence for devitrification. Systematic variations in zoning patterns among pyroxene- and olivine-rich chondrules may indicate that fractionation of low- and high-Ca pyroxene played some role in Ti, Cr, Mn, Si, Al, and some Ca zoning. But direct condensation of elements into hot chondrules, secondary melting of late condensates into the outer portions of chondrules, and subsolidus diffusion of elements into warm chondrules cannot account for the sub-parallel zoning profiles of many elements, the presence of H2O, or elemental abundance patterns. Zoning of moderately volatile elements and Ca may have been produced by hydration of chondrule glass without devitrification during aqueous alteration on the parent asteroid. This could have induced structural changes in the glass allowing rapid diffusion and exchange of elements between altered glass and surrounding matrix and rim material. Calcium was mainly lost during this process, and other nonvolatile elements may have been mobile as well. Some unzoned, low-FeO chondrules appear to have fully altered mesostasis.

  9. 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.

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2004-04-01

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

  13. 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.

  14. 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.

  15. 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.

  16. Chondrules and Nebular Shocks

    E-print Network

    E. I. Chiang

    2002-05-16

    Beneath the fusion-encrusted surfaces of the most primitive stony meteorites lies not homogeneous rock, but a profusion of millimeter-sized igneous spheres. These chondrules, and their centimeter-sized counterparts, the calcium-aluminum-rich inclusions, comprise more than half of the volume fraction of chondritic meteorites. They are the oldest creations of the solar system. Their chemical composition matches that of the solar photosphere in all but the most volatile of elements, reflecting their condensation from the same pristine gas that formed the sun. In this invited editorial, we review the nebular shock wave model of Desch and Connolly (Meteoritics and Planetary Science 2002, 37, 183) that seeks to explain their origin. While the model succeeds in reproducing the unique petrological signatures of chondrules, the origin of the required shock waves in protoplanetary disks remains a mystery. Outstanding questions are summarized, with attention paid briefly to competing models.

  17. Chondrules and Nebular Shocks

    E-print Network

    Chiang, E I

    2002-01-01

    Beneath the fusion-encrusted surfaces of the most primitive stony meteorites lies not homogeneous rock, but a profusion of millimeter-sized igneous spheres. These chondrules, and their centimeter-sized counterparts, the calcium-aluminum-rich inclusions, comprise more than half of the volume fraction of chondritic meteorites. They are the oldest creations of the solar system. Their chemical composition matches that of the solar photosphere in all but the most volatile of elements, reflecting their condensation from the same pristine gas that formed the sun. In this invited editorial, we review the nebular shock wave model of Desch and Connolly (Meteoritics and Planetary Science 2002, 37, 183) that seeks to explain their origin. While the model succeeds in reproducing the unique petrological signatures of chondrules, the origin of the required shock waves in protoplanetary disks remains a mystery. Outstanding questions are summarized, with attention paid briefly to competing models.

  18. 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.

  19. Chondrules in LL3 Cluster Chondrites: Evidence for Interaction of Chondrule Melts with Nebular Gas

    NASA Astrophysics Data System (ADS)

    Metzler, K.; Pack, A.

    2015-07-01

    Cluster chondrites probably formed by hot chondrule accretion. They show evidence for interaction of chondrule melts with surrounding gas, namely oxygen isotope exchange and chemical modification of (type I) chondrules due to open system behaviour.

  20. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

  2. 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

  3. 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.

  4. 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.

  5. 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.

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

    E-print Network

    Beitz, Eike; Mathieu, Romain; Pack, Andreas; Hezel, Dominik C

    2011-01-01

    We developed an experimental setup to test the hypothesis that accretionary dust rims around chondrules formed in the solar nebula at elevated temperatures. Our experimental method allows us to form dust rims around chondrule-analogs while being levitated in an inert-gas flow. We used micrometer-sized powdered San Carlos olivine to accrete individual dust particles onto the chondrule-analog at a temperature of 1100{\\deg}C. The resulting dust-rims were analyzed by means of two different techniques: one sample was investigated with non-destructive micro computer tomography, the other with a scanning electron microscope. Both methods give very similar results for the dust-rim structure and a mean dust-rim porosity of 60 percent, demonstrating that both methods are equally well suited for sample analysis. The chondrule-analog's bulk composition has no measurable effect on the accretion efficiency of the dust. We measured the chemical composition of chondrule-analog and dust-rim to check whether elemental exchange...

  7. 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.

  8. 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 (?{sup 25}Mg), indicating that the correlated variability was imparted by a volatility-controlled process (evaporation/condensation). The mass-independent {sup 26}Mg composition (?{sup 26}Mg*) of chondrules is consistent with single stage formation from an initially homogeneous magnesium reservoir if the observed ?{sup 25}Mg variability was generated by non-ideal Rayleigh-type evaporative fractionation characterized by a ? value of 0.5142, in agreement with experimental work. The magnitude of the mass-dependent fractionation (?300 ppm) is significantly lower than that suggested by the increase in {sup 27}Al/{sup 24}Mg values, indicating substantial suppression of isotopic fractionation during evaporative loss of Mg, possibly due to evaporation at high Mg partial pressure. Thus, the Mg-isotope data of skeletal chondrules from HH237 are consistent with their origin as melts produced in the impact-generated plume of colliding planetesimals. The inferred ?{sup 26}Mg* value of –3.87 ± 0.93 ppm for the CB parent body is significantly lower than the bulk solar system value of 4.5 ± 1.1 ppm inferred from CI chondrites, suggesting that CB chondrites accreted material comprising an early formed {sup 26}Al-free component.

  9. 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.

  10. 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.

  11. Chondrule formation in lightning discharges

    NASA Technical Reports Server (NTRS)

    Horanyi, M.

    1994-01-01

    Chondrules represent a significant mass fraction of primitive meteorites. These millimeter-sized glassy droplets appear to be the products of intensive transient heating events. Their size distribution, chemical and mineral composition, texture, isotope composition suggest that chondrules were produced as a result of short-duration melting followed by rapid cooling of solid precursor particles. Gas-dynamics heating, magnetic reconnection, and electrostatic discharges are thought to be the leading candidates to explain chondrule formation. In this paper we summarize our recent theoretical progress on the effects of 'lightning' in the early solar system and also report on preliminary results from our laboratory experiments. Differential settling of various sized dust particles toward the midplane of the nebula is suspected to build large-scale charge separations that episodically relax via the electric breakdown of the nebular gas. The electrostatic discharge os analogous to lightning in the Earth's atmosphere.

  12. 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.

  13. 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.

  14. 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 ? ? 0.1, and possibly even for solar abundances because of 'sandblasting' by finer dust. A flow with ? ? 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.

  15. The formation conditions of chondrules and chondrites

    USGS Publications Warehouse

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

    2008-01-01

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

  16. 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.

  17. Tungsten diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Van Orman, J. A.

    2014-03-01

    Diffusion of tungsten has been characterized in synthetic forsterite and natural olivine (Fo90) under dry conditions. The source of diffusant was a mixture of magnesium tungstate and olivine powders. Experiments were prepared by sealing the source material and polished olivine under vacuum in silica glass ampoules with solid buffers to buffer at NNO or IW. Prepared capsules were annealed in 1 atm furnaces for times ranging from 45 min to several weeks, at temperatures from 1050 to 1450 °C. Tungsten distributions in the olivine were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for W diffusion in forsterite: D=1.0×10-8exp(-365±28 kJ mol/RT) m s Diffusivities for the synthetic forsterite and natural Fe-bearing olivine are similar, and tungsten diffusion in olivine shows little dependence on crystallographic orientation or oxygen fugacity. The slow diffusivities measured for W in olivine indicate that Hf-W ages in olivine-metal systems will close to diffusive exchange at higher temperatures than other chronometers commonly used in cosmochronology, and that tungsten isotopic signatures will be less likely to be reset by subsequent thermal events.

  18. 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.

  19. Aluminian Low-Ca Pyroxene in a Ca-Al-rich Chondrule from the Semarkona Meteorite

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.

    2006-01-01

    A Ca-AI-rich chondrule (labeled G7) from the Semarkona LL3.0 ordinary chondrite (OC) consists of 73 vol% glassy mesostasis, 22 vol% skeletal forsterite. 3 vol% fassaite (i.e., Al-Ti diopside), and 2 vol% Al-rich, low-Ca pyroxene. The latter phase, which contains up to 16.3 wt% A1203, is among the most AI-rich, low-Ca pyroxene grains ever reported. It is inferred that 20% of the tetrahedral sites and 13% of the octahedral sites in this grain are occupied by Al. Approximately parallel optical extinction implies that the Al-rich, low-Ca pyroxene grains are probably orthorhombic, consistent with literature data that show that A1203 stabilizes the orthoenstatite structure relative to protoenstatite at low pressure. The order of crystallization in the chondrule was forsterite, AI-rich low-Ca pyroxene, and fassaite; the residual liquid vitrified during chondrule quenching. Phase relationships indicate that, for a G7-composition liquid at equilibrium, spinel and anorthite should crystallize early and orthopyroxene should not crystallize at all. The presence of AI-rich orthopyroxene in G7 is due mainly to the kinetic failure of anorthite to crystallize; this failure was caused by quenching of the G7 precursor droplet. Aluminum preferentially enters the relatively large B tetrahedra of orthopyroxene; because only one tetrahedral size occurs in fassaite, this phase contains higher mean concentrations of Al2O3 than the Al-rich orthopyroxene (17.8 and 14.7 wt%, respectively). Chondrule G7 may have formed by remelting an amoeboid olivine inclusion that entered the OC region of the solar nebula during an episode of chondrule formation.

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

    NASA Technical Reports Server (NTRS)

    Lauretta, Dante S.

    2004-01-01

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

  1. 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.

  2. Metallic Chondrules in NWA1390 (H3-6): Clues to Their History from Metallic Cu

    NASA Technical Reports Server (NTRS)

    LaBlue, A. R.; Lauretta, D. S.

    2004-01-01

    A recent study of ordinary chondrites suggests that many long-recognized shock indicators in olivine and pyroxene minerals may be erased by post-shock annealing. Therefore, the presence of other indicators of shock, which can not be erased by subsequent heating, are important to fully characterize the history of chondritic meteorites. One such proposed indicator is metallic Cu, which occurs in at least 2/3 of ordinary chondrites. Here we present a comparative study of two metallic chondrules in the NWA1390 ordinary chondrite, both of which contain appreciable Cu in the Fe,Ni metal phase and one that is partially rimmed by metallic Cu.

  3. 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.

  4. 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.

  5. 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:

  6. 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.

  7. 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 (Bjurböle chondrite), we found a dependence of the photophoretic force on chondrule size.

  8. Multiplicity of chondrule heating events and the coarsening of chondrule textures

    NASA Technical Reports Server (NTRS)

    Wasson, John T.

    1993-01-01

    Our studies of compound chondrules show that most chondrules experienced at least two thermal events that produced appreciable amounts of melt. I suggest that chondrules were subjected to a hierarchy of brief heating events, the number increasing exponentially with decreasing intensity, and that some of intermediate intensity deposited enough heat to partially melt mesostasis glass and promote the growth of mafic mineral grains. This scenario can account for textures that require improbably low monotonic cooling rates in laboratory simulations, and also for the rarity of glassy chondrule textures despite the ease with which these are produced in the laboratory.

  9. 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.

  10. The quasi-universality of chondrule size as a constraint for chondrule formation models

    NASA Astrophysics Data System (ADS)

    Jacquet, Emmanuel

    2014-04-01

    Primitive meteorites are dominated by millimeter-size silicate spherules called chondrules. The nature of the high-temperature events that produced them in the early Solar System remains enigmatic. Beside their thermal history, one important clue is provided by their size which shows remarkably little variation (less than a factor of 6 for the mean chondrule radius of most chondrites) despite the extensive range of ages and heliocentric distances sampled. It is however unclear whether chondrule size is due to the chondrule melting process itself, or has been simply inherited from the precursor material, or yet results from some sorting process. I examine these different possibilities in terms of their analytical size predictions. Unless the chondrule-forming “window” was very narrow, radial sorting can be excluded as a size-determining process because of the large variations it would predict. Molten planetesimal collision or impact melting models, which derive chondrules from the fragmentation of larger melt bodies, would likewise predict too much size variability by themselves; more generally any size modification during chondrule formation is limited in extent by evidence from compound chondrules and the considerable compositional variability of chondrules. Turbulent concentration would predict a low size variability but lack of evidence of any accretion bias in carbonaceous chondrites may be difficult to reconcile with any form of local sorting upon agglomeration. Growth by sticking (especially if bouncing-limited) of aggregates as chondrule precursors would yield limited variations of their final radius in space and time, and would be consistent with the relatively similar size of other chondrite components such as refractory inclusions. This suggests that the chondrule-melting process(es) simply melted such nebular aggregates with little modification of mass.

  11. Artificial meteor ablation studies: Olivine

    NASA Technical Reports Server (NTRS)

    Blanchard, M. B.; Cunningham, G. G.

    1973-01-01

    Artificial meteor ablation was performed on a Mg-rich olivine sample using an arc-heated plasma of ionized air. Experimental conditions simulated a meteor traveling about 12 km/sec at an altitude of 70 km. The mineral content of the original olivine sample was 98% olivine (including traces of olivine alteration products) and 2% chromite. Forsterite content of the original olivine was Fo-89. After ablation, the forsterite content had increased to Fo-94 in the recrystallized olivine. In addition, lamella-like intergrowths of magnetite were prevalent constituents. Wherever magnetite occurred, there was an increase in Mg and a corresponding decrease in Fe for the recrystallized olivine. The Allende fusion crust consisted of a recrystallized olivine, which was more Mg-rich and Fe-deficient than the original meteorite's olivine, and abundant magnetite grains. Although troilite and pentlandite were the common opaque mineral constituents in this meteorite, magnetite was the principal opaque mineral found in the fusion crust.

  12. 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.

  13. 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

  14. 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.

  15. 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 .

  16. 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.

  17. Use of a CO2 laser to prepare chondrule-like spherules from supercooled molten oxide and silicate droplets.

    NASA Technical Reports Server (NTRS)

    Nelson, L. S.; Blander, M.; Keil, K.; Skaggs, S. R.

    1972-01-01

    Chondrule-like spherules were formed from individual freely falling subcooled droplets of alumina, enstatite, forsterite, enstatite-albite and forsterite-albite mixtures that had been melted with a focused continuous CO2 laser beam. Their textures (rimmed, excentro-radial, barred, glassy) are strikingly similar to those of many meteoritic chondrules. It is suggested that the phenomena associated with rapid crystallization from the supercooled melt are responsible for the various textures observed in the artificial spherules as well as in similar meteoritic chondrules. It is suggested that the textures observed would also result from rapid crystallization of relatively slowly cooling molten droplets that may have been produced in larger scale events, including condensation from a nebula of solar composition and solidification in an ambient medium of high temperature.

  18. 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.

  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. The Protostellar Jet Model of Chondrule Formation

    E-print Network

    Kurt Liffman; Michael J. I. Brown

    2006-02-17

    A chondrule formation theory is presented where the chondrule formation zone is located within 0.1 AU of the protosun. This hot, optically thick, inner zone of the solar accretion disk is coincident with the formation region of the protosolar jet. The model assumes that particles, ranging in diameter from 1 micron to 1 cm, can be ejected from the inner-accretion disk by the jet flow, and that the angular momentum of this material is sufficient to eject it from the jet flow. Given these assumptions, any material so ejected, will fly across the face of the accretion disk at speeds greater than the escape velocity of the system. This material can only be recaptured through the action of gas drag. Such a capture process naturally produces aerodynamic size sorting of chondrules and chondrule fragments, while the ejection of refractory dust provides a possible explanation for the observed complementarity between matrix and chondrules. This transfer of material will result in the loss of angular momentum from the upper atmosphere of the outer accretion disk and thereby facilitate the accretion of matter onto the protosun.

  2. 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.

  3. 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.

  4. "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.

  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. Chondrules, matrix and coarse-grained chondrule rims in the Allende meteorite - Origin, interrelationships, and possible precursor components

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.; Wasson, John T.

    1987-01-01

    INAA and broad-beam EMPA are used to determine the bulk compositions of 20 chondrules, 13 coarse-grained chondrule rims, and one nonporphyritic CV chondrule (NPCVC) from CV3 Allende (and of one NPCVC each from Leoville and Vigarano). The data are presented in extensive tables and graphs and analyzed in detail. Five probable chondrule precursor components are deduced, and the solar-nebula processes giving rise to them (and probably to the coarse-grained rims as well) are discussed. It is suggested that the formation of the rimmed chondrules involved nebular reheating in space, after the accretion of dusty coatings.

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

    E-print Network

    Cosmogenic neon in grains separated from individual chondrules: Evidence of precompaction exposure-mail: jdas@syr.edu (Received 30 April 2010; revision accepted 03 November 2012) Abstract­Neon was measured

  9. 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 ?m, 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

  10. 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.

  11. 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.

  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. 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.

  14. 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.

  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. Helium Diffusion in Olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2011-12-01

    Diffusion of helium has been characterized in natural Fe-bearing olivine (~Fo90) and synthetic forsterite. Polished, oriented slabs of olivine were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted olivine were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950°C: D = 3.91x10-6exp(-159 ± 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700°C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in olivine. Diffusion in Fe-bearing olivine (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm experiments, indicating that the results reported here can be reasonably applied to modeling He transport in the upper mantle. The insensitivity of He diffusion to pressure over the investigated range of conditions suggests that compression of the mineral lattice is not sufficient to significantly influence migration of the relatively small helium atoms, which likely diffuse via crystal interstices. The He diffusivities in this work are generally consistent with results from the study of Futagami et al. (1993), who measured He diffusion in natural olivine by outgassing 4He implanted samples, and with the diffusivities measured by bulk-release of 4He and 3He by Shuster et al. (2003), but are about 2 orders of magnitude slower than the recent findings of Tolstikhin et al. (2010) and Blard et al. (2008) . An up-temperature extrapolation of our data also show reasonable agreement with the higher-temperature measurements of Hart (1984). Blard et al. (2008) GCA 72, 3788-3803; Futagami et al. (1993) GCA 57, 3177-3194; Hart (1984) EPSL 70, 297-302; Shuster et al.( 2003) EPSL 217, 19-32; Tolstikhin et al. (2010) GCA 74, 1436-1447

  17. 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.

  18. 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.

  19. 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.

  20. Electrical conduction in olivine

    SciTech Connect

    Schock, R. N.; Duba, A. G.; Shankland, T. J.

    1989-05-10

    This paper reports detailed measurements of electrical conductivitysigma and thermoelectric effect /ital S/ in the mineral olivine and in syntheticforsterite as functions of temperature in the range from 1000/degree/ to1500 /degree/C and oxygen partial pressure in the range from 10/sup /minus/10/ to10/sup 4/ Pa. The two most striking observations are strong conductivityanisotropy in forsterite and a sign change in /ital S/ in olivine at 1390 /degree/C.These results are interpreted to show that both materials have mixed ionic andextrinsic electronic conduction under these conditions. On the basis ofthese interpretations, we infer that forsterite conductivity is dominatedby electronic conduction in the /ital a/ and /ital b/ directions and probably bymovement involving magnesium vacancies in the /ital c/ direction, wherefar higher /ital P//sub O/sub 2//-independent conductivity is observed. Olivineappears to show mixed conduction under all the circumstances observed; at low temperature, electron holes dominate but are superseded bymagnesium vacancies at high temperatures./copyright/ American Geophysical Union 1989

  1. 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.

  2. Fe/Mn in olivine of carbonaceous meteorites

    NASA Technical Reports Server (NTRS)

    Steele, Ian M.

    1993-01-01

    Olivines in primitive meteorites show a range of Fe/Mn both within one grain and among grains suggesting that they have recorded changing conditions during or after growth. Because olivine should be an early forming phase, Fe/Mn is used here to infer these earliest conditions. Initial Fe/Mn in cores of isolated, euhedral forsterite in both C2 and C3 meteorites ranges from 25 to 35 but differs at grain edge. Murchison (C2) forsterites show Fe/Mn approaching 1.0 at the grain edge while Ornans Fe/Mn is near 60 at grain edge. These values are lower than the matrix Fe/Mn for both meteorites and the distinct difference in zoning profile indicates different processes operating during and after grain growth. The Fe/Mn of bulk samples from a particular source such as the Moon is nearly constant. Individual samples show variation suggesting that there is some fractionation of Mn from Fe. Minerals have their individual ranges of Fe/Mn which has been used to recognize different types of olivine within one meteorite. Extreme values of Fe/Mn below 1.0 occur in forsterite from some IDP's, UOC matrix, and C1 meteorites. There are apparently no detailed studies of Fe/Mn variation within single olivine grains. Forsterite grains in C2 and C3 carbonaceous chondrites show complex zoning, and the nearly pure forsterites (Fo greater than approximately 99.5) have high levels of some minor elements including Ti, Al, V, and Sc. There is disagreement on the original source of these grains and both chondrule and vapor growth have been proposed. In addition, there is clear evidence that diffusion has affected the outer margins but in some cases the whole grain. Within the cores, the FeO range is limited, and if growing under constant conditions, the Fe/Mn should be near constant as there is little fractionation of Mn from Fe by forsterite. Additionally, there are apparently no co-crystallizing phases as evidenced by a lack of common inclusions in the forsterites. These observations are now followed by analyses of isolated olivine grains in C2 and C3 meteorites.

  3. 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.

  4. 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 1350°C 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.

  5. Contemporaneous formation of chondrules in distinct oxygen isotope reservoirs

    E-print Network

    Meyers, Stephen R.

    the regional oxygen isotope heterogeneity in the solar nebula over the duration of chondrule formation. A few). Assuming homogeneous distribu- tion of 26 Al in the early Solar System, these initial 26 Al/27 Al ratiosContemporaneous formation of chondrules in distinct oxygen isotope reservoirs Takayuki Ushikubo a

  6. 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.

  7. 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.

  8. Replacement of olivine by serpentine in the carbonaceous chondrite Nogoya (CM2)

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    Coarse (chondrule and isolated) olivine in some CM chondrites is replaced by serpentine in both centripetal and meshwork replacement textures. Locally preserved textures formed by partial replacement of coarse olivine by serpentine in the carbonaceous chondrite Nogoya (CM2) establish unique associations between each individual mass of serpentine and the specific olivine from which that serpentine formed. Electron probe microanalyses show that the composition of serpentine replacing coarse olivine is uniform throughout all analyzed volumes of Nogoya, and is independent of the composition of the olivine being replaced. If, as previously proposed, late-stage alteration fluids were Mg-rich because Fe-source minerals were depleted in earlier stages, then the uniform Mg-rich composition of the serpentine replacing large silicate grains during advanced stages of alteration may indicate diffusional homogenization of the aqueous solutions over progressively larger spatial scales, enabled by long timescales and previously proposed stagnant or slow-moving fluids. The range of olivine compositions replaced in Nogoya is even larger than previously reported from ALH 81002 (CM2). This militates against hypotheses of strong primary-mineral control on the compositions of alteration products, at least at advanced stages of alteration. The serpentine formed by olivine replacement in Nogoya is more magnesian than the counterpart serpentine replacing all anhydrous primary silicates in ALH 81002. This intermeteorite heterogeneity of replacement-serpentine composition between ALH 81002 and Nogoya indicates that the aqueous solutions in which the olivine-serpentine replacement reactions occurred were of different compositions in the two different CM parent-body volumes sampled by ALH 81002 and Nogoya. The more magnesian character of serpentines in Nogoya than in ALH 81002 indicates that the Nogoya aqueous-alteration environment was even more highly evolved toward Mg-rich solutions than the environment indicated by the composition of the serpentine in ALH 81002. Persistence of primary-silicate remnants within centripetal and meshwork serpentine indicates that either the aqueous alteration episodes in the parent-body volumes represented by individual meteorites were too short to allow complete replacement of olivine by serpentine, or one or more reactants (most likely water) were completely consumed before the coarse primary silicate was completely replaced. Seemingly incompatible arguments for and against primary-mineral control of serpentine composition during CM chondrite alteration may be reconciled by considering the different grain sizes and reaction timescales that likely existed in different textural settings.

  9. 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.

  10. 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.

  11. 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 150°C 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.

  12. Chondrules and Isolated Grains in the Fountain Hills Bencubbinite

    NASA Technical Reports Server (NTRS)

    LaBlue, A. R.; Lauretta, D. S.; Killgore, M.

    2004-01-01

    The Fountain Hills (FH) meteorite was recently classified as a Bencubbin-like (CB(sub a)) chondrite, which are part of the CR clan [1]. The FH O-isotopic composition is indistinguishable from CB(sub a) chondrites. Metal and silicate compositions are consistent with the CB(sub a) classification. Significant differences between FH and the other CB(sub a) chondrites were noted. These include abundant porphyritic chondrules and complete lack of sulfide minerals. We are furthering this investigation by analyzing silicate chondrules and isolated grains in FH to determine more about its composition, thermal history, and implications for chondrule formation in the early solar system.

  13. Chondrule Formation via Impact Jetting Triggered by Planetary Accretion

    E-print Network

    Hasegawa, Yasuhiro; Matsumoto, Yuji; Oshino, Shoichi

    2015-01-01

    Chondrules are one of the most primitive elements that can serve as a fundamental clue as 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 corresponds 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$^{-1}$. The previous simulations show 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 by 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-p...

  14. 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.

  15. Oxygen Isotopic Analyses of Water in Bjurböle Matrix and Chondrules

    NASA Astrophysics Data System (ADS)

    Nunn, M.; Thiemens, M. H.

    2011-12-01

    Past oxygen isotopic analyses of the Bjurböle meteorite have been limited to whole rock and chondrule studies. We present here the first oxygen isotopic measurements of water contained in the matrix and chondrules of the L4 equilibrated ordinary chondrite Bjurböle. Water was extracted by vacuum pyrolysis from samples of separated matrix and chondrules from Bjurböle. A new, low volume, ultra low blank system was built specifically for these measurements. Each fraction was pumped overnight on a vacuum line to remove as much adsorbed terrestrial water as possible before heating step-wise to 150, 350, 600 and 1000°C. While heating, evaporated volatiles were collected in a liquid nitrogen cold trap. Water was quantitatively converted to molecular oxygen with bromine pentafluoride. Isotopic abundances were measured on a double-collecting isotope ratio mass spectrometer. The ? 17O values obtained from direct fluorination of Bjurböle chondrules and whole rock and UV laser probe analyses of individual Bjurböle chondrules all cluster around one [1, 2]. Compared to these data, water extracted from the Bjurböle matrix and chondrules is isotopically light (? 17O = 0.5 and 0.7, respectively), presumably reflecting different equilibration histories of water and oxygen-bearing minerals in each component. Additionally, the proximity of ? 17O values of water extracted at lower temperatures to zero indicates low-temperature heating is necessary to remove all adsorbed terrestrial water and obtain the true isotopic signature of extraterrestrial water.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

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

    E-print Network

    Meyers, Stephen R.

    Primordial oxygen isotope reservoirs of the solar nebula recorded in chondrules in Acfer 094; available online 16 May 2012 Abstract Highly precise and accurate ion microprobe analyses of oxygen three that chondrules preserve evidence for oxygen isotope heterogeneity in chondrule-forming regions of the solar

  18. Two chondrule groups each with distinctive rims in Murchison recognized by cathodoluminescence

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    Two groups of chondrules in the Murchison CM chondrite, which have previously been identified on the basis of FeO in the chondrule grains, are readily identified from cathodoluminescence (CL) and belong to those of the ordinary chondrite group A and B chondrules of Sears et al. (1992a). All chondrules are surrounded by fine-grained rims containing forsterite with bright red CL, but on group A chondrules an outer thin rim grades into a much thicker rim, with a lower density of forsterite grains, which in turn grades into the central chondrule. Group B chondrules have only the thin outer rim with a high density of small forsterite grains. This is the first time an unequivocal correlation has been observed between chondrule rim thickness and the composition of the object on which the rim is located. We suggest that while all objects in the meteorite (group B chondrules, refractory inclusions, mineral and chondrule fragments, clasts) acquired a very thin rim during processing in a wet regolith, the thick rims on group A chondrules were formed by aqueous alteration of precursor metal- and sulfide-rich rims which are a characteristic of group A chondrules in ordinary chondrites.

  19. Supernova olivine from cometary dust

    NASA Technical Reports Server (NTRS)

    Messenger, Scott; Keller, Lindsay P.; Lauretta, Dante S.

    2005-01-01

    An interplanetary dust particle contains a submicrometer crystalline silicate aggregate of probable supernova origin. The grain has a pronounced enrichment in 18O/16O (13 times the solar value) and depletions in 17O/16O (one-third solar) and 29Si/28Si (<0.8 times solar), indicative of formation from a type II supernova. The aggregate contains olivine (forsterite 83) grains <100 nanometers in size, with microstructures that are consistent with minimal thermal alteration. This unusually iron-rich olivine grain could have formed by equilibrium condensation from cooling supernova ejecta if several different nucleosynthetic zones mixed in the proper proportions. The supernova grain is also partially encased in nitrogen-15-rich organic matter that likely formed in a presolar cold molecular cloud.

  20. Formation of spinel from olivine

    NASA Astrophysics Data System (ADS)

    Liu, Zongwen; Kelly, Patrick M.; Drennan, John; Mora, Peter; Kanda, Hisao

    2004-03-01

    High-resolution transmission electron microscopy (HRTEM) was used to study the olivine to spinel transformation. HRTEM structure images of Mg2GeO4 olivine deformed under a pressure of 6 GPa at 600 °C clearly show that a shear mechanism dominates the transformation. The transformation is not a nucleation and growth mechanism. It also differs in certain crucial aspects from the type of martensitic transformation proposed before. During the transformation, it is a shear movement that brings the oxygen anions to their positions in the spinel structure. An edge dislocation following each shear then puts the cations in their spinel sites. The Burgers' vector of each dislocation is perpendicular to the anion shear direction.

  1. 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.

  2. THERMAL HISTORIES OF CHONDRULES IN SOLAR NEBULA SHOCKS

    SciTech Connect

    Morris, M. A.; Desch, S. J.

    2010-10-20

    Chondrules are important early Solar System materials that can provide a wealth of information on conditions in the solar nebula, if their formation mechanism can be understood. The theory most consistent with observational constraints, especially thermal histories, is the so-called shock model, in which chondrules were melted in solar nebula shocks. However, several problems have been identified with previous shock models. These problems all pertained to the treatment of the radiation field, namely, the input boundary condition to the radiation field, the proper treatment of the opacity of solids, and the proper treatment of molecular line cooling. In this paper, we present the results of our updated shock model, which corrects for the problems listed above. Our new hydrodynamic shock code includes a complete treatment of molecular line cooling due to H{sub 2}O. Previously, shock models including line cooling predicted chondrule cooling rates exceeding 10{sup 5} K hr{sup -1}. Contrary to these expectations, we have found that the effect of line cooling is minimal; after the inclusion of line cooling, the cooling rates of chondrules are 10-1000 K hr{sup -1}. The reduction in the otherwise rapid cooling rates attributable to line cooling is due to a combination of factors, including buffering due to hydrogen recombination/dissociation, high column densities of water, and backwarming. Our model demonstrates that the shock model for chondrule formation remains consistent with observational constraints.

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

    USGS Publications Warehouse

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

    1987-01-01

    The compositions of the interiors and abraded surfaces of 7 chondrules from Semarkona (LL3.0) were measured by neutron activation analysis. For nonvolatile elements, the lithophile and siderophile element abundance patterns in the surfaces are generally similar to those in the corresponding interiors. Siderophile and chalcophile concentrations are much higher in the surfaces, whereas lithophile concentrations are similar in both fractions. Most of the similarities in lithophile patterns and some of the similarities in siderophile patterns between surfaces and interiors may reflect incomplete separation of the fractions in the laboratory, but for 3 or 4 chondrules the siderophile resemblance is inherent, implying that the surface and interior metal formed from a single precursor assemblage. Metal and sulfide-rich chondrule rims probably formed when droplets of these phases that migrated to the chondrule surface during melting were reheated and incorporated into matrix-like material that had accreted onto the surface. The moderately-volatile to volatile elements K, As and Zn tend to be enriched in the surfaces compared with other elements of similar mineral affinity; both enrichments and depletions are observed for other moderately volatile elements. A small fraction of chondrules experienced fractional evaporation while they were molten. ?? 1987.

  4. 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].

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

  6. 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.

  7. Photophoretic forces on chondrules in drop tower experiments

    NASA Astrophysics Data System (ADS)

    Hesse, A.; Teiser, J.; Wurm, G.

    2011-12-01

    Studies of meteoritic and cometary materials give evidence for radial mixing of solid material within the early solar system. Among other transport mechanisms, photophoresis is a proposed mechanism for radial material transport in protoplanetary disks. Within this study, the photophoretic motion of chondrules in microgravity is investigated in drop tower studies. Chondrules form the meteorite Bjurböle were exposed to an intense laser beam. The acceleration due to photophoresis was observed and tracked with two cameras. The experimental results give evidence that photophoresis indeed is an efficient transport mechanism for chondrules and other small particles in the solar nebula. The measured values for the photophoretic force correspond well to the results of earlier studies and show clearly, that the models for particle transport by photophoresis are in agreement with the experimental data.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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 120º triple junctions. A few coarse (25-50 ?m-sized) patches of plagioclase with 2-18 ?m-thick diopside rinds occur in several places just beneath the rim. The occurrence of 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.

  13. 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.

  14. 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.

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

    E-print Network

    Dullemond, Cornelis Petrus; Johansen, Anders

    2015-01-01

    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 which solidify to become chondrules. Pre-melting of the planetesimals by radioactive decay of 26Al would help producing 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 a 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 e...

  16. 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

  17. Opaque Minerals in the Matrix of the Bishunpur (LL3.1) Chondrite: Constraints on the Chondrule Formation Environment

    NASA Technical Reports Server (NTRS)

    Lauretta, D. S.; Buseck, P. R.; Zega, T. J.

    2001-01-01

    The chemistry and mineralogy of a group of opaque mineral assemblages in the matrix of the Bishunpur LL3.1 ordinary chondrite provide insight into the nebular environment in which they formed. The assemblages consist of a kamacite (Fe,Ni) core that is rimmed by troilite (FeS) and fayalite (Fe2Si04). Accessory phases in the rims include silica (Si02), chromite (FeCr204), whitlockite (Ca3(P04)2), maricite (FeNaP04), magnetite (Fe304), and tetrataenite (FeNi). We suggest that the metal melted in and equilibrated with an igneous chondrule under high- temperature, reducing conditions. In this environment the molten alloys incorporated varied amounts of Si, Ni, P, Cr, and Co, depending on the oxygen fugacity and temperature of the melt. Some of the metal was subsequently expelled from the chondrule interiors into the surrounding nebular gas. As the temperature dropped, the alloy solidified and volatile elements corroded the metal. The main reaction products were troilite and fayalite. Thermodynamic equilibrium calculations are used to constrain the conditions under which these two phases can form simultaneously in the solar nebula. Kinetic factors are used to place a lower limit on the formation temperature. We determine that the metal corroded between 1173 and 1261 K at a total pressure in the range of 1025.0 to 1024.1 bars and a dust/gas ratio of 302 to 355 x relative to solar composition. These conditions are consistent with our model that the metal corroded in a dust- rich region of the solar nebula that was cooling after a chondrule formation event.

  18. Bar Fight Bar

    E-print Network

    Hacker, Randi; Tsutsui, William

    2006-11-29

    Broadcast Transcript: Annoyed with your boss? Got a bone to pick with your spouse? Angry at that sales clerk who ignored you? Come on down to The Rising Sun Anger Release Bar and beat those suckers up. Well, not those ...

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

    E-print Network

    Johansen, Anders; 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 run-away accretion of chondrules within ~3 Myr, forming planetary embryos up to Mars sizes 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 mm-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disk life time outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is...

  20. Crystallization kinetics of olivine-phyric shergottites

    NASA Astrophysics Data System (ADS)

    Ennis, Megan E.; McSween, Harry Y.

    2014-08-01

    Crystal size distribution (CSD) and spatial distribution pattern (SDP) analyses are applied to the early crystallizing phases, olivine and pyroxene, in olivine-phyric shergottites (Elephant moraine [EET] 79001A, Dar al Gani [DaG] 476, and dhofar [Dho] 019) from each sampling locality inferred from Mars ejection ages. Trace element zonation patterns (P and Cr) in olivine are also used to characterize the crystallization history of these Martian basalts. Previously reported 2-D CSDs for these meteorites are re-evaluated using a newer stereographically corrected methodology. Kinks in the olivine CSD plots suggest several populations that crystallized under different conditions. CSDs for pyroxene in DaG 476 and EET 79001A reveal single populations that grew under steady-state conditions; pyroxenes in Dho 019 were too intergrown for CSD analysis. Magma chamber residence times of several days for small grains to several months for olivine megacrysts are calculated using the CSD slopes and growth rates inferred from previous experimental data. Phosphorus imaging in olivines in DaG 476 and Dho 019 indicate rapid growth of skeletal, sector-zoned, or patchy cores, probably in response to delayed nucleation, followed by slow growth, and finally rapid dendritic growth with back-filling to form oscillatory zoning in rims. SPD analyses indicate that olivine and pyroxene crystals grew or accumulated in clusters rather than as randomly distributed grains. These data reveal complex solidification histories for Martian basalts, and are generally consistent with the formation at depth of olivine megacryst cores, which were entrained in ascending magmas that crystallized pyroxenes, small olivines, and oscillatory rims on megacrysts.

  1. 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.; Nesvorný, 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.

  2. 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

  3. 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

  4. 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.

  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. An experimental investigation of olivine morphology

    NASA Technical Reports Server (NTRS)

    Donaldson, C. H.

    1976-01-01

    Results are reported for a morphological study of olivine and an experimental investigation performed to determine the degrees of supercooling and the cooling rates necessary to crystallize particular morphologies. Ten arbitrary categories of three-dimensional olivine crystal shape are identified: polyhedral, granular, hopper, chain, lattice, plate, branching, radiate, feather, and swallow-tail. The morphological study establishes that equant and tabular crystals are the common shapes of olivine, nonequant crystals are elongate parallel to the a or c axis, and skeletal crystals result when a particular form is missing or only partially developed. In the experiment, olivine crystals were grown by melting rock samples above their liquidus temperatures before initiating crystallization. The results show that olivine morphology changes systematically as a function of the degree of melt supercooling, the melt cooling rate, and the normative olivine and water contents of the melt. It is also found that each shape has a specific range of temperature stability which is essentially independent of melt composition.

  7. 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/.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. The origin and history of the metal and sulfide components of chondrules

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    Instrumental and radiochemical neutron activation analysis is used to determine the concentrations of 14 siderophile and other nonlithophilic elements in 31 chondrules from the extremely unequilibrated chondrite Semarkona. The results are presented in tables and graphs, characterized in detail, and compared with the results obtained for lithophile elements in the same samples by Grossman and Wasson (1983). The elements studied are found to be significantly more fractionated than the lithophile elements, with variations in chondrule/whole-rock abundances of up to a factor of 1000, a mean ratio of 0.2, and differences between Ni-rich and Ni-depleted chondrules. It is argued that the metal and sulfides in the chondrules represent the composition of the solar nebula before chondrule formation and already contained the siderophile and chalcophile elements, although some Fe was contained in silicates along with Ni, Co, Au, Ge and Se. The segregation of metals during a molten stage is considered of minor importance.

  15. Derivation of a heterogeneous lithic fragment in the Bovedy L-group chondrite from impact-melted porphyritic chondrules

    NASA Technical Reports Server (NTRS)

    Rubin, A. E.; Keil, K.; Taylor, G. J.; Ma, M.-S.; Schmitt, R. A.; Bogard, D. D.

    1981-01-01

    Results are presented of petrographic, compositional and dating analyses of a light-colored lithic fragment in the L-group Bovedy meteorite that has a composition different from that of the host chondrite. Polished thin sections of the lithic fragment, host, and the fragment-host boundary were examined microscopically and analyzed by electron microprobe, metallic Ni-Fe, and instrumental neutron activation techniques; chips of the fragment were also used for Ar-39/Ar-40 dating and oxygen isotope analyses. The poikilitic textures, olivine, low-Ca pyroxene and kamacite composition and low Na2O, K2O and P2O5 contents of the fragment indicate that it represents a solidified, slightly fractionated impact melt formed from a source rich in porphyritic chondrules. A progressive increase on MgO content across the fragment is accounted for by the heterogeneous nucleation of MgO-rich phases. The Ar data indicate that the Bovedy lithic fragment and its host were partly degassed of radiogenic Ar less than 0.94 billion years ago, probably due to shock. The data are consistent with a cooling rate of about 5 C/million years through 500 C, which must have resulted from the burial of the assemblage beneath insulating material on the parent body at depths of at least several km.

  16. Diffusion of highly charged cations in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.; Liang, Y.

    2012-12-01

    Diffusion of tungsten, titanium and phosphorus have been measured in natural iron-bearing olivine (~Fo90) and synthetic forsterite. Experiments were run under buffered conditions (with iron-wustite or Ni-NiO buffers) in 1-atm furnaces. The sources of diffusant for experiments were MgWO4 for tungsten diffusion, Mg2TiO4 for Ti diffusion, and AlPO4 for P diffusion; in all cases these compounds were pre-reacted at high temperature with Mg2SiO4 or Fe-bearing olivine prior to diffusion anneals. Samples were placed with the source materials in noble metal or silica capsules, which were sealed under vacuum in silica glass ampoules with solid buffers. Rutherford backscattering spectrometry (RBS) was used to measure depth profiles for all sets of experiments; measurements of P were also made with Nuclear Reaction Analysis using the 31P(?,p)34S reaction. These new data suggest marked differences among diffusivities of these cations, with titanium diffusion faster than diffusion of tungsten, but slower than diffusion of phosphorus over the conditions investigated. Diffusivities of all of these elements appear significantly slower than those of divalent cations in olivine. These results will be discussed in context with extant diffusion data for major, trace and minor elements in olivine. The effects of oxygen fugacity and olivine composition on diffusion, and potential implications for diffusion mechanisms will also be considered.

  17. 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.

  18. 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.

  19. 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

  20. 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.

  1. Olivine, and the Origin of Kimberlite N. T. ARNDT1

    E-print Network

    Tommasi, Andrea

    Olivine, and the Origin of Kimberlite N. T. ARNDT1Ã , M. GUITREAU2 , A.-M. BOULLIER3 , A. LE ROEX4 ADVANCE ACCESS PUBLICATION JANUARY 12, 2010 Two types of olivine occur in kimberlites from Greenland or polycrystal- line aggregates that are a common constituent of many kimberlites. Olivine compositions

  2. Chondrule formation by repeated evaporative melting and condensation in collisional debris clouds around planetesimals

    NASA Astrophysics Data System (ADS)

    Ruzicka, Alex

    2012-12-01

    A synthesis of previous work leads to a model of chondrule formation that involves periodic melting of dispersed dust in debris clouds that were generated by collisions between chondritic planetesimals. I suggest that chondrules formed by the passage of nebular shock waves through these dust clumps, which temporarily surrounded disrupted planetesimals. Type I chondrules formed by more intense evaporative heating of fewer particles in tenuous clumps, or at the edges of dense clumps, and type II chondrules formed by less intense evaporative heating of more particles deeper within dense clumps. Chondrules reaccreted by self-gravity into the planetesimals, mixing with less heated dust and rock. This process of disruption, melting, and reaccretion could have repeated many times. In this way, chondrite components of various origins and thermal histories could remain preserved in planetesimals as a distinctive mix of materials for extended periods of time, while still allowing for a repetitive melting process that converted some of the planetesimal debris into chondrules. I also suggest that during chondrule formation, the inner solar nebula gas was evolving by the gradual incorporation and heating of icy bodies depleted in 16O, causing a general increase in gaseous ?17O with time in most places, especially close to the "snow line." In this model, early formed type I chondrules in C chondrites with lower ?17O values were produced inside the snow line, and later formed type I and type II chondrules in C and O chondrites with higher ?17O values were created nearer the snow line after it had moved closer to the young Sun.

  3. Serpentinization of sintered olivine during seawater percolation experiments

    NASA Astrophysics Data System (ADS)

    Luquot, Linda; Andreani, Muriel; Godard, Marguerite; Gouze, Philippe; Gibert, Benoit

    2010-05-01

    Hydration of the mantle lithosphere exposed along detachment faults at slow-spreading ridges leads to strong modification of rock rheological, geophysical and geochemical properties, and to the emission of large amounts of H2 and CH4, and of complex carbon molecules that support primitive ecosystems. The sustainability and efficiency of this hydration process, serpentinisation, and of associated reactions, requires penetration and renewal of fluids at the mineral-fluid interface. However, precipitation of material along flow paths will affect porosity and permeability that, in turn, will have feedbacks effects on the reactions. It is thus necessary to investigate the sustainability of flow paths, and the evolution of reaction rates for a dynamic system under representative conditions. We investigate these processes by percolation experiments carried out under P, T representative conditions, using the ICARE Microlab experimental bench. We present the preliminary results of seawater percolation within samples of sintered San Carlos olivine. The experiments were carried out under a confined pressure of 190 bars and a temperature of 190° C and water flow was set at a constant specific discharge of 0.06 ml/h.. The experiments were performed at very slow flow rate to be more representative of natural systems. ICARE Microlab allows measuring continuously the permeability changes during the percolation experiment and sampling the brine at the outlet of the sample. After 20 days of experiments, poorly crystallized serpentine and iron oxide formed within the micro-cracks while permeability strongly decreases. Such rapid precipitation of serpentine results in clogging of fluid paths. The chemical composition of the outlet fluid is dominated by Si and is depleted in Mg relative to stoechiometric dissolution of olivine during the whole experiment suggesting that brucite possibly formed. SEM and AEM/TEM are used to characterize the reactive interfaces and the neoformed materials.

  4. 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.

  5. Chondrule-like objects and brown glasses in howardites

    NASA Technical Reports Server (NTRS)

    Olsen, Edward J.; Fredriksson, Kurt; Rajan, Sundar; Noonan, Albert

    1990-01-01

    Chondrulelike objects and brown glasses were analyzed in the howardites, Bununu, Malvern, Monticello, Pavlovka, and Yamato 7308. The objects are very similar to chondrules in ordinary and carbonaceous chondrites. Like the brown glasses, the chondrulelike objects could have been produced by impact melting that left some crystalline nuclei, followed by a slower cooling rate than for the glasses. Alternatively, these objects are chondrules implanted from chondrite impactors. They are, however, without rims or any adhering matrix. The brown glasses appear to represent melting of average regolithic surface material, except for Monticello and Y7308, both of which have some siliceous glasses. The siliceous glasses could not have been produced by vapor fractionation but by melting of differentiated lithologies such as fayalitic granites. Impact mechanics indicates that howardites with abundant brown glasses came from an asteroid larger than Vesta (greater than 400 km radius), upon which impacts occurred at relative velocities of up to 5 km/s. Howardites with little or no brown glasses came from a smaller parent body. It is concluded that at least two parent bodies are likely sources for the basaltic achondrites.

  6. 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.

  7. Homogeneous distribution of 26Al in the solar system from the Mg isotopic composition of chondrules.

    PubMed

    Villeneuve, Johan; Chaussidon, Marc; Libourel, Guy

    2009-08-21

    The timing of the formation of the first solids in the solar system remains poorly constrained. Micrometer-scale, high-precision magnesium (Mg) isotopic analyses demonstrate that Earth, refractory inclusions, and chondrules from primitive meteorites formed from a reservoir in which short-lived aluminum-26 (26Al) and Mg isotopes were homogeneously distributed at +/-10%. This level of homogeneity validates the use of 26Al as a precise chronometer for early solar system events. High-precision chondrule 26Al isochrons show that several distinct chondrule melting events took place from approximately 1.2 million years (My) to approximately 4 My after the first solids condensed from the solar nebula, with peaks between approximately 1.5 and approximately 3 My, and that chondrule precursors formed as early as 0.87(-0.16)(+0.19) My after. PMID:19696348

  8. 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.

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

    E-print Network

    Meyers, Stephen R.

    Terminal particle from Stardust track 130: Probable Al-rich chondrule fragment from comet Wild 2 D. INTRODUCTION Thousands of grains were collected by the Stardust spacecraft during its encounter with comet 81P

  10. 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.

  11. 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.

  12. 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.

  13. Mechanisms of electrical conductivity in olivine

    SciTech Connect

    Schock, R.N.; Duba, A.G.; Shankland, T.J.

    1984-01-01

    Data on the electrical conductivity and the thermoelectric effect in single crystals indicate that the charge conduction mechanism in pure magnesium forsterite is electrons. The concentration of electrons can be varied by controlling the number of oxygen vacancies through manipulation of the oxygen pressure. For iron bearing olivine, the conduction mechanism is by electron holes localized on an iron ion. Since iron strongly affects the creep process as well, oxidation of iron is probably accompanied by the production of magnesium vacancies. 15 references.

  14. The I-Xe Record of Long Equilibration in Chondrules from the Unnamed Antarctic Meteorite L3/LL3

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    The unnamed Antarctic meteorite studied here is of primitive chondritic type L3 or LL3, probably of grade 3.5 - 3.6. Detailed mineralogical and SEM analyses have revealed the existence of three distinct chondrule types in this meteorite. Both iron-rich and some iron-poor chondrules are present with variably recrystallized matrices or mesostases reflecting variable equilibration. Patchy equilibration of chondrule mesostases suggests thermal metamorphism after accretion. Additional information is included in the original extended abstract.

  15. 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.

  16. Shock-Wave Heating Model for Chondrule Formation: Prevention of Isotopic Fractionation

    E-print Network

    Hitoshi Miura; Taishi Nakamoto

    2006-07-03

    Chondrules are considered to have much information on dust particles and processes in the solar nebula. It is naturally expected that protoplanetary disks observed in present star forming regions have similar dust particles and processes, so study of chondrule formation may provide us great information on the formation of the planetary systems. Evaporation during chondrule melting may have resulted in depletion of volatile elements in chondrules. However, no evidence for a large degree of heavy-isotope enrichment has been reported in chondrules. In order to meet this observed constraint, the rapid heating rate at temperatures below the silicate solidus is required to suppress the isotopic fractionation. We have developed a new shock-wave heating model taking into account the radiative transfer of the dust thermal continuum emission and the line emission of gas molecules and calculated the thermal history of chondrules. We have found that optically-thin shock waves for the thermal continuum emission from dust particles can meet the rapid heating constraint, because the dust thermal emission does not keep the dust particles high temperature for a long time in the pre-shock region and dust particles are abruptly heated by the gas drag heating in the post-shock region. We have also derived the upper limit of optical depth of the pre-shock region using the radiative diffusion approximation, above which the rapid heating constraint is not satisfied. It is about 1 - 10.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Experimental Deformation of Olivine Single Crystals at Mantle Pressures and Temperatures

    SciTech Connect

    Raterron, P.; Amiguet, E; Chen, J; Li, L; Cordier, P

    2008-01-01

    Deformation experiments were carried out in a deformation-DIA high-pressure apparatus (D-DIA) on oriented San Carlos olivine single crystals, at pressure (P) ranging from 3.5 to 8.5 GPa, temperature (T) from 1373 to 1673 K, and in poor water condition. Oxygen fugacity (fO2) was maintained within the olivine stability field and contact with enstatite powder ensured an orthopyroxene activity aopx = 1. Two compression directions were tested, promoting either [1 0 0] slip alone or [0 0 1] slip alone in (0 1 0) crystallographic plane, here called, respectively, a-slip and c-slip. Constant applied stress (s) and specimen strain rates ({bar {var_epsilon}}) were monitored in situ using time-resolved X-ray synchrotron diffraction and radiography, respectively. Transmission electron microscopy (TEM) investigation of run products revealed that dislocation creep was responsible for sample deformation. Comparison of the obtained high-P deformation data with the data obtained at room-P by Bai et al. [Bai, Q., Mackwell, S.L., Kohlstedt D.L., 1991, High-temperature creep of olivine single crystals. 1. Mechanical results for buffered samples, Journal of Geophysical Research, 96, 2441-2463] - on identical materials deformed at comparable T-sefO2-aopx conditions - allowed quantifying the P effect on a-slip and c-slip rheological laws. A slip transition with increasing pressure, from dominant a-slip to dominant c-slip, is documented. a-slip appears sensitive to pressure, which translates into the high activation volume V*{sub a} = 12 {+-} 4 cm{sup 3}/mol in the corresponding rheological law, while pressure has little effect on c-slip with V*{sub c} = 3 {+-} 4 cm{sup 3}/mol. These results may explain the discrepancy between olivine low-P and high-P deformation data which has been debated in the literature for more than a decade.

  4. A scanning electron microscope study of olivine crystal surfaces

    NASA Technical Reports Server (NTRS)

    Olsen, E. J.; Grossman, L.

    1974-01-01

    SEM photographs were taken of euhedral olivine grains from the Murchison C2 chondrite and several terrestrial and lunar occurrences. In general, the crystal faces of the meteorite grains are rough and uneven, with irregular growth patterns. They are very similar to crystal faces on terrestrial olivine grains that formed by sublimation from a vapor phase. They are very different from the relatively smooth and featureless surfaces of magmatic olivine crystals that precipitated from igneous melts. Qualitatively, the surface morphology of the crystal supports the contention that many euhedral crystals of olivine in C2 meteorites condensed from a gas phase.

  5. 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.

  6. 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.

  7. 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.

  8. Jail Bars

    Atmospheric Science Data Center

    2013-04-22

    ... This effect is greatest when the spacecraft is on the night side of the planet. On February 12, 2000, before the instrument cover ... Jail Bars location:  First Light Images region:  Before the covers were opened ...

  9. 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.

  10. 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.

  11. THE ORIGIN OF BROWN OLIVINE IN MARTIAN DUNITE C. M. Pieters1

    E-print Network

    Hiroi, Takahiro

    Carlos Olivine 45-90 µm [EAC] Human Eye Sensitivity Chassigny Olivine Coarse RGB NWA2737 Olivine 45 the visible through the near-infrared part of the spectrum are shown to be due to nano- phase metallic iron

  12. 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).

  13. 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).

  14. 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.

  15. 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.

  16. Young chondrules in CB chondrites from a giant impact in the early Solar System.

    PubMed

    Krot, Alexander N; Amelin, Yuri; Cassen, Patrick; Meibom, Anders

    2005-08-18

    Chondrules, which are the major constituent of chondritic meteorites, are believed to have formed during brief, localized, repetitive melting of dust (probably caused by shock waves) in the protoplanetary disk around the early Sun. The ages of primitive chondrules in chondritic meteorites indicate that their formation started shortly after that of the calcium-aluminium-rich inclusions (4,567.2 +/- 0.7 Myr ago) and lasted for about 3 Myr, which is consistent with the dissipation timescale for protoplanetary disks around young solar-mass stars. Here we report the 207Pb-206Pb ages of chondrules in the metal-rich CB (Bencubbin-like) carbonaceous chondrites Gujba (4,562.7 +/- 0.5 Myr) and Hammadah al Hamra 237 (4,562.8 +/- 0.9 Myr), which formed during a single-stage, highly energetic event. Both the relatively young ages and the single-stage formation of the CB chondrules are inconsistent with formation during a nebular shock wave. We conclude that chondrules and metal grains in the CB chondrites formed from a vapour-melt plume produced by a giant impact between planetary embryos after dust in the protoplanetary disk had largely dissipated. These findings therefore provide evidence for planet-sized objects in the earliest asteroid belt, as required by current numerical simulations of planet formation in the inner Solar System. PMID:16107841

  17. 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.

  18. Meteorite Ablation Rinds as Analogs for the Origin of Rims on Chondrules

    NASA Astrophysics Data System (ADS)

    Bunch, T.; Paque, J. M.; Reynolds, R.; Podolak, M.; Prialnik, D.

    1993-07-01

    Conventional wisdom holds that UOC chondrule rims were formed in the nebula by dust accretion. Following the accretion stage, some investigators suggest that these porous rims were subjected to thermal alteration that ranged from sintering to melting [e. g., 1-3]. To understand the evolutionary history of chondrules we need to ask: (1) What nebular mechanism(s) concentrated the dust for rapid accretion? (Addressed in a companion paper at this meeting [4]). (2) What thermal event(s) welded or melted the dust? (3) Is this dust solely responsible for the rim composition, or are some rims composed, in part, of the parent chondrule? Production and/or modification of rims during atmospheric entry onto a parent body is a scenario that is testable by examination of ablation rinds produced on meteorites during entry into Earth's atmosphere. Comparison of ablation rind features with opaque rims on UOC chondrules will indicate whether this is a viable method for the production of chondrule rims. Terrestrial ablation rinds on UOCs and carbonaceous chondrites have been examined both texturally and chemically. Ablation rinds have these distinct characteristics: (1) The bulk composition of the rind is a reflection of the bulk chemistry of the host object, including Na, K, and P, but with the exception of much lower S. (2) Boundaries between unmelted bulk meteorite and rind silicates are physically sharp over distances of microns, similar to boundaries between rims and their chondrules. However, compositional transition zones extend inward from the boundaries for 10s of microns. (3) Melted meteorite matrix in the rind is compositionally similar to unmelted matrix and is texturally and chemically similar to rims. (4) Mineral texture and chemistry at chondrule/rim and meteorite/rind interfaces indicate significant thermal processing has occurred. For example, sulfides show high concentrations of included, more refractory phases at the melt interface with a corresponding loss of S. Overall, the comparison of ablation rinds with rims strongly suggests that opaque rims formed by melting of dusty accretion mantles. This melting event may have continued into the outer margins of host chondrules, or may be restricted to the accreted dust. SEM examination of the boundaries between chondrules and rims indicate that both cases probably occur. The major and minor element composition of opaque rims is similar to "accretionary" rims on objects in CM meteorites [5]. We suggest that both types of rims were formed from the same basic anhydrous dust, although CM rims acquired more O^16-bearing component than UOCs. From here, their evolutionary paths diverged: Opaque rims were thermally processed and CM rims were aqueously altered. Calculations of rim melting due to entry into a transient atmosphere of low scale height [6] indicate that encounter velocities in the range 2-4 km/sec are sufficient to melt the outer parts of chondrules. If the thermal conductivity of porous accretionary rims is as low as that of powdered chondrite [7], gas dynamic deceleration can produce totally or partially melted rims on chondrules without melting the chondrule itself. References: [1] Rubin A. and Wasson J. (1987) GCA, 51, 1923-1937. [2] Podolak et al. (1990) Icarus, 84, 254-260. [3] Bunch T. et al (1991) Meteoritics, 26, 326. [4] Cuzzi J. and Dobrovolskis A. (1993) this meeting. [5] Metzler et al. (1992) GCA, 56, 2873- 2898. [6] Podolak et al. (1993) Icarus, in press. [7] Wechsler A. E. and Glaser P. E. (1965) Icarus, 4, 335.

  19. Ringwoodite lamellae in olivine: Clues to olivine–ringwoodite phase transition mechanisms in shocked meteorites and subducting slabs

    PubMed Central

    Chen, Ming; Goresy, Ahmed El; Gillet, Philippe

    2004-01-01

    The first natural occurrence of ringwoodite lamellae was found in the olivine grains inside and in areas adjacent to the shock veins of a chondritic meteorite, and these lamellae show distinct growth mechanism. Inside the veins where pressure and temperature were higher than elsewhere, ringwoodite lamellae formed parallel to the {101} planes of olivine, whereas outside they lie parallel to the (100) plane of olivine. The lamellae replaced the host olivine from a few percent to complete. Formation of these lamellae relates to a diffusion-controlled growth of ringwoodite along shear-induced planar defects in olivine. The planar defects and ringwoodite lamellae parallel to the {101} planes of olivine should have been produced in higher shear stress and temperature region than that parallel to the (100) plane of olivine. This study suggests that the time duration of high pressure and temperature for the growth of ringwoodite lamellae might have lasted at least for several seconds, and that an intracrystalline transformation mechanism of ringwoodite in olivine could favorably operate in the subducting lithospheric slabs in the deep Earth. PMID:15479764

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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°-290°C (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.

  6. 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.

  7. 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.

  8. 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.; Prelevi?, 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 ?m sub-rounded crystals and (ii) groundmass olivines, < 100 ?m 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 ?m) 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.%).

  9. 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).

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. THE FORMATION OF PHYLLOSILICATES IN CHONDRULE FORMING SHOCK WAVES. F. J. Ciesla,1

    E-print Network

    Cohen, Barbara Anne

    THE FORMATION OF PHYLLOSILICATES IN CHONDRULE FORMING SHOCK WAVES. F. J. Ciesla,1 D. S. Lauretta,1. In this study we investigate phyllosilicate reaction kinetics after passage of an adiabatic shock wave in an icy region of the solar nebula. Shock Waves: The thermal evolution of silicates encountering a shockwave

  15. SHOCK WAVES AND TYPE II PO CHONDRULES A. V. Fedkin1

    E-print Network

    immediately behind the shock front experience more energetic collisions, causing much higher peak Ts precursor material of radius 0.5 mm with liq- uidus T 1950±15K (depending on its composition when it reaches, however, chondrule precursor material subjected to shock waves under conditions favoring formation

  16. 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.

  17. 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>?0.6×10-7 in the early Solar System, and among these very few (3) have higher excesses implying Fe60/Fe56?7×10-7 (Mishra et al., 2010; Mishra and Goswami, 2014; Telus et al., 2012). At variance, multi-collector inductively coupled plasma mass spectrometer studies of bulk samples and mineral separates from differentiated meteorites, angrites, achondrites, and chondrules suggest a low abundance of 60Fe/56Fe of ?1.4×10-8 which would rule out the need for an external seeding of the early Solar with stellar 60Fe (Quitté et al., 2011; Tang and Dauphas, 2012). Two Semarkona chondrules and one Efremovka chondrule analyzed in the present study have mass fractionation corrected excess of up to ?75 permil (‰) and give 60Fe isochrons with initial 60Fe/56Fe ratios of (7.8±3.7)×10-7, (3.8±1.6)×10-7, and (2.2±1.1)×10-7 (2?), for Efremovka Ch 1, Semarkona Ch 12, and Semarkona Ch J5 respectively. The higher values of 60Fe/56Fe ratios seen in the chondrules of these least altered meteorites samples concur with and lend greater credence to the suggestion of a massive star as the source of 60Fe, and possibly of other short-lived nuclides, to the early Solar System. However, no definitive explanation (e.g. sample bias, effects of metamorphism, 60Fe heterogeneity) to the apparent disagreement with studies of bulk chondrules and chondrule fragments has been found.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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 200°C and 300°C, 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.

  5. 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.

  6. Galapagos Plume Source Lithology : Implications from Olivine Phenocryst Compositions C. Vidito ,C. Herzberg and D.Geist

    E-print Network

    Geist, Dennis

    83844, USA. Ca (ppm) Mn (ppm) Fe/Mn (ppm) Ni (ppm) Mg-Number Mg-Number Olivines Peridotite Derivative Magmas (13-20% MgO) Olivines Peridotite Derivative Magmas (8-13% MgO) Olivines Peridotite Primary Magmas (8-38% MgO) Olivine Phenocryst Composition Fertile Peridotite Source (3.45% CaO) Olivine Phenocryst

  7. Olivine and pyroxene from the mantle of asteroid 4 Vesta

    NASA Astrophysics Data System (ADS)

    Lunning, Nicole G.; McSween, Harry Y.; Tenner, Travis J.; Kita, Noriko T.; Bodnar, Robert J.

    2015-05-01

    A number of meteorites contain evidence that rocky bodies formed and differentiated early in our solar system's history, and similar bodies likely contributed material to form the planets. These differentiated rocky bodies are expected to have mantles dominated by Mg-rich olivine, but direct evidence for such mantles beyond our own planet has been elusive. Here, we identify olivine fragments (Mg# = 80-92) in howardite meteorites. These Mg-rich olivine fragments do not correspond to an established lithology in the howardite-eucrite-diogenite (HED) meteorites, which are thought to be from the asteroid 4 Vesta; their occurrence in howardite breccias, combined with diagnostic oxygen three-isotope signatures and minor element chemistry, indicates they are vestan. The major element chemistry of these Mg-rich olivines suggests that they formed as mantle residues, in crustal layered intrusions, or in Mg-rich basalts. The trace element chemistry of these Mg-rich olivines supports an origin as mantle samples, but other formation scenarios could be possible. Interpreted as mantle samples, the range of Mg-rich olivine compositions indicates that Vesta's structure differs from that predicted by conventional models: Vesta has a chemically heterogeneous mantle that feeds serial magmatism. The range of olivine major element chemistries is consistent with models of an incompletely melted mantle such as in the model proposed by Wilson and Keil (2013) rather than a whole-mantle magma ocean for Vesta. Trace element chemistries of Mg-rich pyroxenes (Mg# = 85-92) provide support that some of these pyroxenes may represent initial fractional crystallization of mantle partial melts.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Grain boundary diffusion in olivine (Invited)

    NASA Astrophysics Data System (ADS)

    Marquardt, K.; Dohmen, R.

    2013-12-01

    Olivine is the main constituent of Earth's upper mantle. The individual mineral grains are separated by grain boundaries that have very distinct properties compared to those of single crystals and strongly affect large-scale physical and chemical properties of rocks, e.g. viscosity, electrical conductivity and diffusivity. Knowledge on the grain boundary physical and chemical properties, their population and distribution in polycrystalline materials [1] is a prerequisite to understand and model bulk (rock) properties, including their role as pathways for element transport [2] and the potential of grain boundaries as storage sites for incompatible elements [3]. Studies on selected and well characterized single grain boundaries are needed for a detailed understanding of the influence of varying grain boundaries. For instance, the dependence of diffusion on the grain boundary structure (defined by the lattice misfit) and width in silicates is unknown [2, 4], but limited experimental studies in material sciences indicate major effects of grain boundary orientation on diffusion rates. We characterized the effect of grain boundary orientation and temperature on element diffusion in forsterite grain boundaries by transmission electron microscopy (TEM).The site specific TEM-foils were cut using the focused ion beam technique (FIB). To study diffusion we prepared amorphous thin-films of Ni2SiO4 composition perpendicular to the grain boundary using pulsed laser deposition. Annealing (800-1450°C) leads to crystallization of the thin-film and Ni-Mg inter-diffuse into the crystal volume and along the grain boundary. The inter-diffusion profiles were measured using energy dispersive x-ray spectrometry in the TEM, standardized using the Cliff-Lorimer equation and EMPA measurements. We obtain volume diffusion coefficients that are comparable to Ni-Mg inter-diffusion rates in forsterite determined in previous studies at comparable temperatures, with similar activation energies. Grain boundary diffusion perpendicular to the dislocation lines of the small angle grain boundaries proved to be about an order of magnitude faster than volume diffusion, whereas diffusion in high angle grain boundaries is several orders of magnitude faster. We will discuss the variation of element diffusion rates with grain boundary orientation and the temperature- and/or time-induced transition from one diffusion regime to the next regime. This is done using time series experiments and two-dimensional grain boundary diffusion simulations. Finally, we will debate the differences between our data and other data sets that result from different experimental setups, conditions and analyses.

  13. Exposing metal and silicate charges to electrical discharges: Did chondrules form by nebular lightning?

    E-print Network

    C. Güttler; T. Poppe; J. T. Wasson; J. Blum

    2007-12-04

    In order to investigate the hypothesis that dust aggregates were transformed to meteoritic chondrules by nebular lightning, we exposed silicatic and metallic dust samples to electric discharges with energies of 120 to 500 J in air at pressures between 10 and 10^5 Pa. The target charges consisted of powders of micrometer-sized particles and had dimensions of mm. The dust samples generally fragmented leaving the major fraction thermally unprocessed. A minor part formed sintered aggregates of 50 to 500 micrometer. In a few experiments melt spherules having sizes smaller than 180 micrometer in diameter (and, generally, interior voids) were formed; the highest spherule fraction was obtained with metallic Ni. Our experiments indicate that chondrule formation by electric current or by particle bombardment inside a discharge channel is unlikely.

  14. Exposing metal and silicate charges to electrical discharges: Did chondrules form by nebular lightning?

    E-print Network

    Güttler, C; Wasson, J T; Blum, J

    2007-01-01

    In order to investigate the hypothesis that dust aggregates were transformed to meteoritic chondrules by nebular lightning, we exposed silicatic and metallic dust samples to electric discharges with energies of 120 to 500 J in air at pressures between 10 and 10^5 Pa. The target charges consisted of powders of micrometer-sized particles and had dimensions of mm. The dust samples generally fragmented leaving the major fraction thermally unprocessed. A minor part formed sintered aggregates of 50 to 500 micrometer. In a few experiments melt spherules having sizes smaller than 180 micrometer in diameter (and, generally, interior voids) were formed; the highest spherule fraction was obtained with metallic Ni. Our experiments indicate that chondrule formation by electric current or by particle bombardment inside a discharge channel is unlikely.

  15. Effect of Mineralogy on the Rheological Properties of Olivine, Othopyroxene and Olivine/Orthopyroxene Mixtures at High Temperature and Pressure

    NASA Astrophysics Data System (ADS)

    Homburg, J. M.; Mei, S.; Kohlstedt, D. L.

    2013-12-01

    To better understand the influence of mineralogy on the rheological properties of the upper mantle, we have carried out a series of triaxial compressive creep experiments on olivine/orthopyroxene mixtures under high pressures (~6 GPa) and high temperatures (1373 - 1473 K) under anhydrous conditions. Experiments were performed using the deformation-DIA (D-DIA) apparatus on beamline X17B2 at the National Synchrotron Light Source at Brookhaven National Laboratory. Samples of three mineralogical compositions (olivine, orthopyroxene and 50:50 volumetric ratio of olivine:orthopyroxene) were prepared from fine-grained (~10 ?m) mineral separates of San Carlos olivine and orthopyroxene. Orthopyroxene and olivine/orthopyroxene samples were cold pressed to attain a cylinder ~1 mm in length and 1.1 mm in diameter. The cold pressed sample was then stacked with a hot-pressed olivine sample of similar size and assembled with alumina pistons, a boron nitride sleeve and graphite resistance heater into a 6.2-mm edge length cubic pressure medium. Nickel disks were placed at the ends of both samples to act as strain markers. During each experiment, in-situ stress and strain measurements were obtained from X-ray diffraction and radiography, respectively. After annealing the samples at the pressure/temperature conditions of deformation for ~2 hours to insure compaction of the cold pressed sample, experiments were conducted at constant strain rates between 2.2x10^-5 and 3.3x10^-5 s^-1 up to axial strains of 5 to 20%. The orthopyroxene and olivine/orthopyroxene mixture deformed at approximately the same rate with the mixed phase system displaying some weakening relative to the single-phase system. This observation suggests that orthopyroxene may be controlling sample behavior in the mixed phase material. In contrast, the orthopyroxene and olivine/orthopyroxene samples crept ~ 2 - 3 times faster than olivine. This contrast in rheological behavior was observed at lower temperatures/higher differential stresses but not at higher temperatures/lower differential stresses, indicating that the weakening effect of orthopyroxene may be temperature dependent. Alternatively, this behavior may be due to grain size variations between the hot pressed and cold pressed samples; more work needs to be done to better constrain this possibility. Taken together, these findings suggest that variations in orthopyroxene content may significantly alter the rheological behavior of the upper mantle providing an important constraint for future geodynamic models of upper mantle behavior.

  16. 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

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    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.

  19. 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 ?=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.

  20. 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

  1. 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.

  2. A Survey of Olivine Alteration Products Using Raman Spectroscopy

    NASA Technical Reports Server (NTRS)

    Kuebler, K.; Jolliff, B. L.; Wang, A.; Haskin, L. A.

    2004-01-01

    Identification of mineral alteration products will aid in the crucial task of interpreting past Martian environmental conditions, especially aqueous environments. Olivine has been identified at the surface of Mars and is readily altered in aqueous environments. Using Raman spectroscopy, we studied three rocks with altered olivine and compared the data with mineral chemistry from electron microprobe analysis. Although the alteration in all three samples has loosely been called iddingsite their appearances and modes of occurrences differ as described. Alteration products in all three samples are likely fine-grained mixtures.

  3. Petrogenesis of olivine-phyric shergottite Larkman Nunatak 06319: Implications for enriched components in martian basalts

    E-print Network

    Kah, Linda

    Petrogenesis of olivine-phyric shergottite Larkman Nunatak 06319: Implications for enriched-phyric shergottite Larkman Nunatak (LAR) 06319. The meteorite is porphyritic, consisting of megacrysts of olivine (62

  4. Carbonate mineralization in percolated olivine aggregates: Linking effects of crystallographic orientation and fluid flow

    E-print Network

    Cattin, Rodolphe

    , and magnesite, were precipitated on olivine surfaces. The results showed that the dissolution of olivine in the percolated rock. They are mainly located along the moderate (for dolomite) and the minor (for magnesite) flow

  5. B-type olivine fabric and mantle wedge serpentinization beneath the Ryukyu arc

    E-print Network

    B-type olivine fabric and mantle wedge serpentinization beneath the Ryukyu arc Kimberly McCormack,1. Long (2013), B-type olivine fabric and mantle wedge serpentinization beneath the Ryukyu arc, Geophys

  6. 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.

  7. 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 200°C and 300°C, 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.

  8. 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

  9. 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.

  10. Deformation microstructures of olivine in peridotite from Spitsbergen, Svalbard and implications for seismic anisotropy

    E-print Network

    Jung, Haemyeong

    Deformation microstructures of olivine in peridotite from Spitsbergen, Svalbard and implications in the peridotite of Spitsbergen were studied. Seismic anisotropy in the upper mantle can be explained mainly by the lattice- preferred orientation (LPO) of olivine. The LPOs of the olivine in the peridotites were

  11. Martian Dunite NWA 2737: Petrographic constraints on geological history, shock events, and olivine color

    E-print Network

    Treiman, Allan H.

    Martian Dunite NWA 2737: Petrographic constraints on geological history, shock events, and olivine two shock events. The first shock, to stage S5­S6, affected the olivine by producing in it planar­15 nm in diameter. At this stage the olivine became deeply colored, i.e., strongly absorbing at visible

  12. 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.

  13. 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.

  14. Petrogenesis of olivine-phyric shergottite Yamato 980459, revisited

    E-print Network

    and Physics Department, Washington University, St. Louis, MO 63130, USA Received 13 June 2007; accepted megacrysts have magnesian cores (Fo84­86) that appear to be in equilibrium with the Y-980459 whole-rock composition based on Fe­Mg partitioning. However, crystal size distribution (CSD) plots for Y-980459 olivines

  15. 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.

  16. Deformation of olivine in torsion under hydrous conditions

    NASA Astrophysics Data System (ADS)

    Demouchy, Sylvie; Tommasi, Andréa; Barou, Fabrice; Mainprice, David; Cordier, Patrick

    2012-08-01

    We performed torsional deformation experiments on pre-hydrated fine-grained olivine aggregates using an innovative experimental assembly to investigate water weakening in mantle rocks at high shear strains. San Carlos olivine powder was cold-pressed and then hot-pressed under hydrous conditions, producing aggregates with average grain sizes of 7 or 15 ?m. Deformation experiments were performed in a high-resolution gas-medium apparatus equipped with a torsional actuator, under a confining pressure of 300 MPa, a temperature of 1200 °C, and constant shear strain rates ranging from 8 × 10-5 to 1.4 × 10-4 s-1. Maximum shear stresses range from 150 to 195 MPa. These values are 30% lower relative to those determined in previous torsion experiments on dry, fined-grained dunites under similar conditions. Textures and microstructures of the starting and deformed specimens were characterized by scanning and transmission electron microscopy. All deformed aggregates exhibit a shape-preferred orientation marking a foliation and lineation, as well as a reduction in mean grain size from 15 ?m down to 3-4 ?m due to dynamic recrystallization. Olivine crystallographic fabrics developed rapidly (? < 0.1), but their strength, characterized by the J-index, is low compared to naturally deformed peridotites or to polycrystalline olivine deformed at similar finite shear strains under dry conditions. The crystallographic fabrics are consistent with deformation by a dislocation accommodated creep mechanism with activation of multiple {0 k l}[1 0 0] systems, among which the (0 1 0)[1 0 0] slip system is dominant, and minor participation of the (0 1 0)[0 0 1] slip system. Transmission electron microscopy confirmed the occurrence of dislocations with [1 0 0] and [0 0 1] Burgers vectors in most grains. Analysis of unpolarized infrared spectra indicates that hydrogen concentration in the olivine lattice is below the saturation level of 18 ppm wt H2O, which is similar to those typically observed in spinel-bearing peridotite xenoliths, and also provide evidence for water-rich inter-granular material trapped in pores and grain boundaries. Seismic properties computed from the CPO observations correspond to those most commonly observed in naturally deformed mantle peridotites with fast P-wave propagation and S-wave polarization subparallel to the shear direction. These torsion experiments on fine-grained olivine polycrystals under hydrous conditions indicate that water weakening under lithospheric conditions is linked to various defects with hydrogen in the olivine structure, as well as with water-derived species in grain boundaries or pores.

  17. 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.

  18. 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

  19. 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 Skuggafjöll 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.

  20. Geoengineering potential of artificially enhanced silicate weathering of olivine.

    PubMed

    Köhler, 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

  1. 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.

  2. 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).

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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 400°C. 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 (700-800°C). 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.

  8. 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.

  9. O storage capacity of olivine at 8 GPa

    NASA Astrophysics Data System (ADS)

    Withers, Anthony C.; Hirschmann, Marc M.

    2008-04-01

    Olivine crystals were grown in the presence of a hydrous silicate fluid during multi-anvil experiments at 8 GPa and 1,000 1,600°C. Experiments were conducted both in a simple system (FeO MgO SiO2 H2O) and in a more complex system containing additional elements (CaO Na2O Al2O3 Cr2O3 TiO2 FeO MgO SiO2 H2O). Silica activity was buffered by the presence of either pyroxene (high a SiO2) or ferropericlase (low a SiO2), and f_{{text{O}}_{text{2}} } was buffered by the presence of Ni + NiO or Fe + FeO, or constrained by the presence of Fe2O3. Raman spectroscopy was used to identify pyroxene polymorphs in the run products. Clinoenstatite was present in the 1,000°C experiment, and enstatite in experiments at 1,400 1,520°C. The H2O content of olivine was measured using secondary ion mass spectroscopy, and infrared spectroscopy was used to investigate the nature of hydrous defects. The H2O storage capacity of olivine decreases with increasing temperature at 8 GPa. In contrast to previous experimental results at ?2 GPa, no significant effect of varying oxygen fugacity is evident, but H2O storage capacity is enhanced under conditions of low silica activity. No significant growth of low wavenumber (<3,400 cm-1) peaks, generally associated with high f_{{text{O}}_{text{2}} } at low pressure, was observed in the FTIR spectra of olivine from the high f_{{text{O}}_{text{2}} } experiments. Our experiments show that previous high pressure H2O storage capacity measurements for olivine synthesized under more oxidizing conditions than the Earth’s mantle are not likely to be compromised by the f_{{text{O}}_{text{2}} } of the experiments. However, the considerable effect of temperature on H2O storage capacity in olivine must be taken into account to avoid overestimation of the bulk upper mantle H2O storage capacity.

  10. 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.

  11. Fragment-collision model for compound chondrule formation: Estimation of collision probability

    NASA Astrophysics Data System (ADS)

    Miura, Hitoshi; Yasuda, Seiji; Nakamoto, Taishi

    2008-04-01

    We propose a new scenario for compound chondrule formation named as "fragment-collision model," in the framework of the shock-wave heating model. A molten cm-sized dust particle (parent) is disrupted in the high-velocity gas flow. The extracted fragments (ejectors) are scattered behind the parent and the mutual collisions between them will occur. We modeled the disruption event by analytic considerations in order to estimate the probability of the mutual collisions assuming that all ejectors have the same radius. In the typical case, the molten thin ( ˜1mm) layer of the parent surface will be stripped by the gas flow. The stripped layer is divided into about 200 molten ejectors (assuming that the radius of ejectors is 300 ?m) and then they are blown away by the gas flow in a short period of time ( ˜0.01s). The stripped layer is leaving from the parent with the velocity of ˜4cms depending on the viscosity, and we assumed that the extracted ejectors have a random velocity ? v of the same order of magnitude. Using above values, we can estimate the number density of ejectors behind the parent as n˜800cm. These ejectors occupy ˜9% of the space behind the parent in volume. Considering that the collision rate (number of collisions per unit time experienced by an ejector) is given by R=?n?v, where ? is the cross-section of collision [e.g., Gooding, J.K., Keil, K., 1981. Meteoritics 16, 17-43], we obtain R˜36collisions/s by substituting above values. Since most collisions occur within the short duration ( ˜0.01s) before the ejectors are blown away, we obtain the collision probability of P˜0.36, which is the probability of collisions experienced by an ejector in one disruption event. The estimated collision probability is about one order of magnitude larger than the observed fraction of compound chondrules. In addition, the model predictions are qualitatively consistent with other observational data (oxygen isotopic composition, textural types, and size ratios of constituents). Based on these results, we concluded that this new model can be one of the strongest candidates for the compound chondrule formation. It should be noted that all collisions do not necessarily lead to the compound chondrule formation. The formation efficiency and the future works which should be investigated in the forthcoming paper are also discussed.

  12. Infrared spectra of olivine polymorphs: ?, ? phase and spinel

    NASA Astrophysics Data System (ADS)

    Jeanloz, Raymond

    1980-04-01

    Infrared (IR) absorption spectra are presented for olivine (?) and spinel (?) phases of A2SiO4 (A=Fe, Ni, Co) and Mg2GeO4. IR spectra of ? phase (“modified spinel”) Co2SiO4 and of ? Mg2SiO4 are also included. These results provide reference spectra for the identification of olivine high-pressure polymorphs. Isostructural and isochemical correlations are used to support a general interpretation of the spectra and to predict the spectrum of ? Mg2SiO4. A ? Mg2GeO4 sample equilibrated at 1,000° C shows evidence of partial inversion, but one equilibrated at 730° C does not. This suggests that partial inversion could occur in silicate spinels at elevated temperatures and pressures, however no evidence of inversion is seen in the ir spectra of the silicates in this study.

  13. 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.

  14. 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.

  15. 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 60°C 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).

  16. Space Weathering Evolution on Airless Bodies - Laboratory Simulations with Olivine

    NASA Astrophysics Data System (ADS)

    Kohout, Tomas; Cuda, J.; Bradley, T.; Britt, D.; Filip, J.; Tucek, J.; Malina, O.; Kaslik, J.; Siskova, K.; Kletetschka, G.; Zboril, R.

    2013-10-01

    Lunar-type space weathering of airless bodies is associated with nanophase iron (npFe0) production in Fe bearing silicate minerals that is often responsible for observable changes of its reflectance spectra. A new method of controlled npFe0 production on olivine grains was developed in order to quantitatively evaluate spectral changes related to space weathering and presence of npFe0. Through a two-step thermal treatment a series of olivine samples with increasing concentration of iron nanoparticles on the grain surfaces was prepared. The grain size of the npFe0 particles was kept in the same range 5-20 nm). Magnetic methods were used to estimate npFe0 concentration. Compared to fresh olivine, treated samples exhibit the spectral characteristics of lunar type space weathering (darkening, shallowing of 1 µm olivine absorption band, and reddening) related to increasing presence of npFe0. From quantitative point of view, a logarithmic trend was found between spectral changes and npFe0 concentration. One sample with additional population of larger ~50 nm npFe0 particles follows the darkening and the 1 µm band shallowing trend, but does not fully follow the reddening trend. This is due to fact that the larger 40 50 nm sized) npFe0 particles do not contribute to the spectral slope change. The observed logarithmic trend between the spectral changes and the npFe0 concentration give constrains on time evolution of space weathering. In the case of constant micro impact, solar wind and cosmic radiation on a regolith, the npFe0 concentration increases linearly with time while spectral changes related to space weathering evolve logarithmically with time.

  17. 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.

  18. 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.

  19. 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.

  20. The Olivine to Spinel Transformation Unmasked: A Direct Atomic View

    NASA Astrophysics Data System (ADS)

    Drennan, J.; Liu, Z.; Kelly, P.

    2002-12-01

    High-resolution transmission electron microscopy (HRTEM) of partially transformed samples of Mg2GeO4 have revealed a clear picture of the atomic re-arrangements that take place when the olivine form of the compound transforms to the spinel type under the influence of high pressure and temperatures. This important transformation is an anolog of the olivine-spinel transition in mantle silicates and has been the subject of much speculation. In this study it was found that when Mg2GeO4 was subjected to 6Gpa pressure at 600oC for 10 minutes, samples could be produced that contained both structure types with perfectly preserved interface regions. Examination of the atomic structure images of well-prepared specimens revealed a mechanism of transformation, which combines both, a shear component on the anion sub-lattice followed by the passage of a correcting dislocation which very effectively rearranges the cations. The shearing action transforms the hexagonal close packed array of anions in the olivine structure to a packing sequence that defines the face centred close packed structure of the spinel form. The dislocation associated with each shear has a Burgers' vector perpendicular to the anion shear direction and the passage of these dislocations places the cations in the correct spinel sites. These effects are directly observed in atomic resolution images and uniquely define the process, which may have implications in the continuing search for the cause of "deep earthquakes".

  1. 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 1200°C, 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[226×1030.9-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.

  2. The effect of water on the electrical conductivity of olivine.

    PubMed

    Wang, Duojun; Mookherjee, Mainak; Xu, Yousheng; Karato, Shun-ichiro

    2006-10-26

    It is well known that water (as a source of hydrogen) affects the physical and chemical properties of minerals--for example, plastic deformation and melting temperature--and accordingly plays an important role in the dynamics and geochemical evolution of the Earth. Estimating the water content of the Earth's mantle by direct sampling provides only a limited data set from shallow regions (<200 km depth). Geophysical observations such as electrical conductivity are considered to be sensitive to water content, but there has been no experimental study to determine the effect of water on the electrical conductivity of olivine, the most abundant mineral in the Earth's mantle. Here we report a laboratory study of the dependence of the electrical conductivity of olivine aggregates on water content at high temperature and pressure. The electrical conductivity of synthetic polycrystalline olivine was determined from a.c. impedance measurements at a pressure of 4 GPa for a temperature range of 873-1,273 K for water contents of 0.01-0.08 wt%. The results show that the electrical conductivity is strongly dependent on water content but depends only modestly on temperature. The water content dependence of conductivity is best explained by a model in which electrical conduction is due to the motion of free protons. A comparison of the laboratory data with geophysical observations suggests that the typical oceanic asthenosphere contains approximately 10(-2) wt% water, whereas the water content in the continental upper mantle is less than approximately 10(-3) wt%. PMID:17066032

  3. Olivine crystals align during diffusion creep of Earth's upper mantle.

    PubMed

    Miyazaki, Tomonori; Sueyoshi, Kenta; Hiraga, Takehiko

    2013-10-17

    The crystallographic preferred orientation (CPO) of olivine produced during dislocation creep is considered to be the primary cause of elastic anisotropy in Earth's upper mantle and is often used to determine the direction of mantle flow. A fundamental question remains, however, as to whether the alignment of olivine crystals is uniquely produced by dislocation creep. Here we report the development of CPO in iron-free olivine (that is, forsterite) during diffusion creep; the intensity and pattern of CPO depend on temperature and the presence of melt, which control the appearance of crystallographic planes on grain boundaries. Grain boundary sliding on these crystallography-controlled boundaries accommodated by diffusion contributes to grain rotation, resulting in a CPO. We show that strong radial anisotropy is anticipated at temperatures corresponding to depths where melting initiates to depths where strongly anisotropic and low seismic velocities are detected. Conversely, weak anisotropy is anticipated at temperatures corresponding to depths where almost isotropic mantle is found. We propose diffusion creep to be the primary means of mantle flow. PMID:24132289

  4. 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.

  5. From olivine to ringwoodite: a TEM study of a complex process

    NASA Astrophysics Data System (ADS)

    Pittarello, Lidia; Ji, Gang; Yamaguchi, Akira; Schryvers, Dominique; Debaille, Vinciane; Claeys, Philippe

    2015-05-01

    The study of shock metamorphism of olivine might help to constrain impact events in the history of meteorites. Although shock features in olivine are well known, so far, there are processes that are not yet completely understood. In shock veins, olivine clasts with a complex structure, with a ringwoodite rim and a dense network of lamellae of unidentified nature in the core, have been reported in the literature. A highly shocked (S5-6), L6 meteorite, Asuka 09584, which was recently collected in Antarctica by a Belgian-Japanese joint expedition, contains this type of shocked olivine clasts and has been, therefore, selected for detailed investigations of these features by transmission electron microscopy (TEM). Petrographic, geochemical, and crystallographic studies showed that the rim of these shocked clasts consists of an aggregate of nanocrystals of ringwoodite, with lower Mg/Fe ratio than the unshocked olivine. The clast's core consists of an aggregate of iso-oriented grains of olivine and wadsleyite, with higher Mg/Fe ratio than the unshocked olivine. This aggregate is crosscut by veinlets of nanocrystals of olivine, with extremely low Mg/Fe ratio. The formation of the ringwoodite rim is likely due to solid-state, diffusion-controlled, transformation from olivine under high-temperature conditions. The aggregate of iso-oriented olivine and wadsleyite crystals is interpreted to have formed also by a solid-state process, likely by coherent intracrystalline nucleation. Following the compression, shock release is believed to have caused opening of cracks and fractures in olivine and formation of olivine melt, which has lately crystallized under postshock equilibrium pressure conditions as olivine.

  6. A New Spinel-Olivine Oxybarometer: Near-Liquidus Partitioning of V between Olivine-Melt, Spinel-Melt, and Spinel-Olivine in Martian Basalt Composition Y980459 as a Function of Oxygen Fugacity

    NASA Technical Reports Server (NTRS)

    Papike, J. J.; Le, L.; Burger, P. V.; Shearer, C. K.; Bell, A. S.; Jones, J.

    2013-01-01

    Our research on valence state partitioning began in 2005 with a review of Cr, Fe, Ti, and V partitioning among crystallographic sites in olivine, pyroxene, and spinel [1]. That paper was followed by several on QUE94201 melt composition and specifically on Cr, V, and Eu partitioning between pyroxene and melt [2-5]. This paper represents the continuation of our examination of the partitioning of multivalent V between olivine, spinel, and melt in martian olivine-phyric basalts of Y980459 composition [6, 7]. Here we introduce a new, potentially powerful oxybarometer, V partitioning between spinel and olivine, which can be used when no melt is preserved in the meteorite. The bulk composition of QUE94201 was ideal for our study of martian pyroxene-phyric basalts and specifically the partitioning between pyroxene-melt for Cr, V, and Eu. Likewise, bulk composition Y980459 is ideal for the study of martian olivine-phyric basalts and specifically for olivine-melt, spinel-melt, and spinel-olivine partitioning of V as a function of oxygen fugacity.

  7. 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.

  8. A model of the thermal processing of particles in solar nebula shocks: Application to the cooling rates of chondrules

    E-print Network

    Connolly Jr, Harold C.

    A model of the thermal processing of particles in solar nebula shocks: Application to the cooling for the thermal processing of particles in shock waves typical of the solar nebula. This shock model improves apply this shock model to the melting and cooling of chondrules in the solar nebula. We constrain

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

    E-print Network

    Meyers, Stephen R.

    Oxygen isotope systematics of chondrule phenocrysts from the CO3.0 chondrite Yamato 81020: Evidence for two distinct oxygen isotope reservoirs Travis J. Tenner a, , Takayuki Ushikubo a , Erika Kurahashi b October 2012; Available online 29 October 2012 Abstract High-precision oxygen three-isotope measurements

  10. 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.

  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. The fine nebula dust component: A key to chondrule formation by lightning

    NASA Technical Reports Server (NTRS)

    Wasson, J. T.; Rasmussen, K. L.

    1994-01-01

    Our assessment indicates that chondrule formation by lightning is indeed possible in the solar nebula. Previously the overriding objection to the lightning process of chondrule formation has been that low nebula pressures prevented the buildup of large potential differences. The breakdown potential is controlled by the mean free live distance of an electron. We calculate the mean free live distance in pure H2 gas at 2 AU to be approximately 500 m. A fine dust load constituting 4 wt% of the dust in the dusty midplane region leads to a reduced mean free live distance of only 7 m. Very conservatively we estimate the breakdown potential to be at least 10, 1.8, and 0.7 V/cm at 1, 2, and 3 AU respectively. We set the radius of the lightning bolt equal to the kinetic mean free path of the gas. Our calculations based on electron drift velocities in a fully ionized H2 gas show that first strike durations are 0.96, 3.4, and 7.0 ms at 1, 2, and 3 AU respectively, in much better accordance with the meteoritic evidence than previous estimates of 10-100 s.

  13. 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.

  14. Effects of organic ligands and temperature variations on the kinetics of olivine carbonation and the formation of associated secondary phases

    NASA Astrophysics Data System (ADS)

    Sissmann, O.; Daval, D.; Martinez, I.; Brunet, F.; Verlaguet, A.; Pinquier, Y.; Guyot, F. J.

    2011-12-01

    The slow dissolution kinetics of Mg-rich silicates has become a critical issue for the geologic CO2 sequestration in basic rocks. Previous batch carbonation studies on San Carlos olivine [1] performed in CO2 saturated water (at 90°C and P CO2 = 280 bar) have focused on the role that secondary phases, such as amorphous silica layers (SiO2 (am)), have on the transport of reactants from and to the reactive surfaces. The fluid composition remained roughly constant over the duration of the experiment, close to saturation with respect to amorphous silica and with a [Mg2+]/[SiO2 (aq)] ratio close to stoechiometric release, suggesting a passivation of the olivine surface by the silica layer. In order to accelerate the dissolution process, organic ligands such as citrate and acetate were added to the solutions and tested at 1M and 0.1M concentrations in similar batch experiments. An intrinsic increase of the dissolution rate of olivine was expected [2], [3] prior to the formation of a passivating silica layer. Preliminary results confirm this idea since Mg was released in non-stoechimoetric proportions with respect to SiO2 (aq) (found to be in equilibrium with SiO2 (am)). Similarly, a slight increase of temperature (from 90°C to 120°C) accelerated the reaction kinetics as well, possibly impacting the textural properties of SiO2 (am). Current TEM investigations are directed to confirming a possible link between the observed increase of the rate and textural properties of secondary phases. In addition, because carbonate minerals have a retrograde solubility, thermodynamical modelling suggests that this temperature increase should allow the fluid to reach saturation with respect to carbonates before reaching saturation with respect to SiO2 (am). Enough Mg can therefore be released to initiate the formation of carbonates before the silica precipitates and passivates the olivine surface. [1] Daval et al (2011), Chemical Geology, v.284, p.193-209 [2] Grandstaff, D.E. (1986) In: Colman, S.M., Dethier, D.P. Eds., Rates of Chemical Weathering of Rocks and Minerals. 41-57. [3] Krevor and Lackner (2009) Energy Procedia v 1, 4867-4871.

  15. LIME silicates in amoeboid olivine aggregates in carbonaceous chondrites: Indicator of nebular and asteroidal processes

    NASA Astrophysics Data System (ADS)

    Komatsu, Mutsumi; Fagan, Timothy J.; Mikouchi, Takashi; Petaev, Michail I.; Zolensky, Michael E.

    2015-07-01

    MnO/FeO ratios in olivine from amoeboid olivine aggregates (AOAs) reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites. LIME (low-iron, Mn-enriched) olivine was identified in AOAs from Y-81020 (CO3.05), Kaba (CV~3.1), and in Y-86009 (CV3), Y-86751 (CV3), NWA 1152 (CR/CV3), but was not identified in AOAs from Efremovka (CV3.1-3.4) or Allende (CV>3.6). According to thermodynamic models of nebular condensation, LIME olivine is stable at lower temperatures than Mn-poor olivine and at low oxygen fugacities (dust enrichment <10× solar). Although this set of samples does not represent a single metamorphic sequence, the higher subtypes tend to have AOA olivine with lower Mn/Fe, suggesting that Mn/Fe decreases during parent body metamorphism. Y-81020 has the lowest subtype and most forsteritic AOA olivine (Fo>95) in our study, whereas Efremovka AOAs are slightly Fe-rich (Fo>92). AOA olivines from Kaba are mostly forsteritic, but rare Fe-rich olivine precipitated from an aqueous fluid. A combination of precipitation of Fe-rich olivine and diffusion of Fe into primary olivine grains resulted in iron-rich compositions (Fo97-59) in Allende AOAs. Variations from fine-grained, nonporous matrix toward higher porosity and coarser lath-like matrix olivine can be divided into six stages represented by (1) Y-81020, Efremovka, NWA 1152; (2) Y-86751 lithology B; (3) Y-86009; (4) Kaba; (5) Y-86751 lithology A; (6) Allende. These stages are inferred to represent general degree of metamorphism, although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain.

  16. [Study on the FTIR spectra of OH in olivines from mengyin kimberlite].

    PubMed

    Ai, Qun; Yang, Zhi-jun; Zeng, Xiang-qing; Zheng, Yun-long; Hu, Piao-ye

    2013-09-01

    The results of FTIR spectra study of OH in olivines from Mengyin kimberlite show that there are more than 60 OH absorption peaks in the range of 3800-3000 cm(-1). We identified four major spectral features in the OH absorption bands of kimberlitic olivines. One is with nuOH in the range of 3800-3700 cm(-1), which is caused by the vapour of the room circumstance, and can not be regarded as intrinsic or non-intrinsic nuOH of the olivines. Another one is with nuOH in the range of 3710-3620 cm(-1), which belongs to three "water"-bearing minerals including serpentine, talc and Mg-bearing amphiboles, which is the non-intrinsic nuOH of the olivines. There is the possibility that H in hydrous minerals mainly entered into olivines during post-emplacement processes of the kimberlite magma. The third one is with nuOH in the range of 3620-3425 cm(-1), which originated from H occupying the Si-defect in the olivine structure, forming humite-like defects, and/or the defects that H occupies (Mg,Fe)-depletion, which is certainly attributed to the intrinsic nuOH of the olivines. In this case, H possibly entered into olivines following its immersion in the high temperature and rich fluid kimberlite magma in the mantle circumstance. The last one is with nuOH in the range of 3425-3000 cm(-1). In this area, nuOH is assigned to fluid inclusions of the olivines, and is the non-intrinsic nuOH of olivines. Fluid inclusions can enter into the olivines either during post-emplacement processes of the kimberlite magma or during the periods that olivines were formed in the mantle. PMID:24369634

  17. Mid-Infrared Reflectance Spectra of Pulsed Laser Irradiated Olivine Grains

    NASA Astrophysics Data System (ADS)

    Yang, Y. Z.; Yuan, Y.; Wang, Z. W.; Zhang, H.; Jin, W. D.; Hsu, W. B.

    2015-11-01

    To understand the effects of space weathering processes on VNIR and MIR reflectance spectra, we carried out pulsed laser irradiation simulations and reflectance spectroscopic measurements of olivine grains.

  18. Quantifying the Deformation of Leoville Chondrules in 3D: Implications for the Post-Accretional History of the CV3 Parent Body

    NASA Astrophysics Data System (ADS)

    Almeida, N. V.; Smith, C. L.; Sykes, D.; Downes, H.; Ahmed, F.; Russell, S. S.

    2015-07-01

    Micro-CT scanning allows for the three-dimensional analysis of both degree of deformation and direction of preferred orientation of chondrules in the Leoville CV3 meteorite, indicating post-accretional impact as the cause for the foliation.

  19. I-Xe Dating: Comparison of I-Xe and Pb-Pb Ages of Richardton Chondrules and Separated Mineral Phases

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    I-Xe and Pb-Pb ages of individual Richardton chondrules and different mineral phases were compared in order to test the absolute I-Xe age normalization. Additional information is contained in the original extended abstract.

  20. Magmatic history and parental melt composition of olivine-phyric shergottite LAR 06319: Importance of magmatic degassing and olivine antecrysts in Martian magmatism

    NASA Astrophysics Data System (ADS)

    Balta, J. Brian; Sanborn, Matthew; McSween, Harry Y.; Wadhwa, Meenakshi

    2013-08-01

    Several olivine-phyric shergottites contain enough olivine that they could conceivably represent the products of closed-system crystallization of primary melts derived from partial melting of the Martian mantle. Larkman Nunatak (LAR) 06319 has been suggested to represent a close approach to a Martian primary liquid composition based on approximate equilibrium between its olivine and groundmass. To better understand the olivine-melt relationship and the evolution of this meteorite, we report the results of new petrographic and chemical analyses. We find that olivine megacryst cores are generally not in equilibrium with the groundmass, but rather have been homogenized by diffusion to Mg# 72. We have identified two unique grain types: an olivine glomerocryst and an olivine grain preserving a primary magmatic boundary that constrains the time scale of eruption to be on the order of hours. We also report the presence of trace oxide phases and phosphate compositions that suggest that the melt contained approximately 1.1% H2O and lost volatiles during cooling, also associated with an increase in oxygen fugacity upon degassing. We additionally report in situ rare earth element measurements of the various mineral phases in LAR 06319. Based on these reported trace element abundances, we estimate the oxygen fugacity in the LAR 06319 parent melt early in its crystallization sequence (i.e., at the time of crystallization of the low-Ca and high-Ca pyroxenes), the rare earth element composition of the parent melt, and those of melts in equilibrium with later formed phases. We suggest that LAR 06319 represents the product of closed-system crystallization within a shallow magma chamber, with additional olivine accumulated from a cumulate pile. We infer that the olivine megacrysts are antecrysts, derived from a single magma chamber, but not directly related to the host magma, and suggest that mixing of antecrysts within magma chambers may be a common process in Martian magmatic systems.

  1. Deformation of olivine single crystals under lithospheric conditions

    NASA Astrophysics Data System (ADS)

    Demouchy, S.; Tommasi, A.; Cordier, P.

    2012-12-01

    The rheology of mantle rocks at lithospheric temperatures (<1000°C) remains poorly constrained, in contrast to the extensive experimental data on creep of olivine single crystals and polycrystalline aggregates at high temperature (T > 1200°C). Consequently, we have performed tri-axial compression experiments on oriented single crystals and polycrystalline aggregates of San Carlos olivine at temperatures ranging from 800° to 1090°C. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at constant strain rates ranging from 7 × 10-6 s-1 to 1 × 10-4 s-1 . Compression was applied along three different crystallographic directions: [101]c, [110]c and [011]c, to activate the several slip systems. Yield differential stresses range from 88 to 1076 MPa. To constrain hardening, stick-and-slip, or strain localization behaviors, all samples were deformed at constant displacement rate for finite strains between 4 to 23 %. Hardening was observed in all experiments and the maximum differential stress often overcame the confining pressure. EBSD mapping highlights macroscale bending of the crystalline network in three crystals. TEM observations on several samples show dislocations with [100] and [001] Burgers vectors in all samples, but dislocation arrangements vary. The results from the present study permit to refining the power-law expressing the strain rate dependence on stress and temperature for olivine, allowing its application to the lithospheric mantle. Our experiments confirm that previous published high-temperature power flow laws overestimate the strength of lithospheric mantle and that the transition to low-temperature creep occurs at higher temperatures than it has previously been established.

  2. Mineralogical and Raman spectroscopy studies of natural olivines exposed to different planetary environments

    NASA Astrophysics Data System (ADS)

    Weber, I.; Böttger, U.; Pavlov, S. G.; Jessberger, E. K.; Hübers, H.-W.

    2014-12-01

    New lander missions to bodies of our solar system are coming up and thus new techniques are desirable for the in-situ investigation of planetary surface and near surface materials. During the last decade Raman spectroscopy has been developed to become an excellent laboratory tool for fast petrological and mineralogical investigation of terrestrial and extraterrestrial rocks. Consequently, Raman spectroscopy has successfully been proposed for operation on planetary surfaces. In the joint ESA and Roscosmos mission ExoMars a Raman Laser Spectrometer (RLS) will for the first time be applied in space to identify minerals and organic compounds in Martian surface rocks and soils. The present study aims to investigate the possible response of various environmental conditions to Raman spectra in preparation for the ExoMars mission, as well as other space missions in future. For our study we selected five natural olivines with different forsterite (Mg2SiO4) and fayalite (Fe2SiO4) compositions. Olivine as an important rock forming mineral of the Earth upper mantle and an abundant mineral in Martian meteorites is one of the key planetary mineral. The spectra were taken in various environmental conditions that include vacuum down to 10-6 mbar, 8 mbar CO2 atmosphere, and temperatures ranging between room temperature and~8 K resembling those on Mars as well as on the Moon and on asteroids. We have found that forsterite shows only small temperature-related shifts in Raman spectra at very low temperatures indicating relatively weak changes in the lattice modes. Fayalite demonstrates, in addition to temperature dependent changes in the lattice modes found for forsterite, modification of Raman spectra at low Stokes frequencies. This is an effect in the SiO4 internal modes that most probably is caused by the high amount of iron in the mineral structure, which triggers antiferromagnetic transition at low temperatures. No influence of a CO2 atmosphere on Raman spectra for the investigated rock-forming minerals has been observed at any pressure from ambient 1 bar down to a few mbar.

  3. Chromium valences in ureilite olivine and implications for ureilite petrogenesis

    NASA Astrophysics Data System (ADS)

    Goodrich, C. A.; Sutton, S. R.; Wirick, S.; Jercinovic, M. J.

    2013-12-01

    Ureilites are a group of ultramafic achondrites commonly thought to be residues of partial melting on a carbon-rich asteroid. They show a large variation in FeO content (olivine Fo values ranging from ?74 to 95) that cannot be due to igneous fractionation and suggests instead variation in oxidation state. The presence of chromite in only a few of the most ferroan (Fo 75-76) samples appears to support such a model. MicroXANES analyses were used in this study to determine the valence states of Cr (previously unknown) in olivine cores of 11 main group ureilites. The goal of this work was to use a method that is independent of Fo to determine the oxidation conditions under which ureilites formed, in order to evaluate whether the ureilite FeO-variation is correlated with oxidation state, and whether it is nebular or planetary in origin. Two of the analyzed samples, LEW 88774 (Fo 74.2) and NWA 766 (Fo 76.7) contain primary chromite; two others, LAP 03587 (Fo 74.4) and CMS 04048 (Fo 76.2) contain sub-micrometer-sized exsolutions of chromite + Ca-rich pyroxene in olivine; and one, EET 96328 (Fo 85.2) contains an unusual chromite grain of uncertain origin. No chromite has been observed in the remaining six samples (Fo 77.4-92.3). Chromium in olivine in all eleven samples was found to be dominated by the divalent species, with valences ranging from 2.10 ± 0.02 (1?) to 2.46 ± 0.04. The non-chromite-bearing ureilites have the most reduced Cr, with a weighted mean valence of 2.12 ± 0.01, i.e., Cr2+/Cr3+ = 7.33. All low-Fo chromite-bearing ureilites have more oxidized Cr, with valences ranging from 2.22 ± 0.03 to 2.46 ± 0.04. EET 96328, whose chromite grain we interpret as a late-crystallizing phase, yielded a reduced Cr valence of 2.15 ± 0.07, similar to the non-chromite-bearing samples. Based on the measured Cr valences, magmatic (1200-1300 °C) oxygen fugacities (fO2) of the non-chromite-bearing samples were estimated to be in the range IW-1.9 to IW-2.8 (assuming basaltic melt composition), consistent with fO2 values obtained by assuming olivine-silica-iron metal (OSI) equilibrium. For the primary chromite-bearing-ureilites, the corresponding fO2 were estimated (again, assuming basaltic melt composition) to be ?IW to IW+1.0, i.e., several orders of magnitude more oxidizing than the conditions estimated for the chromite-free ureilites. In terms of Fo and Cr valence properties, ureilites appear to form two groups rather than a single “Cr-valence (or fO2) vs. Fo” trend. The chromite-bearing ureilites show little variation in Fo (?74-76) but significant variation in Cr valence, while the non-chromite-bearing ureilites show significant variation in Fo (?77-95) and little variation in Cr valence. These groups are unrelated to petrologic type (i.e., olivine-pigeonite, olivine-orthopyroxene, or augite-bearing). The chromite-bearing ureilites also have lower contents of Cr in olivine than most non-chromite-bearing ureilites, consistent with predictions based on Cr olivine/melt partitioning in spinel saturated vs. non-spinel-saturated systems. Under the assumption that at magmatic temperatures graphite-gas equilibria controlled fO2 at all depths on the ureilite parent body, we conclude: (1) that ureilite precursor materials having the Fo and Cr valence properties now observed in ureilites are unlikely to have been preserved during planetary processing; and (2) that the Fo and Cr valence properties now observed in ureilites are consistent with having been established by high-temperature carbon redox control over a range of depths on a plausible-sized ureilite parent body. The apparent limit on ureilite Fo values around 74-76 suggests that the precursor material(s) had bulk mg# ? that of LL chondrites.

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

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    Our examination of nine CM chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in CM chondrites are not discrete fine-grained rims acquired in the solar nebula as modeled by Metzler et al. [Accretionary dust mantles in CM chondrites: evidence for solar nebula processes. Geochim. Cosmochim. Acta 56, 1992, 2873-28971. Nebular processes that lead to agglomeration produce materials with porosities far higher than those in the dark mantles. We infer that the mantles were produced from porous nebular materials on the CM parent asteroid by impact-compaction (a process that produces the lowest porosity adjacent to chondrules and inclusions). Compaction was followed by aqueous alteration that formed tochilinite, serpentine, Ni-bearing sulfide, and other secondary products in voids in the interchondrule regions. Metzler et al. reported a correlation between mantle thickness and the radius of the enclosed object. In Yamato 791 198 we find no correlation when all sizes of central objects and dark lumps are included but a significant correlation (r(sup 2) = 0.44) if we limit consideration to central objects with radii >35 microns; a moderate correlation is also found in QUE 97990. We suggest that impact-induced shear of a plum-pudding-like precursor produced the observed "mantles"; these were shielded from comminution during impact events by the adjacent stronger chondrules and inclusions. Some mantles in CM chondrites with low degrees of alteration show distinct layers that may largely reflect differences in porosity. Typically, a gray, uniform inner layer is surrounded by an outer layer consisting of darker silicates with BSE-bright speckles. The CM-chondrite objects characterized as "primary accretionary rocks" by Metzler et al. did not form in the nebula, but rather on the parent body. The absence of solar-flare particle tracks and solar-wind-implanted rare gases in these clasts reflect their lithified nature and low surface/volume ratios during the period when they resided in the regolith and were subject to irradiation by solar particles. The clasts are analogous to the light-colored metamorphosed clasts in ordinary-chondrite regolith breccias (which also lack solar-flare particle tracks and solar-wind gas).

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

    NASA Astrophysics Data System (ADS)

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

    2005-09-01

    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. Author contributions: P.A.B. designed research; P.A.B., O.A., G.K.B., A.T.K., O.N.M., L.E.W., and N.W.R. performed research; P.A.B., O.A., G.K.B., and A.T.K. analyzed data; and P.A.B. wrote the paper.This paper was submitted directly (Track II) to the PNAS office.Freely available online through the PNAS open access option.Abbreviations: CAI, Ca-Al-rich refractory inclusion; LA, laser ablation; ICP, inductively coupled plasma.

  6. Phosphorus as indicator of magmatic olivine residence time, morphology and growth rate

    NASA Astrophysics Data System (ADS)

    Sobolev, Alexander; Batanova, Valentina

    2015-04-01

    Phosphorus is among of slowest elements by diffusion rate in silicate melts and crystals (e.g. Spandler et al, 2007). In the same time it is moderately incompatible to compatible with olivine (Brunet & Chazot, 2001; Grant & Kohn, 2013). This makes phosphorus valuable tracer of olivine crystallization in natural conditions. Indeed, it is shown that natural magmatic olivine crystals commonly posses strong and complicated zoning in phosphorus (Milman-Barris et al, 2008; Welsch et al, 2014). In this paper we intend to review phosphorus behavior in olivine in published experimental and natural olivine studies and present large set of new EPMA data on phosphorus zoning in olivine phenocrysts from MORBs, OIBs, komatiites and kimberlites. We will show that sharp olivine zones enriched in phosphorus by a factor of 10-20 over prediction by equilibrium partition may be due to formation of P-rich boundary layer on the interface of fast growing olivine. This is proved by finding of small-size (normally 10 mkm or less) exceptionally P-rich melt inclusions in olivine, which are otherwise similar in composition to typical melt. These observations could provide potential olivine growth speedometer. We will also demonstrate, that sharp zoning in phosphorus may provide valuable information on the residence time of olivine crystals in different environments: magma chambers and conduits as well as mantle sources. This study has been founded by Russian Science Foundation grant 14-17-00491. References: Spandler, et al, 2007, Nature, v. 447, p. 303-306; Brunet & Chazot, 2001, Chemical Geology, v. 176, p. 51-72; Grant & Kohn, 2013, American Mineralogist, v. 98, p. 1860-1869; Milman-Barris et al, 2008, Contr. Min. Petrol. v. 155, p.739-765; Welsch et al, 2014, Geology, v. 42, p.867-870.

  7. 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.

  8. Temperature-dependent Infrared Optical Constants of Olivine and Enstatite

    NASA Astrophysics Data System (ADS)

    Zeidler, S.; Mutschke, H.; Posch, Th.

    2015-01-01

    Since the Infrared Space Observatory (ISO) mission, it has become clear that dust in circumstellar disks and outflows consists partly of crystalline silicates of pyroxene and olivine type. An exact mineralogical analysis of the dust infrared emission spectra relies on laboratory spectra, which, however, have been mostly measured at room temperature so far. Given that infrared spectral features depend on the thermal excitation of the crystal's vibrational modes, laboratory spectra measured at various (low and high) temperatures, corresponding to the thermal conditions at different distances from the star, can improve the accuracy of such analyses considerably. We have measured the complex refractive index in a temperature range of 10-973 K for one mineral of each of those types of silicate, i.e., for an olivine and an enstatite of typical (terrestrial) composition. Thus, our data extend the temperature range of previous data to higher values and the compositional range to higher iron contents. We analyze the temperature dependence of oscillator frequencies and damping parameters governing the spectral characteristics of the bands and calculate absorption cross-sectional spectra that can be compared with astronomical emission spectra. We demonstrate the usefulness of our new data by comparing spectra calculated for a 100 K dust temperature with the ISO SWS spectrum of IRAS 09425-6040.

  9. Systematics of Ni, Co, Cr and V in Olivine from Planetary Melt Systems: Martian Basalts

    NASA Technical Reports Server (NTRS)

    Herd, C. D. K.; Jones, J. H.; Shearer, C. K.; Papike, J. J.

    2001-01-01

    Secondary Ion Mass Spectrometry (SIMS) data for Ni, Co, Cr, and V in olivine in martian basalts is compared to data from lunar and terrestrial basalts. We use experimentally-derived and published D values to calculate as-yet unsampled, olivine-bearing, non-cumulus melt compositions. Additional information is contained in the original extended abstract.

  10. Simultaneous Modeling of Thermopower and Electrical Conduction in Olivine Steven Constable1

    E-print Network

    Key, Kerry

    Simultaneous Modeling of Thermopower and Electrical Conduction in Olivine Steven Constable1 Abstract. Measurements of conductivity and thermopower as a function of oxygen fu- gacity (fO2 ) are used to derive a model for conduction in olivine. Thermopower at 1000­ 1200 C is between 50 and 400 µV/K and has

  11. Hydrous olivine unable to account for conductivity anomaly at the top of the asthenosphere.

    PubMed

    Yoshino, Takashi; Matsuzaki, Takuya; Yamashita, Shigeru; Katsura, Tomoo

    2006-10-26

    The oceanic asthenosphere is observed to have high electrical conductivity, which is highly anisotropic in some locations. In the directions parallel and normal to the plate motion, the conductivity is of the order of 10(-1) and 10(-2) S m(-1), respectively, which cannot be explained by the conductivity of anhydrous olivine. But because hydrogen can be incorporated in olivine at mantle pressures, this observation has been attributed to olivine hydration, which might cause anisotropically high conductivity by proton migration. To examine this hypothesis, here we report the effect of water on electrical conductivity and its anisotropy for hydrogen-doped and undoped olivine at 500-1,500 K and 3 GPa. The hydrous olivine has much higher conductivity and lower activation energy than anhydrous olivine in the investigated temperature range. Nevertheless, extrapolation of the experimental results suggests that conductivity of hydrous olivine at the top of the asthenosphere should be nearly isotropic and only of the order of 10(-2) S m(-1). Our data indicate that the hydration of olivine cannot account for the geophysical observations, which instead may be explained by the presence of partial melt elongated in the direction of plate motion. PMID:17066031

  12. ORIGINAL PAPER The legacy of crystal-plastic deformation in olivine

    E-print Network

    Jung, Haemyeong

    ORIGINAL PAPER The legacy of crystal-plastic deformation in olivine: high-diffusivity pathways Abstract Crystal-plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence of asthenospheric mantle flow. Although crystal-plastic deformation

  13. Olivine friction at the base of oceanic seismogenic Margaret S. Boettcher,1,2

    E-print Network

    New Hampshire, University of

    Olivine friction at the base of oceanic seismogenic zones Margaret S. Boettcher,1,2 Greg Hirth,1 31 January 2007. [1] We investigate the strength and frictional behavior of olivine aggregates demonstrate that deformation was accommodated by frictional processes. Sample strengths were pressure

  14. Mineral replacement rate of olivine by chrysotile and brucite under high alkaline conditions

    E-print Network

    Montes-Hernandez, German

    Mineral replacement rate of olivine by chrysotile and brucite under high alkaline conditions Romain Available online 8 March 2012 Keywords: A1. Mineral replacement rate A1. Serpentinization A1. TG analyses B1. Alkaline medium B2. Chrysotile nanotubes a b s t r a c t Olivine mineral replacement by serpentine is one

  15. Olivine fabric transitions and shear wave anisotropy in the Ryukyu subduction system

    E-print Network

    Olivine fabric transitions and shear wave anisotropy in the Ryukyu subduction system Erik A fabrics with flow-parallel seismically fast directions to a flow-normal B-type olivine fabric in the cold fore-arc mantle of the Ryukyu wedge. We test the B-type fabric hypothesis by comparing observed

  16. Dislocation substructure of mantle-derived olivine as revealed by selective chemical etching and transmission electron microscopy

    USGS Publications Warehouse

    Kirby, S.H.; Wegner, M.W.

    1978-01-01

    Cleaved and mechanically polished surfaces of olivine from peridotite xenoliths from San Carlos, Arizona, were chemically etched using the techniques of Wegner and Christie (1974). Dislocation etch pits are produced on all surface orientations and they tend to be preferentially aligned along the traces of subgrain boundaries, which are approximately parallel to (100), (010), and (001). Shallow channels were also produced on (010) surfaces and represent dislocations near the surface that are etched out along their lengths. The dislocation etch channel loops are often concentric, and emanate from (100) subgrain boundaries, which suggests that dislocation sources are in the boundaries. Data on subgrain misorientation and dislocation line orientation and arguments based on subgrain boundary energy minimization are used to characterize the dislocation structures of the subgrain boundaries. (010) subgrain boundaries are of the twist type, composed of networks of [100] and [001] screw dislocations. Both (100) and (001) subgrain boundaries are tilt walls composed of arrays of edge dislocation with Burgers vectors b=[100] and [001], respectively. The inferred slip systems are {001} ???100???, {100} ???001???, and {010} ???100??? in order of diminishing importance. Exploratory transmission electron microscopy is in accord with these identifications. The flow stresses associated with the development of the subgrain structure are estimated from the densities of free dislocations and from the subgrain dimensions. Inferred stresses range from 35 to 75 bars using the free dislocation densities and 20 to 100 bars using the subgrain sizes. ?? 1978 Springer-Verlag.

  17. The importance of defining chemical potentials, substitution mechanisms and solubility in trace element diffusion studies: the case of Zr and Hf in olivine

    NASA Astrophysics Data System (ADS)

    Jollands, Michael C.; O'Neill, Hugh St. C.; Hermann, Jörg

    2014-09-01

    The diffusion, substitution mechanism and solubility limits of Zr and Hf in synthetic forsterite (Mg2SiO4) and San Carlos olivine (Mg0.9Fe0.1)2SiO4 have been investigated between 1,200 and 1,500 °C as a function of the chemical potentials of the components in the system MgO(FeO)-SiO2-ZrO2(HfO2). The effect of oxygen fugacity and crystallographic orientation were also investigated. The solubilities of Zr in forsterite are highest and diffusion fastest when the coexisting three-phase source assemblage includes ZrSiO4 (zircon) or HfSiO4 (hafnon), and lower and slower, respectively, when the source assemblage includes MgO (periclase). This indicates that Zr and Hf substitute on the octahedral sites in olivine, charge balanced by magnesium vacancies. Diffusion is anisotropic, with rates along the crystal axes increasing in the order a < b < c. The generalized diffusion relationship as a function of chemical activity (as ), orientation and temperature is: where the values of log D 0 are -3.8(±0.5), -3.4(±0.5) and -3.1(±0.5) along the a, b and c axes, respectively. Most experiments were conducted in air ( fO2 = 10-0.68 bars), but one at fO2 = 10-11.2 bars at 1,400 °C shows no resolvable effect of oxygen fugacity on Zr diffusion. Hf is slightly more soluble in olivine than Zr, but diffuses slightly slower. Diffusivities of Zr in experiments in San Carlos olivine at 1,400 °C, fO2 = 10-6.6 bars are similar to those in forsterite at the same conditions, showing that the controls on diffusivities are adequately captured by the simple system (nominally iron-free) experiments. Diffusivities are in good agreement with those measured by Spandler and O'Neill (Contrib Miner Petrol 159:791-818, 2010) in San Carlos olivine using silicate melt as the source at 1,300 °C, and fall within the range of most measurements of Fe-Mg inter-diffusion in olivine at this temperature. Forsterite-melt partitioning experiments in the CaO-MgO-Al2O3-SiO2-ZrO2/HfO2 show that the interface concentrations from the diffusion experiments represent true equilibrium solubilities. Another test of internal consistency is that the ratios of the interface concentrations between experiments buffered by Mg2SiO4 + Mg2Si2O6 + ZrSiO4 or Mg2SiO4 + ZrSiO4 + ZrO2 (high silica activity) to those buffered by Mg2SiO4 + MgO + ZrO2 (low silica activity) agree well with the ratios calculated from thermodynamic data. This study highlights the importance of buffering chemical potentials in diffusion experiments to provide constraints on the interface diffusant concentrations and hence validate the assumption of interface equilibrium.

  18. Bar-biting

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Bar biting is regarded as a stereotypic behavior in which the animal carries out repetitive mouthing and biting of the metal bars in its environmental enclosure. It is commonly seen in sows housed in close confinement, in barren environments, and with restricted access to food. However, it has also ...

  19. The x ray microprobe determination of chromium oxidation state in olivine from lunar basalt and kimberlitic diamonds

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Bajt, S.; Rivers, M. L.; Smith, J. V.

    1993-01-01

    The synchrotron x-ray microprobe is being used to obtain oxidation state information on planetary materials with high spatial resolution. Initial results on chromium in olivine from various sources including laboratory experiments, lunar basalt, and kimberlitic diamonds are reported. The lunar olivine was dominated by Cr(2+) whereas the diamond inclusions had Cr(2+/Cr(3+) ratios up to about 0.3. The simpliest interpretation is that the terrestrial olivine crystallized in a more oxidizing environment than the lunar olivine.

  20. In situ observation of crystallographic preferred orientation of deforming olivine at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Ohuchi, Tomohiro; Nishihara, Yu; Seto, Yusuke; Kawazoe, Takaaki; Nishi, Masayuki; Maruyama, Genta; Hashimoto, Mika; Higo, Yuji; Funakoshi, Ken-ichi; Suzuki, Akio; Kikegawa, Takumi; Irifune, Tetsuo

    2015-06-01

    Simple-shear deformation experiments on polycrystalline olivine and olivine single-crystal were conducted at pressures of 1.3-3.8 GPa and temperatures of 1223-1573 K to understand the achievement of steady-state fabric strength and the process of dynamic recrystallization. Development of crystallographic preferred orientation (CPO) of olivine was evaluated from two-dimensional X-ray diffraction patterns, and shear strain was measured from X-ray radiographs. The steady-state fabric strength of the A-type fabric was achieved within total shear strain of ? = 2. At strains higher than ? = 1, an increase in concentration of the [0 1 0] axes mainly contributes to an increase in fabric strength. At strains higher than ? = 2, the magnitude of VSH/VSV (i.e., ratio of horizontally and vertically polarized shear wave velocities) scarcely increased in most of the runs. The VSH/VSV of peridotite (70 vol.% olivine + 30 vol.% minor phases) having the steady-state A-type olivine fabric coincides with that of recent global one-dimensional models under the assumption of horizontal flow, suggesting that the seismic anisotropy observed in the shallow upper mantle is mostly explained by the development of A-type olivine fabric. Experimental results on the deformation of single-crystal olivine showed that the CPO of olivine is influenced by the initial orientation of the starting single crystal because strain is concentrated in the recrystallized areas and the relic of the starting single crystal remains. In the upper mantle, the old CPO of olivine developed in the past may affect the olivine CPO developed in the present.

  1. Mantle-crust interactions in the oceanic lithosphere: Constraints from minor and trace elements in olivine

    NASA Astrophysics Data System (ADS)

    Sanfilippo, Alessio; Tribuzio, Riccardo; Tiepolo, Massimo

    2014-09-01

    Minor and trace element compositions of olivines are used as probes into the melt-rock reaction processes occurring at the mantle-crust transition in the oceanic lithosphere. We studied mantle and lower crustal sections from the Alpine Jurassic ophiolites, where lithospheric remnants of a fossil slow-spreading ocean are exposed. Olivines from plagioclase-harzburgites and replacive dunites (Fo = 91-89 mol%) and from olivine-rich troctolites and troctolites (Fo = 88-84 mol%) were considered. Positive correlations among the concentrations of Mn, Ni, Co, Sc and V characterize the olivines from the dunites. These chemical variations are reconciled with formation by melts produced by a mixed source consisting of a depleted peridotite and a pyroxene-rich, garnet-bearing component melted under different pressure conditions. We thereby infer that the melts extracted through these dunites channels were not fully aggregated after their formation into the asthenospheric mantle. Olivines from the olivine-rich troctolites and the troctolites are distinct by those in the dunites by lower Ni and higher concentrations of Mn and incompatible trace elements (Ti, Zr, Y and HREE). Fractional crystallization cannot reproduce the chemical variations of the olivines from the olivine-rich troctolites and the troctolites. In these rock-types, the olivines commonly show heterogeneous Ti, Zr, Y and HREE compositions, which produce variable Ti/Y and Zr/Y values. We correlate these olivine characteristics with events of reactive melt migration occurred during the formation of the primitive lower oceanic crust. We propose that the migrating melts formed at the mantle-crust transition via interaction with mantle peridotites during periods of low melt supply.

  2. Remote compositional analysis of lunar olivine-rich lithologies with Moon Mineralogy Mapper (M3) spectra

    USGS Publications Warehouse

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

    2011-01-01

    A systematic approach for deconvolving remotely sensed lunar olivine-rich visible to near-infrared (VNIR) reflectance spectra with the Modified Gaussian Model (MGM) is evaluated with Chandrayaan-1 Moon Mineralogy Mapper (M 3) spectra. Whereas earlier studies of laboratory reflectance spectra focused only on complications due to chromite inclusions in lunar olivines, we develop a systematic approach for addressing (through continuum removal) the prominent continuum slopes common to remotely sensed reflectance spectra of planetary surfaces. We have validated our continuum removal on a suite of laboratory reflectance spectra. Suites of olivine-dominated reflectance spectra from a small crater near Mare Moscoviense, the Copernicus central peak, Aristarchus, and the crater Marius in the Marius Hills were analyzed. Spectral diversity was detected in visual evaluation of the spectra and was quantified using the MGM. The MGM-derived band positions are used to estimate the olivine's composition in a relative sense. Spectra of olivines from Moscoviense exhibit diversity in their absorption features, and this diversity suggests some variation in olivine Fe/Mg content. Olivines from Copernicus are observed to be spectrally homogeneous and thus are predicted to be more compositionally homogeneous than those at Moscoviense but are of broadly similar composition to the Moscoviense olivines. Olivines from Aristarchus and Marius exhibit clear spectral differences from those at Moscoviense and Copernicus but also exhibit features that suggest contributions from other phases. If the various precautions discussed here are weighed carefully, the methods presented here can be used to make general predictions of absolute olivine composition (Fe/Mg content). Copyright ?? 2011 by the American Geophysical Union.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  4. Shock-Wave Heating Model for Chondrule Formation: Hydrodynamic Simulation of Molten Droplets exposed to Gas Flows

    E-print Network

    Hitoshi Miura; Taishi Nakamoto

    2006-11-09

    Millimeter-sized, spherical silicate grains abundant in chondritic meteorites, which are called as chondrules, are considered to be a strong evidence of the melting event of the dust particles in the protoplanetary disk. One of the most plausible scenarios is that the chondrule precursor dust particles are heated and melt in the high-velocity gas flow (shock-wave heating model). We developed the non-linear, time-dependent, and three-dimensional hydrodynamic simulation code for analyzing the dynamics of molten droplets exposed to the gas flow. We confirmed that our simulation results showed a good agreement in a linear regime with the linear solution analytically derived by Sekiya et al. (2003). We found that the non-linear terms in the hydrodynamical equations neglected by Sekiya et al. (2003) can cause the cavitation by producing negative pressure in the droplets. We discussed that the fragmentation through the cavitation is a new mechanism to determine the upper limit of chondrule sizes. We also succeeded to reproduce the fragmentation of droplets when the gas ram pressure is stronger than the effect of the surface tension. Finally, we compared the deformation of droplets in the shock-wave heating with the measured data of chondrules and suggested the importance of other effects to deform droplets, for example, the rotation of droplets. We believe that our new code is a very powerful tool to investigate the hydrodynamics of molten droplets in the framework of the shock-wave heating model and has many potentials to be applied to various problems.

  5. Shock-wave heating model for chondrule formation: Hydrodynamic simulation of molten droplets exposed to gas flows

    NASA Astrophysics Data System (ADS)

    Miura, Hitoshi; Nakamoto, Taishi

    2007-05-01

    Millimeter-sized, spherical silicate grains abundant in chondritic meteorites, which are called as chondrules, are considered to be a strong evidence of the melting event of the dust particles in the protoplanetary disk. One of the most plausible scenarios is that the chondrule precursor dust particles are heated and melt in the high-velocity gas flow (shock-wave heating model). We developed the non-linear, time-dependent, and three-dimensional hydrodynamic simulation code for analyzing the dynamics of molten droplets exposed to the gas flow. We confirmed that our simulation results showed a good agreement in a linear regime with the linear solution analytically derived by Sekyia et al. [Sekyia, M., Uesugi, M., Nakamoto, T., 2003. Prog. Theor. Phys. 109, 717-728]. We found that the non-linear terms in the hydrodynamical equations neglected by Sekiya et al. [Sekiya, M., Uesugi, M., Nakamoto, T., 2003. Prog. Theor. Phys. 109, 717-728] can cause the cavitation by producing negative pressure in the droplets. We discussed that the fragmentation through the cavitation is a new mechanism to determine the upper limit of chondrule sizes. We also succeeded to reproduce the fragmentation of droplets when the gas ram pressure is stronger than the effect of the surface tension. Finally, we compared the deformation of droplets in the shock-wave heating with the measured data of chondrules and suggested the importance of other effects to deform droplets, for example, the rotation of droplets. We believe that our new code is a very powerful tool to investigate the hydrodynamics of molten droplets in the framework of the shock-wave heating model and has many potentials to be applied to various problems.

  6. The Planetesimal Bow Shock Model for Chondrule Formation: More Detailed Simulations in the Near Vicinity of the Planetesimal

    NASA Technical Reports Server (NTRS)

    Hood, Lon L.; Ciesla, Fred J.

    2005-01-01

    Gas dynamic shock waves in a low temperature nebula have been considered to be a leading candidate mechanism for providing the repetitive, short-duration heating events that are believed to have been responsible for the formation of chondrules in chondrites. It has been found, for example, that shocks with Mach numbers greater than 4 or 5 would be capable of rapidly melting 0.1-1 mm sized silicate particles as required by meteoritic data. Near the nebula midplane where chondrite parent bodies are believed to have formed, possible energy sources for generating multiple shocks include mass concentrations in a gravitationally unstable nebula, tidal interactions of proto-Jupiter with the nebula, and bow waves upstream of planetesimals scattered gravitationally into eccentric orbits by proto- Jupiter. In a recent study, we have found that chondrule precursors that are melted following passage through a planetesimal bow shock would likely cool at rates that are too rapid to be consistent with meteoritic evidence. However, that study was limited to the bowshock exterior to about 1.5 planetesimal radii (measured perpendicular to the symmetry axis) to avoid complications interior to this distance where large pressure gradients and lateral flow occur as the gas flows around the planetesimal. In this paper, we reconsider the planetesimal bow shock model and report more detailed numerical simulations of chondrule precursor heating, cooling, and dynamical histories in the near vicinity of a representative planetesimal.

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

    SciTech Connect

    Mishra, R. K.; Goswami, J. N.; Rudraswami, N. G.; Tachibana, S.; Huss, G. R.

    2010-05-10

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

  8. Martian Dunite NWA 2737: Petrographic Constraints on Geological History, Shock Events, and Olivine Color

    SciTech Connect

    Treiman,A.; Dyar, M.; McCanta, M.; Noble, S.; Pieters, C.

    2007-01-01

    Meteorite Northwest Africa (NWA) 2737 is the second known chassignite, an olivine-rich igneous rock with mineral compositions and isotopic ratios that suggest it formed on Mars. NWA 2737 consists of ?85% vol. olivine (Mg, molar Mg/(Mg + Fe), of 78.3 {+-} 0.4%), which is notable because it is black in hand sample and brown in thin section. Other minerals include chromite, pyroxenes (augite, pigeonite, orthopyroxene), and diaplectic glass of alkali-feldspar composition. Aqueous alteration is minimal and appears only as slight dissolution of glass. NWA 2737 formed by accumulation of olivine and chromite from a basaltic magma; the other minerals represent magma trapped among the cumulus grains. Minerals are compositionally homogeneous, consistent with chemical equilibration in late and postigneous cooling. Two-pyroxene thermometry gives equilibration temperatures 1150 C, implying a significant time spent at the basalt solidus. Olivine-spinel-pyroxene equilibria give ?825 C (possibly the T of mesostasis crystallization) at an oxidation state of QMF-1. This oxidation state is consistent with low Fe3+ in olivine (determined by EMP, Moessbauer spectra, and synchrotron micro-XANES spectroscopy) and with {approx}10% of the iron in pyroxene being Fe3+. NWA 2737 experienced two shock events. The first shock, to stage S5-S6, affected the olivine by producing in it planar deformation features, intense mosaicism and lattice strain, and abundant droplets of iron-nickel metal, 5-15 nm in diameter. At this stage the olivine became deeply colored, i.e., strongly absorbing at visible and near-infrared (NIR) wavelengths. This shock event and its thermal pulse probably occurred at {approx}170 Ma, the Ar-Ar age of NWA 2737. The colored olivine is cut by ribbons of coarser, uncolored olivine with long axes along [100] and shorter axes on {l_brace}021{r_brace} planes: These are consistent with the easy slip law for olivine [100]{l_brace}021{r_brace}, which is activated at moderate strain rate at high temperature. Within these ribbons the olivine was coarsened and the iron metal globules coalesced to micron-sized grains. The ribbons also are mosaicized and cut by planar fractures, which bespeak a second shock event, possibly that of ejection from Mars. The deeply colored olivine in NWA 2737 is unusual and represents a new 'ground truth' type for remote sensing of Mars. Understanding the occurrence of the brown color in olivine in NWA 2737 places important constraints on interpretation of optical measurements.

  9. Magmatic plumbing at Lucky Strike volcano based on olivine-hosted melt inclusion compositions

    NASA Astrophysics Data System (ADS)

    Wanless, V. D.; Shaw, A. M.; Behn, M. D.; Soule, S. A.; Escartín, J.; Hamelin, C.

    2015-01-01

    we present volatile, major, and trace element concentrations of 64 olivine-hosted melt inclusions from the Lucky Strike segment on the mid-Atlantic ridge. Lucky Strike is one of two locations where a crustal melt lens has been seismically imaged on a slow-spreading ridge. Vapor-saturation pressures, calculated from CO2 and H2O contents of Lucky Strike melt inclusions, range from approximately 300-3000 bars, corresponding to depths of 0.5-9.9 km below the seafloor. Approximately 50% of the melt inclusions record crystallization depths of 3-4 km, corresponding to the seismically imaged melt lens depth, while an additional ˜35% crystallize at depths > 4 km. This indicates that while crystallization is focused within the melt lens, significant crystallization also occurs in the lower crust and/or upper mantle. The melt inclusions span a range of major and trace element concentrations from normal to enriched basalts. Trace element ratios at all depths are heterogeneous, suggesting that melts are not efficiently homogenized in the mantle or crust, despite the presence of a melt lens. This is consistent with the transient nature of magma chambers proposed for slower-spreading ridges. To investigate the petrogenesis of the melt inclusion compositions, we compare the measured trace element compositions to theoretical melting calculations that consider variations in the melting geometry and heterogeneities in the mantle source. The full range of compositions can be produced by slight variations in the proportion of an Azores plume and depleted upper mantle components and changes in the total extent of melting.

  10. Nearshore oblique sand bars

    NASA Astrophysics Data System (ADS)

    Ribas, F.; FalquéS, 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.

  11. Infrared spectra of olivine polymorphs - Alpha, beta phase and spinel

    NASA Technical Reports Server (NTRS)

    Jeanloz, R.

    1980-01-01

    The infrared absorption spectra of several olivines (alpha phase) and their corresponding beta phase (modified spinel) and spinel (gamma) high-pressure polymorphs are determined. Spectra were measured for ground and pressed samples of alpha and gamma A2SiO4, where A = Fe, Ni, Co; alpha and gamma Mg2GeO4; alpha Mg2SiO4; and beta Co2SiO4. The spectra are interpreted in terms of internal, tetrahedral and octagonal, and lattice vibration modes, and the spinel results are used to predict the spectrum of gamma Mg2SiO4. Analysis of spectra obtained from samples of gamma Mg2GeO4 heated to 730 and 1000 C provides evidence that partial inversion could occur in silicate spinels at elevated temperatures and pressures.

  12. Serpentinization of Sintered Olivine during Seawater Percolation Experiments

    NASA Astrophysics Data System (ADS)

    Luquot, L.; Andreani, M.; Godard, M.; Gouze, P.; Gibert, B.; Lods, G.

    2010-12-01

    Hydration of the mantle lithosphere exposed at slow spreading ridges leads to significant changes of the rock rheological, geophysical, mineralogical and geochemical properties, and to the production of large amounts of H2 and CH4, and of complex carbon molecules that support primitive ecosystems. The onset and efficiency of these hydrothermal processes requires penetration and renewal of fluids at the mineral-fluid interface. However, the mechanisms and the depth of fluid penetration are still poorly understood. Moreover, serpentinization is exovolumic, if a mass-conservative system is assumed, or chemical elements are leached out to conserve rock volume. Thus, the durability and extent of serpentinisation depends of the system capacity to create space and/or to drive mass transfers. In order to investigate these hydrodynamic and chemical mechanisms, we did a series of laboratory experiments during which seawater was injected in sintered San Carlos olivine samples at conditions representative of low temperature ultramafic hydrothermal systems. The percolation-reaction experiments were carried out using the ICARE 2 experimental bench at a confined pressure of 19 MPa and a temperature of 190°C; water flow was set at a constant specific discharge of 0.06 mL/h. During experiments (up to 23 days), permeability decreases continuously although the high Si concentrations in outlet fluids indicate steady olivine dissolution. Fluids are also depleted in Fe and Mg, suggesting precipitation of Fe- and Mg-rich mineral phases; SEM and AEM/TEM analyses of the reacted samples allowed to characterize hematite and poorly crystallized serpentine, both formed at the expense of olivine. Mass balance calculations indicate that, on average, 15 wt. % olivine was dissolved while the same mass of serpentine (+/- brucite) was formed; concurrently, porosity decreased from ~ 12% to 5 %. We infer that the structure of the newly formed serpentine resulted in the clogging of fluid paths and explain the decrease of permeability during experiments. Hematite (<1 wt.%) is also observed, indicating redox reactions. The estimated total hydrogen content of outlet fluids is 4.5 mmol/kg. Although these values are in the same range as those measured at the Lost City hydrothermal vent (e.g., Kelley et al, 2001), they are significantly lower than theoretical estimates of hydrogen composition of serpentinisation fluids (e.g., 21-170 mmol/kg, Wetzel & Shock, 2000). We infer that these differences result, in part, from poor fluid renewal at the mineral interface during experiments, and maybe also in natural systems. These experimental results are used to constrain numerical reactive transport models and better understand the scale and efficiency of serpentinization reactions (effective reaction rates in porous/fractured media) at the scale of spreading ridges. Ref.: Kelley et al., Nature, 412, 145-149, 2001; Wetzel & Shock, JGR, 105, 8319-8340, 2000.

  13. Phyllosilicate and Olivine around a Fracture in Nili Fossae

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) took this observation of part of the Nili Fossae region at the western margin of the Isidis impact basin at 3:07 (UTC) on December 12, 2006, near 21.9 degrees north latitude, 78.2 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 a gigantic impact on the surface of Mars early in the planet's history. The image of the Isidis basin at the top left is the colored elevation data from the Mars Orbiter Laser Altimeter (MOLA) overlain on a digital image mosaic from the Viking mission. Reds represent higher elevations, and blue lower elevations. The western rim of the Isidis basin has numerous, concentric troughs (or 'fossae') which may have formed during faulting associated with the impact event. Since then, the Nili Fossae region has since been heavily eroded, and is one of the most mineralogically diverse spots on Mars.

    This CRISM image targets one of region's smaller fractures. The image is shown overlain on the Viking digital image mosaic at lower left. The lower right CRISM image was constructed from three visible wavelengths (0.71, 0.60 and 0.53 microns in the red, green and blue image planes, respectively) and is close to what the human eye would see. The blue on the right of the image is an artifact from light scattering in the atmosphere. The upper right image was constructed from three infrared channels (2.38, 1.80 and 1.15 microns in the red, green and blue image planes, respectively) to highlight the mineralogy of the area. The bright green areas are rich in 'phyllosilicates,' a category of minerals including clays. The purple material along the walls of the fracture likely contains small amounts of the iron- and magnesium-rich mineral pyroxene. The yellow-brown material contains the iron- and magnesium-rich mineral olivine. Olivine and pyroxene are minerals associated with igneous activity.

    Overlaying CRISM data with images from the High-Resolution Imaging Science Experiment (HiRISE) camera shows that the phyllosilicates are in small, eroded outcrops of rock. The olivine is most abundant in sand dunes on the surface. The use of these two instruments together reveals more about the history of the region: Olivine sands covered the area shown in the image after the interaction of water and rock formed the phyllosilicates and after the fracture formed.

    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.

  14. Collisional Processing of Comet Surfaces: Impact Experiments into Olivine

    NASA Technical Reports Server (NTRS)

    Lederer, S. M.; Jensen, E. A.; Cintala, M. J.; Smith, D. C.; Nakamura-Messenger, K.; Keller, L. P.; Wooden, D. H.; Fernandez, Y. R.; Zolensky, M. E.

    2011-01-01

    A new paradigm has emerged where 3.9 Ga ago, a violent reshuffling reshaped the placement of small bodies in the solar system (the Nice model). Surface properties of these objects may have been affected by collisions caused by this event, and by collisions with other small bodies since their emplacement. In addition, objects in the Kuiper Belt are believed to undergo extensive collisional processing while in the Kuiper Belt. Physical manifestations of shock effects (e.g., planar dislocations) in minerals typically found in comets will be correlated with spectral changes (e.g. reddening, loss and shift of peaks, new signatures) to allow astronomers to better understand geophysical impact processing that has occurred on small bodies. Targets will include solid and granular olivine (forsterite), impacted over a range of impact speeds with the Experimental Impact Laboratory at NASA JSC. Analyses include quantification of the dependence of the spectral changes with respect to impact speed, texture of the target, and temperature.

  15. Stereochemically constrained complex organic molecules extracted from olivine crystal matrix

    NASA Astrophysics Data System (ADS)

    Gerasimenko, I.; Freund, F. T.; Imanaka, H.; Rodgers, R.

    2011-12-01

    Paradoxically, the dense solid state of magmatic minerals is a medium, in which organic synthesis can take place. The reason is that gas-fluid components such as H2O, CO/CO2/N2 and H2S are omnipresent in terrestrial magmatic environments. Any silicate mineral that crystallizes from such magmas will incorporate small quantities of the fluid-phase components in the form of structurally incompatible low-z impurities. During cooling the solute species undergo a redox conversion, resulting in chemically reduced low-z elements. To the extent that these low-z impurities are diffusively mobile, they will exsolve to the surface and/or to major structural defects inside the crystal matrix such as dislocations. Dislocations provide a 3-D structured environment, where the low-z impurities will tend to form stereochemically constrained polyatomic Cn-H-O-N-S entities, which we call organic protomolecules. In Nature, during weathering, such protomolecules will be released into the environment in the form of complex organic molecules. In our study we crush samples under clean conditions as a way to expose Cn-H-O-N-S entities at the fracture surfaces. We conduct identical experiments with selected large olivine single crystals, mm-sized olivine from peridiotite nodules from the San Carlos Volcanic Field, Arizona, and the vesiculated basalt that had carried the nodules upward in the volcanic conduit. We Soxhlet-extract the crushed powders with water, THF and ethyl acetate. The extracts are analyzed at the FTICR-MS facility at Florida State University using ultrahigh resolution Mass Spectrometry techniques capable of determining the chemical composition of the organic molecules up to 600 amu and more. So far we have found several analog sequences of oxygen-rich aliphatic hydrocarbons, families with up to 34 carbon atoms, probably poly-carboxylic acids, and some families containing sulfur.

  16. Olivine friction at the base of oceanic seismogenic zones

    USGS Publications Warehouse

    Boettcher, M.S.; Hirth, G.; Evans, B. M.

    2007-01-01

    We investigate the strength and frictional behavior of olivine aggregates at temperatures and effective confining pressures similar to those at the base of the seismogenic zone on a typical ridge transform fault. Triaxial compression tests were conducted on dry olivine powder (grain size ???60 ??m) at effective confining pressures between 50 and 300 MPa (using Argon as a pore fluid), temperatures between 600??C and 1000??C, and axial displacement rates from 0.06 to 60 ??m/s (axial strain rates from 3 ?? 10-6 to 3 ?? 10-3 s-1). Yielding shows a negative pressure dependence, consistent with predictions for shear enhanced compaction and with the observation that samples exhibit compaction during the initial stages of the experiments. A combination of mechanical data and microstructural observations demonstrate that deformation was accommodated by frictional processes. Sample strengths were pressure-dependent and nearly independent of temperature. Localized shear zones formed in initially homogeneous aggregates early in the experiments. The frictional response to changes in loading rate is well described by rate and state constitutive laws, with a transition from velocity-weakening to velocity-strengthening at 1000??C. Microstructural observations and physical models indicate that plastic yielding of asperities at high temperatures and low axial strain rates stabilizes frictional sliding. Extrapolation of our experimental data to geologic strain rates indicates that a transition from velocity weakening to velocity strengthening occurs at approximately 600??C, consistent with the focal depths of earthquakes in the oceanic lithosphere. Copyright 2007 by the American Geophysical Union.

  17. Effect of Sulfur on Siderophile Element Partitioning Between Olivine and Martian Primary Melt

    NASA Technical Reports Server (NTRS)

    Usui, T.; Shearer, C. K.; Righter, K.; Jones, J. H.

    2011-01-01

    Since olivine is a common early crystallizing phase in basaltic magmas that have produced planetary and asteroidal crusts, a number of experimental studies have investigated elemental partitioning between olivine and silicate melt [e.g., 1, 2, 3]. In particular, olivine/melt partition coefficients of Ni and Co (DNi and DCo) have been intensively studied because these elements are preferentially partitioned into olivine and thus provide a uniquely useful insight into the basalt petrogenesis [e.g., 4, 5]. However, none of these experimental studies are consistent with incompatible signatures of Co [e.g., 6, 7, 8] and Ni [7] in olivines from Martian meteorites. Chemical analyses of undegassed MORB samples suggest that S dissolved in silicate melts can reduce DNi up to 50 % compared to S-free experimental systems [9]. High S solubility (up to 4000 ppm) for primitive shergottite melts [10] implies that S might have significantly influenced the Ni and Co partitioning into shergottite olivines. This study conducts melting experiments on Martian magmatic conditions to investigate the effect of S on the partitioning of siderophile elements between olivine and Martian primary melt.

  18. Oxygen isotopic composition of individual olivine grains from the Allende meteorite

    NASA Technical Reports Server (NTRS)

    Weinbruch, S.; Zinner, E. K.; El Goresy, A.; Steele, I. M.; Palme, H.

    1993-01-01

    The oxygen isotopic composition of a variety of individual olivine grains (including refractory forsterite grains, cores of isolated olivine grains, FeO-rich rims, and individual matrix olivine grains) from the Allende CV3 meteorite was investigated by ion microprobe mass spectrometry, in order to obtain information on the formation mechanism of these samples. It was found that the most primitive (i.e., refractory) olivine in Allende is far less enriched in O-16 than are spinel and pyroxene in Ca,Al-rich inclusions, suggesting that Allende olivine must have formed in an environment that is less enriched in O-16 compared to the gas from which Ca,Al-inclusions are formed. FeO-rich (26-30 wt pct) rims of isolated olivine grains are significantly higher in delta-O-17 and delta-O-18 than forsteritic cores, suggesting that these rims formed by condensation from an oxidized gas with higher delta-O-17 than delta-O-18. Matrix olivine was found to be highest in FeO and to have the lowest enrichment in O-16.

  19. Magnetic properties of natural and synthetic olivines: high-field measurements

    NASA Astrophysics Data System (ADS)

    Ferre, E. C.; Martin-Hernandez, F.

    2004-12-01

    Olivine [(Fex, Mg1-x)2 SiO4] is an orthosilicate solid solution between fayalite [Fe2 SiO4] and forsterite [Mg2 SiO4]. Olivine is a major constituent of the Earth mantle that is abundant in oceanic and continental peridotites and mantle xenoliths. The magnetic properties of olivines have been previously investigated using gem quality natural crystals known as peridots (Zabargad) or using laboratory grown synthetic crystals. Magnetic investigations are generally performed using low magnetic field or neutron diffraction techniques. Optical microscopy and TEM imagery reveal that most olivine crystals host iron oxides formed by exsolution during cooling. Theoretically, the magnetic susceptibility of olivine should decrease linearly from fayalite to fayalite as a function of the Fe content. The magnetic behavior should range from antiferromagnetic at high Fe content, paramagnetic at intermediate Fe contents and diamagnetic at very low Fe contents. New magnetic measurements, performed on various high field instruments (vibrating sample magnetometer, torque magnetometer, cantilever magnetometer), both on natural and synthetic samples, display ferromagnetic behavior, interpreted as due to the systematic presence of titanomagnetite inclusions in olivine crystals. These results emphasize the need to conduct measurements in high field in order to isolate the intrinsic paramagnetic properties of olivines. These measurements demonstrate the orthorhombic nature of the intrinsic paramagnetic properties, but also yield new data concerning the relationship between crystallographic axes, magnetic anisotropy and other physical anisotropies: [100] = K1, [010] = K2 and [001] = K3. Preliminary results also indicate substantial variations in degree of paramagnetic anisotropy (P) and paramagnetic shape factor (T). For Fo92, P = 1.359 and T = -0.845. These intrinsic paramagnetic properties are used to model the magnetic behavior of olivine across a range of temperatures relevant to planetary exploration. They are also used to evaluate the possible effects of olivine deformation on its intrinsic properties. For example, deformation-induced striped iron zoning is anticipated to strongly modify crystal magnetic anisotropy.

  20. Melt Connectivity and Its Effect on Grain Growth in Natural Olivine Aggregates: An Experimental Study

    NASA Astrophysics Data System (ADS)

    Hashim, L.; Sifre, D.; Précigout, J.; Gardés, E.; Le Trong, E.; Gaillard, F.

    2014-12-01

    To better constrain the rheology of the mantle, experimental studies on olivine grain growth have been conducted (Faul and Scott, 2006; Karato, 1989; Nichols and Mackwell, 1991) since the grain size is an important parameter under dynamic regimes (e.g. diffusion creep and grain boundary sliding). In order to better define the melt effect on the rheological response of a partially molten olivine aggregate, we have experimentally investigated the effect of melt on olivine grain growth and the connectivity of this melt phase. Experiments were performed in 3/4" piston cylinders at 500 MPa confining pressure, different temperatures (i.e. 1100°C, 1250°C and 1400°C) and four durations (1h, 12h, 72h and 15 days). Starting material was composed of natural San Carlos olivine (5 ?molivines were previously handpicked and annealed under controlled oxygen fugacity conditions close to the FMQ buffer. After the experiments, the melt connectivity was assessed through scanning electron microscope (SEM) images in backscattered electron mode. Electron backscatter diffraction (EBSD) maps of each sample were also collected in order to determine the olivine grain sizes as a function of time and melt content. References Faul, U. H., Scott, D., 2006. Grain growth in partially molten olivine aggregates. Contributions to Mineralogy and Petrology 151 (1), 101-111. Karato, S.-I., 1989. Grain growth kinetics in olivine aggregates. Tectonophysics 168 (4), 255-273. Nichols, S. J., Mackwell, S. J., 1991. Grain growth in porous olivine aggregates. Physics and Chemistry of Minerals 18 (4), 269-278. Sifré, D., Gardés, E., Massuyeau, M., Hashim, L., Hier-Majumder, S., Gaillard, F., 2014. Electrical conductivity during incipient melting in the oceanic low-velocity zone. Nature 509 (7498), 81-85.

  1. H Diffusion in Olivine and Pyroxene from Peridotite Xenoliths and a Hawaiian Magma Speedometer

    NASA Technical Reports Server (NTRS)

    Peslier, A. H.; Bizimis, M.

    2014-01-01

    Hydrogen is present as a trace element in olivine and pyroxene and its content distribution in the mantle results from melting and metasomatic processes. Here we examine how these H contents can be disturbed during decompression. Hydrogen was analyzed by FTIR in olivine and pyroxene of spinel peridotite xenoliths from Salt Lake Crater (SLC) nephelinites which are part of the rejuvenated volcanism at Oahu (Hawaii) [1,2]. H mobility in pyroxene resulting from spinel exsolution during mantle upwelling Most pyroxenes in SLC peridotites exhibit exsolutions, characterized by spinel inclusions. Pyroxene edges where no exsolution are present have less H then their core near the spinel. Given that H does not enter spinel [3], subsolidus requilibration may have concentrated H in the pyroxene adjacent to the spinel exsolution during mantle upwelling. H diffusion in olivine during xenolith transport by its host magma and host magma ascent rates Olivines have lower water contents at the edge and near fractures compared to at their core, while the concentrations of all other chemical elements appear homogeneous. This suggests that some of the initial water has diffused out of the olivine. Water loss from the olivine is thought to occur during host-magma ascent and xenolith transport to the surface [4-6]. Diffusion modeling matches best the data when the initial water content used is that measured at the core of the olivines, implying that mantle water contents are preserved at the core of the olivines. The 3225 cm(sup -1) OH band at times varies independantly of other OH bands, suggesting uneven H distribution in olivine defects likely acquired during mantle metasomatism just prior to eruption and unequilibrated. Diffusion times (1-48 hrs) combined with depths of peridotite equilibration or of magma start of degassing allow to calculate ascent rates for the host nephelinite of 0.1 to 27 m/s.

  2. Minor and trace elements in olivines as probes into early igneous and mantle melting processes

    NASA Astrophysics Data System (ADS)

    Foley, Stephen F.; Prelevic, Dejan; Rehfeldt, Tatjana; Jacob, Dorrit E.

    2013-02-01

    The trace element composition of olivine is a rapidly growing research area that has several applications of great potential. Mantle olivines can be distinguished from volcanic olivines by lower concentrations of Ca (<700 ppm), Ti (<70 ppm), and often Cr. The melting of pyroxenites derived from recycled ocean crust can be recognized in volcanic olivines by correlations of Mn, Al, Sc and Co in addition to Ni. High Ni is characteristic of olivine derived from olivine-free source rocks, but alone it does not distinguish between recycling of ocean crust, continental crust, mantle wedge hybridization, and intra-mantle melt migration. Trace elements help to identify different types of non-peridotitic ultramafic rocks, including those not formed by ocean crust recycling. High Li may be caused by recycling of continental crust, as in Mediterranean post-collisional volcanics or by interaction with carbonatitic melts, and correlation with further elements such as Zn, Na, Ti and Ca will help to identify minerals in the source assemblages, such as phlogopite, spinel, garnet, amphiboles and carbonates, and thus the source of the olivine-free assemblages. Olivines often store the earliest chemical signals of melt loss in peridotites, but later absorb trace elements from passing melts, and are thus excellent monitors of the chemistry of metasomatic agents. Trace elements distinguish between Ti-enrichment by silicate melt metasomatism (high Ti, low Ca) and high-Ca signatures associated with plumes and rift regions that may be due to carbonate-silicate melts. Li may be enriched in olivine in the orogenic mantle, indicating the involvement of melted continental crustal material. Experimental data on element partitioning and diffusion currently partly conflicts with information from natural rocks.

  3. Using Diffusion Modeling to Understand Ni Variability and Magmatic Histories of Hawaiian Olivines

    NASA Astrophysics Data System (ADS)

    Lynn, K. J.; Garcia, M. O.; Shea, T.

    2014-12-01

    The Ni content of olivine has been used extensively for inferring the source lithology, and depth and temperature of generation for basaltic magma in various tectonic settings. Conflicting interpretations have been derived using Ni because Hawaiian basalts show large variations in olivine Ni content (up to a factor of two) for a given forsterite (Fo). A detailed study of historical basalts at Kilauea volcano was undertaken using high-precision EPMA to better understand the cause of Ni variation in Hawaiian basalts. Experimental studies predict that Ni abundance in olivine should be positively correlated with Fo during growth. Element maps and core-rim transects of crystals strongly zoned in Fo show that many Kilauea olivines violate this relationship. They have decoupled profiles in which Fo decreases towards the rim by up to 5 mol% and Ni remains nearly constant. Here, we evaluate whether the Ni variability and Fo-Ni decoupling result from (1) diffusive re-equilibration and/or (2) sectioning effects rather than being primary growth features of those olivines. We used 1D diffusion modeling of Mg, Ni, and Ca from EPMA profiles to determine if decoupling is caused by diffusive re-equilibration. Calculated timescales (e.g. 2.2-3.1 yr) are in excellent agreement for all elements and transects within individual crystals, suggesting that the Fo-Ni decoupling is a primary growth feature of the olivine. Sectioning effects on Fo-Ni zoning were evaluated using 3D diffusion models of numerical olivines, which were constructed using realistic morphologies found in nature. Off-center and highly oblique sections have Fo and Ni extremums offset from the geometric center in 2D sections. Analyses of normally zoned olivine with decoupled Fo-Ni will yield similar Ni at variable Fo, introducing "Ni-enriched", low Fo data. These "Ni-enriched" olivine compositions may contribute to the range of interpretations derived from current datasets

  4. Olivines in the Kaba carbonaceous chondrite and constraints on their formation

    NASA Technical Reports Server (NTRS)

    Hua, X.; Buseck, P. R.

    1993-01-01

    Kaba is unique in containing almost pure fayalitic olivine (Fo(sub 0.1)). Its coexistence with pure forsterite up to Fo(sub 99.6) and normal (Fo(sub 92) to Fo(sub 59)) and reversely (Fo(sub 0.4) to Fo(sub 4.7)) zoned olivines suggest that the Kaba olivines are in thermodynamic disequilibrium and experienced a complicated history. The fayalite is sufficiently pure that it is unlikely that it could have been produced by fractional crystallization. A gas-solid reaction under oxidizing conditions (H2O/H2 ratio approximately 10) is probably responsible for its formation.

  5. 3D Quantitative Confocal Laser Microscopy of Ilmenite Volume Distribution in Alpe Arami Olivine

    NASA Astrophysics Data System (ADS)

    Bozhilov, K. N.

    2001-12-01

    The deep origin of the Alpe Arami garnet lherzolite massif in the Swiss Alps proposed by Dobrzhinetskaya et al. (Science, 1996) has been a focus of heated debate. One of the lines of evidence supporting an exhumation from more than 200 km depth includes the abundance, distribution, and orientation of magnesian ilmenite rods in the oldest generation of olivine. This argument has been disputed in terms of the abundance of ilmenite and consequently the maximum TiO2 content in the discussed olivine. In order to address this issue, we have directly measured the volume fraction of ilmenite of the oldest generation of olivine by applying confocal laser scanning microscopy (CLSM). CLSM is a method which allows for three-dimensional imaging and quantitative volume determination by optical sectioning of the objects. The images for 3D reconstruction and measurements were acquired from petrographic thin sections in reflected laser light with 488 nm wavelength. Measurements of more than 80 olivine grains in six thin sections of our material yielded an average volume fraction of 0.31% ilmenite in the oldest generation of olivine from Alpe Arami. This translates into 0.23 wt.% TiO2 in olivine with error in determination of ±0.097 wt.%, a value significantly different from that of 0.02 to 0.03 wt.% TiO2 determined by Hacker et al. (Science, 1997) by a broad-beam microanalysis technique. During the complex geological history of the Alpe Arami massif, several events of metamorphism are recorded which all could have caused increased mobility of the mineral components. Evidence for loss of TiO2 from olivine is the tendency for high densities of ilmenite to be restricted to cores of old grains, the complete absence of ilmenite inclusions from the younger, recrystallized, generation of olivine, and reduction in ilmenite size and abundance in more serpentinized specimens. These observations suggest that only olivine grains with the highest concentrations of ilmenite are close to the original amount of TiO2 incorporated in the olivine. Our measurements show maximum volume fraction of ilmenite of 1.21%, corresponding to 0.9±0.38 wt.% of TiO2. Even the most conservative scenario reveals concentration of TiO2 in olivine of more than 0.5 wt.%, a value comparable to that reported by Dobrzhinetskaya et al. (1996) and an order of magnitude greater than any previous measurement of TiO2 in olivine. Experiments by Dobrzhinetskaya et al. (Chem. Geol, 2000) found that such high solubility can occur, but only at P>10GPa at mantle temperatures.

  6. Cellular Precipitates Of Iron Oxide in Olivine in a Stratospheric Interplanetary Dust Particle

    NASA Technical Reports Server (NTRS)

    Rietmeijer, Frans J. M.

    1996-01-01

    The petrology of a massive olivine-sulphide interplanetary dust particle shows melting of Fe,Ni-sulphide plus complete loss of sulphur and subsequent quenching to a mixture of iron-oxides and Fe,Ni-metal. Oxidation of the fayalite component in olivine produced maghemite discs and cellular intergrowths with olivine and rare andradite-rich garnet. Cellular reactions require no long-range solid-state diffusion and are kinetically favourable during pyrometamorphic oxidation. Local melting of the cellular intergrowths resulted in three dimensional symplectic textures. Dynamic pyrometamorphism of this asteroidal particle occurred at approx. 1100 C during atmospheric entry flash (5-15 s) heating.

  7. Reactive flow as dominant evolution process in the lowermost oceanic crust: evidence from olivine of the Pineto ophiolite (Corsica)

    NASA Astrophysics Data System (ADS)

    Sanfilippo, Alessio; Tribuzio, Riccardo; Tiepolo, Massimo; Berno, Davide

    2015-10-01

    The Jurassic Pineto ophiolite from Corsica exposes a ~1-km-thick troctolite-olivine-gabbro sequence, interpreted to represent a lowermost sector of the gabbroic oceanic crust from a (ultra-)slow spreading system. To constrain the petrogenesis of the olivine-gabbros, minor and trace element analyses of olivine (forsterite = 84-82 mol%) were carried out. Olivine from the olivine-gabbros is depleted in incompatible trace elements (Sc, V, Ti, Y, Zr and heavy rare earth elements) with respect to olivines from associated troctolites. Depleted incompatible element compositions are also shown by olivine (forsterite = 86 mol%) from a clinopyroxene-rich troctolite. The incompatible element compositions of olivine argue against a petrogenetic process entirely driven by fractional crystallization. We propose that melts migrating through an olivine-plagioclase crystal mush chemically evolved by reaction with the existing minerals, changing in composition as it flowed upward. The melt residual from these interactions led to partial dissolution of preexisting olivine and to crystallization of clinopyroxene, generating olivine-gabbro bodies within a troctolite matrix. Reactive flow was the major evolution process active in the ~1-km crustal transect exposed at the Pineto ophiolite, producing lithological variations classically attributed to fractional crystallization processes.

  8. Cr, Mn, and Ca distributions for olivine in angritic systems: Constraints on the origins of Cr-rich and Ca-poor core olivine in angrite LEW87051

    NASA Technical Reports Server (NTRS)

    Mikouchi, T.; Mckay, G.; Le, L.

    1994-01-01

    Angrite meteorites are a type of basaltic achondrites that are noted for their very old cyrstallization ages (4.55 b.y.) and unusual chemical and mineralogical properties. In spite of great interest, only four angrites have been found. LEW87051 is the smallest one which weighs 0.6 g. It is a porphyritic rock with coarse subhedral to euhedral olivines set in a fine-grained groundmass which clearly represents a crystallized melt. The largest uncertainty about the petrogenesis of LEW87051 is the relationship between the large olivine crystals and the groundmass. Prinz et al. suggests that olivines are xenocrysts, while McKay et al. proposed a fractional cyrstallization model based on experimental studies. However, the crystals have Cr-rich and Ca-poor cores which do not match experimental olivines. Although Jurewicz and McKay tried to explaine the zoning of the rim by diffusion, some features are not explained. There also exists a definite composition boundary of Fe(2+) and MnO between the core and the rim. To clarify the origin of these olivines, we have performed experiments using LEW87051 analogs to measure the effects of oxygen fugacity on distribution coefficients of various elements in an angritic system.

  9. Rapid Microwave-Assisted Solvothermal Synthesis of Non-Olivine Cmcm Polymorphs of LiMPO4 (M = Mn, Fe, Co, and Ni) at Low Temperature and Pressure.

    PubMed

    Assat, Gaurav; Manthiram, Arumugam

    2015-10-19

    Lithium transition-metal phosphates, LiMPO4 (M = Mn, Fe, Co, and Ni), have attracted significant research interest over the past two decades as an important class of lithium ion battery cathode materials. However, almost all of the investigations thus far have focused on the olivine polymorph that exists in the orthorhombic Pnma space group. In this study, a distinct orthorhombic but non-olivine polymorph of LiMPO4, described by a Cmcm space group symmetry, has been synthesized with M = Mn, Fe, Co, and Ni. Of these, LiMnPO4 in the Cmcm space group is reported for the first time. A rapid microwave-assisted solvothermal (MW-ST) heating process with tetraethylene glycol (TEG) as the solvent and transition-metal oxalates as precursors facilitates the synthesis of these materials. The peak reaction temperatures and pressures were below 300 °C and 30 bar, respectively, which are several orders of magnitude lower than those of the previously reported high-pressure (gigapascals) method. X-ray diffraction (XRD) confirms the crystal structure with the Cmcm space group, and scanning electron micrographs indicate a submicrometer thin platelet-like morphology. The synthesis process conditions have been optimized to obtain impurity-free samples with the correct stoichiometry, as characterized by XRD and inductively coupled plasma-optical emission spectroscopy (ICP-OES). Upon heat treatment to higher temperatures, an irreversible transformation of the metastable Cmcm polymorphs into olivine is observed by XRD and Fourier transform infrared spectroscopy. Although the electrochemical activity of these polymorphs as lithium ion cathodes turns out to be poor, the facile synthesis under mild conditions has permitted easy access to these materials in a nanomorphology, some of which were not even possible before. PMID:26428928

  10. An Olivine-Rich Crater in Tyrrhena Terra

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image of the ejecta of a crater in the Tyrrhena Terra region was taken by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) at 0328 UTC on February 23, 2007 (10:28 p.m. EST on February 22, 2007), near 13 degrees south latitude, 67 degrees east longitude. CRISM's image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 18 meters (60 feet) across. The region covered is roughly 9 kilometers (5.6 miles) wide at its narrowest point.

    Named for a classic albedo feature, Tyrrhena Terra is an extensive, heavily-cratered part of Mars' southern highlands, some 2,300 kilometers (1,430 miles) at its broadest extent. It is located to the northeast of the Hellas basin. The region imaged by CRISM is to the north of Hellas Planitia and just east of the crater Huygens in Tyrrhena Terra's western end.

    The uppermost image in the montage above reveals the location of the CRISM image on a mosaic taken by the Mars Odyssey spacecraft's Thermal Emission Imaging System (THEMIS). The CRISM image is located inside a large, flat-floored crater measuring about 52 kilometers (32 miles) across. The image includes a small crater and its ejecta blanket, an apron of material thrown out during a crater's formation, both located inside the larger crater.

    The lower left image is an infrared false-color image that reveals the extent of the ejecta blanket. It also includes ejecta from another small crater located just east of the CRISM image.

    The lower right image shows the strengths of mineral absorptions, and reveals the composition of the ejecta and surrounding material. The ejecta surrounding the small impact crater is thickest at the crater's rim, and becomes thinner to discontinuous at the blanket's outer edge. This small crater's ejecta blanket shows an enhanced spectral signature of the mineral olivine, as does the ejecta from the small crater just out of view to the east. In contrast the surrounding material is rich in the volcanic mineral pyroxene. This relationship demonstrates the layered characteristic of rocks forming the southern highlands: olivine-rich rock was buried by pyroxene-rich materials on the larger crater's floor, probably volcanic lavas. Later, the small crater penetrated the pyroxene-rich rock, excavated the underlying olivine-bearing unit, and deposited it as ejecta.

    CRISM is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, Laurel, Md., the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter and the Mars Science Laboratory for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, built the orbiter.

  11. Trace element composition of olivine - implications for the evolution of the olivine gabbro-troctolite-hosted Voisey's Bay Ni-Cu-Co sulfide deposit, Labrador

    NASA Astrophysics Data System (ADS)

    Bulle, F.; Layne, G. D.

    2011-12-01

    The Mesoproterozoic Voisey's Bay intrusion is part of the Nain Plutonic Suite, which transects the 1.85 Ga collisional boundary between the Proterozoic Churchill Province and the Archean Nain Province in Eastern Labrador. The intrusion comprises a group of troctolitic to olivine gabbroic bodies linked by olivine gabbro dikes; together these rocks host the world-class Voisey's Bay Ni-Cu-Co sulfide deposit. Zones of massive and disseminated sulfide mineralization (Reid Brook, Discovery Hill, Mini-Ovoid and Ovoid) occur within a dike and at the entry line of this dike into a larger intrusion termed the Eastern Deeps [1, 2, 3]. At least two pulses of magma have generated the intrusion and the associated sulfide mineralization; an initial surge that achieved sulfide saturation by interacting with upper crustal rocks, and a later pulse of fresh, undepleted magma that forced the initial magma upwards and both remobilized the immiscible sulfide liquid and upgraded it in metal content [1, 2, 3]. Previous research [1, 2] has shown that the Ni content of olivine from the distinct sulfide-bearing host rocks is highly variable, and also indicative of both magma mixing and interaction of silicate magmas with sulfide. To further validate the significance of the olivine chemistry as a tracer for ore-forming petrological processes, we have determined the abundances of Cr, Mn, Co, Ni, Zn in olivines from the various mafic lithologies of the Eastern Deeps intrusion using Secondary Ion Mass Spectrometry. We present systematic variations in Mn, Co, Ni and Zn with Fo-content in olivines for both sulfide-free and sulfide-bearing zones. Olivines from mineralized and brecciated troctolitic/gabbroic zones display significantly higher Mn (up to 11,000 ppm) and Zn (up to 550 ppm) concentrations than those from nominally barren counterparts. The barren troctolite, broadly termed normal troctolite (NT), is a petrographically homogenous plagioclase and olivine cumulate. However, olivine compositional data establish the presence of "reef-like" horizons with, for instance, elevated Ni concentrations (up to 2,500 ppm), versus surrounding horizons where values of ? 1,500 ppm are predominant. These horizons correspond with deflections in the whole-rock MgO, Fe2O3 and MnO contents. If these horizons are widespread and traceable laterally within the intrusion it would imply that: (1) a "cryptic-layering" might be preserved in olivines from the otherwise homogenous NT - indicating either crystallization from an input of fresh, undepleted mafic magma, or an interaction of those olivines with a Ni-rich sulfide liquid [1, 2], (2) the high Mn and Zn concentrations, coupled with lower forsterite values, are probably a result of crystallization from a country rock-contaminated mafic magma, and therefore, might act as a mineral-based indicator for the assimilation of upper crustal material. These observations may assist in developing a signature for olivines that have been in contact with highly contaminated (and thus potentially sulfide saturated) magmas. [1] Li et al. (2000) Econ. Geol. 95, 771-799. [2] Li and Naldrett (1999) Lithos 47, 1-31. [3] Lightfoot and Naldrett (1999) GAC Vol. 13, 1-30.

  12. Optical absorption and radiative heat transport in olivine at high temperature

    NASA Technical Reports Server (NTRS)

    Shankland, T. J.; Nitsan, U.; Duba, A. G.

    1979-01-01

    Results are presented of measurements of the optical absorption spectra (300-8000 nm) of olivine as a function of temperature (300-1700 K) under conditions of controlled and known oxygen fugacity within the stability field of the samples. The absorption spectra are used to calculate the temperature-dependent radiative transfer coefficient of olivine and to numerically study the accuracy of the method. The present absorption measurements in olivine under oxidizing conditions known to be within the olivine stability field indicate that the effective radiative conductivity K(R) is lower than that obtained in previous studies under different experimental conditions. The lower value of K(R) makes it more likely that some of the earth's internal heat is removed by convection and less likely that thermal models involving conduction and radiation alone will satisfactorily explain thermal conditions in the earth's mantle.

  13. FULL PAPER Open Access Characterization of olivine fabrics and mylonite in

    E-print Network

    Jung, Haemyeong

    of the surrounding anorthosite complex is displayed in ultramafic lenses as a modal variation in olivine, pyroxenes, and spinel, and the Caledonian eclogite-facies structure in the surrounding anorthosite gabbro is represented

  14. Comparison of the Temperature Effects on Reflectance Spectra of Fresh and Experimentally Space Weathered Olivine

    NASA Astrophysics Data System (ADS)

    Corley, L. M.; Gillis-Davis, J. J.; Lucey, P. G.

    2015-11-01

    Reflectance spectra of fresh and laser irradiated olivine are measured at temperatures between 100–255 K to determine if an anticorrelation between temperature and reflectance in LOLA data is due to the influence of temperature on space weathering.

  15. Relation of the spectroscopic reflectance of olivine to mineral chemistry and some remote sensing implications

    NASA Technical Reports Server (NTRS)

    King, Trude V. V.; Ridley, W. Ian

    1987-01-01

    High-resolution visible and near-IR diffuse spectral reflectance are used to systematically investigate apparent wavelength shifts as a function of mineral chemistry in the Fe/Mg olivine series from Fo(11) to Fo(91). The study also shows that trace amounts of nickel can be spectrally detected in the olivine structure. Significant compositional information can only be extracted at relatively high resolution, because the overall spectral characteristics of the olivines change only subtly as a function of the Fe/Mg ratio. This laboratory study is expected to aid in the interpretation of remotely sensed data from both terrestrial and extraterrestrial bodies. Terrestrial applications may include the recognition of ultramafic, ultrabasic, and basaltic terrains which in themselves may have mineral potential. Among extraterrestrial applications, the asteroids are obvious candidates for further examination. Some permutations of Fe-Mg-Ni relations in olivines are discussed as they apply to the interpretation of asteroid surfaces and other extraterrestrial bodies.

  16. Simultaneous precipitation of magnesite and lizardite from hydrothermal alteration of olivine under high-carbonate alkalinity

    E-print Network

    Montes-Hernandez, German

    Simultaneous precipitation of magnesite and lizardite from hydrothermal alteration of olivine under alteration High-carbonate alkalinity Magnesite Lizardite Crystal growth Hydrothermal systems The present, competitive precipitation of magnesite and serpentine (preferentially lizardite type) was clearly determined

  17. Calorimetric Investigation of Olivine Carbonation as a mechanism of Carbon Sequestration

    E-print Network

    Qiu, Bo

    method due to the long-term stability of product minerals, magnesite and quartz. Examining reaction rate and thermodynamics of olivine-CO2-H2O reaction to form magnesite and quartz can provide data needed to determine

  18. Serpentine Mineral Replacements of Natural Olivine and their Seismic Implications: Oceanic

    E-print Network

    Demouchy, Sylvie

    that of the peridotite. These results have some relevance to the seismic anisotropy of serpen- tinized mantle. Anisotropy with increasing serpentinization. KEY WORDS: serpentinized peridotite; lizardite; antigorite^olivine topotaxy

  19. ELEMENTAL ABUNDANCE CONSTRAINTS ON CONDENSATION OF ALLENDE MATRIX OLIVINE. L. Grossman1

    E-print Network

    at 1450-1250K at reasonable nebular pressures, causing the co-condensing olivine to be pure forsterite+ to condense at equilibrium, it must diffuse into the interiors of previously condensed forsterite grains

  20. Are Megacrysts in Olivine-Phyric Shergottites Xenocrysts, Phenocrysts, or Something Else?

    NASA Astrophysics Data System (ADS)

    Balta, J. B.; McSween, H. Y.

    2011-03-01

    We argue based on detailed analyses and modeling of shergottite LAR 06319 that its olivines are antecrysts, formed from a melt similar to the current groundmass and entrained from a cumulate pile prior to eruption.

  1. Olivine-Orthopyroxene Equilibrium in Metal-rich Systems: Applications to Achondrites and Equilibrated Chondrites

    NASA Technical Reports Server (NTRS)

    Lauretta, D. S.; Benedix, G. K.; McCoy, T. J.

    2003-01-01

    Olivine and orthopyroxene are major minerals in every type of stony meteorite. The majority of achondritic meteorites and silicate-bearing iron meteorites have experienced high temperatures. If these temperatures persisted for an extended period of time then the iron contents of olivine and orthopyroxene should be in equilibrium. In their study of ungrouped clasts and chondritic meteorites, suggested that the equilibrium compositions of olivine and orthopyroxene should fall on a mixing line between LL chondrites and aubrites. Here we show that this is not necessarily the case and that a range of FeO contents in olivine and orthopyroxene can be in equilibrium with each other. The key parameters that determine the equilibrium Fe content in these minerals are temperature, oxygen fugacity (fO2), and silica activity (aSiO2).

  2. Systematic Ion Irradiation Experiments to Olivine: Comparison with Space Weathered Rims of Itokawa Regolith Particles

    NASA Astrophysics Data System (ADS)

    Matsumoto, T.; Tsuchiyama, A.; Watanabe, N.; Yasuda, K.; Miyake, A.; Nakauchi, Y.; Okada, T.; Abe, M.; Yada, T.; Uesugi, M.; Karouji, Y.; Nakato, A.; Hashiguschi, M.; Kumagai, K.

    2015-11-01

    We performed H and He ion irradiation experiments using olivine fragments, in order to reveal formation time-scales of space weathered rims and formation processes of blisters by solar wind irradiation.

  3. First-principles investigation of Li intercalation kinetics in phospho-olivines

    E-print Network

    Malik, Rahul

    2013-01-01

    This thesis focuses broadly on characterizing and understanding the Li intercalation mechanism in phospho-olivines, namely LiFePO? and Li(Fe,Mn)PO?, using first-principles calculations. Currently Li-ion battery technology ...

  4. Phase behavior and phase transformation kinetics during electrochemical cycling of lithium transition metal olivine compounds

    E-print Network

    Meethong, Nonglak

    2009-01-01

    Olivine LiMPO4 (M = Fe, Mn, Co, Ni) compounds have received most attention from the battery research community as the cathodes for Li-ion batteries because of several advantages, including a high theoretical capacity, 170 ...

  5. An Interactive Computer Program for Simulating the Effects of Olivine Fractionation from Basaltic and Ultrabasic Liquids.

    ERIC Educational Resources Information Center

    Pearce, Thomas H.

    1983-01-01

    Describes interactive computer program (listing available from author) which simulates olivine fractionation from basaltic/ultrabasic liquid. The menu-driven nature of the program (for Apple II microcomputer) allows students to select ideal Rayleigh fractionation or equilibrium crystallization. (JN)

  6. Measurement of Activation Volume of Dry Olivine at High Pressure

    NASA Astrophysics Data System (ADS)

    Durham, W. B.; Kohlstedt, D. L.; Mei, S.; Dixon, D. A.; Wang, L.

    2007-12-01

    Despite considerable effort to measure the activation volume V* of creep of olivine using a new generation of high-pressure deformation machines, namely the Rotational Drickamer Apparatus (RDA) and the Deformation- DIA (D-DIA) in conjunction with synchrotron x-ray sources, progress has been marred by a combination of an apparently weak signal (i.e., low V*) and measurement noise. The latter has a broad spectrum of causes, from inherent limitations of measurement systems (of stress, primarily) to limited time available for creep experiments at synchrotron sources to investigator-induced variations of sample state during measurement. We report here measurements following a significant advance in regulation of sample state: deforming polycrystalline olivine in a dry state under more uniform mechanical conditions gives us our first clear signal of a positive activation volume. The advance has been made possible by a choice of assembly materials that assures anhydrous conditions around the sample, and a technique for testing in the absence of a thermocouple within the sample assembly. The key to the anhydrous assembly is a self-gasketing D-DIA cube of hybrid composition: a sphere of mullite embedded in a cube of unfired pyrophyllite, where the diameter of the sphere matches the edge length of the cube (6-mm in our case). Unfired pyrophyllite is an excellent gasketing material, being soft and (in notable contrast with mullite) non-friable. Additionally, as a cube-filling "web" around the mullite sphere, the pyrophyllite is ideally configured for D-DIA self gasketing: maximum volume at the cube corners, minimum (zero) volume at cube faces. Thus the configuration under pressure is a bone-dry mullite pressure medium gasketed by pyrophyllite. Removal of the thermocouple from the deformation piston results in a demonstrably more symmetric deformation column within the assembly for the entire duration of the experiment, and the absence of the thermocouple is reliably compensated by off-line calibration of furnace power vs temperature. Results of creep experiments in the new cell indicate a value of V*/n (where n is the stress exponent) of 3 ± 1 × 10-6 m3/mol between 3 and 6 GPa. The value of n will be better resolved in future experiments, but if the deformation is in the dislocation creep regime (n ~ 3.5), then V* ~ 10 × 10-6 m3/mol.

  7. Water in Olivine and its High-Pressure Polymorphs

    NASA Astrophysics Data System (ADS)

    Thomas, S. M.; Jacobsen, S. D.; Bina, C. R.; Reichart, P.; Moser, M.; Dollinger, G.; Hauri, E. H.

    2014-12-01

    Theory and high-pressure experiments imply a significant water storage capacity of nominally anhydrous minerals (NAMs), such as olivine, wadsleyite and ringwoodite, composing the Earth's upper mantle and transition zone to a depth of 660 km. The presence of water, dissolved as OH into such nominally anhydrous high-pressure silicates, notably influences phase relations, melting behavior, conductivity, elasticity, viscosity and rheology. The first direct evidence for hydration of the transition zone has recently been reported by Pearson et al. (2014) and Schmandt et al. (2014). Knowledge of absolute water contents in NAMs is essential for modeling the Earth's interior water cycle. To take advantage of IR spectroscopy as highly sensitive water quantification tool, mineral-specific absorption coefficients are required. Such calibration constants can be derived from hydrogen concentrations determined by independent techniques, such as secondary ion mass spectrometry (SIMS), Raman spectroscopy or proton-proton(pp)-scattering. Broad beam pp-scattering has been performed on double-polished mm-sized mineral platelets (Thomas et al. 2008), but until recently analysis was not feasible for smaller samples synthetized in high-pressure apparati. Here we present first results from pp-scattering microscopy studies on ?m-sized single crystals of hydrous olivine, wadsleyite and ringwoodite, which were synthesized at various pressure-temperature conditions in a multi-anvil press. The method allows us to quantify 3D distributions of atomic hydrogen in ?m dimensions. These self-calibrating measurements were carried out at the nuclear microprobe SNAKE at the Munich tandem accelerator lab using a 25 MeV proton microbeam. We provide hydrogen depth-profiles, hydrogen maps and H2O concentrations. Pp-scattering data and results from independent Raman and SIMS analyses are in good agreement. Water contents for a set of high-pressure polymorphs with varying Fe-concentrations range from 0.8 wt% to 2.5 wt% H2O. From experimental data for Fo83, Fo87, Fo90 and Fo100 compositions we calculate mineral-specific absorption coefficients for the quantification of H2O using IR-spectroscopy, compare them with previously estimated values and discuss IR calibrations for major phases of the Earth's mantle.

  8. The formation of IIE iron meteorites investigated by the chondrule-bearing Mont Dieu meteorite

    NASA Astrophysics Data System (ADS)

    van Roosbroek, N.; Debaille, V.; Pittarello, L.; Goderis, S.; Humayun, M.; Hecht, L.; Jourdan, F.; Spicuzza, M. J.; Vanhaecke, F.; Claeys, Ph.

    2015-07-01

    A 435 kg piece of the Mont Dieu iron meteorite (MD) contains cm-sized silicate inclusions. Based on the concentration of Ni, Ga, Ge, and Ir (8.59 ± 0.32 wt%, 25.4 ± 0.9 ppm, 61 ± 2 ppm, 7.1 ± 0.4 ppm, respectively) in the metal host, this piece can be classified as a IIE nonmagmatic iron. The silicate inclusions possess a chondritic mineralogy and relict chondrules occur throughout the inclusions. Major element analysis, oxygen isotopic analysis (?17O = 0.71 ± 0.02‰), and mean Fa and Fs molar contents (Fa15.7 ± 0.4 and Fs14.4 ± 0.5) indicate that MD originated as an H chondrite. Because of strong similarities with Netschaëvo IIE, MD can be classified in the most primitive subgroup of the IIE sequence. 40Ar/39Ar ages of 4536 ± 59 Ma and 4494 ± 95 Ma obtained on pyroxene and plagioclase inclusions show that MD belongs to the old (~4.5 Ga) group of IIE iron meteorites and that it has not been perturbed by any subsequent heating event following its formation. The primitive character of MD sheds light on the nature of its formation process, its thermal history, and the evolution of its parent body.

  9. Clast-laden nature and the origin of Luna 24 olivine-vitrophyres

    NASA Technical Reports Server (NTRS)

    Basu, A.; Mckay, D. S.; Fruland, R. M.

    1978-01-01

    The study shows that Luna 24 olivine-vitrophyric particles are actually fragments of clast-laden melt and are not from a very low titanium (VLT) mare basalt flow. Diversity of composition and clast population, and morphological similarity to ropy glasses suggest an impact melt origin. Compositionally, the olivine-vitrophyres resemble the high magnesian VLT basalts, which may have been the target and source of the impact melt.

  10. Angrite LEW87051: Are the olivines pheno's or xeno's? A continuing story

    NASA Technical Reports Server (NTRS)

    Jurewicz, A. J. G.; Mckay, G. A.

    1993-01-01

    The achondrite LEW87051 is a porphyritic basalt consisting of large subhedral to euhedral zoned olivines in a finer-grained groundmass. The texture of this groundmass looks remarkably like a quenched melt. However, although the rock is clearly igneous, its exact origins and history are under dispute. From petrographic observations, Prinz felt that the large olivines were xenocrysts and that the zoning reflected interaction with an unrelated, CAI-enriched melt. McKay et al. was able to model the olivines as phenocrysts, whose zoning was the result of a parent melt that changed in composition as material crystallized, e.g., fractional crystallization in a closed system, and calculated a parent melt composition. Jurewicz and McKay compared the calculated parent melt composition with actual partial melts from CV and CM chondrites. They showed that the calculated melt was substantially different from equilibrium melts of these chondrites; however, the LEW87051 groundmass composition was similar to some of the low temperature partial melts, although slightly enriched in AN (or depleted in OL) components. This study presents the results of an independent petrologic look at other olivines in LEW87051 and the preliminary results of a quantitative model for the major zoning in these olivines as diffusive-exchange with an olivine-saturated, low temperature angritic melt.

  11. Single-Crystal Elasticity of San Carlos Olivine in the Earth's Mantle

    NASA Astrophysics Data System (ADS)

    Mao, Z.; Lin, J. F.; Fan, D.; Yang, J.; Zhuravlev, K. K.; Tkachev, S. N.

    2014-12-01

    Olivine is the most abundant mineral in the Earth's upper mantle. Studies on the elasticity of olivine attracted extensive research interests in the past few decades and have provided important constraints on the composition and structure of the Earth's upper mantle. Of particular importance is the single-crystal elasticity of olivine which is essential for understanding the anisotropy structure of the upper mantle. However, previous experimental studies on the single-crystal elasticity of olivine are limited to high pressure and ambient temperature or high temperature and ambient pressure. Much of our current knowledge on the velocity and anisotropy structures of the upper mantle heavily relies on extrapolations of limited experimental results. Here, we have studied the single-crystal elasticity of San Carlos olivine, [(Mg0.9Fe0.1)2SiO4], up to 20 GPa and 900 K using Brillouin spectroscopy and X-ray diffraction in an externally-heated diamond anvil cell at GSECARS of the Advanced Photon Source, Argonne National Laboratory. The simultaneously high pressure-temperature experiments allow us to investigate the combined effect of pressure and temperature on the velocity and anisotropy of olivine. These results have been applied to model the velocity structure, Vp and Vs anisotropy, Vp/Vs ratio, and Poisson's ratio of the Earth's upper mantle. Comparing the modeling results with seismic observations allow us to have a more comprehensive understanding on the velocity and anisotropy structure of the Earth's upper mantle.

  12. Particle dynamics and aggregation of crystals in a magma chamber with application to Kilauea Iki olivines

    NASA Astrophysics Data System (ADS)

    Schwindinger, Kathleen R.

    1999-03-01

    Crystals settling in relative proximity to each other will settle faster than their respective Stokes' velocities ( US) due to their mutual interactions. Pairs of equant spheres (within 100 diameters of each other) are accelerated to 1.55 US. Modification of Han and Lawler's [Han, M., Lawler, D.F., 1991. Interactions of two settling spheres: settling rates and collision efficiency. Journal of Hydraulic Engineering 117 (10) 1269-1289] equations to include inertia shows that the velocities of a pair of spheres differ and change during descent, allowing them to come into contact. In quiescent settling experiments with olivine-shaped clay prisms, the pairs of prisms usually settled faster than their US. The clay prisms aggregated 80% of the time, with the pairs of prisms rotating and tumbling as they fall, coming into and out of contact. Size variations in Kilauea Iki olivines control aggregation during quiescent settling. The settling velocities of individual crystals are variable, increasing when they are incorporated into aggregates. A suspension of olivine crystals (more than 0.01 vol.%) in a magma will settle slower than the average Stokes' velocities, except when a buoyant phase is present. Addition of a buoyant phase, such as CO 2 bubbles, can increase the settling velocity of the olivines when the total concentration (olivine plus bubbles) ( ?) is <35%, or carry the olivines in a packed bed when ?>35%.

  13. Characterization and Petrologic Interpretation of Olivine-Rich Basalts at Gusev Crater, Mars

    NASA Technical Reports Server (NTRS)

    McSween, H. Y.; Wyatt, M. B.; Gellert, R.; Bell, J. F., III; Morris, R. V.; Herkenhoff, K. E.; Crumpler, L. S.; Milam, K. A.; Stockstill, K. R.; Tornabene, L. L.; Arvidson, R. E.; Bartlett, P.; Blaney, D.; Cabrol, N. A.; Christensen, P. R.; Clark, B. C.; Crisp, A.; DesMarais, D. J.; Economou, T.; Farmer, J. D.; Farrand, W.; Ghosh, A.; Golombek, M.; Gorevan, S.; Greeley, R.

    2006-01-01

    Rocks on the floor of Gusev crater are basalts of uniform composition and mineralogy. Olivine, the only mineral to have been identified or inferred from data by all instruments on the Spirit rover, is especially abundant in these rocks. These picritic basalts are similar in many respects to certain Martian meteorites (olivine-phyric shergottites). The olivine megacrysts in both have intermediate compositions, with modal abundances ranging up to 20-30%. Associated minerals in both include low-calcium and high-calcium pyroxenes, plagioclase of intermediate composition, iron-titanium-chromium oxides, and phosphate. These rocks also share minor element trends, reflected in their nickel-magnesium and chromium-magnesium ratios. Gusev basalts and shergottites appear to have formed from primitive magmas produced by melting an undepleted mantle at depth and erupted without significant fractionation. However, apparent differences between Gusev rocks and shergottites in their ages, plagioclase abundances, and volatile contents preclude direct correlation. Orbital determinations of global olivine distribution and compositions by thermal emission spectroscopy suggest that olivine-rich rocks may be widespread. Because weathering under acidic conditions preferentially attacks olivine and disguises such rocks beneath alteration rinds, picritic basalts formed from primitive magmas may even be a common component of the Martian crust formed during ancient and recent times.

  14. Characterization and petrologic interpretation of olivine-rich basalts at Gusev Crater, Mars

    USGS Publications Warehouse

    McSween, H.Y.; Wyatt, M.B.; Gellert, Ralf; Bell, J.F.; Morris, R.V.; Herkenhoff, K.E.; Crumpler, L.S.; Milam, K.A.; Stockstill, K.R.; Tornabene, L.L.; Arvidson, R.E.; Bartlett, P.; Blaney, D.; Cabrol, N.A.; Christensen, P.R.; Clark, B.C.; Crisp, J.A.; Des Marais, D.J.; Economou, T.; Farmer, J.D.; Farrand, W.; Ghosh, A.; Golombek, M.; Gorevan, S.; Greeley, R.; Hamilton, V.E.; Johnson, J.R.; Joliff, B.L.; Klingelhofer, G.; Knudson, A.T.; McLennan, S.; Ming, D.; Moersch, J.E.; Rieder, R.; Ruff, S.W.; Schrorder, C.; de Souza, P.A.; Squyres, S.W.; Wanke, H.; Wang, A.; Yen, A.; Zipfel, J.

    2006-01-01

    Rocks on the floor of Gusev crater are basalts of uniform composition and mineralogy. Olivine, the only mineral to have been identified or inferred from data by all instruments on the Spirit rover, is especially abundant in these rocks. These picritic basalts are similar in many respects to certain Martian meteorites (olivine-phyric shergottites). The olivine megacrysts in both have intermediate compositions, with modal abundances ranging up to 20-30%. Associated minerals in both include low-calcium and high-calcium pyroxenes, plagioclase of intermediate composition, iron-titanium-chromium oxides, and phosphate. These rocks also share minor element trends, reflected in their nickel-magnesium and chromium-magnesium ratios. Gusev basalts and shergottites appear to have formed from primitive magmas produced by melting an undepleted mantle at depth and erupted without significant fractionation. However, apparent differences between Gusev rocks and shergottites in their ages, plagioclase abundances, and volatile contents preclude direct correlation. Orbital determinations of global olivine distribution and compositions by thermal emission spectroscopy suggest that olivine-rich rocks may be widespread. Because weathering under acidic conditions preferentially attacks olivine and disguises such rocks beneath alteration rinds, picritic basalts formed from primitive magmas may even be a common component of the Martian crust formed during ancient and recent times. Copyright 2006 by the American Geophysical Union.

  15. Geochemistry and origin of metal, olivine clasts, and matrix in the Dong Ujimqin Qi mesosiderite

    NASA Astrophysics Data System (ADS)

    Kong, Ping; Su, Wen; Li, Xianhua; Spettel, Bernhard; Palme, Herbert; Tao, Kejie

    2008-03-01

    The Dong Ujimqin Qi mesosiderite is the first recorded fall of a stony-iron meteorite in China. According to silicate textures and metal composition, this meteorite is classified as a member of subgroup IB. Instrumental neutron activation analyses (INAA) of metals show that the matrix metal has lower concentrations of Os, Ir, Re, and Pt, but higher concentrations of Ni and Au than the 7.5 cm metal nodule present in the meteorite. We attribute these compositional differences to fractional crystallization of molten metal. Studies of olivine clasts show that FeO contents are uniform in individual olivine crystals but are variable for different olivine clasts. Although concentrations of rare earth elements (REEs) change within olivine clasts, they all exhibit a vee-shaped pattern relative to CI chondrites. The relatively high concentrations of REEs in olivine and the shape of REE patterns require a liquid high in REEs and especially in light REEs. As such a liquid was absent from the region where basaltic and gabbroic clasts formed, mesosiderite olivine must have formed in a part of the differentiated asteroid that is different from the location where other mesosiderite silicate clasts formed.

  16. Disclinations provide the missing mechanism for deforming olivine-rich rocks in the mantle.

    PubMed

    Cordier, Patrick; Demouchy, Sylvie; Beausir, Benoît; Taupin, Vincent; Barou, Fabrice; Fressengeas, Claude

    2014-03-01

    Mantle flow involves large strains of polymineral aggregates. The strongly anisotropic plastic response of each individual grain in the aggregate results from the interactions between neighbouring grains and the continuity of material displacement across the grain boundaries. Orthorhombic olivine, which is the dominant mineral phase of the Earth's upper mantle, does not exhibit enough slip systems to accommodate a general deformation state by intracrystalline slip without inducing damage. Here we show that a more general description of the deformation process that includes the motion of rotational defects referred to as disclinations can solve the olivine deformation paradox. We use high-resolution electron backscattering diffraction (EBSD) maps of deformed olivine aggregates to resolve the disclinations. The disclinations are found to decorate grain boundaries in olivine samples deformed experimentally and in nature. We present a disclination-based model of a high-angle tilt boundary in olivine, which demonstrates that an applied shear induces grain-boundary migration through disclination motion. This new approach clarifies grain-boundary-mediated plasticity in polycrystalline aggregates. By providing the missing mechanism for describing plastic flow in olivine, this work will permit multiscale modelling of the rheology of the upper mantle, from the atomic scale to the scale of the flow. PMID:24572356

  17. Disclinations provide the missing mechanism for deforming olivine-rich rocks in the mantle

    NASA Astrophysics Data System (ADS)

    Cordier, Patrick; Demouchy, Sylvie; Beausir, Benoît; Taupin, Vincent; Barou, Fabrice; Fressengeas, Claude

    2014-03-01

    Mantle flow involves large strains of polymineral aggregates. The strongly anisotropic plastic response of each individual grain in the aggregate results from the interactions between neighbouring grains and the continuity of material displacement across the grain boundaries. Orthorhombic olivine, which is the dominant mineral phase of the Earth's upper mantle, does not exhibit enough slip systems to accommodate a general deformation state by intracrystalline slip without inducing damage. Here we show that a more general description of the deformation process that includes the motion of rotational defects referred to as disclinations can solve the olivine deformation paradox. We use high-resolution electron backscattering diffraction (EBSD) maps of deformed olivine aggregates to resolve the disclinations. The disclinations are found to decorate grain boundaries in olivine samples deformed experimentally and in nature. We present a disclination-based model of a high-angle tilt boundary in olivine, which demonstrates that an applied shear induces grain-boundary migration through disclination motion. This new approach clarifies grain-boundary-mediated plasticity in polycrystalline aggregates. By providing the missing mechanism for describing plastic flow in olivine, this work will permit multiscale modelling of the rheology of the upper mantle, from the atomic scale to the scale of the flow.

  18. Water in Pyroxene and Olivine from Martian Meteorites

    NASA Technical Reports Server (NTRS)

    Peslier, A. H.

    2012-01-01

    Water in the interior of terrestrial planets can be dissolved in fluids or melts and hydrous phases, but can also be locked as protons attached to structural oxygen in lattice defects in nominally anhydrous minerals (NAM) like olivine, pyroxene, or feldspar [1-3]. Although these minerals contain only tens to hundreds of ppm H2O, this water can amount to at least one ocean in mass when added at planetary scales because of the modal dominance of NAM in the mantle and crust [4]. Moreover these trace amounts of water can have drastic effects on melting temperature, rheology, electrical and heat conductivity, and seismic wave attenuation [5]. There is presently a debate on how much water is present in the martian mantle. Secondary ionization mass spectrometry (SIMS) studies of NAM [6], amphiboles and glass in melt inclusions [7-10], and apatites [11, 12] from Martian meteorites report finding as much water as in the same phases from Earth's igneous rocks. Most martian hydrous minerals, however, generally have the relevant sites filled with Cl and F instead of H [13, 14], and experiments using Cl [15] in parent melts can reproduce Martian basalt compositions as well as those with water [16]. We are in the process of analyzing Martian meteorite minerals by Fourier transform infrared spectrometry (FTIR) in order to constrain the role of water in this planet s formation and magmatic evolution

  19. Steady diffusion model for olivine-plagioclase corona growth

    NASA Astrophysics Data System (ADS)

    Nishiyama, Tadao

    1983-02-01

    This paper describes an application of a steady diffusion model ( JOESTEN, 1977) to an olivineplagioclase corona and some new results about a theoretical background on the steady diffusion equations. The olivine-plagioclase corona in a metanorite from Mt. Ikoma. Japan, has a layer sequence of olivinecummingtonite-hornblende + spinel-plagioclase. An analysis of a set of steady diffusion equations for the corona in the four-component system, MgO-AlO 3/2-SiO 2-Na 0.1Ca 0.9O 0.95 (NC) with excess H 2O. successfully gives the exchange cycle ( FISHER, 1973) in the layer sequence with specific values of the phenomenological coefficients' ratios; L MgMg/L SiSi, L MgMg/L AlAl and L MgMg/L NCNC. The factor which controls most strictly the stability of the layer sequence under isobaric-isothermal conditions is L MgMg/L AlAl. Theoretical considerations on the steady diffusion equations show that the L-ratios does not depend on concentrations even if the phenomenological coefficients themselves are functions of concentrations. Equivalence of the steady state condition and the minimum rate of entropy production law ( PRIGOGINE, 1967) is also proved for the system with fixed chemical potential gradients under isobaric-isothermal conditions, such as reaction bands. These results give a strong background for the model.

  20. Diffusion modelling of coronas around olivine in an open system

    NASA Astrophysics Data System (ADS)

    Ashworth, J. R.; Birdi, J. J.

    1990-09-01

    An open-system modification is introduced to Joesten's theory for steady-state diffusion-controlled growth of layered structures. The modified theory produces a model which is fully consistent with data for coronas between olivine and plagioclase from NE Scotland, having the layer sequence Pl|Hbl + Spl|Hbl|Opx|Ol. Relative immobility of Al and Si, inferred from the two-mineral symplectite, leads to the useful approximation of closure to Al and Si. The resulting model is consistent with Al, Si immobility, because it requires an Onsager diffusion coefficient for Al ( LAlAl) lower by an order of magnitude than that for Mg, while L AlAl/L SiSi?1 . Iron is less constrained than Mg to be mobile, with Ca and Na unconstrained, because their fluxes are relatively small. The results are insensitive to small errors in the data, except in Al and Si contents. Low Al/Si in plagioclase, as an example, requires lower L AlAl/L SiSi in the model. Variation of metasomatic inputs can explain the layer sequence Pl|Hbl + Spl|Opx + Spl|Opx|Ol, reported in the literature but not accounted for by the more restricted version of the theory previously available. The modified theory remains simple, and is likely to be applicable to other coronas, though complex examples may reveal its limitations.

  1. 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.

  2. Reaction rim growth on olivine in silicic melts: Implications for magma mixing

    USGS Publications Warehouse

    Coombs, M.L.; Gardner, J.E.

    2004-01-01

    Finely crystalline amphibole or pyroxene rims that form during reaction between silicic host melt and cognate olivine xenocrysts, newly introduced during magma mixing events, can provide information about the timing between mixing and volcanic eruptions. We investigated rim growth experimentally by placing forsteritic olivine in rhyolitic and rhyodacitic melts for times between 25 and 622 h at 50 and 150 MPa, H2O-saturated, at the Ni-NiO buffer. Rims of orthopyroxene microlites formed from high-silica rhyolite and rhyodacite melts at 885??C and 50 MPa, and in the rhyolite at 150 MPa and 885??C. Rims of amphibole with lesser orthopyroxene formed in the rhyolite at 150 MPa and 800??C and in the rhyodacite at 150 MPa and 885??C. Irregular, convolute olivine edges and mass balance between olivine, melt, and rim phases show that olivine partly dissolved at all conditions. Iron-rich zones at the exteriors of olivines, which increased in width parabolically with time, show that Fe-Mg interdiffusion occurring in olivines was not outpaced by olivine dissolution. Linear increases of the square of rim widths with time suggest that diffusion within the melt is the rate-controlling process for olivine dissolution and rim growth. Rims grew one-half to one order-of-magnitude faster when melt water contents were doubled, unless conditions were far above the liquidus. Rim growth rate in rhyolite increases from 0.055 ?? 0.01 ??m2/h at 885 ??C and 50 MPa to 0.64 ?? 0.13 ??m2/h at 800 ??C and 150 MPa. Melt composition has a lesser effect on rim growth rates, with growth rate increasing as melt SiO2 content decreases. Pyroxene rims on olivines in andesite erupted from Arenal volcano (Costa Rica) grew at a rate of 3.0 ?? 0.2 ??m2/h over an eleven-year period. This rate is faster than those of the experiments due to lower melt viscosity and higher temperatures, and suggests that a magma mixing event preceded the start of the eruption by days.

  3. 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…

  4. Temperature Dependence and Recoil-free Fraction Effects in Olivines Across the Mg-Fe Solid Solution

    NASA Technical Reports Server (NTRS)

    Sklute, E. C.; Rothstein, Y.; Dyar, M. D.; Schaefer, M. W.; Menzies, O. N.; Bland, P. A.; Berry, F. J.

    2005-01-01

    Olivine and pyroxene are the major ferromagnesian minerals in most meteorite types and in mafic igneous rocks that are dominant at the surface of the Earth. It is probable that they are the major mineralogical components at the surface of any planetary body that has undergone differentiation processes. In situ mineralogical studies of the rocks and soils on Mars suggest that olivine is a widespread mineral on that planet s surface (particularly at the Gusev site) and that it has been relatively unaffected by alteration. Thus an understanding of the characteristics of Mossbauer spectra of olivine is of great importance in interpreting MER results. However, variable temperature Mossbauer spectra of olivine, which are needed to quantify recoil-free fraction effects and to understand the temperature dependence of olivine spectra, are lacking in the literature. Thus, we present here a study of the temperature dependence and recoil-free fraction of a series of synthetic olivines.

  5. 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.

  6. Abiotic Versus Biotic Weathering Of Olivine As Possible Biosignatures

    NASA Technical Reports Server (NTRS)

    Longazo, Teresa G.; Wentworth, Susan J.; Clemett, Simon J.; Southam, Gordon; McKay, David S.

    2001-01-01

    We are investigating the weathering of silicate minerals by both purely inorganic, and biologically mediated processes using field-emission scanning electron microscopy (FESEM) and energy dispersive x-ray spectroscopy (EDS). By resolving surface textures and chemical compositions of weathered surfaces at the sub-micron scale we hope to be able to distinguish abiotic from biotic weathering processes and so establish a new biosignature applicable to the study of astromaterials including but not limited to the Martian meteorites. Sterilized olivine grains (San Carlos, Arizona) no more than 1-2 mm in their longest dimension were optically assayed to be uniform in color and free of inclusions were selected as weathering subjects. Prior to all experiments surface morphologies and Fe/Mg ratios were determined for each grain using FE-SEM and EDS. Experiments were divided into two categories abiotic and biotic and were compared with "naturally" weathered samples. For the preliminary experiments, two trials (open and closed to the ambient laboratory environment) were performed under abiotic conditions, and three trials under biotic conditions (control, day 1 and day 2). The open system abiotic trials used sterile grains heated at 98 C and 200 C for both 24 and 48 hours in 1L double distilled de-ionized water. The closed system abiotic trials were conducted under the same conditions but in a sealed two layer steel/Teflon "bomb" apparatus. The biotic trials used sterile grains mounted in a flow-through device attached to a wellhead on the Columbia River aquifer. Several discolored, altered, grains were selected to document "natural" weathering surface textures for comparison with the experimental samples. Preliminary results indicate there are qualitative differences in weathered surface textures among all the designed experiments. The olivine grains in abiotic trials displayed etching, pitting, denticulate margins, dissolution and clay formation. The scale of the features ranged from tens to a few microns with textures that remained relatively sharp and were crystallographically controlled. These results were comparable to that observed in the "naturally" weathered comparison/reference grains. Chemical analysis by EDS indicates these textures correlated with the relative loss of Mg and Fe cations by diffusional processes. In contrast the biotic results indicated changes in the etching patterns on the scale of hundreds of nm, which are neither sharp nor crystallographically controlled (nanoetching). Organisms, organic debris and/or extracellular polymeric substances (biofilm) were often in close proximity or direct contact with the nanoetching. While there are many poorly constrained variables in natural weathering experiments to contend with, such as the time scale, the chemistry of the fluids and degree of biologic participation, some preliminary observations can be made: (1) certain distinct surface textures appear correlated with the specific processes giving rise to these textures; (2) the process of diffusing cations can produce many similar styles of surface textural changes; and (3) the main difference between abiotic and biotically produced weathering is the scale (microns versus nanometers) and the style (crystallographically versus noncrystallographically controlled) of the textural features. Further investigation into nanosize scale surface textures should attempt to quantify both textures and chemical changes of the role of microorganisms in the weathering of silicates. Additional experiments addressing nanoscale textures of shock features for comparison with the current data set.

  7. Experimental constraints on formation of hematite in olivine at high pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Zhang, Yanfei; Wang, Chao; Wu, Yao; Liu, Wenlong; Jin, Zhenmin

    2015-10-01

    Iron-rich oxides, such as magnetite or hematite, have been reported in olivine grains in many orogenic garnet peridotites from continental collision zones. Whether these iron-rich minerals originate from dry oxidation, dehydrogenation-oxidation or exsolution from a precursor wadsleyite phase is debatable. This paper explores high-pressure and high-temperature experiments in a hydrous harzburgite system, by taking advantage of electron backscattered diffraction (EBSD) analyses, to examine the formation of hematite in olivine. Experimental results show that hematite can be formed within olivine grains at pressures >6 GPa and temperatures in the 1073-1473 K range. EBSD analysis suggests that hematite rods (not associated with clinopyroxene) and host olivine have the following crystallographic relations: < 0001 rangle _{{Hem}} // [100]_{{Ol}} , < 10{-}10rangle _{{Hem}} //[001]_{{Ol}} , < 11{-}20rangle _{{Hem}} //[010]_{{Ol}} , which are consistent with those observed in natural garnet peridotite from the Dabie-Sulu ultra-high-pressure (UHP) metamorphic terrane. It is postulated that both hydroxide (OH-) and hydrogen (H+) ions have the potential to oxidize Fe2+ to Fe3+, followed by rapid dehydrogenation and slow Fe diffusion, thus forming hematite within the olivine grains. It is proposed that dehydrogenation-oxidation is the most likely formation mechanism of hematite inclusions within olivine, with the following two requirements: an ample amount of H2O and specific P- T conditions (>6 GPa, at 1073 K). Such conditions are consistent with those calculated in natural garnet peridotites from the Dabie-Sulu UHP metamorphic terranes. The present study also indicates that hematite (or magnetite?) inclusions in olivine contain important clues about the tectonic evolution of UHP rocks in continental crust collision zones.

  8. Experimental constraints on formation of hematite in olivine at high pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Zhang, Yanfei; Wang, Chao; Wu, Yao; Liu, Wenlong; Jin, Zhenmin

    2015-06-01

    Iron-rich oxides, such as magnetite or hematite, have been reported in olivine grains in many orogenic garnet peridotites from continental collision zones. Whether these iron-rich minerals originate from dry oxidation, dehydrogenation-oxidation or exsolution from a precursor wadsleyite phase is debatable. This paper explores high-pressure and high-temperature experiments in a hydrous harzburgite system, by taking advantage of electron backscattered diffraction (EBSD) analyses, to examine the formation of hematite in olivine. Experimental results show that hematite can be formed within olivine grains at pressures >6 GPa and temperatures in the 1073-1473 K range. EBSD analysis suggests that hematite rods (not associated with clinopyroxene) and host olivine have the following crystallographic relations: < 0001 rangle _{{Hem}} // [100]_{{Ol}} , < 10{-}10rangle _{{Hem}} //[001]_{{Ol}} , < 11{-}20rangle _{{Hem}} //[010]_{{Ol}} , which are consistent with those observed in natural garnet peridotite from the Dabie-Sulu ultra-high-pressure (UHP) metamorphic terrane. It is postulated that both hydroxide (OH-) and hydrogen (H+) ions have the potential to oxidize Fe2+ to Fe3+, followed by rapid dehydrogenation and slow Fe diffusion, thus forming hematite within the olivine grains. It is proposed that dehydrogenation-oxidation is the most likely formation mechanism of hematite inclusions within olivine, with the following two requirements: an ample amount of H2O and specific P-T conditions (>6 GPa, at 1073 K). Such conditions are consistent with those calculated in natural garnet peridotites from the Dabie-Sulu UHP metamorphic terranes. The present study also indicates that hematite (or magnetite?) inclusions in olivine contain important clues about the tectonic evolution of UHP rocks in continental crust collision zones.

  9. Calculations of Li Ion Diffusion in Olivine Phosphates

    SciTech Connect

    Dathar, Gopi Krishna Phani; Sheppard, Daniel; Stevenson, Keith J.; Henkelman, Graeme

    2011-09-13

    Kinetic pathways of Li-ion diffusion in olivine phosphates are calculated from density functional theory (DFT). Previously reported theoretical diffusion rates for Li ions and vacancies in defect-free crystalline FePO? and LiFePO? are six orders of magnitude faster than experimentally measured values. This discrepancy can be resolved by considering the different components of Li kinetics, including diffusion in the bulk, on the surface, in the presence of defects, and in varying local environments. Using DFT+U, we quantify each of these effects and determine that, while bulk diffusion is affected by strain and Li concentration, these are not significant enough to explain the slow diffusion observed in experiment. However, surface diffusion is observed to have have high barriers, which could contribute to slow kinetics in nanostructured cathodes. Anti-site defects also provide a possible explanation for slow diffusion, but only for vacancy diffusion in LiFePO?, which has a barrier of 0.71 eV, compared to 0.29 eV in defect-free channels. In FePO?, a concerted Li-ion diffusion mechanism around the anti-site defect is found to have a low barrier of 0.35 eV, allowing for facile cross-channel diffusion at room temperature. The difference between Li-ion and vacancy diffusion is understood in terms of a favorable coordination between Li ions and localized electrons on Fe centers at the transition states for Li-ion hopping in FePO?. Greater distances between vacancies and holes at the transition states for vacancy diffusion lead to higher diffusion barriers.

  10. Kolsky Bar Impact Test Facility

    SciTech Connect

    Contreras, P.; Montoya, J.

    1998-12-31

    Testing for the Kolsky Bar is conducted at Los Alamos National Laboratory, Los Alamos, New Mexico. The Kolsky bar is operated by the Dynamic testing team of NMT-11, (Nuclear Material Technology Division) to enable measurements of stress-strain characteristics for the MST-8 (Material Science and Technology) personnel. The Kolsky Bar is located at the Plutonium Facility at TA-55 (Tech Area).

  11. Ion microprobe analyses of oxygen three-isotope ratios of chondrules from the Sayh al Uhaymir 290 CH chondrite using a multiple-hole disk

    E-print Network

    Meyers, Stephen R.

    Ion microprobe analyses of oxygen three-isotope ratios of chondrules from the Sayh al Uhaymir 290@geology.wisc.edu (Received 13 September 2010; revision accepted 14 March 2011) Abstract­The ion microprobe is the only) from the Sayh al Uhaymir (SaU) 290 CH chondrite were analyzed by ion microprobe at the University

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

    SciTech Connect

    DeHart, J.M.; Lu Jie; Benoit, P.H.; Sears, D.W.G. ); Lofgren, G.E. )

    1992-10-01

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

  13. 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.

  14. Space Weathering in Olivine and the Mineralogy of (Some) M-Class Asteroids

    NASA Astrophysics Data System (ADS)

    Britt, Daniel; Kohout, Tomas; Schelling, Patrick; Consolmagno, Guy J.

    2014-11-01

    One aspect of space weathering of airless bodies is the production of nanophase iron (npFe0) from Fe bearing silicate minerals. The combined effects of low oxygen fugacity and solar-wind implanted H tend to result in strongly-reduced surfaces that can be chemically activated by heating due to micrometeorite impacts. The mineral kinetics of olivine makes it particularly vulnerable to reduction, decomposition, and npFe0 production. Kohout et al. has recently developed a new method of controlled npFe0 production on olivine powder grains that mimics the essential features of this weathering process and was developed to quantitatively evaluate spectral changes related to space weathering and presence of npFe0. Compared to fresh olivine the treated samples exhibit spectral characteristics of space weathering including spectral darkening, shallowing and attenuation of 1 µm olivine absorption band, and reddening. The attenuation of the 1 µm band significantly shrinks the band FWHM and shifts the much reduced band center to shorter wavelengths around 0.95 µm. These spectral changes are related to increasing amounts of npFe0 and the disruption of the crystal structure of the parent olivine. Significantly, the darkened, reddened, and band attenuated olivine spectra are a close match to a number of M-class asteroids. What is particularly interesting is the match with the weak absorption band near 0.95 µm seen in many M-class asteroids (i.e. 16 Psyche, 22 Kalliope, 55 Pandora to name a few). One of the major issues in asteroid science is the relative scarcity of olivine asteroids (the ”Great Dunite Shortage” coined by Bell et al in Asteroids II). One possibility worth further study is that asteroidal olivine may be hidden by the relative ease with which it weathers. The surface chemical and micrometeorite environment in the asteroid belt may produce over time a spectrum for an olivine-rich surface that is remarkably similar to that of an M-class asteroid.

  15. Space weathering simulations through controlled growth of iron nanoparticles on olivine

    NASA Astrophysics Data System (ADS)

    Kohout, Tomáš; ?uda, Jan; Filip, Jan; Britt, Daniel; Bradley, Todd; Tu?ek, Ji?í; Skála, Roman; Kletetschka, Gunther; Kašlík, Josef; Malina, Ond?ej; Šišková, Karolína; Zbo?il, Radek

    2014-07-01

    Airless planetary bodies are directly exposed to space weathering. The main spectral effects of space weathering are darkening, reduction in intensity of silicate mineral absorption bands, and an increase in the spectral slope towards longer wavelengths (reddening). Production of nanophase metallic iron (npFe0) during space weathering plays major role in these spectral changes. A laboratory procedure for the controlled production of npFe0 in silicate mineral powders has been developed. The method is based on a two-step thermal treatment of low-iron olivine, first in ambient air and then in hydrogen atmosphere. Through this process, a series of olivine powder samples was prepared with varying amounts of npFe0 in the 7-20 nm size range. A logarithmic trend is observed between amount of npFe0 and darkening, reduction of 1 ?m olivine absorption band, reddening, and 1 ?m band width. Olivine with a population of physically larger npFe0 particles follows spectral trends similar to other samples, except for the reddening trend. This is interpreted as the larger, ?40-50 nm sized, npFe0 particles do not contribute to the spectral slope change as efficiently as the smaller npFe0 fraction. A linear trend is observed between the amount of npFe0 and 1 ?m band center position, most likely caused by Fe2+ disassociation from olivine structure into npFe0 particles.

  16. Space weathering simulations through controlled growth of iron nanoparticles on olivine

    NASA Astrophysics Data System (ADS)

    Kohout, T.; ?uda, J.; Filip, J.; Britt, D.; Bradley, T.; Tu?ek, J.; Skála, R.; Kletetschka, G.; Kašlík, J.; Malina, O.; Šišková, K.; Zbo?il, R.

    2014-07-01

    Airless planetary bodies are directly exposed to space weathering. The main spectral effects of space weathering are darkening, reduction in intensity of silicate mineral absorption bands, and an increase in the spectral slope towards longer wavelengths (reddening). Production of nanophase metallic iron (npFe^{0}) during space weathering plays a major role in these spectral changes. A laboratory procedure for the controlled production of npFe^{0} in silicate mineral powders has been developed. The method is based on a two-step thermal treatment of low-iron olivine, first in ambient air and then in a hydrogen atmosphere. Through this process, a series of olivine powder samples was prepared with varying amounts of npFe^{0} in the 7-20-nm size range. A logarithmic trend is observed between the amount of npFe^{0} and darkening, reduction of 1-? m olivine absorption band, reddening, and the 1-? m band width. Olivine with a population of physically larger npFe^{0} particles follows spectral trends similar to other samples, except for the reddening trend. This is interpreted as follows: the larger, ˜40-50-nm sized npFe^{0} particles do not contribute to the spectral slope change as efficiently as the smaller npFe^{0} fraction. A linear trend is observed between the amount of npFe^{0} and the 1-? m band center position, most likely caused by the Fe^{2+} disassociation from the olivine structure into npFe^{0} particles.

  17. Olivine to spinel transformation in Mg2SiO4 via faulted structures

    NASA Astrophysics Data System (ADS)

    Boland, J. N.; Liu, L.-G.

    1983-05-01

    The olivine-to-spinel (alpha-to-gamma) transformation in forsterite (Mg2SiO4) was studied by transmission electron microscopy. Synthetic olivine was compressed in a diamond-anvil cell to about 220 kbar, laser heated to 1000 C, and air quenched; pressure was released over 30 min, and the ion-thinned central 50-micron region was examined in an electron microscope. The presence of residual olivine (less than one percent) was confirmed by X-ray powder diffraction. Olivine and spinel were found to be intercalated, a transformational growth pattern consistent with a martensitic transformation, and this explanation of the phenomena is supported by the orientation relationship of the two phases and the high density of stacking faults and dislocations in the residual olivine grains. The transformation mechanism for Mg2SiO4 is thus seen as similar to that proposed for Fe2SiO4 and different from that in Mg2GeO4 and Ni2SiO4.

  18. Atomic-scale simulation of space weathering in olivine and orthopyroxene

    NASA Astrophysics Data System (ADS)

    Quadery, Abrar H.; Pacheco, Shaun; Au, Alan; Rizzacasa, Natalie; Nichols, Joshua; Le, Timothy; Glasscock, Cameron; Schelling, Patrick K.

    2015-04-01

    Classical molecular dynamics was used to study the annealing of anion and cation Frenkel defects in olivine and orthopyroxene minerals. While it was found that for both minerals, reorganization of the Si-O bonds, often accompanied by large Si displacements, occurs to maintain the fourfold coordination of the SiO4 tetrahedra, important differences are observed in their annealing behavior. Specifically, cation defects are substantially more mobile in olivine than in orthopyroxene leading to rapid annihilation of cation Frenkel defects and formation of extended defects in olivine. By contrast, the diffusion rate of anion defects in orthopyroxene is much higher than that in olivine and also exhibits large anisotropy. Consequently, it was found that diffusion in orthopyroxene occurs without significant annihilation of anion Frenkel defects or trapping of anion interstitials or vacancies into clusters. The results obtained here are discussed in the context of space weathering of olivine and orthopyroxene. Specifically, two important observations are made which may explain previous experimental results. First, ion irradiation experiments that show reduced tolerance for radiation damage in orthopyroxene may be explained by the rapid, one-dimensional anion mobility which prevents healing of the lattice. Second, laser heating experiments which show that orthopyroxene has enhanced tolerance to reduction and the evolution of nanophase Fe inclusions could be due to the observed rapid anion diffusion in orthopyroxene, which might allow the bulk to act as a reservoir for the surface.

  19. Galactic Bars in Cosmological Context

    E-print Network

    Isaac Shlosman

    2008-12-03

    Galactic disks can form in asymmetric potentials of the assembling dark matter (DM) halos, giving rise to the first generation of gas-rich bars. Properties of these bars differ from canonical bars analyzed so far. Moreover, rapid disk growth is associated with the influx of clumpy DM and baryons along the large-scale filaments. Subsequent interactions between this substructure and the disk can trigger generations of bars, which can explain their ubiquity in the Universe. I provide a brief summary of such bar properties and argue that they fit naturally within the broad cosmological context of a hierarchical buildup of structure in the universe.

  20. Bar coded retroreflective target

    DOEpatents

    Vann, Charles S. (Fremont, CA)

    2000-01-01

    This small, inexpensive, non-contact laser sensor can detect the location of a retroreflective target in a relatively large volume and up to six degrees of position. The tracker's laser beam is formed into a plane of light which is swept across the space of interest. When the beam illuminates the retroreflector, some of the light returns to the tracker. The intensity, angle, and time of the return beam is measured to calculate the three dimensional location of the target. With three retroreflectors on the target, the locations of three points on the target are measured, enabling the calculation of all six degrees of target position. Until now, devices for three-dimensional tracking of objects in a large volume have been heavy, large, and very expensive. Because of the simplicity and unique characteristics of this tracker, it is capable of three-dimensional tracking of one to several objects in a large volume, yet it is compact, light-weight, and relatively inexpensive. Alternatively, a tracker produces a diverging laser beam which is directed towards a fixed position, and senses when a retroreflective target enters the fixed field of view. An optically bar coded target can be read by the tracker to provide information about the target. The target can be formed of a ball lens with a bar code on one end. As the target moves through the field, the ball lens causes the laser beam to scan across the bar code.

  1. Olivine + halides: a recipe for iron mobilization in volcanic ash?

    NASA Astrophysics Data System (ADS)

    Hoshyaripour, G.; Hort, M. K.; Langmann, B.

    2013-12-01

    During the last decade, scientific evidences strongly suggest that volcanic ash iron has fertilization impact upon the surface ocean. Still, it is not well constrained how the insoluble iron in ash (i.e., as a component in minerals and also glass) could be mobilized during volcanic eruptions and atmospheric transport. Here we investigate the volcanic plume controls on ash iron solubility. We develope a conceptual box model to simulate the high, mid and low temperature chemical, physical and thermodynamic processes in eruption plumes to better constrain the iron mobilization in volcanic ash. We take into account the interaction of different species in a solid-liquid-gas system representing various volcanic settings (convergent plate, divergent plate and hot spot). Results show that the hot core of a volcanic plume (T>600°C) does not produce soluble iron directly but significantly controls the Fe mineralogy and oxidation state at the ash surface. The final iron mineralogy at the ash surface (i.e. the ash's oxidation front with 1-100 nm thickness) is likely to be independent of temperature and oxygen fugacity and is closely correlated to the ratio of H2 and H2S content of the magmatic gas to the amount of entrained oxygen. As the plume continues rising and cooling, sulfuric acid condenses at about 150°C followed by water condensation at about 50°C which also dissociates sulfuric acid and produces H+ ions in the liquid phase. The aqueous phase scavenges the surrounding gas species (e.g. SO2, HCl, HF) and concurrently dissolves the ash surface constituents. Since HCl is about 4 orders of magnitudes more soluble than SO2, its dissolution mainly controls the pH of the liquid. Hence, high HCl concentrations in the gas phase results in lower pH in the aqueous phase (pH<0.5) and consequently an increase in the ash dissolution rate. Moreover reduced iron carrying minerals (e.g. fayalite) show a much higher dissolution rate in comparison with oxidized species (e.g. hematite). Thus, the presence of the reduced iron species in the mineral assemblage seems to be more favorable for the soluble iron production. We conclude that bio-available iron production is weakly correlated with the tectonic setting and is instead controlled by the halide content of the eruption plume and the oxidation state of the iron at the ash mineral assemblage (e.g. presence of olivine). This hypothesis could satisfactorily explain the extraordinary iron release from the ash of Hekla eruption in 2000 and also the fertilization impact caused by the ash erupted from Kasatochi in 2008.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  3. Chemical zoning and diffusion of Ca, Al, Mn, and Cr in olivine of springwater pallasite

    NASA Technical Reports Server (NTRS)

    Zhou, Y.; Steele, Ian M.

    1993-01-01

    The pallasites, consisting mainly of Fe-Ni metal and olivine, are thought to represent the interior of a planetary body which slowly cooled from high temperature. Although the olivines are nearly homogeneous, ion microprobe studies revealed variations of Ca, Ti, Co, Cr, and Ni near grain edges. These variations were thought to represent diffusion in response to falling temperature of the parent body. Pallasite cooling rates have been estimated based on kamacite taenite textures but results differ by x100. In principle elemental profiles in olivine can allow estimates of cooling rate if diffusion coefficients are known; in addition, given a cooling rate, diffusion coefficients could be derived. Data are presented which show that apparent diffusion profiles can be measured for Al, Ca, Cr, and Mn which qualitatively agree with expected diffusion rates and have the potential of providing independent estimates of pallasite cooling rates.

  4. Modeling the creep properties of olivine by 2.5-dimensional dislocation dynamics simulations

    NASA Astrophysics Data System (ADS)

    Boioli, Francesca; Carrez, Philippe; Cordier, Patrick; Devincre, Benoit; Marquille, Matthieu

    2015-07-01

    In this work we performed 2.5-dimensional (2.5D) dislocation dynamics simulations coupling climb with the glide dislocation motion to model the creep behavior of olivine, one of the main component of the Earth's upper mantle. In particular, we present an application of this method to determine the creep strain rate in a material with high lattice resistance, such as olivine. We show that by including the climb mechanism we reach steady state creep conditions. Moreover, we find that a creep power law with a stress exponent close to 3 can be extracted from our simulations and we provide a model based on Orowan's law to predict the creep strain rates in the high temperature and low stress regime. The model presented is relevant to describe the plastic flow of olivine in the Earth's mantle deformation conditions and can be useful to derive the high temperature creep behavior of other materials.

  5. Geochemistry of Pallasite Olivines and the Origin of Main-Group Pallasites

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, D. W.; Rumble, D., III

    2006-01-01

    Main-group pallasites (PMG) are mixtures of iron-nickel metal and magnesian olivine thought to have been formed at the core-mantle boundary of an asteroid [1]. Some have anomalous metal compositions (PMG-am) and a few have atypically ferroan olivines (PMG-as) [2]. PMG metal is consistent with an origin as a late fractionate of the IIIAB iron core [2]. Most PMG olivines have very similar Fe/Mg ratios, likely due to subsolidus redox reaction with the metal [3]. In contrast, minor and trace elements show substantial variation, which may be explained by either: (i) PMG were formed at a range of depths in the parent asteroid; the element variations reflect variations in igneous evolution with depth, (ii) the pallasite parent asteroid was chemically heterogeneous; the heterogeneity partially survived igneous processing, or (iii) PMG represent the core-mantle boundaries of several distinct parent asteroids [4, 5]. We have continued doing major, minor and trace elements by EMPA and INAA on a wider suite of PMG olivines, and have begun doing precise oxygen isotope analyses to test these hypotheses. Manganese is homologous with Fe(2+), and can be used to distinguish between magmatic and redox processes as causes for Fe/Mg variations. PMG olivines have a range in molar 1000*Mn/Mg of 2.3-4.6 indicating substantial igneous fractionation in olivines with very similar Fe/Mg (0.138-0.148). The Mg-Mn-Fe distributions can be explained by a fractional crystallization-reduction model; higher Mn/Mg ratios reflect more evolved olivines while Fe/Mg is buffered by redox reactions with the metal. There is a positive association between Mn/Mg and Sc content that is consistent with igneous fractionation. However, most PMG olivines fall within a narrow Mn/Mg range (3.0-3.6), but these show a substantial range in Sc (1.00-2.29 micro-g/g). Assuming fractional crystallization, this Sc range could have resulted from approx.65% crystallization of an ultramafic magma. This is inconsistent with formation at the core-mantle boundary of a single asteroid [4]. One alternative is that the PMG are fragments of several asteroids, and these could have had different initial Sc contents, Mn/Mg and differences in igneous history. Our preliminary O isotope data and those of [6, 7] do not support this, although the coverage of PMG olivines is incomplete. The PMG-as Springwater is not easily fit in any scenario. Its olivine has among the highest Mn/Mg suggesting it is one of the most evolved, but the lowest Sc content suggesting it is the least evolved. The O isotopic composition of Springwater olivine is the same as that of other PMG. Thus there is no indication that it represents a distinct parent asteroid. Our preliminary O isotopic data favor a single PMG parent asteroid. In this case, the olivines are more likely melt-residues, and that the parent asteroid was initially heterogeneous in chemical, but not isotopic, composition.

  6. Diffusive modification of primary zoning in olivine cores in Angrite LEW 87051. [Abstract only

    NASA Technical Reports Server (NTRS)

    Mikouchi, T.; Mckay, G.; Miyamoto, M.; Takeda, H.

    1994-01-01

    Angrite LEW 87051 consists of large olivine crystals set in a fine-grained groundmass that clearly represents a crystallized melt. A few olivines contain Ca-poor, Cr-rich cores that crystallized from a very different melt than the outer part of the crystals constituting the majority of olivine in LEW 87051. We evaluate a model in which the cores formed through fractional crystallization of one melt, then were incorporated into a different melt as xenocrysts, whereupon the original zoning patterns were modified by diffusion. Using a similar approach, we calculate zoning patterns for the cores that would result from perfect fractional crystallization, compare them with the observed zoning, and determine whether the differences could result from diffusive modification consistent with known diffusion rates for Ca, Mn, and Cr. Using distribution coefficients from the 1400 C, IW + 1 experiments, we computed CaO, Cr2O3, and MnO abundances in the hypothetical parent melt by inverting the olivine at the centers of the cores. We further assumed that the primary zoning profile for CaO is essentially unmodified, because the diffusion rate of Ca in olivine is slow. We carried out the fractional crystallization calculation until the calculated Ca content was that observed at break in zoning profiles at the outer edge of the core. We then normalized the distance of this calculated profile to the length of the observed profile in the olivine core and calculated profiles for MnO and Cr2O3. The CaO zoning profile agrees well with the observed profile. The observed MnO profile is slightly higher than the calculated profile near the edge. Diffusion calculations indicate that reversal of the general trend of primary zoning through diffusion would require that diffusion of Cr is 5-10x faster than that of Mn.

  7. Comet-like mineralogy of olivine crystals in an extrasolar proto-Kuiper belt.

    PubMed

    de Vries, B L; Acke, B; Blommaert, J A D L; Waelkens, C; Waters, L B F M; Vandenbussche, B; Min, M; Olofsson, G; Dominik, C; Decin, L; Barlow, M J; Brandeker, A; Di Francesco, J; Glauser, A M; Greaves, J; Harvey, P M; Holland, W S; Ivison, R J; Liseau, R; Pantin, E E; Pilbratt, G L; Royer, P; Sibthorpe, B

    2012-10-01

    Some planetary systems harbour debris disks containing planetesimals such as asteroids and comets. Collisions between such bodies produce small dust particles, the spectral features of which reveal their composition and, hence, that of their parent bodies. A measurement of the composition of olivine crystals (Mg(2-2x)Fe(2x)SiO(4)) has been done for the protoplanetary disk HD?100546 (refs 3, 4) and for olivine crystals in the warm inner parts of planetary systems. The latter compares well with the iron-rich olivine in asteroids (x???0.29). In the cold outskirts of the ??Pictoris system, an analogue to the young Solar System, olivine crystals were detected but their composition remained undetermined, leaving unknown how the composition of the bulk of Solar System cometary olivine grains compares with that of extrasolar comets. Here we report the detection of the 69-micrometre-wavelength band of olivine crystals in the spectrum of ??Pictoris. Because the disk is optically thin, we can associate the crystals with an extrasolar proto-Kuiper belt a distance of 15-45 astronomical units from the star (one astronomical unit is the Sun-Earth distance), determine their magnesium-rich composition (x = 0.01?±?0.001) and show that they make up 3.6?±?1.0 per cent of the total dust mass. These values are strikingly similar to those for the dust emitted by the most primitive comets in the Solar System, even though ??Pictoris is more massive and more luminous and has a different planetary system architecture. PMID:23038467

  8. Rheological contrast between olivine and garnet at high pressures under anhydrous conditions

    NASA Astrophysics Data System (ADS)

    Mei, S.; Suzuki, A. M.; Kohlstedt, D. L.; Durham, W. B.; Dixon, N. A.

    2010-12-01

    In this study, we carried out experiments investigating the rheological contrast between olivine and garnet, two major components of the mantle, at mantle temperatures and pressures. Experiments were carried out using a deformation-DIA at the National Synchrotron Light Source at Brookhaven National Laboratory. Samples were fabricated from powdered minerals; olivine was from San Carlos and garnet from the Dabie-Sulu orogenic belt in China. In the experiments, a cold-pressed cylinder of fine-grained olivine and one of garnet, each with a diameter of ~1.1 mm and a length of ~0.8 mm, were stacked together, separated by a nickel foil disk. This duplex sample was assembled with alumina pistons, a boron nitride sleeve, and graphite resistance heater into a 6.2-mm edge length cubic mullite-pyrophyllite pressure cell. Experiments were carried out at 1373 - 1573 K and pressures of 3 - 5 GPa. With the synchrotron x-ray beam, a time series of in-situ radiographs enables monitoring of the instantaneous lengths of both deforming samples at the same temperature, pressure, and load. At our experimental conditions, both samples deform with stress exponents of n ? 3 and with activation energies of Q ? 300 kJ/mol. Samples of olivine deform only a factor of ~1.5 faster than samples of garnet of similar grain size, indicating that there is no significant rheological contrast between samples of olivine and garnet under anhydrous conditions. This result, which is the first direct comparison of the rheological behavior of olivine and garnet, provides a solid basis for modeling the rheological structures of subducted lithosphere.

  9. XANES Measurements of Cr Valence in Olivine and their Applications to Planetary Basalts (Invited)

    NASA Astrophysics Data System (ADS)

    Bell, A. S.; Burger, P.; Le, L.; Shearer, C. K.; Papike, J.; Sutton, S. R.; Newville, M.; Jones, J. H.

    2013-12-01

    The oxidation state and partitioning behavior of trace Cr in terrestrial and planetary basaltic magmas has long been a subject of petrologic inquiry. We have performed a series of experiments designed to examine the relationship between oxygen fugacity and the ratio of divalent to trivalent Cr present in olivine crystals grown from a basaltic liquid. The experimental olivine crystals were grown at fO2 values ranging from IW-1 to IW+3.4. The melt composition used in this work was modeled after the bulk composition of the primitive, basaltic martian meteorite Yamato 980459 (Y-98). Chromium valence in the olivine crystals was measured with X-ray-Absorption-Near-Edge-Spectroscopy (XANES) at the Advanced Photon Source, Argonne National Laboratory. Chromium K-edge XANES data were acquired with the x-ray microprobe of GSECARS beamline 13-ID-E. Beam focusing was accomplished with dynamically-figured Kirkpatrick-Baez focusing mirrors; this configuration yielded a beam focused to a final spot size of ~ 4 ?m2. Results from the XANES measurements indicate that the ratio of divalent to trivalent Cr in the olivine is systematically correlated with fO2 in a manner that is consistent with the expected redox systematics for Cr2+- Cr3+ in the melt. In this way, measurements of the Cr2+/Cr3+ in olivine phenocrysts can indirectly reveal information about the Cr valence ratio and fO2 the liquid from which it grew even in the absence of a quenched melt phase. Although the results from the experiments presented in this work specifically apply to the Yamato 98 parental liquid, the concepts and XANES analytical techniques used in this study present a novel, generalized methodology that may be applicable to any olivine-bearing basalt. Furthermore, the XANES based measurements are made on a micron-scale, thus potential changes of the Cr2+/Cr3+ in the melt occurring during crystallization may be recorded in detail.

  10. Reaction-induced fracturing during olivine serpentinization: A mechanistic investigation at the interface scale

    NASA Astrophysics Data System (ADS)

    Plümper, O.; Røyne, A.; Malthe-Sørenssen, A.; King, H. E.; Jamtveit, B.

    2012-04-01

    Serpentinization of the Earth's impermeable upper mantle is one of the most fundamental metamorphic hydration reactions. It governs lithospheric weakening, geochemical subduction zone input and possibly even the formation of life-essential building blocks. Serpentinization relies on fluid pathway generation due to low initial permeability and the large positive solid volume change associated with hydration. Although these pathways can be produced as a tectonic stress response, there is substantial evidence that the volume increase during olivine serpentinization itself generates stresses sufficient to fracture the rock. Nonetheless, the actual fracturing mechanism during olivine serpentinization is largely unexplored. Unconstrained batch experiments (Okamoto et al. 2011, this study) produce comparable hierachial fracture patterns to those found in natural samples demonstrating that no external forces (e.g., tensile stress) are required for fracturing to take place. Combining this with the observation that fluid-mediated mineral replacement advances via an interface-coupled dissolution-reprecipitation mechanism (e.g., Putnis 2009) without solid-state diffusion into the dissolving mineral indicates that classical (stress) corrosion cracking mechanisms cannot describe fracturing during olivine serpentinization. By uniting micro- and nanostructural characteristics ubiquitous to serpentinized olivine grains with a coupled diffusion-reaction-deformation model and crack growth theory this study explores the sub-critical fracturing mechanism at the interfacial scale. We present a new multistep reaction process and test the feasibility of a molecular wedge-assisted fracturing mechanism based on the following ubiquitously identified features: (1) no rotation of grain domains during fragmentation, (2) isotropic fracture orientation distribution with a uniform average width of individual finite length serpentine veins, (3) cumulative fragment area distribution with a log-normal scaling behavior following a hierachical fracturing model, (4) etch pit development at olivine-lizardite reaction interfaces, (5) crack initiation at these surface perturbations and (6) amorphous layer formation during olivine dissolution prior to serpentine nucleation (e.g., Rumori et al. 2004). Based on these observations we propose an entirely self-propagating reaction-driven fracturing process, where fractures nucleate at dissolution-induced surface perturbations assisted by a molecular wedge of amorphous 'gel', followed by further olivine dissolution and serpentine (±brucite) reprecipitation coupled with the force of crystallization. This process results in the observed hierarchical fracture network. Our results suggest that the mechanical force needed to advance serpentinization at the grain-scale does not rely on external forces but is due to interface-coupled, chemomechanical feedback during olivine re-equilibration in the presence of a fluid phase. Nevertheless, the influence of tectonic forces will need to be accounted for at larger scales.

  11. Acoustic emissions produced by anticrack faulting during the olivine-spinel transformation

    NASA Astrophysics Data System (ADS)

    Green, H. W., II; Scholz, C. H.; Tingle, T. N.; Young, T. E.; Koczynski, T. A.

    1992-04-01

    Anticrack faulting during the phase transformations of olivine to its denser polymorphs is a principal contender for the mechanism of deep-focus earthquakes. The original work on Mg2GeO4 established that initiation of faulting by this mechanism is not due to brittle fracture, and subsequent experiments on olivine of mantle composition showed that it can operate at pressures of at least 14 GPa. Acoustic emissions accompanying anticrack faulting in Mg2GeO4 are reported, thereby confirming that this mechanism involves a dynamic instability accompanied by elastic radiation.

  12. First finding of burkeite in melt inclusions in olivine from sheared lherzolite xenoliths.

    PubMed

    Korsakov, Andrey V; Golovin, Alexander V; De Gussem, Kris; Sharygin, Igor S; Vandenabeele, Peter

    2009-08-01

    For the first time burkeite was observed as a daughter phase in the melt inclusions in olivine by Raman spectroscopy. The olivine comes from sheared lherzolite xenoliths from the Udachnaya-East kimberlite pipe (Yakutia, Russia). This anhydrous sulfate-carbonate mineral (Na(6)(CO(3))(SO(4))(2)) is generally considered to be a characteristic mineral in saline soils or in continental lacustrine evaporite deposits. Recently, however, this mineral was identified in hydrothermal fluids. Our observations indicate that burkeite can also be formed from a mantle-derived melt. PMID:19058996

  13. Short- and long-term olivine weathering in Svalbard: implications for Mars.

    PubMed

    Hausrath, E M; Treiman, A H; Vicenzi, E; Bish, D L; Blake, D; Sarrazin, P; Hoehler, T; Midtkandal, I; Steele, A; Brantley, S L

    2008-12-01

    Liquid water is essential to life as we know it on Earth; therefore, the search for water on Mars is a critical component of the search for life. Olivine, a mineral identified as present on Mars, has been proposed as an indicator of the duration and characteristics of water because it dissolves quickly, particularly under low-pH conditions. The duration of olivine persistence relative to glass under conditions of aqueous alteration reflects the pH and temperature of the reacting fluids. In this paper, we investigate the utility of 3 methodologies to detect silicate weathering in a Mars analog environment (Sverrefjell volcano, Svalbard). CheMin, a miniature X-ray diffraction instrument developed for flight on NASA's upcoming Mars Science Laboratory, was deployed on Svalbard and was successful in detecting olivine and weathering products. The persistence of olivine and glass in Svalbard rocks was also investigated via laboratory observations of weathered hand samples as well as an in situ burial experiment. Observations of hand samples are consistent with the inference that olivine persists longer than glass at near-zero temperatures in the presence of solutions at pH approximately 7-9 on Svalbard, whereas in hydrothermally altered zones, glass has persisted longer than olivine in the presence of fluids at similar pH at approximately 50 degrees C. Analysis of the surfaces of olivine and glass samples, which were buried on Sverrefjell for 1 year and then retrieved, documented only minor incipient weathering, though these results suggest the importance of biological impacts. The 3 types of observations (CheMin, laboratory observations of hand samples, burial experiments) of weathering of olivine and glass at Svalbard show promise for interpretation of weathering on Mars. Furthermore, the weathering relationships observed on Svalbard are consistent with laboratory-measured dissolution rates, which suggests that relative mineral dissolution rates in the laboratory, in concert with field observations, can be used to yield valuable information regarding the pH and temperature of reacting martian fluids. PMID:19191538

  14. The olivine-ilmenite thermometer. [partitioning effect of temperature on iron ions and magnesium

    NASA Technical Reports Server (NTRS)

    Andersen, D. J.; Lindsley, D. H.

    1979-01-01

    It is noted that the partitioning of Fe(2+) and Mg between olivine and ilmenite is temperature-dependent and can serve as a geothermometer if the activity-composition relations are determined. The paper reports on the study of the partitioning from 700-980 C at 1 kbar and 800-900 C at 13 kbar, and develops a solution model to account for the nonideality of olivine in the binary system fosterite-fayalite and for ilmenite in the ternary system ilmenite-geikielite-hematite. A comparison with crystallization experiments shows that this thermometer may be safely extrapolated to temperatures higher than those of the exchange experiments.

  15. Experimental shock metamorphism of mono- and polycrystalline olivine - A comparative study

    NASA Technical Reports Server (NTRS)

    Bauer, J. F.

    1979-01-01

    The paper reports on a series of controlled shock recovery experiments which have been performed on over 40 samples including monocrystalline, polycrystalline, dunite, and porous particulate olivine-bearing targets. Results of the mineralogical and petrological analyses of these samples are used to establish a general and comparative diagnosis of shock effects generated in various olivine-bearing materials. Finally, some experiments are conducted under different ambient pO2 conditions so that information on the distribution of observed impact features is derived as a function not only of peak pressure and texture of the target sample, but also of specific environmental conditions.

  16. Olivine Composition of the Mars Trojan 5261 Eureka: Spitzer IRS Data

    NASA Technical Reports Server (NTRS)

    Lim, L. F.; Burt, B. J.; Emery, J. P.; Mueller, M.; Rivkin, A. S.; Trilling, D.

    2011-01-01

    The largest Mars trojan, 5261 Eureka, is one of two prototype "Sa" asteroids in the Bus-Demeo taxonomy. Analysis of its visible/near-IR spectrum led to the conclusion that it might represent either an angritic analog or an olivine-rich composition such as an R chondrite. Spitzer IRS data (5-30 micrometers) have enabled us to resolve this ambiguity. The thermal-IR spectrum exhibits strong olivine reststrahlen features consistent with a composition of approximately equals Fo60-70. Laboratory spectra of R chondrites, brachinites, and chassignites are dominated by similar features.

  17. Ringwoodite Lamellae in Olivine from the S6 Chondrite Tenham: The Transformation Mechanism

    NASA Astrophysics Data System (ADS)

    Xie, Z.; Sharp, T. G.; Decarli, P. S.

    2006-12-01

    Ringwoodite lamellae in partially transformed olivine have been reported to occur in the shock-induced melt veins or near the melt veins in heavily shocked (S6) chondrites [1-4]. These features were interpreted to have formed by a coherent intracrystalline transformation mechanism like that observed in experimentally transformed samples by Kerschhofer et al. [5-7]. However, our SEM and TEM observations on the partially transformed olivine suggest that the transformation is incoherent and occurs along specific orientation [4], which is in agreement with the new interpretation of ringwoodite lamellae based on new SEM and SXRD observations [8]. Here we report more detailed TEM results, which are crucial to understand the transformation mechanism. Abundant ringwoodite lamellae were found in olivine grains, which occur as host-rock fragments entrained in melt veins and pockets. These partially transformed olivines are commonly intergrown with enstatite and plagioclase in multi-phase fragments. High-resolution SEM images reveal that the ringwoodite lamellae are not continuous, but rather polycrystalline ringwoodite with crystal size about 1 mm. Preliminary TEM results show that olivine are heavily deformed or occur as fine olivine grains, and ringwoodite lamellae consist of individual ringwoodite grains in the matrix of olivine fine grains. The discontinuous lamellar textures that we observe strongly suggest that the lamellae consist of many distinct ringwoodite crystallites rather than single-crystal lamella. It is possible that lamellae of polycrystalline ringwoodite in olivine could form by a mechanism analogous to the formation of planar deformation features (PDF), representing preferential transformation along specific crystallographic defect planes of the host phase. [1 Chen et al. (2004) Proceedings. of NAS 101(42), 15033-15037. [2] Ohtani et al. (2004) EPSL 227(3-4), 505- 515. [3] Beck, et al. (2005) Nature 435, 1071-1074. [4] Xie and Sharp (2006), LPSC XXXVII, 2306.pdf. [5] Kerschhofer et al. (1996) Science 274 (5284), 79-81. [6] Kerschhofer et al. (1998) Mineralogical magazine 62(5),617-638. [7] Kerschhofer et al. (2000) PEPI 121, 59-76. [8] Chen et al. (2006) Meteoritics Planet. Sci. (41), 731-737.

  18. A valid Margules formulation for an asymmetric ternary solution - Revision of the olivine-ilmenite thermometer, with applications

    NASA Technical Reports Server (NTRS)

    Andersen, D. J.; Lindsley, D. H.

    1981-01-01

    A derivation of a valid asymmetric ternary Margules expression for the excess free energy is presented, and the olivine-ilmenite thermometer is revised accordingly. Although the effect on the thermometer is relatively small, the revision results in improved precision. Estimated temperatures of equilibration are presented for olivine and ilmenite from lunar and terrestrial rocks.

  19. Stress, strain, and B-type olivine fabric in the fore-arc mantle: Sensitivity tests using

    E-print Network

    van Keken, Peter

    Stress, strain, and B-type olivine fabric in the fore-arc mantle: Sensitivity tests using high-arc mantle. The presence of B-type olivine fabric in the mantle wedge may provide an explanation that provide insights into the distribution and magnitude of B-type fabric using two-dimensional, high

  20. B-type olivine fabric in the mantle wedge: Insights from high-resolution non-Newtonian subduction zone models

    E-print Network

    van Keken, Peter

    B-type olivine fabric in the mantle wedge: Insights from high-resolution non-Newtonian subduction of subduction zones. These include 3-D flow effects, parallel melt filled cracks, and B-type olivine fabric. We predict the distribution of B- type and other fabrics with high-resolution thermal and stress models

  1. Multi-$\\bar{K}$ hypernuclei

    E-print Network

    D. Gazda; E. Friedman; A. Gal; J. Mares

    2009-10-20

    Relativistic mean field calculations of multi-$\\bar{K}$ hypernuclei are performed by adding $K^-$ mesons to particle-stable configurations of nucleons, $\\Lambda$ and $\\Xi$ hyperons. For a given hypernuclear core, the calculated $\\bar{K}$ separation energy $B_{\\bar{K}}$ saturates with the number of $\\bar{K}$ mesons for more than roughly 10 mesons, with $B_{\\bar{K}}$ bounded from above by 200 MeV. The associated baryonic densities saturate at values 2-3 times nuclear-matter density within a small region where the $\\bar{K}$-meson densities peak, similarly to what was found for multi-$\\bar{K}$ nuclei. The calculations demonstrate that particle-stable multistrange $\\{N,\\Lambda,\\Xi \\}$ configurations are stable against strong-interaction conversions $\\Lambda \\to N \\bar{K}$ and $\\Xi \\to N \\bar{K} \\bar{K}$, confirming and strengthening the conclusion that kaon condensation is unlikely to occur in strong-interaction self-bound strange hadronic matter.

  2. A new systematic approach using the Modified Gaussian Model: Insight for the characterization of chemical composition of olivines, pyroxenes and olivine-pyroxene mixtures

    NASA Astrophysics Data System (ADS)

    Clénet, Harold; Pinet, Patrick; Daydou, Yves; Heuripeau, Frédérick; Rosemberg, Christine; Baratoux, David; Chevrel, Serge

    2011-05-01

    An automatic procedure has been implemented on the original MGM approach ( Sunshine et al., 1990) in order to deal with an a priori unknown mafic mineralogy observed in the visible-near infrared by reflectance spectroscopy in the case of laboratory or natural rock spectra. We consider all the mixture possibilities involving orthopyroxene, clinopyroxene and olivine, and use accordingly for each configuration different numbers of Gaussians, depending on the potential complexity of the mixture. A key issue is to initialize the MGM procedure with a proper setting for the Gaussians parameters. An automatic analysis of the shape of the spectrum is first performed. The continuum is handled with a second order polynomial adjusted on the local maxima along the spectrum and Gaussians parameters initial settings are made on the basis of laboratory results available in the literature in the case of simple mixtures of mafic minerals. The returned MGM solutions are then assessed on spectroscopic grounds and either validated or discarded, on the basis of a mineralogical sorting. The results presented in this paper are a first quantitative step to characterize both modal and chemical compositions of pyroxenes and olivines. A demonstration of the methodology on specific examples of binary and ternary olivine-pyroxenes mixtures has been made, which shows that the different non-linear effects which affect the Gaussian parameters (center and strength) can be successfully handled. Of note is the fact that the band center positions associated with the different mafic minerals are not set here in the inverse problem, and thus the MGM outputs are truly informative of the chemical composition of pyroxenes and olivines. With the consideration of some limits on the detection thresholds, these results are quite promising for increasing the operational use of the Modified Gaussian Model with large hyperspectral data sets in view of establishing detailed mineralogical mappings of magmatic units.

  3. Reduced chromium in olivine grains from lunar basalt 15555 - X-ray Absorption Near Edge Structure (XANES)

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Jones, K. W.; Gordon, B.; Rivers, M. L.; Bajt, S.; Smith, J. V.

    1993-01-01

    The oxidation state of Cr in 200-micron regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using X-ray Absorption Near Edge Structure (XANES). Reference materials had previously been studied by optical absorption spectroscopy and included Cr-bearing borosilicate glasses synthesized under controlled oxygen fugacity and Cr-doped olivines. The energy dependence of XANES spectral features defined by these reference materials indicated that Cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene. These results, coupled with the apparent f(02)-independence of partitioning coefficients for Cr into olivine, imply that the source magma was dominated by divalent Cr at the time of olivine crystallization.

  4. Electrical relaxation studies of olivine type nanocrystalline LiMPO4 (M=Ni, Mn and Co) materials

    NASA Astrophysics Data System (ADS)

    Cheruku, Rajesh; Kruthika, G.; Govindaraj, G.; Vijayan, Lakshmi

    2015-11-01

    The olivine type LiMPO4 (M=Ni, Mn and Co) materials were synthesized by solution combustion technique using glycine as fuel. The structural characterizations were explored to confirm the phase formation of materials. The scanning electron microscope was used to identify the morphology of olivine materials. The local structure and chemical bonding between MO6 octahedral and (PO4)3- tetrahedral groups were probed by Raman spectroscopy. Grain and grain boundaries were contributed for ion relaxation and dc conduction in olivine materials. Two orders of enhancement in ionic conductivity was observed in these olivine materials than the reported value. Among all the explored olivine samples, LiMnPO4 showed highest enhancement in conductivity due to weak Li-O bonding and largest unit cell volume.

  5. Telling zoned from zoned: LA-MC-ICPMS and SIMS iron isotopic measurements of olivine

    NASA Astrophysics Data System (ADS)

    Sio, C.; Dauphas, N.; Teng, F.; Chaussidon, M.; Helz, R. L.; Roskosz, M.

    2012-12-01

    Previous studies have revealed that iron and magnesium isotopes may be used to distinguish diffusion-driven zoning from crystal growth zoning in olivine crystals [1-3]. In magmatic systems, Mg-rich olivine is an early crystallizing phase. As the melt evolves, it becomes more Fe-rich, so that in reaching equilibrium, Fe diffuses into and Mg diffuses out of the initial olivine crystal. Because light isotopes diffuse faster than heavy isotopes [4], such diffusion-driven mechanism is accompanied with 1) a negative correlation of Fe and Mg isotopes, and 2) a negative correlation of Fe isotopes and a positive correlation of Mg isotopes with Fo#. Teng et al. [1] showed these correlations in olivine fragments from Kilauea Iki lava lake. Sio et al. [3] used microdrilling techniques to spatially resolve the same correlations in an olivine phenocryst from the Kilauea Iki lava lake. LA-MC-ICPMS and SIMS were used to measure Fe isotopes in the same olivine phenocryst [5]. These techniques provide lateral and depth resolution approximately an order of magnitude higher than microdrilling. There is perfect agreement in iron isotopic measurements between these three techniques. The rim of the olivine is at -0.2 ‰ and the core is at -1.3 ‰ in ?56Fe relative to IRMM-014. The thermal history and petrography of the Kilauea Iki lava lake is known, so diffusion-controlled zoning in the olivine phenocryst may be modeled as in a laboratory experiment. After measuring the crystallographic orientation of the olivine with TEM in a FIB section, th