Sample records for barred olivine chondrules

  1. The primary liquid condensation model and the origin of barred olivine chondrules

    NASA Astrophysics Data System (ADS)

    Varela, M. E.; Kurat, G.; Zinner, E.

    2006-10-01

    Barred olivine (BO) chondrules are some of the most striking objects in chondrites. Their ubiquitous presence and peculiar texture caught the attention of researchers and, as a consequence, considerable effort has been expensed on unraveling their origin(s). Here we report on a detailed study of two types of chondrules: the Classic and the Multiple-Plate Type of BO chondrules from the Essebi (CM2), Bishunpur (LL3.1), Acfer 214 (CH3) and DAG 055 (C3-UNGR) chondrites, and discuss the petrographic and chemical data of their major mineral phases and glasses. Glasses occur as mesostasis or as glass inclusions, the latter either enclosed inside the olivine bars (plates) or still connected to the mesostasis. The chemical composition of all glasses, characterized by being Si-Al-Ca-rich and free of alkali elements, is similar to those of the constituents (the building blocks, such as chondrules, aggregates, inclusions, mineral fragments, etc.) of CR and CV3 chondrites. They all have high trace element contents ( ˜10×CI) with unfractionated CI-normalized abundances of refractory trace elements and depletions in moderately volatile and volatile elements with respect to the refractory trace elements. The presence of alkali elements (Na + K + Rb) is coupled with a low Ca content and is only observed in those glasses that have behaved as open systems. This result supports the previous finding that Ca was replaced by alkalis (e.g., Na-Ca exchange), presumably through a vapor-solid reaction. The glasses apparently are the quenched liquid from which the olivine plates crystallized. However, they do not show any chemical fractionation that could have resulted from the crystallization of the olivines, but rather have a constant chemical compositions throughout the formation of the chondrule. In a previous contribution we were able to demonstrate the role of these liquids in supporting crystal growth directly from the vapor. Here we extend application of the primary liquid condensation model to formulate a new model for the origin of BO chondrules. The primary liquid condensation model is based on the ability of dust-enriched solar-nebula gas to directly condense into a liquid, provided the gas/dust ratio is sufficiently low. Thus, we propose that chondrules can be formed by condensation of a liquid droplet directly from the solar nebula. The extensive variability in chemical composition of BO chondrules, which ranges from alkali-poor to alkali-rich, can be explained by elemental exchange reactions with the cooling nebula. We calculate the chemical composition of the initial liquid droplet from which BO chondrules could have formed and speculate about the physical and chemical conditions that prevail in the specific regions of the solar nebula that can promote creation of these objects.

  2. Formation conditions of pyroxene-olivine and magnesian olivine chondrules

    SciTech Connect

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

    1990-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Ruzicka, Alex; Floss, Christine; Hutson, Melinda

    2012-01-01

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

  4. 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.

  5. 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.

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

    Microsoft Academic Search

    Minoru Uehara; Norihiro Nakamura

    2006-01-01

    Dynamic crystallization experiments are conducted under a magnetic field to determine both magnetic and mineralogical properties of chondrules. The experiment reproduced synthetic dusty olivine samples that were formed by a high temperature reduction of an initially fayalitic olivine. Backscattered-electron microscopy observations confirmed that synthetic dusty olivine contains abundant fine, submicron-sized Ni-poor Fe inclusions in the cores of MgO-rich olivine grains,

  7. 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.

  8. Transmission electron microscopy of chondrule minerals in the Allende meteorite: constraints on the thermal and deformational history of granular olivine-pyroxene chondrules

    NASA Astrophysics Data System (ADS)

    Müller, Wolfgang Friedrich; Weinbruch, Stephan; Walter, Rudolf; Müller-Beneke, Gerhild

    1995-02-01

    The microstructures of minerals of three granular olivine-pyroxene chondrules from the Allende carbonaceous chondrite have been studied by methods of transmission electron microscopy, including electron diffraction and energy dispersive X-ray microanalysis. The main issue is to deduce the thermal and deformational history of the chondrules. The chondrules consist dominantly of olivine (Fa 3-36), mostly Mg-rich ones ( < Fa 15), and low-Fe ( < 3 mol%) pyroxenes along the join Mg 2Si 2O 6?CaMgSi 2O 6. In addition, Ca-rich plagioclase (An 80-An 90), awaruite, magnetite, whitlockite, pentlandite, troilite, Mg?Fe?Cr?Al spinels, sodalite, nepheline and corundum were observed. Pyroxenes found are orthopyroxene (Opx), clinoenstatite (Cen), pigeonite (Pig), lamellar intergrowth of pigeonite and diopside (Pig/Di) on (001) and diopside (Di). The assemblages and chemical compositions of Pig, Pig/Di and Di indicate a subsolidus closure temperature of approximately 1345°C. The lamellar intergrowth Pig/Di was formed by exsolution. The average wavelength ? (periodicity) of the lamellae is 29 nm in chondrule 1, 25 nm in chondrule 2 and 33 nm in chondrule 3. A cooling rate between 25 and 0.4°C/h for the temperature interval 1350-1200°C is estimated from the wavelength ? of the exsolution lamellae. Independent information on the cooling rate is provided by the size of the b-antiphase domains (APDs) of Ca-rich plagioclase, which reflects the time-and temperature-dependent ordering of Al/Si. The size (average diameter) of the domains is 10-30 nm. Comparison with isothermal annealing experiments on Ca-rich plagioclases (An 70-An 100) yields a cooling rate between 12 and 0.03°C/h. Cooling rates derived from the microstructure of pyroxene and plagioclase are at least one order of magnitude lower than those obtained from dynamic crystallization experiments (e.g. Hewins, R. H. Meteorites and the Early Solar System, pp. 660-679, 1988). However, our estimate is only valid in a small temperature interval. This period of slow cooling is followed by quenching, as indicated by the absence of orthoenstatite lamellae in clinoenstatite, suggesting high cooling rates ? 10 4°C/h at a temperature of ˜ 1000°C (Brearley, A. J. and Jones, R. H., Lunar Planet. Sci.XXIV, 185-186, 1993). Olivine and pyroxene grains are frequently intersected by veins - interpreted as former cracks - filled with Fe-rich olivine and chromitic and hercynitic spinels. Formation of the veins occurred after exsolution of clinopyroxene into Pig/Di. Steep Fe and Mg concentration gradients between Fe-rich veins and the surrounding Mg-rich olivine were observed. Here, Fe/Mg interdiffusion is limited to approximately 1 ?m. This observation indicates fast cooling in the solar nebula and low temperature, not exceeding approximately 330°C, in the parent body. The few deformation effects demonstrate that the Allende meteorite in total was never subjected to shock waves with a peak pressure exceeding 5 GPa.

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

    PubMed

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

    2008-06-24

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

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

    PubMed Central

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

    2008-01-01

    Peace River is one of the few shocked members of the L-chondrites clan that contains both high-pressure polymorphs of olivine, ringwoodite and wadsleyite, in diverse textures and settings in fragments entrained in shock-melt veins. Among these settings are complete olivine porphyritic chondrules. We encountered few squeezed and flattened olivine porphyritic chondrules entrained in shock-melt veins of this meteorite with novel textures and composition. The former chemically unzoned (Fa24–26) olivine porphyritic crystals are heavily flattened and display a concentric intergrowth with Mg-rich wadsleyite of a very narrow compositional range (Fa6–Fa10) in the core. Wadsleyite core is surrounded by a Mg-poor and chemically stark zoned ringwoodite (Fa28–Fa38) belt. The wadsleyite–ringwoodite interface denotes a compositional gap of up to 32 mol % fayalite. A transmission electron microscopy study of focused ion beam slices in both regions indicates that the wadsleyite core and ringwoodite belt consist of granoblastic-like intergrowth of polygonal crystallites of both ringwoodite and wadsleyite, with wadsleyite crystallites dominating in the core and ringwoodite crystallites dominating in the belt. Texture and compositions of both high-pressure polymorphs are strongly suggestive of formation by a fractional crystallization of the olivine melt of a narrow composition (Fa24–26), starting with Mg-rich wadsleyite followed by the Mg-poor ringwoodite from a shock-induced melt of olivine composition (Fa24–26). Our findings could erase the possibility of the resulting unrealistic time scales of the high-pressure regime reported recently from other shocked L-6 chondrites. PMID:18562280

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

    E-print Network

    September 2008 Abstract Chondrules and isolated forsterites in five low-subtype ordinary chondrites [NWA, and isolated forsterite grains, show evidence for igneous fractionation under disequilibrium conditions, and multiple episodes of chondrule break-up in some cases. Forsterite grains, including normal grains

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

    SciTech Connect

    Miura, H. [Graduate School of Natural Sciences, Nagoya City University, Yamanohata 1, Mizuho-cho, Mizuho-ku, Nagoya, Aichi 467-8501 (Japan); Yamamoto, T., E-mail: miurah@nsc.nagoya-cu.ac.jp [Center for Planetary Science, Kobe University, 7-1-48, Minamimachi, Minatojima, Chuo-ku, Kobe 650-0047 (Japan)

    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.

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

    SciTech Connect

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

    1988-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  15. 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.

  16. 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. (Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany, F.R.))

    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.

  17. 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.

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

    E-print Network

    Jacquet, Emmanuel; Gounelle, Matthieu

    2015-01-01

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

  19. 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.

  20. 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.

  1. Refractory precursor components in an Allende ferromagnesian chondrule

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1995-03-01

    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 >40% of all unequilibrated ordinary chondrites), and the group A5 chondrules in the least metamorphosed ordinary chondrites which have many similarities to chondrules in the highly metamorphosed 'equilibrated' chondrites. Since composition provides insights into both primary formation properties of the chondrules and the effects of metamorphism on the entire assemblage it is possible to determine the petrographic type of RC075 as 3.1 with unique certainty. Similarly, the new scheme can be applied to individual chondrules without knowledge of the petrographic type of the host chondrite, which makes it especially suitable for studying breccias. Finally, the new scheme has revealed the existence of chondrules not identified by previous techniques and which appear to be extremely important. Like group A1 and A2 chondrules (but unlike group B1 chondrules) the primitive group A5 chondrules did not supercool during formation, but unlike group A1 and A2 chondrules (and like group B1 chondrules) they did not suffer volatile loss and reduction during formation. It is concluded that the compositional classification scheme provides important new insights into the formation and history of chondrules and chondrites which would be overlooked by previous schemes.

  4. 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.

  5. Genetic Relationships Among Type I and II Chondrules and Matrix of Chondrites

    NASA Astrophysics Data System (ADS)

    Nagahara, H.

    1992-07-01

    It is now being accepted that chondrules were formed from pre- existing solids through complete or incomplete melting and that chondrules and fine-grained matrix materials were formed in oxidizing conditions where olivine solid solution was stable and not in the solar nebula of the average composition. As has been pointed out (e.g. 1-3), chondrules and matrix should have been genetically related because of constant bulk composition of chondrites in spite of various chondrule/matrix ratios. The recently calculated phase diagram of the olivine solid solution system (4) well explains their genetic relationships. At pressures above the triple point of forsterite (4x10^-4 bar, 1890 degrees C), the phase diagrams are the same as that at 1 bar. At pressures between the triple points of forsterite and fayalite (5x10^-8 bar, 1205 degrees C), liquid-bearing fields lie below the gas and solid field in the Fe-rich portion of the system. At pressures below the triple point of fayalite, the phase diagram has a gas-solid loop with a large Mg/Fe difference between coexisting solid and gas (5). X(sub)Mg of chondrules in ordinary chondrites ranges from 0.7 to 0.95 and that in carbonaceous chondrites from 0.5 to 1.0, and mostly between 0.8 and 0.90 for both C and O chondrites. Although chondrules are of multi-component, their compositions can be roughly shown by the olivine system. At pressures of 10^-4-10^-5 bar, olivine (X(sub)Mg<0.9) melts to become magnesian olivine and iron-rich liquid when heated, and X(sub)Mg of olivine and liquid are not so largely different. In this case, vaporization hardly takes place because olivine and liquid are below the vaporous curves of the system. Type I were formed in such a condition. At higher temperatures or lower pressures, liquid is not stable and highly magnesian olivine and gas with highly ferrous olivine composition are stable. Vaporization of the fayalite component takes place in this condition, resulted in remaining highly magnesian olivine. Therefore, Type II were formed at higher temperature or lower pressure than Type I. The present model does not require reduction for the formation of Type I (3,6). Difference in pressure is due to the degree of enrichment of the dust component relative to hydrogen gas. This model is consistent with the facts that (a) olivines in Type I chondrules are weakly zoned but those in Type II are strongly zoned, (b) liquid (groundmass of chondrules) in Type I is essentially FeO-free of which Mg/Fe distribution between olivine and liquid is often smaller than equilibrium value, but liquid in Type II is rich in FeO of which Mg/Fe distribution is in equilibrium, and (c) liquid in Type I chondrules are rich in refractory elements (Al, Ca, Ti, and Cr) but that in Type II is rich in mildly volatile elements (Fe, Mn, and alkalis) (6,7). Presence of alkalis in some Type I chondrules may be due to phase diagram of complex systems. Matrix olivine (mainly Fo(sub)50) are thought to be condensates from gas originated from partial evaporation of the olivine component at high temperatures responsible for formation of Type I chondrules. Condensation of iron-rich olivine from gas with iron-rich olivine composition has been experimentally shown (8). This model well explains the fine- grained but euhedral nature of matrix olivine. References: (1) Anders, E. (1987) Phil. Trans. R. Soc. Lond. A323, 287-304. (2) Nagahara, H. (1990) Meteoritics 25, 389-390. (3) Grossman, J. N. (1991) Meteoritics 26, 340-341. (4) Nagahara, H. et al. (1992) LPSC XXIII, 959-960. (5) Nagahara, H. et al. (1991) Meteoritics 26, 376. (6) Jones, R. (1990) Geochim. Cosmochim. Acta. 54, 1785-1802. (7) Jones, R. (1989) Proc. 19th Lunar Planet. Sci. Conf., 523-536. (8) Nagahara, H. et al. (1989) Nature, 315, 516-518.

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

    Microsoft Academic Search

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

    1988-01-01

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

  7. Shock Effects in Olivine from Mocs Chondrite

    NASA Astrophysics Data System (ADS)

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

    1995-09-01

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

  8. Boron in Chondrules

    NASA Astrophysics Data System (ADS)

    Hoppe, P.; Goswami, J. N.; Krähenbühl, U.; Marti, K.

    2001-10-01

    Isotopic compositions and abundances of boron were measured in sixteen chondrules from seven chondrites by ion microprobe mass spectrometry. The chondrules are of the porphyritic, barred, and radial type and host meteorites include carbonaceous, ordinary, and enstatite chondrites. Boron abundances are generally low with average boron concentrations of between 80 and 500 ppb. These abundances are lower than those of bulk chondrites (0.35 to 1.2 ppm; Zhai et al., 1996), confirming earlier suggestions that boron is mostly contained in the matrix. No significant variation in the 11B/10B ratio is observed among these chondrules, outside our experimental error limits of several permil, and B-isotopic compositions agree with those reported for bulk chondrites. The lack of a significant isotope fractionation between chondrules and matrix implies that the low boron abundances are not the result of a Rayleigh fractionation during chondrule formation. Isotopic heterogeneities within individual chondrules are constrained to be < +/-20% at >95% confidence level at a spatial scale of 20-30 um, significantly lower than the value of about +/-40% previously reported for chondrules from carbonaceous and ordinary chondrites (Chaussidon and Robert, 1995, 1998). The observed B-isotopic homogeneity does not conflict with the presence of decay products from extinct 10Be, with (10Be/9Be)0 ~ 10-3, as was inferred for calcium-aluminum-rich inclusions. Extinct 10Be in chondrules would shift the abundance ratio 11B/10B at best by several permil because of their commonly observed low Be/B ratios (<2). The results show that potential B-isotopic heterogeneities in the solar nebula due to the presence of components with different B-isotopic signatures, such as boron produced by high-energy galactic cosmic rays (11B/10B ~ 2.5), or by the hypothetical low-energy particle irradiation (11B/10B ~ 3.5-11) or boron from type II supernovae (11B/10B >> 1), did not survive the chondrule formation processes to a measurable extent.

  9. Troilite in the chondrules of type-3 ordinary chondrites: Implications for chondrule formation

    NASA Astrophysics Data System (ADS)

    Rubin, Alan E.; Sailer, Alan L.; Wasson, John T.

    1999-08-01

    The presence of primary troilite in chondrules requires that nebular temperatures were <650 K (the 50% condensation temperature of S) at the time of chondrule formation and that chondrules were molten for periods short enough (?10 s) to avoid significant volatilization of S. We examined 226 intact chondrules of all textural types from eight unshocked to weakly shocked ordinary chondrite falls of low petrologic type to determine the origin of troilite in chondrules; 68 chondrules are from LL3.0 Semarkona. There is a high probability that troilite is primary (i.e., was present among the chondrule precursors) if it is completely embedded in a mafic silicate phenocryst, located within one-half radius of the apparent chondrule center and is part of an opaque assemblage with an igneous texture. Based on these criteria, 13% of the chondrules in Semarkona and in the set as a whole contain primary troilite. Most of the remaining chondrules contain troilite that is probably primary, but does not meet all three criteria. Troilite occurs next to tetrataenite in some opaque spherules within low-FeO chondrules in Semarkona, implying that the Ni required to form the tetrataenite came from the troilite. Troilite can accommodate 5 mg/g Ni at high temperatures (>1170 K) but much less Ni at lower temperatures; because this is far higher than the metamorphic temperature inferred for Semarkona (˜670 K), the troilite must be primary. Primary troilite fitting the three criteria occurs in a smaller fraction of low-FeO [FeO/(FeO + MgO) in olivine and/or low-Ca pyroxene not greater than 0.075] than high-FeO porphyritic chondrules in Semarkona (9% vs. 33%). Coarse-grained low-FeO porphyritic chondrules appear to contain somewhat more troilite on average than those of medium grain size. We found a few troilite-free, metallic-Fe-Ni-bearing, low-FeO chondrules that contain Na 2O-bearing augite and Na 2O- and K 2O-rich mesostasis; these chondrules were probably formed after ambient nebular temperatures cooled below 910 K (the 50% condensation temperature of Na) and before they reached 650 K. Literature reports of rare fayalitic microchondrules in the rims around a few normal-size chondrules suggest that chondrule formation persisted until nebular temperatures cooled below 500 K. Secondary troilite occurs in a few percent of Semarkona chondrules as thin veins mobilized by shock; troilite or pyrrhotite in the outer portions of some chondrules occur within opaque assemblages containing magnetite, carbide, Ni-rich sulfide, awaruite, and Co-rich kamacite produced by parent-body hydrothermal alteration.

  10. Trace Element Distributions Within UOC Chondrules

    NASA Astrophysics Data System (ADS)

    Alexander, C. M. O'd.

    1992-07-01

    Chondrules are the most abundant and arguably the most enigmatic objects in the ordinary chondrites. Simulations of chondrules textures have placed limits on the range of cooling rates (100-3000 degrees C/hr) and peak temperatures (1600-1550 degrees C) chondrules experienced during their formation (Hewins, 1988). Also bulk analyses have been used to constrain the compositions of the chondrule precursor components (e.g., Grossman and Wasson, 1982). However, little is known of the distribution of trace elements between the various chondrule components. Yet these trace element distributions, here measured in porphyritic chondrules from Semarkona, Chainpur, and Bishunpur, are potentially useful additional tools in the study of chondrule cooling rates, chondrule-rim/matrix relationships, and possibly chondrule precursors. The olivine and low-Ca pyroxene trace element contents (Figs. 1 and 2) are remarkably unfractionated compared to those expected from equilibrium distribution coefficients, but are similar to the patterns observed in synthetic chondrules cooled at 1000-2000 degrees C/hr (Kennedy et al., 1992). Such fast cooling rates as these data imply are close to the upper limit for porphyritic chondrules estimated from simulation experiments (Hewins, 1988). With the exception of Na, K, and Eu, the incompatible lithophiles are concentrated in the glass, typically by a factor of 10 relative to the bulk meteorite and in more or less CI-like proportions. The rims and matrix are generally enriched in Na, K, and Eu (Alexander, 1991), possibly because these elements have been partially volatilized from chondrules and recondensed on the fine-grained material. However, the three chondrule glass-rim pairs studied to date show no striking correlation between degree of volatile depletion of the glass and enrichment of the rims. The olivine, pyroxene, and glass compositions share some similarities with the lithophile chondrule precursor components identified by Grossman and Wasson (1982) from bulk chondrule analyses. The most significant difference between the two is the correlation of Mg with the refractory incompatible elements in the Grossman and Wasson data, whereas within the chondrules Mg is mostly in the minerals and the refractory incompatables are in the glass. However, a compilation of published chondrule analyses suggests this correlation in the bulk data may not be very strong, prompting a reexamination of the origin of the chondrule precursors. Alexander C. M. O'D. (1991) Meteoritics (abstract) 26, 312. Grossman J. N. and Wasson J. T. (1982) Geochim. Cosmochim. Acta 46, 1081-1099. Hewins R. H. (1988) In Meteorites and the early solar system (eds. J. F. Kerridge and M. S. Mathews), pp. 660-679. Kennedy A. K., Lofgren G. E. and Wasserburg G. J. (1992) Lunar Planet. Sci (abstract) 23, 679-670. Figure 1, which in the hard copy appears here, shows mean and standard error of 12 olivines from porphyritic chondrule. Figure 2, which in the hard copy apears here, shows mean and standard error of nine low-Ca pyroxenes from porphyritic chondrules.

  11. 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.

  12. The group A3 chondrules of Krymka: Further evidence for major evaporative loss during the formation of chondrules

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    Like Semarkona (type 3.0), Krymka (type 3.1) contains two distinct types of chondrule (namely groups A and B) which differ in their bulk compositions, phase compositions, and CL properties. The group A chondrules in both meteorites show evidence for major loss of material by evaporation(i.e. elemental abundance patterns, size, redox state, olivine-pyroxene abundances). Group A and B chondrules probably formed from common or very similar precursors by the same processes acting with different intensities, group A suffering greater mass-loss by evaporation and reduction of FeO and SiO2. While Krymka chondrules share many primary mineralogical and compositional properties with Semarkona chondrules, the minimal metamorphism it has suffered has also had a significant effect on its chondrules.

  13. Retention of sodium during chondrule melting

    SciTech Connect

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

    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.

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

    NASA Astrophysics Data System (ADS)

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

    1991-02-01

    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.

  15. 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.

  16. Vesicles in Experimental Chondrules as Clues to Chondrule Precursors

    NASA Astrophysics Data System (ADS)

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

    1993-07-01

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

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

    NASA Technical Reports Server (NTRS)

    Amelin, Yuri; Krot, Alexander N.

    2005-01-01

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

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

    Microsoft Academic Search

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

    2011-01-01

    We have examined Fe\\/Mn systematics of 34 type IIA chondrules in eight highly unequilibrated CO, CR, and ordinary chondrites using new data from this study and prior studies from our laboratory. Olivine grains from type IIA chondrules in CO chondrites and unequilibrated ordinary chondrites (UOC) have significantly different Fe\\/Mn ratios, with mean molar Fe\\/Mn = 99 and 44, respectively. Olivine

  19. Troilite in the Chondrules of Type-3 Ordinary Chondrites: Implications for Chondrule Formation

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.; Sailer, Alan L.; Wasson, John T.

    1999-01-01

    The presence of primary troilite in chondrules requires that nebular temperatures were <650 K (the 50% condensation temperature of S) at the time of chondrule formation and that chondrules were molten for periods short enough (less than or equal to 10 s) to avoid significant volatilization of S. We examined 226 intact chondrules of all textural types from eight unshocked to weakly shocked ordinary chondrite falls of low petrologic type to determine the origin of troilite in chondrules; 68 chondrules are from LL3.0 Semarkona. There is a high probability that troilite is primary (i.e , was present among the chondrule precursors) if it is completely embedded in a mafic silicate phenocryst, located within one-half radius of the apparent chondrule center and is part of an opaque assemblage with an igneous texture Based on these criteria, 13% of the chondrules in Semarkona and in the set as a whole contain primary troilite. Most of the remaining chondrules contain troilite that is probably primary, but does not meet all three criteria. Troilite occurs next to tetratacnite in some opaque spherules within low-FeO chondrules in Semarkona, implying that the Ni required to form the tetrataenite came from the troilite Troilite can accommodate 5 mg/g Ni at high temperatures (> 1170 K) but much less Ni at lower temperatures; because this is far higher than the metamorphic temperature inferred for Semarkona (approx. 670 K), the troilite must be primary Primary troilite fitting the three criteria occurs in a smaller fraction of low-FeO [FeO/(FeO + MgO) in olivine and/or low-Ca pyroxene not greater than 0.0751 than high-FeO porphyritic chondrules in Semarkona (9% vs 33%) Coarse-grained low-FeO porphyritic chondrules appear to contain somewhat more troilite on average than those of medium grain size We found a few troilite-free, metallic-Fe-Ni-bearing, low-FeO chondrules that contain Na2O-bearing augite and Na2O- and K2O-rich mesostasis; these chondrules were probably formed after ambient nebular temperatures cooled below 910 K (the 50% condensation temperature of Na) and before they reached 650 K Literature reports of rare fayalitic microchondrules in the rims around a few normal-size chondrules suggest that chondrule formation persisted until nebular temperatures cooled below 500 K Secondary troilite occurs in a few percent of Semarkona chondrules as thin veins mobilized by shock; troilite or pyrrhotite in the outer portions of some chondrules occur within opaque assemblages containing magnetite, carbide, Ni-rich sulfide, awaruite, and Co-rich kamacite produced by parent-body hydrothermal alteration.

  20. 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.

  1. 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.

  2. Energetics of chondrule formation

    NASA Technical Reports Server (NTRS)

    Levy, E. H.

    1988-01-01

    Meteorite chondrules apparently were formed as a result of localized, transient heating events in the protoplanetary nebula. Such transient events, which seem to have heated the chondrules to temperatures in excess of 1500 C for not more than a few minutes, are not easily explicable in terms of the canonically accepted evolutionary processes of the nebular disk. Thus the occurrence of extraordinary dynamical processes may be indicated by the presence of chondrules and, consequently, the existence of chondrules poses questions fundamental to the understanding of protoplanetary and protostellar systems. This chapter briefly considers the gross energetics, as well as some related questions, of chondrule formation and the implications for several previously proposed sources of chondrule formation energy, including gravitational infall of the nebula, energy derived from solid-body impacts within the nebula, and energy liberated by dissipative evolution of the nebula itself.

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

    NASA Astrophysics Data System (ADS)

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

    1993-07-01

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

  4. Silica Under- and Oversaturated Mineral Assemblages in Chondrule Mesostases

    NASA Astrophysics Data System (ADS)

    Bridges, J. C.; Hutchison, R.

    1995-09-01

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

  5. 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.

  6. Cathodoluminescence observations of in situ aqueous destruction of chondrules in the Murchison CM chondrite

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    A low-power cathodoluminescence (CL) mosaic of a 1x2 cm section of the Murchison CM chondrite contains chondrules of two types: one contains olivines with red CL and is thought to be the equivalent of group A chondrules of Sears et.; and one without observable CL, which is probably equivalent to their group B chondrules. Both types of chondrule contain dust mantles with a characteristic uniform red CL due to very fine-grained forsterites, but the mantles of group A chondrules have a complex internal structure and are much thicker than the relatively thin rims on the group B chondrules. The variety of internal textures and the progressive integration of the objects with the surrounding matrix suggests to us that these features are large group A chondrules in the process of being destroyed by aqueous alteration. Prior to aqueous alteration, group A chondrules in CM chondrites were larger than group B chondrules, which is contrary to the situation in ordinary chondrites and were apparently destroyed more rapidly than group B chondrules by aqueous alteration.

  7. 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.

  8. 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.

  9. Oxygen-isotopic Compositions of Relict and Host Grains in Chondrules in the Yamato 81020 CO3.0 Chondrite

    NASA Technical Reports Server (NTRS)

    Kunihiro, Takuya; Rubin, Alan E.; McKeegan, Kevin D.; Wasson, John T.

    2006-01-01

    We report the oxygen-isotope compositions of relict and host olivine grains in six high-FeO porphyritic olivine chondrules in one of the most primitive carbonaceous chondrites, CO3.0 Yamato 81020. Because the relict grains predate the host phenocrysts, microscale in situ analyses of O-isotope compositions can help assess the degree of heterogeneity among chondrule precursors and constrain the nebular processes that caused these isotopic differences. In five of six chondrules studied, the DELTA O-17 (=delta O-17 - 0.52 (raised dot) delta O-18) compositions of host phenocrysts are higher than those in low-FeO relict grains; the one exception is for a chondrule with a moderately high-FeO relict. Both the fayalite compositions as well as the O-isotope data support the view that the low-FeO relict grains formed in a previous generation of low-FeO porphyritic chondrules that were subsequently fragmented. It appears that most low-FeO porphyritic chondrules formed earlier than most high-FeO porphyritic chondrules, although there were probably some low-FeO chondrules that formed during the period when most high-FeO chondrules were forming.

  10. 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.

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

    Microsoft Academic Search

    C. Ferraris; L. Folco; M. Mellini

    2002-01-01

    Sixteen texturally different (porphyritic, barred, radial, cryptocrystalline) FeO-rich chondrules from the unequilibrated ordinary chondrites Brownfield, Frontier Mountain (FRO) 90003 and FRO 90032 were characterized by optical and scanning electron microscopy and then thoroughly studied by transmission and analytical electron microscopy. Nanotextural and nanochemical data indicate similar thermal evolution for chondrules of the same textural groups; minor, yet meaningful differences occur

  12. 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.

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

    Microsoft Academic Search

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

    1997-01-01

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

  14. Case study of chondrule alteration with IR spectroscopy in NWA 2086 CV3 meteorite

    NASA Astrophysics Data System (ADS)

    Kereszturi, A.; Gyollai, I.; Szabó, M.

    2015-02-01

    Analyzing the alteration in an olivine chondrule of the NWA 2086 CV3 meteorite, infrared spectral, electron microprobe and optical microscopic observations were correlated to each other. The intensity and wavelength positions of olivine peaks changed characteristically with the progression of alteration and related Fe/Mg substitution inward of the chondrule. Moderate to good correlations were identified between Fo% composition and positions of 830 and 860 cm-1 IR peaks. The disappearance of 1020 cm-1 peak by structural change happens already at a low level alteration without changing the optical appearance of the mineral. The existence of the 980 cm-1 peak is found to be an indicator of the intact phase of olivine. While profiles perpendicular to the chondrule's perimeter showed that the alteration progressed 15-20 ?m distance inward without observable fractures (probablly by some diffusion related process), the "alteration distance" from various obvious fractures inside the chondrule was only 3-5 ?m distance. These observations suggest that the substitution was more effective close to the matrix, and also related to some fluids that although were able to circulate along the large internal fractures too, did not produce such strong substitution there, like what happened close to the matrix. It was also demonstrated that the poorly exploited contact mode observations with ATR based reflection method in infrared spectroscopy provide a useful tool to analyze the alteration at micrometer scale without much sample preparation, and enable identifying alterations already at such a low level where the olivines still look optically intact.

  15. Origins of Al-rich chondrules: Clues from a compound Al-rich chondrule in the Dar al Gani 978 carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Zhang, Ai-Cheng; Itoh, Shoichi; Sakamoto, Naoya; Wang, Ru-Cheng; Yurimoto, Hisayoshi

    2014-04-01

    Aluminum-rich chondrules are one of the most interesting components of primitive chondrites, because they have characteristics that are similar to both Ca, Al-rich inclusions (CAIs) and ferromagnesian chondrules. However, their precursor and formation history remain poorly constrained, especially with respect to their oxygen isotopic distributions. In this study, we report on the petrography, mineralogy, oxygen isotope ratios, and rare-earth-element compositions of a sapphirine-bearing Al-rich chondrule (SARC) in the ungrouped chondrite Dar al Gani (DaG) 978. The SARC has a complex core-mantle-rim texture; while both the core and the mantle are mainly composed of Al-rich enstatite and anorthite with minor amounts of mesostasis, these regions are distinguished by the presence of Fe-rich spinel and sapphirine in the core and their absence in the mantle. The rim of the SARC consists mainly of Fe-rich olivine, enstatite, and Fe-Ni metal. Spinel and some olivine grains in the SARC are 16O-rich, with ?17O values down to -20‰ and -23‰, respectively. Enstatite, sapphirine, and most olivine grains have similar ?17O values (? -7‰), which are lower than those of anorthite and the mesostasis (including augite therein) (?17O: ? -3‰). Mesostasis from both the core and mantle have Group II rare-earth-element (REE) patterns; however, the core mesostasis has higher REE concentrations than the mantle mesostasis. These observations provide a strong indication that the SARC formed by the melting and crystallization of a mixture of materials from Group II CAIs and ferromagnesian chondrules. Both spinel and olivine with 16O-rich features could be of relict origin. The 16O-poor isotopic compositions of most components in Al-rich chondrules can be explained by oxygen isotopic exchange between the melt and 16O-poor nebular gas (?17O: ? -7‰) during melting in chondrule-forming regions; whereas the anorthite and mesostasis could have experienced further oxygen isotopic exchange with a relatively 16O-poor reservoir (?17O: ? -3‰) on the parent body, likely during fluid-assisted thermal metamorphism. During the same thermal metamorphism event, spinel, olivine, some enstatite, and the mesostasis experienced Mg-Fe exchange to various extents. The 16O-rich spinel and olivine in the SARC are of relict origin. The high bulk Al2O3 contents, the presence of relict spinel, and the characteristic Group II REE composition in mesostasis strongly indicate that the precursor of the Al-rich portion of the SARC is a mixture of materials from CAIs and ferromagnesian chondrules. The Al-rich portion of the SARC experienced melt-gas oxygen isotope exchange in the chondrule-forming region, which could well explain why the oxygen isotopic compositions of most Al-rich chondrules are similar to those of ferromagnesian chondrules. The presence of 16O-rich olivine indicates that AOAs contributed in some manner to the formation of ferromagnesian chondrules. After accretion onto the parent body of DaG 978, components in the SARC experienced oxygen and Fe-Mg exchange to various degrees, likely during fluid-assisted thermal metamorphism.

  16. 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.

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

    PubMed

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

    2005-04-21

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

  18. 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.

  19. 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.

  20. Chondrules as Natural Analogs for Metal Segregation: Analyses from 3D Synchrotron Imaging

    NASA Astrophysics Data System (ADS)

    Rushmer, T. A.; Clark, S. M.; Parkinson, D.

    2013-12-01

    Chondrules from the Bjurböle meteorite have been imaged by x-ray tomography to develop 3D visualization in order to use the chondrules as starting material in experimental deformation experiments aimed at unravelling the evolution of planetesimal-sized bodies. The Bjurböle chondrite is an olivine-hypersthene bearing meteorite and classified as an L/LL4. It fell in 1899, March 12 at 10:30 pm. Bjurböle has been used in several previous studies as it is abundant and has a range of chondrule sizes. Chrondrules themselves allow for the study of the early solar system and were formed ~2-3 My after the CAIs. However, we are using the chondrules as small metal-silicate natural analogs for metal-silicate deformation experiments. The critical first step is to characterize them. We have collected 3D textural data from 14 chondrules by synchrotron-based high resolution hard x-ray microtomography imaging. A series of two-dimensional images is collected as the sample is rotated, and tomographic reconstruction yields the full 3D representation of the sample. Virtual slices through the 3D object in any arbitrary direction can be visualized, or the full data set can be visualized by volume rendering. More importantly, automated image filtering and segmentation allows the extraction of boundaries between the various phases. The volumes, shapes, and distributions of each phase, and the connectivity between them, can then be quantitatively analysed. The imaging data show that the Bjurböle chondrules fall into two main groups. Those with abundant quenched glass and those bearing crystals of olivine and pyroxene, with minor glass. The metal and sulfide mainly line the outside of the chondrules as has been previously described, but the crystal-bearing chondrules also contain centrally located and widely distributed metal and sulfide. We are using these data to prepare the chondrules for experimental deformation studies. Figure 1 shows Bjurböle chondrule 8 (BB8). Image analyses has focused on distribution of FeNi (red) and FeS (gold). Metal and sulfide are concentrated on the outer edges but finely distributed internally. Scale is ~ 1 mm. Figure 1: FeNi and FeS distribution in BB 8.

  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. Olivine Thermometry

    NSDL National Science Digital Library

    Keith Putirka

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

  4. 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.

  5. 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.

  6. 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 [Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350 (Denmark)] [Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350 (Denmark)

    2013-10-10

    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.

  7. 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.

  8. Petrology, trace element abundances and oxygen isotopic compositions of a compound CAI-chondrule object from Allende

    NASA Astrophysics Data System (ADS)

    Wakaki, S.; Itoh, S.; Tanaka, T.; Yurimoto, H.

    2013-02-01

    We report the petrology, trace element abundances and oxygen isotopic characteristics of a compound CAI-chondrule object, WI-025, found in the Allende CV3 chondrite. The WI-025 is an irregularly shaped inclusion consisting of three texturally and chemically distinct portions: the interior portion, the igneous rim and the intermediate zone located between these two portions. The interior portion consists of anorthite, spinel, olivine and Al-bearing low-Ca pyroxene. The major element chemistry of the interior portion corresponds to that of Al-rich chondrules and is of intermediate character between fine-grained spinel-rich CAIs and ferromagnesian chondrules. The interior portion has abundant 16O-rich spinel (?17O = -14.2 to -24.7) and displays a group II CAI-like REE composition. These observations indicate that the interior portion contains a CAI component formed by fractional condensation. The major and trace element chemistry of the interior portion indicate that the CAI had subsequently assimilated chondrule materials through partial melting. The maximum heating temperature of the partial melting is estimated at approximately 1400 °C, similar to the maximum heating temperature of Type-B CAIs. The oxygen isotopic compositions of the olivine and low-Ca pyroxene (?17O = -6.3) in the interior portion indicate that the partial melting and chondrule assimilation took place under a moderately 16O-poor nebular gas. The igneous rim is texturally and chemically similar to ferromagnesian chondrules and entirely surrounds the interior portion. The oxygen isotopic compositions of the olivine and low-Ca pyroxene in the igneous rim are indistinguishable from those of the interior olivine and Al-bearing low-Ca pyroxenes. These observations indicate that a chondrule material, which was melted in the same nebular gas as the interior portion, was accreted to the interior portion. The intermediate zone represents a reaction zone accompanying the igneous rim formation. The formation history of WI-025 can be summarized by the following processes: (1) original CAI formation, (2) partial melting and chondrule assimilation, (3) igneous rim formation and (4) secondary alteration on the parent body.

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

    NASA Astrophysics Data System (ADS)

    Jones, R. H.

    1993-06-01

    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.

  10. EXPERIMENTAL INVESTIGATION OF Ti and Fe VALENCE IN CHONDRULE-LIKE MELTS DURING COOLING UNDER CHANGING REDOX CONDITIONS AT LOW PARTIAL PRESSURES. S. B. Simon1

    E-print Network

    Grossman, Lawrence

    EXPERIMENTAL INVESTIGATION OF Ti and Fe VALENCE IN CHONDRULE-LIKE MELTS DURING COOLING UNDER: Detection of Ti3+ in type I (Fe/(Fe+Mg) of olivine and pyroxene ]. Trivalent Ti is not ex- pected to occur in FeO-bearing silicates, as the Ti2O3- TiO2 (pure oxide) buffer

  11. 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.

  12. Mn-Cr isotopic systematics of individual Chainpur chondrules. [Abstract only

    NASA Technical Reports Server (NTRS)

    Nyquist, L.; Lindstrom, D.; Wiesmann, H.; Martinez, R.; Bansal, B.; Mittlefehldt, D.; Shih, C.-Y.; Wentworth, S.

    1994-01-01

    Twenty-eight chondrules separated from Chainpur (LL3.4) were surveyed for abundances of Mn, Cr, Na, Fe, Sc, Hf, Ir, and Zn by Instrumental Neutron Activation Analysis (INAA). Six, weighting 0.6-1.5 mg each, were chosen for Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray (EDX) and high-precision Ce-isotopic studies. LL-chondrite-normalized (Mn/Fe)(sub LL) and (Sc/Fe)(sub LL) were found to be useful in categorizing them. Five chondrules (CH-16, -17, -18, -23, and -28) were in the range 0.5 less than (Mn/Fe)(sub LL) less than 1. 4 and 0.5 less than (Sc/Fe)(sub LL) less than 1.4. The sixth (CH-25) had (Mn/Fe)(sub LL) and (Sc/Fe)(sub LL) ratios of 0.40 and 8.1, respectively, and was enriched in the refractory lithophile elements Sc and Hf and the refractory siderophile element Ir by 2.7 and 4.4x LL abundances respectively. SEM/EDX of exterior surfaces of the chondrules showed they consisted of varying proportions of low- and high-Ca pyroxenes, olivine, glass, kamacite/taenite, and Fe-sulfides. Chromium-53/chromium-52 for the six chondrules and bulk Chainpur (WR) are presented. Chromium-54/chromium-52 is close to terrestrial and does not correlate with Mn/Cr. We provisionally ignore the possibility of initial Cr isotopic heterogeneities among the chondrules. Omitting both the CH-25 and WR data, a linear regression gives initial (Mn-53/Mn-55)(sub I) = 8 +/- 4 x 10(exp -6), corresponding to chondrule formation at Delta(t)(sub LEW) = -9 +/- 4 Ma prior to igneous crystallization of the LEW 86010 angrite. If initial (Mn-53/Mn-55)(sub 0) in the solar system were as high as approximately 4.4 x 10(exp -5) when Allende CAI formed, our data suggest Chainpur chondrules formed approximately 9 Ma later, in qualitative agreement with 'late' I-Xe formation ages for most Chainpur chondrules.

  13. The origin of chondrules: Constraints from matrix composition and matrix-chondrule complementarity

    NASA Astrophysics Data System (ADS)

    Palme, Herbert; Hezel, Dominik C.; Ebel, Denton S.

    2015-02-01

    One of the major unresolved problems in cosmochemistry is the origin of chondrules, once molten, spherical silicate droplets with diameters of 0.2 to 2 mm. Chondrules are an essential component of primitive meteorites and perhaps of all early solar system materials including the terrestrial planets. Numerous hypotheses have been proposed for their origin. Many carbonaceous chondrites are composed of about equal amounts of chondrules and fine-grained matrix. Recent data confirm that matrix in carbonaceous chondrites has high Si/Mg and Fe/Mg ratios when compared to bulk carbonaceous chondrites with solar abundance ratios. Chondrules have the opposite signature, low Si/Mg and Fe/Mg ratios. In some carbonaceous chondrites chondrules have low Al/Ti ratios, matrix has the opposite signature and the bulk is chondritic. It is shown in detail that these complementary relationships cannot have evolved on the parent asteroid(s) of carbonaceous chondrites. They reflect preaccretionary processes. Both chondrules and matrix must have formed from a single, solar-like reservoir. Consequences of complementarity for chondrule formation models are discussed. An independent origin and/or random mixing of chondrules and matrix can be excluded. Hence, complementarity is a strong constraint for all astrophysical-cosmochemical models of chondrule formation. Although chondrules and matrix formed from a single reservoir, the chondrule-matrix system was open to the addition of oxygen and other gaseous components.

  14. 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.

  15. A compositional classification scheme for meteoritic chondrules

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    A compositionally based classification scheme for chondrules is proposed that will help in systematizing the wealth of data available and disentangling the effects of nebular and subsequent processes. The classification is not by texture or the composition of a single phase, or a mixture of these two, but rather is a comprehensive, systematic approach which uses the composition of the two main chondrule components. This scheme is applicable to over 95 percent of the chondrules and is easily applied using an electron microprobe. It stresses the original diversity of the chondrules and the complex yet facile way in which they respond to parent-body metamorphism. Results using this classification scheme suggest that arguments against an important role of chondrules in determining the compositional trends of the chondrites have been premature.

  16. 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.

  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. Photophoretic strength on chondrules. 1. Modeling

    SciTech Connect

    Loesche, Christoph; Wurm, Gerhard; Teiser, Jens [Faculty of Physics, University of Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg (Germany); Friedrich, Jon M. [Department of Chemistry, Fordham University, Bronx, NY 10458 (United States); Bischoff, Addi, E-mail: christoph.loesche@uni-due.de [Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster (Germany)

    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.

  19. 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.

  20. 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:

  1. 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

  2. Chondrule formation in the radiative accretional shock

    NASA Technical Reports Server (NTRS)

    Ruzmaikina, T. V.; Ip, W.

    1994-01-01

    The physical, mineralogical, and isotopic properties of chondrules strongly indicate that they were formed by the rapid melting and resolidification of preexisting solids composed of primitive material. The chondrule precursors were heated to temperatures of about 1800 K in short high-temperature events, followed by cooling with a rate of 10(exp 2)-10(exp 3) K/hr. A heat input of about 1500 J/g is required to heat chondrule precursors to such a temperature and melt them. Lightning discharges and flares in the solar nebula, and heating of the chondrule precursors by friction with gas decelerated in the accretional shock or in a shock (of unspecified origin) within the solar nebula, have been discussed as possible mechanisms for chondrule formation. One advantage of chondrule formation in large-scale shocks is that a lot of dust material can be processed. An accretional shock, which is produced by infalling gas of the presolar cloud when it collides with the solar nebula, belongs to this type of shock. In 1984 Wood considered the possibility of chondrule formation in the accretional shock by heating of chondrule precursors by gas drag. He concluded that the density in the accreting material is much lower than needed to melt silicates at the distance of the asteroid belt if the accreting matter had the cosmic ratio of dust to gas, and the mass of the solar nebula did not exceed 2 solar mass units. Melting of chondrule precursors is difficult because of their effective cooling by thermal radiation. Suppression of the radiative cooling of individual grains in dust swarms, which are opaque to thermal emission, was considered to be the only possible means of chondrule formation in solar nebula shocks. Previous models of solid grain melting in solar nebula shocks have neglected gas cooling behind the shock front, i.e., they considered adiabatic shocks. In this paper we show that large dust grains could be heated much stronger than was supposed by these authors, because of effects associated with the gas cooling.

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

    Microsoft Academic Search

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

    2001-01-01

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

  4. On the origin of porphyritic chondrules

    SciTech Connect

    Blander, M. [Argonne National Lab., IL (United States); Unger, L. [Purdue Univ., Westville, IN (United States); Pelton, A.; Ericksson, G. [Ecole Polytechnique, Montreal, PQ (Canada)

    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.

  5. Partitioning of Trace Elements Between Pyroxene and Liquid in a Porphyritic Pyroxene Chondrule in Semarkona

    NASA Astrophysics Data System (ADS)

    Jones, R. H.; Layne, G. D.

    1993-07-01

    The unequilibrated chondrite Semarkona (LL3.0) enables us to investigate primary properties of chondrules that have not been overprinted by secondary processes. Electron microprobe studies of the compositions and zoning properties of silicate phases in these chondrules have helped to interpret crystallization behavior and, hence, offer important insights into formation conditions [e.g., 1,2]. However, the behavior of trace elements in these systems has not been investigated, largely because of the difficulties encountered in analyzing such elements in chondrule silicates. Here we report preliminary ion microprobe data obtained on coexisting pyroxene and glass phases from a pyroxene-rich chondrule in Semarkona. Trace elements analyzed are REE (La, Ce, Nd, Sm, Eu, Dy, Er, Yb), Sr, Y, and Zr. The chondrule studied is a typical example of textural type IAB [2]. It contains phenocrysts of olivine (Fa(sub)3) and clinoenstatite and a glassy mesostasis occupying approximately 15 vol% of the chondrule. Augite (Fs(sub)3, Wo(sub)44) occurs as narrow (10-micrometer) rims on clinoenstatite phenocrysts. Clinoenstatite is FeO-poor (Fs(sub)3, Wo(sub)0.4) and shows little zoning in major and minor elements. Trace-element analyses have been carried out on clinoenstatite, augite, and glass in this chondrule. REE contents in clinoenstatite are extremely low, lying in the range 0.01-0.1 x CI, and show a smooth increase in abundance from La to Yb. REE abundances are enriched in both augite and glass at levels approximately 4-10 x CI, with a small negative Eu anomaly in augite and a small positive Eu anomaly in glass. Olivine is likely to contain REE abundances similar to low-Ca pyroxene [3]. These relative abundances are consistent with closed-system crystallization of the chondrule, assuming that its bulk composition has chondritic abundances of REE [4]. Trace-element partition coefficients (Ds) for the two pyroxene phases are shown in Fig. 1. Clinoenstatite Ds vary smoothly, increasing from 0.0006 (La) to 0.02 (Yb). These data are broadly consistent with equilibrium D values obtained experimentally [3]. However, chondrule Ds for the LREE and Sr are consistently higher than equilibrium experimental values. This could be attributed to the effect of rapid cooling in chondrules [3]. Values for D(sub)Y and D(sub)Zr are also consistent with the experimental data. For augite, the Ds we determined are approximately flat, at values around 1, with a decrease in the LREE and a negative Eu anomaly. The chondrule data are consistently higher than equilibrium experimental data for pyroxenes of composition Wo(sub)40 [5]. This may also be attributable to the effect of rapid cooling rate. However, the partitioning behavior of REE in Ca-rich pyroxene as a function of melt composition is not fully understood. D(sub)Sr, D(sub)Y, and D(sub)Zr are comparable with REE values, consistent with the data of [6]. In summary, trace-element partitioning among chondrule silicate phases appears to be entirely consistent with closed-system crystallization of the chondrule. Data such as these will be valuable in assessing the origins of, and relationships between, various chondritic components. They may also provide a valuable tool for studying metamorphism in ordinary chondrites. This work is supported by NASA grant NAGW-3347 (J. J. Papike). SIMS analyses were performed at the UNM/SNL Ion Microprobe Facility, a joint operation of the Institute of Meteoritics, UNM, and Sandia National Laboratories. References: [1] Jones R. H. (1990) GCA, 54, 1785-1802. [2] Jones R. H. (1992) LPS XXIII, 631-632. [3] Kennedy A. K. et al. (1993) EPSL, 115, 177-195. [4] Grossman J. N. et al. (1988) In Meteorites and the Early Solar System, 619- 659. [5] McKay G. et al. (1986) GCA, 50, 927-937. [6] Hart S. R. and Dunn T. (1993) CMP, 113, 1-8. Fig. 1 appears here in the hard copy.

  6. Detection of new olivine-rich locations on Vesta

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  7. 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.

  8. A new astrophysical setting for chondrule formation.

    PubMed

    Krot, A N; Meibom, A; Russell, S S; Alexander, C M; Jeffries, T E; Keil, K

    2001-03-01

    Chondrules in the metal-rich meteorites Hammadah al Hamra 237 and QUE 94411 have recorded highly energetic thermal events that resulted in complete vaporization of a dusty region of the solar nebula (dust/gas ratio of about 10 to 50 times solar). These chondrules formed under oxidizing conditions before condensation of iron-nickel metal, at temperatures greater than or equal to 1500 K, and were isolated from the cooling gas before condensation of moderately volatile elements such as manganese, sodium, potassium, and sulfur. This astrophysical environment is fundamentally different from conventional models for chondrule formation by localized, brief, repetitive heating events that resulted in incomplete melting of solid precursors initially residing at ambient temperatures below approximately 650 K. PMID:11230691

  9. Chondrule-matrix relationships in chondritic meteorites

    NASA Technical Reports Server (NTRS)

    Brearley, A. J.

    1994-01-01

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

  10. Origin of plagioclase-olivine inclusions in carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

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

    1991-02-01

    The origin of plagioclase-olivine inclusions (POIs) from three CV chondrites and one ungrouped chondrite was investigated by examining the chemical, mineralogical, and isotopic characteristics of a group of POIs from these chondrites. Results of these analyses demonstrate that the mixing and the partial melting processes in these inclusions were superimposed on more ancient isotopically heterogeneous material. A comparison of the essential characteristics of POIs and CAIs suggests that the major processes leading to the formation of POIs (such as condensation, dust/gas fractionation, aggregation of chemically and isotopically disparate materials, and partial melting) are common to most CAIs and chondrules. A scenario for the origin of POIs is proposed, showing that the homogeneity of the final assemblage (whether a POI, a CAI, or a chondrite) is primarily a reflection of the thermal history rather than the nature of precursor materials.

  11. 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.

  12. "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.

  13. Distribution of some highly volatile elements in chondrules

    NASA Astrophysics Data System (ADS)

    Kim, J. S.; Marti, K.

    1994-07-01

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

  14. Magnetic Record of Ordinary Chondrite Chondrules

    NASA Astrophysics Data System (ADS)

    Kohout, T.; Kletetschka, G.

    2007-12-01

    The magnetic record of individual chondrules has been examined on two low-metamorphic grade ordinary chondrites - Bjurböle (L4) and Avanhandava (H4). The chondrule magnetic conglomerate study was done by removing oriented chondrules from the meteorite. The magnetic directions of the chondrules in both meteorites seems to be randomly oriented within both meteorites. The paleofield method based on the REM ratio (NRM/SIRM; Natural Remanent Magnetization / Saturation Isothermal Remanent Magnetization) calibrated for the TRM (Thermal Remanent Magnetization; Kletetschka et al., 2004) magnetization process reveals approximate paleofields between 5 ?T and 20 ?T (REM ~ 0.002) for Avanhandava chondrules and between 12 ?T and 45 ?T (REM ˜ 0.0015-0.0048) for Bjurböle chondrules. However, the timing of the magnetizing process remains unclear. The random pattern of the individual chondrule magnetic directions suggest that the chondrules were not remagnetized by recent terrestrial weathering nor by the exposure to the artificial magnetic fields. However the effect of post aggregation metamorphism (reaching 400 - 600°C) and impact related shock demagnetization on the parent body may be responsible for partial or complete loss of the magnetic information carried by the lower coercivity grains. In the case of Avanhandava meteorite this can be observed in the REM ratio. The values of REM ratio calculated in low AF (alternating Field) demagnetizing fields are progressively lower than in the higher AF fields. The Bjurböle meteorite contains significant fraction of the tetrataenite mineral. The origin of tetrataenite is related to the slow ordering of the FeNi lattice at temperatures below ~ 350°C). Thus the origin of tetrataenite must be post-metamorphic ruling out the high temperature TRM scenario. The origin of the magnetization in the Bjurböle chondrules are most likely associated to the post-metamorphic low temperature processes (i.e. electric discharges or impact related shock remanent magnetization on the parent body). The random magnetic directions in this meteorite can be partly controlled by the strong magnetic anisotropy of tetrataenite. Moreover, the paleofield method based on REM ratio (Kletetschka et al., 2004) is calibrated for the TRM magnetizing scenario and not for low temperature acquisition processes and thus of limited use in the Bjurböle case. The results of the paleofield studies of the Avanhandava meteorite shows that the paleofield carried out by its chondrules can be significantly underestimated due to post-formation metamorphic and impact events. Those processes can in the same way influence the paleointensity results previously published for other chondritic meteorites. The interpretation of Bjurböle data may be even more difficult due to the presence of tetrataenite. Acknowledgements: Authors would like to thank to Peter J. Wasilewski from NASA/GSFC for constructive consultations and access to the laboratory facilities. References: Kletetschka, G., Acuna, M. H., Kohout, T, Wasilewski, P. J., and Connerney, J. E. P. (2004), An empirical scaling law for acquisition of thermoremanent magnetization, Earth Planet. Sci. Lett., 226, 521- 528.

  15. 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.

  16. 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

  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. Shape, size, and distribution of magnetic particles in Bjurbole chondrules

    NASA Technical Reports Server (NTRS)

    Nava, David F.

    1994-01-01

    Chondrules from the Bjurbole chondritic meteorite (L4) exhibit saturation remanence magnetization (SIRM) values which vary over three orders of magnitude. REM values (Natural Remanence Magnetization/SIRM) for Allende (C3V) and Chainpur (LL3) are less than 0.01 but in Bjurbole some chondrules were found to have REM values greater than 0.1 with several greater than 0.2. REM values greater than 0.1 are abnormal and cannot be acquired during weak field cooling. If exposure to a strong field (whatever the source) during the chondrules' history is responsible for the high REM values, was such history associated with a different processing which might have resulted in different shape, size, and distribution of metal particles compared to chondrules having REM values of less than 0.01? Furthermore, magnetic hysteresis results show a broad range of magnetic hardness and other intrinsic magnetic properties. These features must be related to (1) size and amount of metal; and (2) properties of, and amount of, tetrataenite in the chondrules (all chondrules thus far subjected to thermomagnetic analysis show the presence of tetrataenite). A scanning electron microscopy (SEM) study is underway to determine the relationship between the shape, size, and distribution of metal particles within individual chondrules and the magnetic properties of these chondrules. Results from the SEM study in conjunction with magnetic property data may also help to discern effects from possible lightning strikes in the nebula prior to incorporation of the chondrules into the parent body.

  20. Shape, size, and distribution of magnetic particles in Bjurbole chondrules

    NASA Astrophysics Data System (ADS)

    Nava, David F.

    1994-03-01

    Chondrules from the Bjurbole chondritic meteorite (L4) exhibit saturation remanence magnetization (SIRM) values which vary over three orders of magnitude. REM values (Natural Remanence Magnetization/SIRM) for Allende (C3V) and Chainpur (LL3) are less than 0.01 but in Bjurbole some chondrules were found to have REM values greater than 0.1 with several greater than 0.2. REM values greater than 0.1 are abnormal and cannot be acquired during weak field cooling. If exposure to a strong field (whatever the source) during the chondrules' history is responsible for the high REM values, was such history associated with a different processing which might have resulted in different shape, size, and distribution of metal particles compared to chondrules having REM values of less than 0.01? Furthermore, magnetic hysteresis results show a broad range of magnetic hardness and other intrinsic magnetic properties. These features must be related to (1) size and amount of metal; and (2) properties of, and amount of, tetrataenite in the chondrules (all chondrules thus far subjected to thermomagnetic analysis show the presence of tetrataenite). A scanning electron microscopy (SEM) study is underway to determine the relationship between the shape, size, and distribution of metal particles within individual chondrules and the magnetic properties of these chondrules. Results from the SEM study in conjunction with magnetic property data may also help to discern effects from possible lightning strikes in the nebula prior to incorporation of the chondrules into the parent body.

  1. A short duration of chondrule formation in the solar nebula: evidence from 26Al in Semarkona ferromagnesian chondrules

    Microsoft Academic Search

    Noriko T. Kita; Hiroko Nagahara; Shigeko Togashi; Yuichi Morishita

    2000-01-01

    The 26Al–26Mg systems of five ferromagnesian chondrules from the least metamorphosed ordinary chondrite Semarkona (LL3.0) were studied using a secondary ion mass spectrometer. Their glass or plagioclase portions contain excesses of 26Mg, and in two chondrules the 26Mg excesses are well correlated with 27Al\\/24Mg, which demonstrates the in-situ decay of 26Al. The initial 26Al\\/27Al ratios in these chondrules obtained from

  2. 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.

  3. Chondrule formation by impact? The cooling rate

    NASA Astrophysics Data System (ADS)

    Kluger, F.; Weinke, H. H.; Kiesl, W.

    Different sets of initial conditions for impacts of stray objects on solid surfaces of planetary bodies or asteroids have been computed for cooling times of chondrules. The results of the calculations indicate cooling times shorter than 60 seconds for condensed matter from 10 to the 4th to 10 to the 15th g generated by impact and initial temperatures of the gas phase formed up to presumed degeneracy limit of 150,000 K. To retain solid impact products originated that way on meteorite parent bodies by gravitational forces, a target diameter of at least 800 km is required. It is shown that chondrule formation by impact seems to be an unlikely event.

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

    SciTech Connect

    Mcsween, H.Y. Jr.

    1985-09-01

    The petrologic and chemical properties of the ferromagnesian chondrules in the Allende carbonaceous chondrite were examined in terms of the isotopic composition and the correlations between isotopic patterns. Areas of thin sections were studied with a SEM and bulk chemical fractions of 12 constituents were quantified to calculate correlations with petrologic features. A possible correlation between (CaO + Al2O2)/MgO and oxygen isotopes imply the formation of oxygen isotopic compositions in the chondrules by exchanges between isotopically heavy nebular gases and O-16 enriched solids. Different rates of gaseous exchange occurred with the various types of chondrules. Factors which may have controlled the exchanges are discussed. 21 references.

  5. Olivine in Antarctic micrometeorites - Comparison with other extraterrestrial olivine

    NASA Technical Reports Server (NTRS)

    Steele, Ian M.

    1992-01-01

    The compositions of 5-micron or larger Mg-rich olivines from 26 Antarctic micrometeorite particles were examined and compared with those of other extraterrestrial olivine. The following differences were noted between the Antarctic meteorites and the generally recognized meteorite groups: (1) while refractory-rich (e.g., high Al2O3 or CaO) are common in C2, C3, and UOC meteorites, there are only rare, or possibly no refractory-rich olivines in Antarctic micrometeorites; (2) Mg-rich olivine compositions with FeO less than 1.9 wt pct are underrepresented in the Antarctic micrometeorites, relative to other unequilibrated meteorites; and (3) no Mn-rich, high-Mg olivines were found similar to those described in interplanetary dust, C1, C2, C3, and UOC meteorites.

  6. Oxygen-isotopic Compositions of Low-FeO relicts in High-FeO Host Chondrules in Acfer 094, a Type 3.0 Carbonaceous Chondrite Closely Related to CM

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.; Kunihiro, Tak; Wasson, John T.

    2006-01-01

    With one exception, the low-FeO relict olivine grains within high-FeO porphyritic chondrules in the type 3.0 Acfer 094 carbonaceous chondrite have DELTA O-17 ( = delta O-17 - 0.52 X delta O-18) values that are substantially more negative than those of the high-FeO olivine host materials. These results are similar to observations made earlier on chondrules in C03.0 chondrites and are consistent with two independent models: (1) Nebular solids evolved from low-FeO, low-DELTA O-17 compositions towards high-FeO, more positive DELTA O-17 compositions; and (2) the range of compositions resulted from the mixing of two independently formed components. The two models predict different trajectories on a DELTA O-17 vs. log Fe/Mg (olivine) diagram, but our sample set has too few values at intermediate Fe/Mg ratios to yield a definitive answer. Published data showing that Acfer 094 has higher volatile contents than CO chondrites suggest a closer link to CM chondrites. This is consistent with the high modal matrix abundance in Acfer 094 (49 vol.%). Acfer 094 may be an unaltered CM chondrite or an exceptionally matrix-rich CO chondrite. Chondrules in Acfer 094 and in CO and CM carbonaceous chondrites appear to sample the same population. Textural differences between Acfer 094 and CM chondrites are largely attributable to the high degree of hydrothermal alteration that the CM chondrites experienced in an asteroidal setting.

  7. Mineral Magnetism of Dusty Olivine: A Potential Carrier of Pre-Accretionary Remanence?

    NASA Astrophysics Data System (ADS)

    Harrison, R. J.; Lappe, S.; Feinberg, J. M.; Russell, S.; Bromiley, G.; Bastos da Silva Fanta, A.; Dunin-Borkowski, R.

    2009-12-01

    The mechanism and location of chondrule formation is an important question in cosmochemistry. The remanent magnetisation of chondrules may provide clues to their formation environment, but requires magnetic carriers with extraordinary thermal and magnetic stability. Recently, the search for a suitable magnetic carrier has focussed on ‘dusty olivine’: relict grains that survived the chondrule heating event without fully melting. Dusty olivine grains contain submicron inclusions of metallic Fe-Ni, formed by sub-solidus reduction of the Fe-bearing olivine during heating. The Fe inclusions within dusty olivine potentially possess the ideal magnetic characteristics for acquiring and maintaining primary remanence. Here we describe a mineral magnetic characterisation of synthetic dusty olivine formed by laboratory reduction of terrestrial olivine. Crushed olivine grains were packed in a graphite crucible and reduced in a CO atmosphere at 1350°C for 10 minutes, before quenching into water. Samples were characterised by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), temperature-dependent magnetic susceptibility (?-T), and first-order-reveral-curve (FORC) diagrams. The results demonstrate the potential, as well as the pitfalls, of using dusty olivine for paleomagnetism. Microscopy reveals abundant Fe-Ni particles with sizes ranging from > 1 ?m to < 20 nm. ?-T reveals the presence of both a bcc-Fe phase with Tc = 770°C and bcc/fcc Fe-Ni phases with varying Ni content. The presence of Ni complicates the magnetic properties due to the effect of the bcc-fcc martensitic transition. Evidence for Fe-Ni redistribution within the particles at high temperature is found in the ?-T measurements, which leads to the formation of a ferromagnetic Ni-rich alloy with fcc structure and Tc = 200°C. Further complications arise due to the formation of magnetite above 300°C, and its subsequent transformation to wustite above 580 °C. EBSD analysis reveals the presence of magnetite rims on the surface of some large Fe inclusions that have been exposed to air. FORC analysis demonstrates the presence of MD signals associated with > 1 ?m Fe particles, as well as an SD-like signal with broad coercivity distribution (extending to over 500 mT in some cases) and a narrow vertical spread. Comparison with TEM observations indicates that the coercivity distribution is consistent with SD particles dominated by shape anisotropy. This work highlights the combination of high magnetic stability and thermal stability that make dusty olivine a potential carrier of pre-accretionary remanence. It also demonstrates that a thorough characterisation of the Fe particles within natural dusty olivine and a detailed understanding of the mineral magnetic phase relations is necessary in order to design an effective paleointensity protocol capable of extracting the value of the paleofield.

  8. 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

  9. 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.

  10. Fractionation of B and Li in the Solar Nebula or in Chondrules: Insight from Chondrule Formation Experiments

    NASA Technical Reports Server (NTRS)

    Xiong, Y.-L.; Hewins, R. H.; Cetiner, Z.; Wood, S. A.

    2002-01-01

    Chondrule formation experiments suggest that the B/Li ratios of synthesized chondrules are always lower than that of the starting material, and that the B/Li ratios systematically decrease with decreasing cooling rates at constant temperature. Additional information is contained in the original extended abstract.

  11. CHONDRULE FORMATION IN BOW SHOCKS AROUND ECCENTRIC PLANETARY EMBRYOS

    SciTech Connect

    Morris, Melissa A.; Desch, Steven J.; Athanassiadou, Themis [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404 (United States); Boley, Aaron C., E-mail: melissa.a.morris@asu.edu [Department of Astronomy University of Florida, Gainesville, FL 32611 (United States)

    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.

  12. 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.

  13. 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.

  14. The formation of chondrules: petrologic tests of the shock wave model

    PubMed

    Connolly Jr HC; Love

    1998-04-01

    Chondrules are millimeter-sized rounded igneous rocks within chondritic meteorites. Their textures and fractionated mineral chemistries suggest that they formed by repeated, localized, brief (minutes to hours) melting of cold aggregates of mineral dust in the protoplanetary nebula. Astrophysical models of chondrule formation have been unable to explain the petrologically diverse nature of chondrites. However, a nebular shock wave model for chondrule formation agrees with many of the observed petrologic and geochemical properties of chondrules and shows how particles within the nebula are sorted by size and how rims around chondrules are formed. It also explains the volatile-rich nature of chondrule rims and the chondrite matrix. PMID:9525858

  15. Irradiation Histories of CAIs and LL3/CB Chondrules

    NASA Astrophysics Data System (ADS)

    Wielandt, D.; Bizzarro, M.

    2014-09-01

    Spallogenic 40K anomalies in LL3 chondrules and CV3 CAIs suggest that they experienced irradiating conditions prior to accretion on their respective parent bodies, arguing against midplane dead zone storage for the entirety of their nebular storage.

  16. 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.

  17. The Formation of Chondrules at High Gas Pressures in the Solar Nebula

    Microsoft Academic Search

    Albert Galy; Edward D. Young; Richard D. Ash; R. Keith O'Nions

    2000-01-01

    High-precision magnesium isotope measurements of whole chondrules from the Allende carbonaceous chondrite meteorite show that some aluminum-rich Allende chondrules formed at or near the time of formation of calcium-aluminum-rich inclusions and that some others formed later and incorporated precursors previously enriched in magnesium-26. Chondrule magnesium-25\\/magnesium-24 correlates with [magnesium]\\/[aluminum] and size, the aluminum-rich, smaller chondrules being the most enriched in the

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

    E-print Network

    Grossman, Lawrence

    SHOCK WAVES AND TYPE II PO CHONDRULES A. V. Fedkin1 , L. Grossman1,2 , and F. J. Ciesla1 . 1 Dept of Type II chondrules, water enrichment is neces- sary [3]. Nebular shock waves have been suggested those in experiments that yield chondrule textures. Shock wave thermal histories have been in

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    Recent experiments have been designed to produce chondrule textures via flash melting while simultaneously studying the nature of chondrule precursors. However, these experiments have only been concerned with silicate starting material. This is a preliminary report concerning what effects elemental carbon, when added to the silicate starting material, has on the origin of chondrules produced by flash melting.

  1. 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.

  2. THERMAL HISTORIES OF CHONDRULES IN SOLAR NEBULA SHOCKS

    SciTech Connect

    Morris, M. A.; Desch, S. J., E-mail: melissa.a.morris@asu.ed [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404 (United States)

    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. 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.

  4. Supernova olivine from cometary dust.

    PubMed

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

    2005-07-29

    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. PMID:15994379

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

    Microsoft Academic Search

    Alexander N. Krot; Klaus Keil

    2002-01-01

    Anorthite-rich chondrules in CR and CH carbonaceous chondrites consist of magnesian low-Ca pyroxene and forsterite phenocrysts, FeNi-metal nodules, interstitial anorthite, Al-Ti-Cr-rich low-Ca and high-Ca pyroxenes, and crystalline mesostasis composed of silica, anorthite and high-Ca pyroxene. Three anorthite-rich chondrules contain relic Ca, Al-rich inclusions composed of anorthite, spinel, +\\/-Al-diopside, and +\\/-forsterite. A few chondrules contain regions which are texturally and mineralogically

  6. 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.

  7. 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.

  8. 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

  9. 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...

  10. Refractory residues, condensates and chondrules from solar furnace experiments

    NASA Technical Reports Server (NTRS)

    King, E. A.

    1982-01-01

    Vertical access solar furnace experiments have produced refractory residues, condensates and chondrules that are similar to components of chondritic meteorites. In particular, Ca-Al-rich refractory residues similar in chemistry to inclusions in carbonaceous chondrites have been produced by partial evaporation of basaltic bulk rock samples. Fe-Mg-Si-rich condensates with distinctive microbotryoidal morphology have been collected from the same sample runs. Particle coatings and aggregates with virtually identical microbotryoidal morphology and major element chemistry have been identified in both the Allende and Murchison meteorites. Spattered drops from melt beads undergoing heating and partial evaporation resemble some meteoritic chondrules in their mineralogies, textures, grain size, and sorting. The spatter mechanism is highly efficient in the production of chondrules. If any of the refractory inclusions in chondrites are, in fact, partial evaporation residues, many meteoritic fluid drop chondrules must have been formed by this process. The hot central portion of the solar nebula, acting on a cloud of dust and gas, is the probable source of heat required to produce the fractionated chemistry and physical state of many of the components of chondritic meteorites.

  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. Opaque minerals in the matrix of the Bishunpur (LL3.1) chondrite: constraints on the chondrule formation environment

    NASA Astrophysics Data System (ADS)

    Lauretta, Dante S.; Buseck, Peter R.; Zega, Thomas J.

    2001-04-01

    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 (Fe 2SiO 4). Accessory phases in the rims include silica (SiO 2), chromite (FeCr 2O 4), whitlockite (Ca 3(PO 4) 2), maricite (FeNaPO 4), magnetite (Fe 3O 4), 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 10 -5.0 to 10 -4.1 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.

  13. 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.

  14. 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...

  15. 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.

  16. 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.

  17. Chondrule-like particles provide evidence of early Archean meteorite impacts, South Africa and western Australia

    NASA Technical Reports Server (NTRS)

    Lowe, D. R.; Byerly, G. R.

    1985-01-01

    The evolution of the Earth and the Earth crust was studied. Two layers, that contain abundant unusual spherical particles which closely resemble chondroules were identified. Chondrules occur on small quantities in lunar soil, however, they are rare in terrestrial settings. Some chondrules in meteorites were formed on the surfaces of planet sized bodies during impact events. Similar chondrule like objects are extremely rare in the younger geologic record and these abundances are unknown in ancient deposits, except in meteorites. It is suggested that a part of the Earth's terminal bombardment history, and conditions favoring chondrule formation existed on the early Earth.

  18. 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.

  19. 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.

  20. Magnetocentrifugal jets and chondrule formation in protostellar disks

    NASA Astrophysics Data System (ADS)

    Salmeron, Raquel; Ireland, Trevor

    2014-01-01

    Chondrite meteorites are the building blocks of the solar nebula, out of which our Solar System formed. They are a mixture of silicate and oxide objects (chondrules and refractory inclusions) that experienced very high temperatures, set in a matrix that remained cold. Their prevalence suggests that they formed through a very general process, closely related to stellar and planet formation. However the nature and properties of the responsible mechanism have remained unclear. The evidence for a hot solar nebula provided by this material seems at odds with astrophysical observations of forming stars. These indicate that the typical temperatures of protostellar disks are too low to melt and vapourise silicate minerals at the radial distances sampled by chondrule-bearing meteorites. Here, we show that processing of precursors in a protostellar outflow at radial distances of about 1 - 3 AU can heat them to their melting points and explain their basic properties, while retaining association with the colder matrix.

  1. 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.

  2. Experimental Study of Olivine-rich Troctolites

    NASA Astrophysics Data System (ADS)

    Mu, S.; Faul, U.

    2014-12-01

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

  3. Olivine as tar removal catalyst for biomass gasifiers: Catalyst characterization

    Microsoft Academic Search

    Lopamudra Devi; Menno Craje; Peter Thüne; Krzysztof J. Ptasinski; Frans J. J. G. Janssen

    2005-01-01

    In the present paper olivine is considered as a prospective in-bed tar removal catalyst for fluidized bed biomass gasifiers. The catalytic activity of olivine is investigated via steam reforming reaction of naphthalene as a model biomass tar compound. It is observed that the calcination of olivine improves the performance of the catalyst. Calcination of olivine is done with air at

  4. doi:10.1016/S0016-7037(03)00494-0 Chondrule textures and precursor grain size: an experimental study

    E-print Network

    doi:10.1016/S0016-7037(03)00494-0 Chondrule textures and precursor grain size: an experimental of the precursors, especially grain size, must affect the textures of the chondrules they yield when heated. We the observed textural distribution of chondrules, which are predominantly porphyritic. The simplest model

  5. Mg tracer diffusion in synthetic forsterite and San Carlos olivine as a function of P, T and fO 2

    Microsoft Academic Search

    Sumit Chakraborty; John R. Farver; Richard A. Yund; David C. Rubie

    1994-01-01

    We present new experimental data on Mg tracer diffusion in oriented single crystals of forsterite (Fo100) and San Carlos olivine (Fo92) between 1000–1300° C. The activation energies of diffusion are found to be 400 (±60) kJ\\/mol (˜96 kcal\\/mol) and 275 (±25) kJ\\/mol (˜65 kcal\\/ mol) in forsterite and San Carlos olivine, respectively, along [001] at a fO2 of 10-12 bars.

  6. Primary trapped melt inclusions in olivine in the olivine-augite-orthopyroxene ureilite Hughes 009

    Microsoft Academic Search

    Cyrena Anne Goodrich; Anna Maria Fioretti; Mario Tribaudino; Gianmario Molin

    2001-01-01

    We describe the first known occurrence of primary melt inclusions in a ureilite. The ureilite is Hughes 009, one of a small number of ureilites whose primary mineralogy is olivine-augite-orthopyroxene, rather than olivine-pigeonite. Hughes 009 has a coarse-grained, equilibrated texture typical of ureilites, and homogeneous primary mineral compositions: olivine — mg 87.3; augite — mg 89.2, Wo 37.0, Al2O3 =

  7. Cations in olivine, Part 2: Diffusion in olivine xenocrysts, with applications to petrology and mineral physics

    Microsoft Academic Search

    Amy J. G. Jurewicz; E. Bruce Watson

    1988-01-01

    Diffusivities for calcium, iron, magnesium, manganese and aluminum have been measured for St. John's olivine undergoing cation exchange with synthetic basaltic melts. The variety of temperature, pressure and fO2 conditions under which the diffusivities were measured complement the equilibrium-partitioning study of calcium in olivine-bearing basalts by Jurewicz and Watson, 1988. Olivine was found to be anisotropic with respect to the

  8. Olivine on Vesta: clues for the interior

    NASA Astrophysics Data System (ADS)

    De Sanctis, M. C.; Ammannito, E.; McSween, H.; Mittlefehldt, D. W.; Capaccioni, F.; Capria, M. T.; Frigeri, A.; Fonte, S.; Longobardo, A.; Magni, G.; Marchi, S.; Palomba, E.; Pieters, C. M.; Tosi, F.; Zambon, F.; Raymond, C. A.; Russell, C. T.; Sunshine, J.

    2013-09-01

    Data from the Dawn VIR (Visible InfraRed mapping Spectrometer) instrument [1,2] have been used to characterize and map the distribution of minerals on Vesta. Howardite, eucrite and diogenite meteorites represent the basaltic crust and possibly ultramafic mantle samples of Vesta, the only surviving large basaltic differentiated rocky protoplanet. Olivine is a major component of the mantles of differentiated bodies, including Vesta. Here we report on the discovery of olivine and its constraints on the Vesta evolution models.

  9. High Temperature Oxygen Isotope Exchange Between Chondrule Melt and H2O: An Experimental Approach

    NASA Astrophysics Data System (ADS)

    Di Rocco, T.; Pack, A.

    2014-09-01

    We investigate whether the O isotope composition of chondrules is the result of exchange with a surrounding gas by conducting time- and ƒO2-dependent oxygen isotope exchange experiments between a chondrule analogue melt and an H2O-rich gas phase.

  10. Micromagnetic coercivity distributions and interactions in chondrules with implications for paleointensities of the early solar system

    Microsoft Academic Search

    Gary Acton; Qing-Zhu Yin; Kenneth L. Verosub; Luigi Jovane; Alex Roth; Benjamin Jacobsen; Denton S. Ebel

    2007-01-01

    Chondrules in chondritic meteorites record the earliest stages of formation of the solar system, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 chondrules from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the

  11. Gas dynamic heating of chondrule precursor grains in the solar nebula

    Microsoft Academic Search

    L. L. Hood; M. Horanyi

    1991-01-01

    In the present investigation of solar nebula gasdynamic processes which may account for the melting of chondrule precursor grains, both drag heating due to grain relative motion and heating due to collisions with gas molecules in thermal motion are considered in conjunction with the effect of thermally emitted radiation on grain heating and cooling. The melting of chondrule-sized grains is

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

    E-print Network

    Grossman, Lawrence

    Magnesium isotopic fractionation in chondrules from the Murchison and Murray CM2 carbonaceous). The compositions of CM2 chondrules are consistent with isotopic fractionation toward heavy Mg being associated) Abstract­We present high-precision measurements of the Mg isotopic compositions of a suite of types I

  13. Incompatible Trace Element Abundances in Hawaiian Olivines

    NASA Astrophysics Data System (ADS)

    Yu, G.; Huang, S.; Mukhopadhyay, S.; Jacobsen, S. B.

    2009-12-01

    Our understanding of trace elements partitioning between olivine and silicate melt is clouded by large variations in values of partition coefficients presented in the literature. In general, partition coefficients from phenocryst-matrix results are higher than those from experimental equilibration and in-situ measurements (such as LA-ICP-MS and Ion-probe) (Blard and Farley, 2008; Lee et al., 2007). This discrepancy is possibly caused by the presence of melt or micromineral inclusions in the analyzed phenocrysts, or contamination of grain boundaries by enriched glasses or accessory phases or uranium pick up from alteration of olivines. To further investigate why analysis of natural phenocrysts usually results in relative high apparent D’s for incompatible trace elements, six aliquots of olivine grains from a single sediment sample of Waimea river watershed, on the western side of the island of Kauai, Hawaii, were analyzed by solution ICP-MS at Harvard University for trace element concentrations. Two aliquots of olivines were leached in 1% oxalic acid for 45-60 min at 90 OC before dissolution. Leached and unleached olivines mostly show positive linear correlations in plots of incompatible trace elements versus La, which possibly indicates mixing lines between olivine and one end-member with higher incompatible element concentration (possibly melt inclusion). Assuming La concentration in olivine is zero, we estimate concentration of other incompatible elements in olivines using intercepts of these mixing lines. We obtain that U and Th concentration in the olivines to be about 1 ppb and 0.1 ppb respectively, corresponding to apparent DUol/melt and DThol/melt of 0.003 and 0.0001 if host lave has U of 0.3 ppm and Th of 1ppm (Gayer et al.,2008). Recently, helium isotopic measurements were made in these olivines (Gayer et al., 2008) and the results yield a basin-wide average erosion rate of 0.056 mma-1 for Waimea river watershed. Gayer et al. (2008) argued that radiogenic 4He in these ~4.5 Ma old olivines is negligible using DUol/melt=2×10-5 and DThol/melt=5×10-5 (Beattie 1993; Kennedy et al., 1993) and 0.3 ppm U and 1 ppm Th for host lavas. This assumption has been challenged by Blard and Farley (2008), who argued that radiogenic 4He in these olivines are significant and could affect the calculated erosion rate by a factor of 10-100. They used apparent DUol/melt and DThol/melt ranging between 0.03 and 0.1, which were obtained from analyses of whole natural phenocrysts and host lava (Blard and Farley, 2008). In contrast, using our measured U and Th contents in the Kauai olivines suggest revisions to erosion rates on order of only 15%. Therefore, Blard and Farley (2008)’s apparent D values may not be representative of Kauai olivines and their assertion that Gayer et al. (2008)’s erosion rates from Hawaii require revision by more than a factore of 10 is incorrect.

  14. FIRST Ti-XANES ANALYSES OF OLIVINE IN AMOEBOID OLIVINE AGGREGATES

    E-print Network

    Grossman, Lawrence

    FIRST Ti-XANES ANALYSES OF OLIVINE IN AMOEBOID OLIVINE AGGREGATES S. B. Simon1 , S. R. Sutton1]. Their primary phases are very 16 O-rich [3], indicating formation in a solar gas. We measured the valence of Ti in oli- vine in two AOAs (a) to see if they contain Ti3+ , the presence of which would suggest formation

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

    PubMed

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

    2006-05-25

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

  16. Raman spectra of shocked minerals. I - Olivine

    NASA Technical Reports Server (NTRS)

    Heymann, D.; Celucci, T. A.

    1988-01-01

    The Raman spectra of olivine contained in a chip of the Twin Sisters Peak (Washington) dunite shocked to 22.2 GPa is shown to be identical to that of unshocked olivine in the same rock. The Raman spectra of powder of the rock shocked to 20.1 GPa and of chips shocked to 59.5 GPa and 60.7 GPa display strong and broad low-frequency features with crests at 475/cm, 556/cm, and 572/cm, and broad high-frequency features near 1100/cm. It is suggested that these features are due to the formation of olivine glass with a considerable degree of three-dimensional Si-O-Si linkage having scattered domains of greatly variable grain size, internal structure, and chemical composition.

  17. 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.

  18. 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

  19. Synthetic olivine supported nickel catalysts for gasification of glycerol

    Microsoft Academic Search

    Duangduen Atong; Chiravoot Pechyen; Duangdao Aht-Ong; Viboon Sricharoenchaikul

    2011-01-01

    Olivine and olivine-supported nickel catalysts were synthesized and tested to study their potential to be used as active in-bed materials for steam reforming\\/gasification of glycerol waste. Olivine was synthesized by a co-precipitation method followed by wet impregnation of nickel. Ni\\/olivine calcined at 800°C and then reduced at 700°C exhibited a desirable phase with the highest surface area and nickel content.

  20. A Chemical Model of Micrometeorite Impact into Olivine

    NASA Technical Reports Server (NTRS)

    Sheffer, A. A.; Melosh, H. J.

    2005-01-01

    Laboratory simulations of space weathering using laser irradiation have been successful in reproducing space weathering characteristics such as the reduction of olivine to form nanophase iron particles. However, the chemistry of the reduction of Fe2+ in olivine to Fe metal has not been fully explored. We present a thermodynamic model of olivine undergoing post-impact cooling and decompression.

  1. 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.

  2. Oxygen Isotopes of Al-Rich Chondrules from Unequilibrated Ordinary Chondrites

    NASA Astrophysics Data System (ADS)

    Hsu, W.; Guan, Y.; Jiang, Y.; Wang, Y.

    2012-09-01

    Oxygen isotopes indicate that ARCs from UOCs are not simple mixtures of ferromagnesian chondrules and CAIs. Instead, they probably experienced higher-degree oxygen isotopes exchange with 16O-poor nebular gas reservoir during multiple heating events.

  3. Microstructural and Chemical Study of Fe-Ni Metal Inside Semarkona Chondrules

    NASA Astrophysics Data System (ADS)

    Reisener, R. J.; Goldstein, J. I.

    1999-03-01

    Fe-Ni metal inside Semarkona chondrules is a mixture of kamacite and tetrataenite. The basic microstructure is plessite. We interpret metal thermal history in terms of the plessite microstructure and metal phase compositions.

  4. Bar Graph

    NSDL National Science Digital Library

    2010-01-01

    This lesson is designed to give students experience creating and reading bar graphs. The lesson provides links to a practice data set and the bar graph activity so that students can practice making bar graphs and check their work using the activity. Finally, the lesson provides a suggested follow-up to this lesson.

  5. 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.

  6. Micrometeorite craters discovered on chondrule-like objects from kapoeta meteorite.

    PubMed

    Brownlee, D E; Rajan, R S

    1973-12-28

    Craters attributable to hypervelocity impacts of micrometeorites have been discovered on rare chondrule-like objects from the gas-rich meteorite Kapoeta. These chondrule-like objects, probably generated by impacts themselves, provide further evidence for the regolith origin of Kapoeta. The micrometeorite flux at the time of formation of the meteorites was probably an order of magnitude higher than the present flux, but the solar luminosity could not have been higher than 1.7 times its present value. PMID:17733113

  7. I-Xe Dating of Small Chondrules from the Bjurbole Meteorite Using RELAX

    Microsoft Academic Search

    J. A. Whitby; J. D. Gilmour; R. D. Ash; G. Turner

    1995-01-01

    Chondrules from the Bjurbole L4 meteorite have been widely used as a standard for I-Xe dating because of the good high temperature 129Xe-128Xe correlation [1] and small spread in their apparent ages determined by this technique. As part of an ongoing study [2,3], I-Xe analyses have been performed on several Bjurbole chondrules of sizes smaller than have hitherto been studied

  8. Boron and Lithium Isotope Variations in Chondrules: The Signature of Presolar Nucleosynthesis

    Microsoft Academic Search

    M. Chaussidon; F. Robert

    1996-01-01

    We report here the preliminary results of tests concerning two major implications of the boron isotope variations that were recently found in meteoritic chondrules (Chaussidon and Robert 1995, Nature 374, 337-339). (1) Freshly nucleosynthetized boron with variable 11B\\/10B ratios must have been preserved as solid grains in the solar nebula and implanted or embedded in the newly formed chondrules. Therefore,

  9. Primary trapped melt inclusions in olivine in the olivine-augite-orthopyroxene ureilite Hughes 009

    NASA Astrophysics Data System (ADS)

    Goodrich, Cyrena Anne; Fioretti, Anna Maria; Tribaudino, Mario; Molin, Gianmario

    2001-02-01

    We describe the first known occurrence of primary melt inclusions in a ureilite. The ureilite is Hughes 009, one of a small number of ureilites whose primary mineralogy is olivine-augite-orthopyroxene, rather than olivine-pigeonite. Hughes 009 has a coarse-grained, equilibrated texture typical of ureilites, and homogeneous primary mineral compositions: olivine - mg 87.3; augite - mg 89.2, Wo 37.0, Al 2O 3 = 1.6 wt.%; orthopyroxene - mg 88.3, Wo 4.9. It shows only limited secondary reduction effects and no petrographically recognizable carbon phases, which indicates that its original carbon content was lower than in most ureilites. The melt inclusions occur in olivine crystals. They are concentrated in the central regions of their hosts, showing elongate (mostly 20-60 ?m in maximum dimension), negative olivine crystal shapes and parallel alignment. These and other features indicate that they were trapped during initial growth of their hosts from a liquid, and are likely to be representative samples of that liquid. They consist of glass and single, subhedral crystals of high-Ca pyroxene, with minor Cr-rich spinel and metal-phosphide-sulfide spherules. They are surrounded by halos of olivine with rounded outlines defined by tiny bits of metal and thin arcs of glass. Pyroxenes within each inclusion show zonation patterns indicating that they nucleated at the olivine/ liquid interface with compositions close to that of the primary augite, and then grew inward with dramatically increasing Al 2O 3 (to 10.8 wt.%), Wo (to ?50), TiO 2 and Cr 2O 3 contents. Glasses within each inclusion are relatively homogeneous. Glasses from all inclusions show well-defined trends of CaO, TiO 2, Cr 2O 3, Na 2O and SiO 2 vs. Al 2O 3, (16-23 wt.%) that can be modelled as resulting principally from crystallization of various amounts of the pyroxene. The halos, which represent olivine that grew from the trapped melts, are zoned in Cr and Ca with concentrations decreasing inward, reflecting cocrystallization of pyroxene; they have homogeneous Fe/Mg identical to that of the primary olivine, indicating reequilibration with the host. We develop a petrologic model for the postentrapment history (crystallization, reaction and reequilibration) of the inclusions, based on which we reconstruct the composition of the primary trapped liquid (PTL). The PTL was saturated only with olivine. This result implies that Hughes 009 is a cumulate (consistent with the high Mn/Mg ratio of its olivine and a low abundance of graphite) and that the composition of the PTL is close to that of its parent magma. The low-pressure equilibrium crystallization sequence predicted by MAGPOX calculations for the PTL (olivine ? augite ? plagioclase ? pigeonite) is not, however, consistent with the primary mineralogy of Hughes 009. If the conditions of these calculations are, indeed, appropriate, then complex processes such as magma mixing must have been involved in the petrogenesis of this ureilite. This conclusion is consistent with other evidence that the olivine-augite-orthopyroxene ureilites record a more complex magmatic evolution than is evident in the olivine-pigeonite ureilites. TEM investigations of microtextural features in all phases and XRD determination of Fe 2+-Mg site distribution in orthopyroxene have elucidated the cooling and shock history of this ureilite. Hughes 009 experienced an extremely high cooling rate (7 ± 5°C/h at the closure T of 630°C) late in its evolution, and two distinguishable shock events - the first at peak pressures of 5 to 10 GPa, resulting in mechanical polysynthetic twinning in augite and orthopyroxene and mild undulatory extinction in olivine; and the second at lower pressures, resulting only in brecciation and redistribution of metal. Its late history is similar to that of most ureilites, and probably reflects impact excavation.

  10. 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.

  11. Toward a unified hydrous olivine electrical conductivity law

    NASA Astrophysics Data System (ADS)

    Gardés, Emmanuel; Gaillard, Fabrice; Tarits, Pascal

    2014-12-01

    has long been proposed that water incorporation in olivine has dramatic effects on the upper mantle properties, affecting large-scale geodynamics, and triggering high electrical conductivity. But the laboratory-based laws of olivine electrical conductivity predict contrasting effects of water, precluding the interpretation of geophysical data in term of mantle hydration. We review the experimental measurements of hydrous olivine conductivity and conclude that most of data are consistent when errors in samples water contents are considered. We report a new law calibrated on the largest database of measurements on hydrous olivine oriented single crystals and polycrystals. It fits most of measurements within uncertainties, and is compatible with most of geophysical data within petrological constraints on mantle olivine hydration. The conductivity anisotropy of hydrous olivine might be higher than dry olivine, but preferential orientation should produce moderate anisotropy (˜0-0.8 log unit). In the oceanic mantle, the enhancement of olivine conductivity is limited to ˜1 log unit in the maximum range of mantle olivine water concentrations (0-500 wt ppm). Strongest enhancements are expected in colder regions, like cratonic lithospheres and subduction settings. High conductivities in melt-free mantle require great depths and high water concentrations in olivine (>0.1 S/m at >250 km and >200 wt ppm). Thus, the hydration of olivine appears unlikely to produce the highest conductivities of the upper mantle.

  12. Shock-produced olivine glass: First observation

    USGS Publications Warehouse

    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, (Mg0.88Fe 0.12SiO4 recovered from peak pressures of about 56 ?? 109 pascals revealed the presence of amorphous zones located within crystalline regions with a high density of tangled dislocations. This is the first reported observation ofolivine 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 ?? 109 pascals and that further TEM observations of naturally shocked olivines may demonstrate the presence of glass.

  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. Micromagnetic Coercivity Distributions and Interactions in Chondrules With Implications for Paleointensities of the Early Solar System

    NASA Astrophysics Data System (ADS)

    Yin, Q.; Acton, G.; Verosub, K. L.; Jovane, L.; Roth, A.; Jacobsen, B.; Ebel, D. S.

    2006-12-01

    Chondrules in chondritic meteorites record the earliest stages of formation of the Solar System, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 chondrules from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the three meteorites. The coercivity distributions are log-normal shaped, with Bjurbole distributions being bimodal or trimodal. Allende FORC distributions have coercivities that extend out to about 250-350 mT, with little or no interaction above 10 mT. Karoonda FORC distributions are triangular shaped with high interactions at low coercivity and progressively lower interactions out to the peak coercivity of about 130 mT. In Bjurbole chondrules, a high coercivity mode (400-700 mT) arising from tetrataenite interacts strongly with one or more lower coercivity modes in a manner unlike that seen in terrestrial rocks. Such strong interactions have the potential to bias paleointensity estimates. Moreover, because a significant portion of the coercivity distributions for most of the chondrules is <10 mT, low-coercivity magnetic overprints are common. Therefore, paleointensities based on the REM method, which rely on ratios of the natural remanent magnetization (NRM) to the saturation isothermal remanent magnetization (IRM) without magnetic cleaning, will probably be biased. The paleointensity bias is found to be about an order of magnitude for most chondrules with low-coercivity overprints. Paleointensity estimates based on a method we call REMc, which uses NRM/IRM ratios after magnetic cleaning, avoid this overprinting bias. Allende chondrules, which are the most pristine and possibly record the paleofield of the early Solar System, have a mean REMc paleointensity of 10.4 ?T. Karoonda and Bjurbole chondrules, which have experienced some thermal alteration, have REMc paleointensities of 4.6 and 3.2 ?T, respectively.

  15. Micromagnetic coercivity distributions and interactions in chondrules with implications for paleointensities of the early solar system

    NASA Astrophysics Data System (ADS)

    Acton, Gary; Yin, Qing-Zhu; Verosub, Kenneth L.; Jovane, Luigi; Roth, Alex; Jacobsen, Benjamin; Ebel, Denton S.

    2007-03-01

    Chondrules in chondritic meteorites record the earliest stages of formation of the solar system, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 chondrules from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the three meteorites. The coercivity distributions are lognormal shaped, with Bjurbole distributions being bimodal or trimodal. The highest-coercivity mode in the Bjurbole chondrules is derived from tetrataenite, which interacts strongly with the lower-coercivity grains in a manner unlike that seen in terrestrial rocks. Such strong interactions have the potential to bias paleointensity estimates. Moreover, because a significant portion of the coercivity distributions for most of the chondrules is <10 mT, low-coercivity magnetic overprints are common. Therefore paleointensities based on the REM method, which rely on ratios of the natural remanent magnetization (NRM) to the saturation isothermal remanent magnetization (IRM) without magnetic cleaning, will probably be biased. The paleointensity bias is found to be about an order of magnitude for most chondrules with low-coercivity overprints. Paleointensity estimates based on a method we call REMc, which uses NRM/IRM ratios after magnetic cleaning, avoid this overprinting bias. Allende chondrules, which are the most pristine and possibly record the paleofield of the early solar system, have a mean REMc paleointensity of 10.4 ?T. Karoonda and Bjurbole chondrules, which have experienced some thermal alteration, have REMc paleointensities of 4.6 and 3.2 ?T, respectively.

  16. 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).

  17. 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).

  18. Magnesium isotopic systematics of chondrules and CAIs from Allende, Murchison, Murray and Bjurbole. F.-, M. Wadhwa1,

    E-print Network

    Grossman, Lawrence

    Magnesium isotopic systematics of chondrules and CAIs from Allende, Murchison, Murray and Bjurbole: Several recent studies have demon- strated that high-precision Mg isotope systematics of chondrules and calcium-aluminum-rich inclusions (CAIs) can provide unique insights into the timing and conditions

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Fedkin and Grossman: Fayalite Content of Chondritic Olivine 279 The Fayalite Content of Chondritic Olivine

    E-print Network

    Grossman, Lawrence

    enrichment factors near the maximum produced in coagulation and settling models, together with C1 chondrite dust whose O content has been enhanced by admixture of water ice, can yield olivine condensate grains during condensation of a so- lar gas. 1.2. Dust-enriched Systems While thermodynamic treatments

  4. 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.

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

    PubMed

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

    1993-01-01

    A theoretical model of aerodynamic heating of a meteoric particle upon entry into a parent body atmosphere is presented. The model includes the effects of melting, vaporization, and heat conduction into the particle interior. Properties of chondrule rims are interpreted in the context of the model. We conclude that the formation of true melt rims by atmospheric entry requires that a low-melting-temperature component be fractionated in the outer part of the chondrule prior to rim formation, and that the range of thermal alteration effects observed in UOC chondrites reflects the variety of encounter conditions and chondrite types. Further tests of the model are suggested. PMID:11540090

  6. 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.

  7. 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.

  8. Mn-Cr isotopic systematics of Chainpur chondrules and bulk ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Nyquist, L.; Lindstrom, D.; Wiesmann, H.; Bansal, B.; Shih, C.-Y.; Mittlefehldt, D.; Martinez, R.; Wentworth, S.

    1994-01-01

    We report on ongoing study of the Mn-Cr systematics of individual Chainpur (LL3.4) chondrules and compare the results to those for bulk ordinary chondrites. Twenty-eight chondrules were surveyed for abundances of Mn, Cr, Na, Fe, Sc, Hf, Ir, and Zn by INAA. Twelve were chosen for SEM/EDX and high-precision Cr-isotopic studies on the basis of LL-chondrite-normalized Mn(LL), Sc(LL), (Mn/Fe)(LL), and (Sc/Fe)(LL) as well as their Mn/Cr ratios. Classification into textural types follows from SEM/EDX examination of interior surfaces.

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

    NASA Astrophysics Data System (ADS)

    Ammannito, E.; de Sanctis, M. C.; Palomba, E.; Longobardo, A.; Mittlefehldt, D. W.; McSween, H. Y.; Marchi, S.; Capria, M. T.; Capaccioni, F.; Frigeri, A.; Pieters, C. M.; Ruesch, O.; Tosi, F.; Zambon, F.; Carraro, F.; Fonte, S.; Hiesinger, H.; Magni, G.; McFadden, L. A.; Raymond, C. A.; Russell, C. T.; Sunshine, J. M.

    2013-12-01

    Olivine is a major component of the mantle of differentiated bodies, including Earth. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta, which is the lone surviving, large, differentiated, basaltic rocky protoplanet in the Solar System. Only a few of these meteorites, the orthopyroxene-rich diogenites, contain olivine, typically with a concentration of less than 25 per cent by volume. Olivine was tentatively identified on Vesta, on the basis of spectral and colour data, but other observations did not confirm its presence. Here we report that olivine is indeed present locally on Vesta's surface but that, unexpectedly, it has not been found within the deep, south-pole basins, which are thought to be excavated mantle rocks. Instead, it occurs as near-surface materials in the northern hemisphere. Unlike the meteorites, the olivine-rich (more than 50 per cent by volume) material is not associated with diogenite but seems to be mixed with howardite, the most common surface material. Olivine is exposed in crater walls and in ejecta scattered diffusely over a broad area. The size of the olivine exposures and the absence of associated diogenite favour a mantle source, but the exposures are located far from the deep impact basins. The amount and distribution of observed olivine-rich material suggest a complex evolutionary history for Vesta.

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

    PubMed

    Ammannito, E; De Sanctis, M C; Palomba, E; Longobardo, A; Mittlefehldt, D W; McSween, H Y; Marchi, S; Capria, M T; Capaccioni, F; Frigeri, A; Pieters, C M; Ruesch, O; Tosi, F; Zambon, F; Carraro, F; Fonte, S; Hiesinger, H; Magni, G; McFadden, L A; Raymond, C A; Russell, C T; Sunshine, J M

    2013-12-01

    Olivine is a major component of the mantle of differentiated bodies, including Earth. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta, which is the lone surviving, large, differentiated, basaltic rocky protoplanet in the Solar System. Only a few of these meteorites, the orthopyroxene-rich diogenites, contain olivine, typically with a concentration of less than 25 per cent by volume. Olivine was tentatively identified on Vesta, on the basis of spectral and colour data, but other observations did not confirm its presence. Here we report that olivine is indeed present locally on Vesta's surface but that, unexpectedly, it has not been found within the deep, south-pole basins, which are thought to be excavated mantle rocks. Instead, it occurs as near-surface materials in the northern hemisphere. Unlike the meteorites, the olivine-rich (more than 50 per cent by volume) material is not associated with diogenite but seems to be mixed with howardite, the most common surface material. Olivine is exposed in crater walls and in ejecta scattered diffusely over a broad area. The size of the olivine exposures and the absence of associated diogenite favour a mantle source, but the exposures are located far from the deep impact basins. The amount and distribution of observed olivine-rich material suggest a complex evolutionary history for Vesta. PMID:24196707

  11. Diffusion and partition coefficients of minor and trace elements in San Carlos olivine at 1,300°C with some geochemical implications

    NASA Astrophysics Data System (ADS)

    Spandler, Carl; O'Neill, Hugh St. C.

    2009-11-01

    Lattice diffusion coefficients have been determined for 19 elements (Li, Be, Na, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Eu, Gd, Lu and Hf) in a single crystal of San Carlos olivine as a function of crystallographic orientation, at 1,300°C, 1 bar and fO2 = 10-8.3 bars, by equilibration with a synthetic silicate melt. Results for Li, Na, V, Cr, Fe and Zn are from diffusion of these elements out of the olivine, starting from their indigenous concentrations; those for all other elements are from diffusion into the olivine, from the silicate melt reservoir. Our 25-day experiment produced diffusion profiles 50 to > 700 ?m in length, which are sufficiently long that precise analyses could be achieved by scanning laser ablation inductively coupled plasma mass spectrometry, even at concentration levels well below 1 ?g g-1. For the divalent cations Ca, Mn, Fe and Ni, profiles were also obtained by electron microprobe analysis. The results of the two methods agree well with each other, and are consistent with divalent cation diffusion coefficients previously determined using different experimental methodologies. Olivine/melt partition coefficients retrieved from the data are also consistent with other published partitioning data, indicating that element incorporation and transport in olivine in our experiment occurred via mechanisms appropriate to natural conditions. Most of the examined trace elements diffuse through olivine at similar rates to the major octahedral cations Fe and Mg, showing that cation charge and radius have little direct influence on diffusion rates. Aluminium and P remain low and constant in the olivine, implying negligible transport at our analytical scale, hence Al and P diffusion rates that are at least two orders of magnitude slower than the other cations studied here. All determined element diffusivities are anisotropic, with diffusion fastest along the [001] axis, except Y and the REEs, which diffuse isotropically. The results suggest that element diffusivity in olivine is largely controlled by cation site preference, charge balance mechanisms and point-defect concentrations. Elements that are present on multiple cation sites in olivine (e.g. Be and Ti) and trivalent elements that are charge-balanced by octahedral site vacancies tend to diffuse at relatively fast rates.

  12. 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

  13. 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.

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

    SciTech Connect

    Ogliore, R. C.; Huss, G. R.; Nagashima, K. [Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Butterworth, A. L.; Gainsforth, Z.; Stodolna, J.; Westphal, A. J. [Space Sciences Laboratory, University of California at Berkeley, Berkeley, CA 94720 (United States); Joswiak, D. [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Tyliszczak, T. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

    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.

  15. Chondrule-forming Shock Waves in the Solar Nebula by X-Ray Flares

    Microsoft Academic Search

    T. Nakamoto; M. R. Hayashi; N. T. Kita; S. Tachibana

    2005-01-01

    The shock wave heating model is considered to be one of the most plausible models for chondrule formation. However, the generation mechanism of appropriate shock waves is still under debate. Here, we examined X-ray flares as the shock wave generation mechanism. X-ray flares are energetic momentum ejection phenomena accompanying many T Tauri stars. We used magnetohydrodynamics (MHD) simulations to follow

  16. 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.

  17. Relative strengths of orthopyroxene and olivine at asthenospheric conditions

    NASA Astrophysics Data System (ADS)

    Holyoke, C. W., III; Raterron, P.; Girard, J.

    2014-12-01

    Orthopyroxene is the second most common mineral in the Earth's upper mantle. However, very little is known about its strength relative to olivine and clinopyroxene, both of which are well studied. Analyses of microstructures in peridotites containing orthopyroxene and olivine that were deformed at lithospheric conditions (relatively low temperatures and pressures) indicate that the orthopyroxene is stronger than surrounding olivine. In contrast, analyses of microstructures in asthenospheric peridotite xenoliths indicate that olivine and orthopyroxene have similar strengths. In order to better determine the pressure, temperature and strain rate sensitivity of the strength of orthopyroxene aggregates, we have performed an experimental study on stacked cylinders of orthopyroxene aggregates and olivine aggregates in the D-DIA. Cylinders of Bamble orthopyroxene (d~5-30 microns) or San Carlos olivine (d~25 microns) were hot-pressed in-situ at 1300oC for 1 hour prior to deformation. Although the assemblies and powders were dried at >100oC for >12 hours prior to installation in the apparatus, minor concentrations of water were observed (OPx ~ 500 H/106 Si; Ol ~ 200 H/106 Si). Multiple deformation steps were performed in each experiment over a range of strain rates (5x10-6 to 2x10-4/s) at a single temperature and pressure (T = 1000 - 1400oC and P = 2 - 5 GPa). At almost all conditions tested in these experiments, the orthopyroxene aggregates deformed at the same strain rate as the olivine cylinders, indicating both materials have the same stress exponent and very similar activation enthalpy. The microstructures observed in both the orthopyroxene and olivine cylinders are consistent with dislocation creep and lattice preferred orientations consistent with those observed in naturally deformed peridotites. These results indicate that at asthenospheric mantle conditions, the strengths of orthopyroxene and olivine in the dislocation creep field are very similar.

  18. The iodine-xenon system in clasts and chondrules from ordinary chondrites: Implications for early solar system chronology

    NASA Astrophysics Data System (ADS)

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

    2000-05-01

    We have studied the iodine-xenon system in chondrules and clasts from ordinary chondrites. Cristobalite bearing clasts from Parnallee (LL3.6) closed to xenon loss 1-4 Ma after Bjurböle. Feline (a feldspar and nepheline rich clast also from Parnallee) closed at 7.04 +/- 0.15 Ma. 2 out of 3 chondrules from Parnallee that yielded well defined initial iodine ratios gave ages identical to Bjurböle's within error. A clast from Barwell (L5) has a well-defined initial iodine ratio corresponding to closure 3.62 +/- 0.60 Ma before Bjurböle. Partial disturbance and complete obliteration of the I-Xe system by shock are revealed in clasts from Julesburg (L3.6) and Quenggouk (H4) respectively. Partial disturbance by shock is capable of generating anomalously high initial iodine ratios. In some cases these could be misinterpreted, yielding erroneous ages. A macrochondrule from Isoulane-n-Amahar contains concentrations of iodine similar to 'ordinary' chondrules but, unlike most ordinary chondrules, contains no radiogenic 129Xe. This requires resetting 50 Ma or more later than most chondrules. The earliest chondrule ages in the I-Xe, Mn-Cr and Al-Mg systems are in reasonable agreement. This, and the frequent lack of evidence for metamorphism capable of resetting the I-Xe chronometer, leads us to conclude that (at least) the earliest chondrule I-Xe ages represent formation. If so, chondrule formation took place at a time when sizeable parent bodies were present in the solar system.

  19. Olivine diogenites: The mantle of the eucrite parent body

    SciTech Connect

    Sack, R.O.; Azeredo, W.J.; Lipschutz, M.E. (Purdue Univ., IN (USA))

    1991-04-01

    Two olivine-rich Antarctic diogenites (ALH A77256 and ALH 84001) of the howardite-eucritediogenite (HED) meteorite association have olivine/pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites. Based on chemical data and petrological analysis, these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body (EPB). Mineral assemblages in these olivine-rich diogenites record a continuum in thermal histories from initial partial melting (1150-1200{degree}C) to subsolidus re-equilibration (795 {plus minus} 55{degree}C). The small number of olivine-rich diogenites known hints that only the outer portion of the EPB has been sampled.

  20. 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.

  1. Thermo-Reflectance Spectra of Eros: Unambiguous Detection of Olivine

    NASA Technical Reports Server (NTRS)

    Lucey, P. G.; Hinrichs, J. L.; Urquhart-Kelly, M.; Wellnitz, D.; Bell, J. F., III; Clark, B. E.

    2001-01-01

    Olivine is readily detected on 433 Eros using the new thermo-reflectance spectral technique applied to near-IR spectra obtained at Eros by the NEAR spacecraft. Additional information is contained in the original extended abstract.

  2. Mineralogy of Olivine-hosted Inclusions from the Omolon Pallasite

    NASA Astrophysics Data System (ADS)

    Sharygin, V. V.; Kovyazin, S. V.; Podgornykh, N. M.

    2006-03-01

    This paper is concerning mineralogy of olivine-hosted inclusions from the Omolon pallasite. Troilite, kamacite, nickelphosphide, taenite, stanfieldite, chromite, whitlockite, eskolaite and Si-O-bearing phase were found in metal-sulfide blebs.

  3. Olivine and Pyroxene Diversity in the Crust of Mars

    Microsoft Academic Search

    J. F. Mustard; F. Poulet; A. Gendrin; J.-P. Bibring; Y. Langevin; B. Gondet; N. Mangold; G. Bellucci; F. Altieri

    2005-01-01

    Data from the Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) on the Mars Express spacecraft identify the distinct mafic, rock-forming minerals olivine, low-calcium pyroxene (LCP), and high-calcium pyroxene (HCP) on the surface of Mars. Olivine- and HCP-rich regions are found in deposits that span the age range of geologic units. However, LCP-rich regions are found only in

  4. Diffusion and mobility of electrically conducting defects in olivine

    Microsoft Academic Search

    S. Constable; A. Duba

    2002-01-01

    Electrical conductivity of lherzolite (65% olivine), measured as a function of time after changes in the oxygen fugacity\\u000a (f\\u000a o2) of the surrounding CO2\\/CO atmosphere, is used to infer the diffusivity of the point defects responsible for conduction in olivine. A total of 63\\u000a equilibration runs at temperatures of 900, 1000, 1100, and 1200??C were fit using nonlinear parameter estimation

  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. Petrogenesis of olivine-phyric shergottite Yamato 980459, revisited

    Microsoft Academic Search

    Tomohiro Usui; Harry Y. McSween Jr.; Christine Floss

    2008-01-01

    Primitive magmas provide critical information on mantle sources, but most Martian meteorites crystallized from fractionated melts. An olivine-phyric shergottite, Yamato 980459 (Y-980459), has been interpreted to represent a primary melt, because its olivine megacrysts have magnesian cores (Fo84–86) that appear to be in equilibrium with the Y-980459 whole-rock composition based on Fe–Mg partitioning. However, crystal size distribution (CSD) plots for

  7. Application Bar

    Microsoft Academic Search

    Henry Lee; Eugene Chuvyrov

    \\u000a When you’re ready to program your Windows Phone 7 application in Visual Studio, you’ll know what general features your application\\u000a will provide. Each of the major application features will need to be accessible via a shortcut or some form of a navigation\\u000a menu. For Windows Phone 7 applications, Microsoft recommends that you use a standard Windows Phone 7 Application Bar

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    Thermal emission spectra of the largest asteroid 1 Ceres obtained from the Kuiper Airborne Observatory display features that may provide information on its surface mineralogy. A plot of the Ceres spectrum (calibrated using alpha Boo as a standard) divided by a standard thermal model (STM) is shown. Also shown is the emissivity spectrum deduced from reflectivity measurements for olivine grains <5 microns in diameter. The general shape of the Ceres and the olivine curves agree in essential details, such as the maxima from 8 to 12 microns, the minimum between 12 and 14 microns, the broad peak near 17.5 micron, and the slope beyond 22 micron. (Use of the 10 to 15-micron grain reflectivities provides a better match to the 12- to 14-micron dip. We used a value of unity for beta, the beaming factor associated with small-scale surface roughness in our STM. Adjustment of beta to a lower value raises the long-wavelength side of the Ceres spectrum, providing an even better match to the olivine curve.) The emissivity behavior roughly matches the emission coefficients which were calculated for olivine particles with a particle radius of 3 microns. Their calculations show not only the negative slope from 23 to 25 pm, but a continued decrease past 30 micron. The Ceres emissivity is thus similar to that of small olivine grains from 8 to 30 micron, but olivine's emissivity is lower from 5 to 8 pm.

  9. A transmission electron microscope study of pyroxene chondrules in equilibrated L-group chondrites

    NASA Astrophysics Data System (ADS)

    Watanabe, S.; Kitamura, M.; Morimoto, N.

    1985-01-01

    Analytical electron microscopy is used to investigate the fine structures and chemical compositions of pyroxenes in ion-thinned specimens of rock chips from the L chondrites Allan Hills 77252, Fukutomi, and Satsuma. The results are presented graphically and characterized in detail. The differences noted between the pyroxenes of L3 and those of L3-4 and L4-5 chondrules are interpreted as evidence for more rapid cooling in L3, while shock deformations obscure the original thermal history of L6. The similar periodicities of the spinodal decomposition textures in the Ca-rich pyroxenes of the L3, L3-4, and L4-5 chondrules are attributed to the lack of a significant reheating event in the equilibrated chondrites.

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

    NASA Astrophysics Data System (ADS)

    Robert, F.; Chaussidon, M.

    2003-04-01

    Introduction: Large Boron isotopic variations have been reported in individual chondrules from several meteorites [1, 2]. These variations were interpreted as resulting from the incomplete mixing of two isotopically distinct sources of Boron. Spallation is the only known nucleosynthetic process that can yield Boron in substantial amounts at the scale of the Universe. Therefore it has been proposed that the two sources observed in chondrules correspond to two different types of spallation reactions, namely at high and low energies. Indeed, in the case of Boron, the 11B/10B ratio is sensitive to the energy at which the spallation reaction takes place. Since this report of large B isotopic variations in chondrules, two observations have allowed to identify the natural conditions under which at least one of such spallation reactions may have taken place in the early solar system. First, X-ray observations of T-Tauri stars have revealed daily outbursts which mimic the present day solar activity during the emission of flares [3]. Second, the decay product (i.e. 10B) of the short lived radio-isotope 10Be was discovered in Calcium-Aluminum-rich inclusions (CAIs) [4]. This is an indication that spallation did occurr in the solar system, shortly (i.e. less than a few million years) before the formation of the CAIs. In addition the possible occurrence of 7Be in CAIs suggests that this duration can be as short as a few months [5]. Sampling and Results: In the 8 chondrules from Mokoia, the ?11B values range between -39±6.8 ppm and -0.6±7.8 ppm (2 sigma). In one Boron depleted area of one chondrule, the ?11B value was found to be as low as -68.5 ppm and -61.5 ppm (±29; 2 sigma). In one chondrule from Mokoia the ?11B values range between -33.7±5.4 ppm and -3.8±5.4 ppm. These data confirm with a resolution of ? ±6 ppm the presence of a significant Boron isotopic heterogeneity,.The ?^7Li were also measured along with the ^delta11B. They range from -53.7±2.4 and -0.15±1.6 ppm (2 sigma) in the 8 chondrules of the Mokoia meteorite. Therefore the heterogeneity in B has its counterpart for Li. Interpretation: A two end member mixing model members can be proposed : ?11B ?0 ppm and ?11B<= -70 ppm. The value of 0 ppm is still significantly different from the matrix value reported by [6] (+19.2 ppm) and thus the possible contamination of the chondrule by their surrounding matrix is highly unlikely. The second end member should have ?11B and ?^7Li values le-70 ppm and le-50 ppm, respectively, resulting from Li and B produced at high energy by spallation reactions (E >= 100 MeV/nucleon, ?11B =-375 ?^7Li = -830 ppm). References: [1] Chaussidon M., Robert F. (1995) Nature 374, 337-339. [2] Chaussidon M. and Robert F. (1998) Earth Planet Sci. Lett. 164, 577-589. [3] Montmerle T. (1999) MPE Report : Astronomy with Radioactivities, 225-236. [4] McKeegan K., Chaussidon M., Robert F. (2000) Science 289, 1334-1337. [5] Chaussidon M., Robert F. McKeegan K. (2002) Abst. 33th LPSC #1563 [6] Hoppe et al., (2001) MAPS, 36, 1331-1343. [7] Zhai M et al., (1996) Geochim. Cosmochim. Acta 60, 4877-4881.

  11. On the formation of meteoritic chondrules by aerodynamic drag heating in the solar nebula

    NASA Technical Reports Server (NTRS)

    Wood, J. A.

    1984-01-01

    During the formation of the solar nebula, interstellar grains were falling into the nebula with velocities of the order of 10 km/s at the radial distance where the meteorites were to form. This kinetic energy is 20 times the amount of thermal energy needed to melt the grains. The grains were decelerated by aerodynamic drag in the nebula. Where grain-rich parcels of interstellar material fell into the nebula, heat generated by drag could not be radiated away because of the opacity imparted to the system by the grains, and high temperatures were reached. In this situation presolar aggregations of grains would melt to form chondrules. Many of the properties of chondrules (and also Ca/Al-rich inclusions) are consistent with their formation by this means. The infall-heating concept provides a new framework in which the formation and significance of chondritic meteorites can be understood.

  12. 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.

  13. Size-selective concentration of chondrules and other small particles in protoplanetary nebula turbulence

    Microsoft Academic Search

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

    2000-01-01

    Size-selective concentration of particles in a weakly turbulent\\u000aprotoplanetary nebula may be responsible for the initial collection of\\u000achondrules and other constituents into primitive body precursors. This paper\\u000apresents the main elements of this process of turbulent concentration. In the\\u000aterrestrial planet region, both the characteristic size and size distribution\\u000aof chondrules are explained. \\

  14. 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.

  15. Minor and trace element partitioning between pyroxene and melt in rapidly cooled chondrules

    SciTech Connect

    Jones, R.H. [Univ. of New Mexico, Albuquerque, NM (United States); Layne, G.D. [Univ. of New Mexico, Albuquerque, NM (United States)]|[Woods Hole Oceanographic Institution, MA (United States)

    1997-05-01

    We present minor and trace element (REE, Sr, Y, and Zr) data for pyroxenes and mesostases in four porphyritic chondrules from the Semarkona ordinary chondrite. Apparent partition coefficients for clinoenstatite, orthoenstatite, pigeonite, and augite are compared with experimental and petrologic data from the literature, and the effects on apparent partition coefficients of the rapid cooling rates at which chondrules crystallized are evaluated. For most elements, the effects of cooling at rates of hundreds of degrees per hour cannot be distinguished from variations in equilibrium data resulting from differences in temperature or composition. However, for LREE apparent partition coefficients are significantly higher than comparable equilibrium data, and the ratio of HREE/LREE partition coefficients is lower, particularly for Ca-poor pyroxene. We attribute this flattening of REE patterns to the effect of rapid cooling. Apparent partition coefficients of all REE and Y in augite are higher than equilibrium data, particularly in one chondrule with a high ALO, content. We suggest that this may be attributed to an increase in the uptake of trivalent trace element cations in the pyroxene crystal structure as a result of charge-balanced substitutions with API cations. 32 refs., 6 figs., 3 tabs.

  16. 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.

  17. SHOCK WAVE MODELS: DEPENDENCE OF THERMAL HISTORY AND TYPE II CHONDRULE COMPOSITION ON WATER AND DUST ENRICHMENT. A. V. Fedkin1

    E-print Network

    Grossman, Lawrence

    SHOCK WAVE MODELS: DEPENDENCE OF THERMAL HISTORY AND TYPE II CHONDRULE COMPOSITION ON WATER of chondrules in nebular shock waves [1-3] have investigated the effects of gas pressure, shock velocity subjected to a 7 km/sec shock wave from [2], Fedkin et al. [5] were able to reproduce the mineralogical

  18. 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.

  19. Global investigation of olivine on Mars: Insights into crust and mantle compositions

    NASA Astrophysics Data System (ADS)

    Ody, A.; Poulet, F.; Bibring, J.-P.; Loizeau, D.; Carter, J.; Gondet, B.; Langevin, Y.

    2013-02-01

    present the distribution of olivine on Mars, derived from spectral parameters based on the 1 µm olivine absorption band. The olivine can be defined with respect to two spectral end-members: type 1 corresponds to olivine with low iron content and/or small grain size and/or small abundance, and type 2, which corresponds to olivine with higher iron content and/or larger grain size and/or larger abundance. The spatial and statistical analysis of the global olivine distribution points out five major geological settings where olivine is detected: (1) Early Hesperian olivine-bearing smooth crater floors and flat intercrater plains throughout the southern highlands; (2) olivine deposits around the three main basins Argyre, Hellas, and Isidis; (3) olivine in intercrater dunes, crater ejecta, or extended deposits in the northern plains; (4) olivine associated with outcrops and sand in the floor of Valles Marineris; and (5) olivine-bearing butte outcrops in the vicinity of Hellas. The geological context, the age, and the composition of the olivine detections associated with these five major geological settings are detailed. Their origin and the implication of their occurrence on the composition of the Martian mantle and crust, as well as on the evolution of Mars volcanism are discussed.

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

    NASA Technical Reports Server (NTRS)

    Witteborn, Fred. C.; Roush, Ted L.; Cohen, Martin

    1999-01-01

    Thermal emission spectra of the largest asteroid, 1 Ceres, obtained from the Kuiper Airborne Observatory display features that may provide information about its surface mineralogy. The emissivity, obtained by dividing the spectra by a standard thermal model, is compared with emissivity spectra of olivines and phyllosilicates deduced via Kirchoff's law from reflectivity measurements. The spectra provide a fairly good match to fine grained olivines (0 to 5 micrometer size range). The smoothness of the spectrum beyond 18 micrometers is an indication of particles smaller than 50 micrometers. While the abrupt rise in emissivity near 8 micrometers matches many silicates, the distinct emissivity minimum centered near 12.8 micrometers is consistant with iron-poor olivines, but not with phyllosilicates. It suggests the presence of opaques and does not exclude a mixture with organics and fine-grained phyllosilicates.

  1. The identification of crystalline olivine in cometary silicates

    NASA Astrophysics Data System (ADS)

    Campins, H.; Ryan, E. V.

    1989-06-01

    An intermediate-resolution spectrum of the 8-13 micron region in comet Halley is obtained which shows a prominent silicate emission feature with structure not observed before in other comets or in interstellar silicates. The presence of a strong 11.3 micron peak reported by Bregman and coworkers is confirmed, and evidence is found for additional structure in the band. By comparison with spectra of interplanetary dust particles and laboratory silicates, it is concluded that small crystalline olivine particles are a major component of the silicates in this comet; other silicates (e.g., amorphous or hydrated) must also be present. The identification of crystalline olivine in this part of the spectrum is supported by the observation of four peaks in 20-50 micron airborne spectra of this comet which have also been attributed to olivine.

  2. Water Retention and Rheology of Ti-doped, Synthetic Olivine

    NASA Astrophysics Data System (ADS)

    Faul, U.; Jackson, I.; Fitz Gerald, J. D.

    2012-12-01

    Upper mantle flow laws are currently based almost entirely on experiments with olivine from San Carlos in Arizona. Synthetically produced olivine enables the exploration of the effects of trace elements on the rheology. We have conducted a range of experiments in a gas medium apparatus with solution-gelation derived olivine that show that titanium is the most effective in binding water in the olivine structure. The FTIR signature of this structurally bound water is most similar to that of water-undersaturated natural olivine with absorption bands at 3575 and 3525 cm-1. Water added, titanium-free solgel contains little water after hotpressing and shows adsorption bands at wavenumbers near 3200 cm-1. Noble metal capsules such as Pt or AuPd, providing more oxidizing conditions, are more effective in retaining water. Experiments with NiFe-lined welded Pt capsules retain no more water than NiFe lined samples without Pt capsule. Water retention is, however, again dependent on trace element content, with Ti doped samples containing tens of ppm after hotpressing. By comparison undoped samples run under the same conditions contain little water, again with different FTIR spectra to Ti-doped samples. Our experiments suggest that Ti by itself, or with water contents at the FTIR detection limit enhances diffusion creep rates relative to undoped, dry solgel olivine. Water contents around 10 ppm in NiFe wrapped samples show an enhancement of strain rates of more than one order of magnitude. The addition of Ti, together with the presence of water, also enhances grain growth. For more coarse-grained samples in the dislocation creep regime the enhancement of the stain rate as a function of water content is approximately consistent with the flow laws of Hirth and Kohlstedt (2003).

  3. intro, 2 bars main riff, 4 bars

    E-print Network

    Reiners, Peter W.

    intro, 2 bars main riff, 4 bars verse riff 1: G G if you like to gamble, I tell you I'm your man G G you win some, loose some, it's all the same to me main riff with fill 1, 4 bars verse riff 2: D C the pleasure is to play it makes no difference what you say main riff with fill 1, 2 bars verse riff 2: D C I

  4. 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.

  5. Magnetic Paleofield of Avanhandava H4 Chondrite's Matrix and Chondrules - Implications on Magnetic Fields in Early Solar System.

    NASA Astrophysics Data System (ADS)

    Kohout, T.; Pesonen, L. J.

    2005-12-01

    The Avanhandava (H4) fall occurred in 1952 in Brazil. A total of 9.33 kg had been preserved after the meteorite brake up during the impact [1]. The meteorite contains large (0.1 - 2.0 mm) chon-drules that have clearly delineated boundaries with matrix. This characteristic allows us to pick up oriented individual chondrules and study their magnetic properties. The chondrules of the Avanhandava meteorite show a low and randomly oriented NRM (10-2 - 10-1 mAm2/kg). In contrast the matrix is strongly (100 - 101 mAm2/kg) and uniformly magnet-ized [2]. Various methods for paleofield determination have been applied on matrix and individual chondrules in order to determine possi-ble magnetizing processes and paleofields in early solar systems.. The laboratory experiments reveal approximate paleofields for matrix similar to present geomagnetic field. The paleofield de-termined for chondrules is approximately one order of magnitude lower comparing to values obtained for matrix. That suggests that chondrules are not magnetically contaminated by geomagnetic or artificial fields and they acquired their NRM prior their aggregation to Avanhandava parent body (random NRM directions). The matrix shows remarkable traces of terres-trial weathering and is uniformly magnetized. The paleofield re-sult for matrix indicates possible remagnetization caused by ter-restrial weathering. The terrestrial weathering of ordinary chon-drites is observed even on falls stored in museums and can sig-nificantly influence meteorite magnetic records [3, 4]. References: [1] Paar W. et al. 1976. Revista Brasileira de Geo-ciencias 6: 201-210. [2] Kohout T. and Pesonen L. J. 2005. 68th Annual Meteoritical Society Meeting: 5202. [3] Kohout T. et al. 2004. Physics and Chemistry of the Earth 29: 885-897. [4] Lee M. R. and Bland P. A. 2004. Geochimica et Cosmochimica Acta 68: 893-916.

  6. 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.

  7. Mineral replacement rate of olivine by chrysotile and brucite under high1 alkaline conditions2

    E-print Network

    Paris-Sud XI, Université de

    1 Mineral replacement rate of olivine by chrysotile and brucite under high1 alkaline conditions2 3 replaced by18 chrysotile and brucite under high alkaline conditions. In our study, olivine replacement19 between olivine and chrysotile-brucite minerals. Coupled dissolution-precipitation21 led to the alteration

  8. Metastable olivine wedge and deep dry cold slab beneath southwest Japan Hitoshi Kawakatsu a,

    E-print Network

    Kawakatsu, Hitoshi

    Metastable olivine wedge and deep dry cold slab beneath southwest Japan Hitoshi Kawakatsu a Available online 28 January 2011 Keywords: metastable olivine receiver function slab mantle transition zone plates (slabs) due to kinetic effects, and it has been suggested that metastable olivine may persist

  9. 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 on geological history, shock events, and olivine color, J. Geophys. Res., 112, E04002, doi:10.1029/2006JE002777 two shock events. The first shock, to stage S5­S6, affected the olivine by producing in it planar

  10. Challenges in detecting olivine on the surface of 4 Vesta

    NASA Astrophysics Data System (ADS)

    Beck, Andrew W.; McCoy, Timothy J.; Sunshine, Jessica M.; Viviano, Christina E.; Corrigan, Catherine M.; Hiroi, Takahiro; Mayne, Rhiannon G.

    2013-11-01

    Identifying and mapping olivine on asteroid 4 Vesta are important components to understanding differentiation on that body, which is one of the objectives of the Dawn mission. Harzburgitic diogenites are the main olivine-bearing lithology in the howardite-eucrite-diogenite (HED) meteorites, a group of samples thought to originate from Vesta. Here, we examine all the Antarctic harzburgites and estimate that, on scales resolvable by Dawn, olivine abundances in putative harzburgite exposures on the surface of Vesta are likely at best in the 10-30% range, but probably lower due to impact mixing. We examine the visible/near-infrared spectra of two harzburgitic diogenites representative of the 10-30% olivine range and demonstrate that they are spectrally indistinguishable from orthopyroxenitic diogenites, the dominant diogenitic lithology in the HED group. This suggests that the visible/near-infrared spectrometer onboard Dawn (VIR) will be unable to resolve harzburgites from orthopyroxenites on the surface of Vesta, which may explain the current lack of identification of harzburgitic diogenite on Vesta.

  11. Scanning electron microscope observation of dislocations in olivine

    Microsoft Academic Search

    S. Karato

    1987-01-01

    Dislocations in olivine decorated by oxidation in air were observed with a scanning electron microscope (SEM) using a backscattered electron image (BEI). The decorated dislocations (and grain boundaries) were found to give clear bright images in this mode, indicating an increase of mean atomic number near the dislocation cores (and grain boundaries). This method of dislocation observation has a resolution

  12. Shock effects in olivine and implications for Hugoniot data

    Microsoft Academic Search

    Raymond Jeanloz

    1980-01-01

    Deformation produced in single-crystal olivine samples by shock wave stresses ranging between 16 and 75 GPa are documented by microscopy and spectroscopy. No evidence was found for phase transformation throughout the 'mixed-phase' region (about 25 to 70 GPa) contrary to expectations based on the current interpretations of Hugoniot data. Samples retrieved from peak pressures above 20 GPa exhibit extensive plastic

  13. ORIGINAL PAPER Dislocation recovery in fine-grained polycrystalline olivine

    E-print Network

    . Kokkonen · J. D. Fitz Gerald · A. Barnhoorn · U. H. Faul · I. Jackson Received: 10 February 2009 / Accepted interest for experimental research (Mei and Kohlstedt 2000; Karato and Jung 2003; Jackson et al. 2004; Du on the use of pure polycrystalline iron-bearing olivine, (Mg,Fe)2SiO4, synthesized from lab- oratory reagents

  14. 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.

  15. 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.

  16. 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.

  17. 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).

  18. 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.

  19. 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.

  20. VAPOR PRESSURES AND EVAPORATION COEFFICIENTS OF FE, NA AND K OVER CHONDRULE COMPOSITION MELTS. A. V. Fedkin1

    E-print Network

    Grossman, Lawrence

    VAPOR PRESSURES AND EVAPORATION COEFFICIENTS OF FE, NA AND K OVER CHONDRULE COMPOSITION MELTS. A. V Institute, University of Chicago, Chicago, IL 60637. avf@uchicago.edu. Introduction: Although vapor, , RTm2 P J x v xx x = in which ,P,m v xx and x are the molecular weight, equilibrium vapor pressure

  1. 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.

  2. Formation of chondrules in magnetic winds blowing through the proto-asteroid belt

    NASA Astrophysics Data System (ADS)

    Salmeron, Raquel; Ireland, Trevor R.

    2012-04-01

    Chondrite meteorites are believed to represent the building blocks of the solar nebula, out of which our solar system formed. They are a mixture of silicate and oxide objects (chondrules and refractory inclusions) that experienced extremely high temperatures, set in a matrix that remained relatively cold. The prevalence of chondrites suggests that they formed through a very general process, related to stellar and planet formation. The nature of this mechanism, however, remains obscure as astronomical observations of star-forming regions suggest a relatively cold environment. Here we show how refractory objects could have been thermally processed in a radially-extended wind, accelerated magnetically from the surfaces of a protostellar disc. In this scenario, refractory precursor aggregates are heated while being lifted in the wind, growing through amalgamation, and eventually becoming heavy enough to drop back to the disc, where they assemble with the matrix. We show that processing at radial distances of about 1-3 AU can produce temperatures in the appropriate regime to melt chondrules and explain their basic properties, while retaining association with the colder material that provides the chondrite matrix. This mechanism is very general, as these energetic winds are commonly associated with stellar formation.

  3. 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.

  4. High shear strain of olivine aggregates: rheological and seismic consequences.

    PubMed

    Bystricky, M; Kunze, K; Burlini, L; Burg, J

    2000-11-24

    High-pressure and high-temperature torsion experiments on olivine aggregates in dislocation creep show about 15 to 20% strain weakening before steady-state behavior, characterized by subgrain-rotation recrystallization and a strong lattice preferred orientation. Such weakening may provide a way to focus flow in the upper mantle without a change in deformation mechanism. Flow laws derived from low strain data may not be appropriate for use in modeling high strain regions. In such areas, seismic wave propagation will be anisotropic with an axis of approximate rotational symmetry about the shear direction. In contrast to current thinking, the anisotropy will not indicate the orientation of the shear plane in highly strained, recrystallized olivine-rich rocks. PMID:11090352

  5. Effects of hydration on the elastic properties of olivine

    Microsoft Academic Search

    Steven D. Jacobsen; Fuming Jiang; Zhu Mao; Thomas S. Duffy; Joseph R. Smyth; Christopher M. Holl; Daniel J. Frost

    2008-01-01

    Water, dissolved as hydroxyl (OH)? into the solid silicate minerals of the upper mantle can reduce adiabatic wave speeds through associated defects. Here we report Brillouin spectroscopy measurements of the sound velocities and single-crystal elastic constants of hydrous forsterite (hy-Fo100) and hydrous olivine (hy-Fo97) containing 0.8–0.9 wt% H2O. The samples, synthesized at 12 GPa and 1250°C, represent nearly the maximum

  6. Effects of hydration on the elastic properties of olivine

    Microsoft Academic Search

    Steven D. Jacobsen; Fuming Jiang; Zhu Mao; Thomas S. Duffy; Joseph R. Smyth; Christopher M. Holl; Daniel J. Frost

    2008-01-01

    Water, dissolved as hydroxyl (OH)- into the solid silicate minerals of the upper mantle can reduce adiabatic wave speeds through associated defects. Here we report Brillouin spectroscopy measurements of the sound velocities and single-crystal elastic constants of hydrous forsterite (hy-Fo100) and hydrous olivine (hy-Fo97) containing 0.8-0.9 wt% H2O. The samples, synthesized at 12 GPa and 1250°C, represent nearly the maximum

  7. Olivine and pyroxene-rich deposits in Holden Crater, Mars

    NASA Astrophysics Data System (ADS)

    Glotch, T. D.

    2006-12-01

    Holden crater is a ~150 km diameter crater centered at 326 E, 26S breached in the south by Uzboi Vallis. Holden has been proposed as a possible landing site for the Mars Science Laboratory (MSL) rover and has been the subject of intense scrutiny due to its potential as a paleolake basin. Near the region where Uzboi Vallis breaches the southern Holden Crater wall are layered rocks that have been suggested to be aqeously deposited. Additionally, fan-shaped deposits originate in the southern and western crater walls that have been interpreted as alluvial fans and fan deltas. New analyses of THEMIS and TES data indicate that both the basement and layered rocks - those interpreted to have been deposited in an aqueous environment - near the breach point of Holden crater are olivine and pyoxene- rich. Based on THEMIS IR imagery, these units have a higher thermal inertia than the surrounding terrain. The higher-TI units correspond with lighter-toned layered units seen in THEMIS Vis and MOC imagery that also have a distinct mafic signature in THEMIS daytime IR false-color decorrelation stretch images. The fan deposit in western Holden Crater, which has been proposed as a specific landing site for MSL may also have an elevated olivine abundance based on TES data. High olivine and pyroxene abundances in the sedimentary units of Holden crater do not preclude the presence of water in the history of the crater. However, based on analysis of TES and THEMIS data over the region, there is no evidence for extended chemical weathering present at the surface. Olivine-rich bedrock is likely to be a regional property as it is also present in chaos terrain to the northeast of Holden which is the source of the Landon Vallis outflow channel. These regions should be considered high priority targets for future investigations by OMEGA and CRISM.

  8. Noble Gas Partitioning Between Olivine and Melt to 2 GPa

    Microsoft Academic Search

    S. W. Parman; S. P. Kelley; C. J. Ballentine; J. A. van Orman; G. Holland

    2009-01-01

    We have extended our experimental measurements of noble gas partition coefficients to 2 GPa in the piston-cylinder device. The experimental set-up involves surrounding wafers of gem quality San Carlos olivine (250-1000 microns thick, 3-4 mm diameter) with diamond powder or vitreous carbon spheres. A layer of melt is placed at the bottom of the capsule which infiltrates the porous media

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2006-10-01

    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 (<200km 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 4GPa for a temperature range of 873-1,273K for water contents of 0.01-0.08wt%. 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 ~10-2wt% water, whereas the water content in the continental upper mantle is less than ~10-3wt%.

  11. 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

  12. Diffusion creep of dry, melt-free olivine

    NASA Astrophysics Data System (ADS)

    Faul, Ulrich H.; Jackson, Ian

    2007-04-01

    Deformation experiments were conducted on fine-grained (3-6 ?m), fully synthetic Fo90 olivine aggregates in a gas-medium apparatus at 300 MPa confining pressure and temperatures of 1150-1360°C. The strain rates of the solution-gelation-derived and therefore genuinely melt-free, dry samples are about two orders of magnitude lower than the strain rates for nominally melt-free aggregates at the same pressure and temperature conditions and grain size. Benchmark deformation tests with Anita Bay dunite and mild steel reproduce published data. The creep strength of melt-added sol-gel olivine is similar to the published creep strength of dry, melt-bearing olivine derived from natural rocks. Nonlinear least-squares fits to the melt-free deformation data give an activation energy of 484 kJ/mol, a stress exponent of 1.4, and a grain-size exponent of 3 over a range of stresses from 15 to 210 MPa. These results suggest that small amounts of melt may be similarly effective in reducing the creep strength of upper mantle rocks as small amounts of water. However, a possible contribution of grain boundary composition to the observed differences in rheology in the absence of melt cannot be conclusively ruled out by the current experiments.

  13. The morphology and surface features of olivine in kimberlite lava: implications for ascent and emplacement mechanisms

    NASA Astrophysics Data System (ADS)

    Jones, T. J.; Russell, J. K.; Porritt, L. A.; Brown, R. J.

    2013-12-01

    Many kimberlite rocks contain large proportions of ellipsoidal-shaped xenocrystic olivine grains that are derived mainly from the disaggregation of peridotite. Xenocrystic olivine grains from a lava erupted from the Quaternary Igwisi Hills kimberlites, Tanzania, are compared to phenocrystic olivine, liberated from picritic lavas, and mantle olivine, liberated from a fresh peridotite xenolith, in order to examine the potential modification of olivine surface textures due to transport from the mantle to the surface within kimberlite magmas. Image analysis, SEM imagery and laser microscopy reveals significant differences in the surface features and morphologies of the three crystal populations. Xenocrystic olivine grains are characterised by rough surfaces, ellipsoidal shapes and impact pits. Mantle olivines are characterised by flaked surfaces and indented shapes consistent with growth as a crystal aggregates. Phenocrystic olivines are smooth-surfaced and exhibit flat crystal faces. We infer that the distinctive shapes and surfaces of xenocrystic olivine grains resulted from three distinct mechanical processes attending their rapid transport from their source in the mantle lithosphere: (1) penetrative flaking from micro-tensile failure induced by rapid decompression; (2) sustained abrasion and attrition arising from particle-particle collisions between grains in a turbulent, volatile-rich flow regime, and; (3) higher energy particle-particle collisions that produced impact cavities superimposed on decompression structures. The combination of these processes during the rapid ascent of kimberlite magmas is responsible for the distinctive ellipsoidal shape of olivine xenocrysts found in kimberlites worldwide.

  14. Chondrule trace element geochemistry at the mineral scale Emmanuel JACQUET1*

    E-print Network

    Demouchy, Sylvie

    . Results are similar in all three meteorites. Mesostasis has rare earth element (REE) concentrations of 10­20 · CI. Low-Ca pyroxene has light REE (LREE) concentrations near 0.1 · CI and heavy REE (HREE) near 1. The coarsest olivine crystals tend to have the most fractionated REE patterns, indicative of equilibrium

  15. 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.

  16. 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.

  17. 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.

  18. Olivine Morphology and Trace Element Fractionation in Metal of Main Group Pallasites

    NASA Astrophysics Data System (ADS)

    Kissin, S. A.

    2009-05-01

    Pallasites are stony-iron meteorites consisting largely of olivine macrocrysts in a matrix of iron-nickel alloy in the form of kamacite-taenite intergrowth. Pallasites have been divided into Main Group (PMG), Eagle Station Grouplet (PES) and ungrouped (IrUn) also called pyroxene pallasites. Within PMG, six have anomalous metal contents (PMGam) and five have anomalous olivine compositions (PMGas). The morphologies of olivine macrocrysts in PMG are essentially of two types, angular or rounded. Of 19 normal PMG whose compositions and olivine morphologies are known, 17 have angular olivines. In the remaining two PMG, olivines are rounded as well as those of three PMGam and three PMGas. Experimental studies have demonstrated that rounding of olivines in molten iron-nickel alloy occurs in short times on a geological scale. Metallic cooling rates for PMG have been shown to be rapid at high temperature and slow at low temperature. Detailed analyses have demonstrated that angular olivines are compositionally zoned and therefore not in equilibrium with metal. These conditions imply that molten metal was injected into angular olivines fractured by an impact event. However, the presence of rounded olivine macrocrysts in PMGam and PMGas, as well as in two normal PMG, implies that these pallasites have retained an earlier generation of olivine. A long-standing theory for the origin of pallasites is that they represent the core-mantle boundary of a parent- body, subsequently disrupted by impact and injected by impact-melted metal. A relationship between the trace element fractionation trend in group IIIAB iron meteorites and metal of PMG is evident in that normal members cluster at the end of this fractionation trend. However, the theory does not account for the presence of rounded olivine macrocrysts. Log trace element vs log Au plots of indicate that most PMGam members exhibit the same fractionation trend as that seen for group IIIAB irons, and these correlate with PMGam and PMGas members with rounded olivines. The rounded olivine marcrocrysts may represent pre-impact olivines trapped in fractionating group IIIAB metal. Some scatter in these plots may be attributed to crystallization of melt trapped among olivine macrocrysts. Thus, the core-mantle boundary theory for the original of PMG is consistent with the evidence seen in olivine macrocrysts.

  19. 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).

  20. Normalized Homologous Temperature of Olivine: Implications for the Effect of Iron Content on Mantle Deforamtio

    NASA Astrophysics Data System (ADS)

    Wang, Q.

    2012-12-01

    The flow laws and fabric transition of olivine under different thermal-mechanical conditions are generally obtained from HP-HT experiments on San Carlos olivine (Fo90), which hampers our understanding of the effect of iron content on the mantle flow and deforamtion. Because the melting temperature is related with the strength of the bonds binding a crystalline material together, the normalized homologous temperature T/Tm(P), is defined by the ratio between the absolute temperature of olivine and its melting point Tm at certain pressure P. Using the forsterite-fayalite melting loop at room pressure, the generalized mean is adopted to predict the dependence of Tm on pressure and iron content of olivine up to 7.5 GPa. Using T/Tm(P), we can evaluate the integreted effect of temperature and pressure on the deformation mechanisms of olivine. A new olivine fabric diagram is set up as a function T/Tm(P) and water content. The result indicates that the A-type olivine fabric becomes dominant at T/Tm(P) > 0.72, while the B- and C-type olivine fabrics are favorable at T/Tm(P) < 0.7, no matter their water content. Partial melting will produce resudies with higher Fo number in olivine, and consequently, a more rigid mantle with higher Tm. The relatively smaller T/Tm(P) of olivine beneath cratons can explain the long-term stability of the continental roots. In addition, a 2D profile of olivine T/Tm(P) for the oceanic lithosphere shows good correlation between T/Tm(P) and the distribution of earthquakes. Therefore T/Tm(P) of olivine can be used as a parameter to model the rheology of the upper manlte, especailly when taking into account of the compostional change in different tectonic processes.

  1. Partition of Ni between olivine and sulfide and its application to Ni-Cu sulfide deposits

    Microsoft Academic Search

    M. E. Fleet; N. D. MacRae

    1983-01-01

    Equilibration of natural olivine with (Fe, Ni)S in sealed silica glass tubes yields a value for the distribution constant for Ni\\/Fe exchange (KD3) of 27.7±3.5, for 1,200° C, product olivine and sulfide compositions in the ranges 96 to 97 mol% Fo and 15 to 70 mol% NiS, respectively, and run durations of 28 days. Electron microprobe analysis of product olivine

  2. Phosphorus zoning in olivine of Kilauea Iki lava lake, Hawaii

    NASA Astrophysics Data System (ADS)

    Fabbrizio, Alessandro; Beckett, John R.; Baker, Michael B.; Stolper, Edward M.

    2010-05-01

    Kilauea Iki lava lake was formed when the lavas of the 1959 summit eruption of Kilauea volcano ponded in Kilauea Iki pit crater, as described by [1]. The main chamber of this lake has been drilled repeatedly from 1960 to 1981 as the lake has cooled and crystallized and partial descriptions of core can be found in [2-7]. The bulk of the core consists of a gray, olivine-phyric basalt matrix [3]. Rapid diffusion of divalent cations through olivine at magmatic temperatures can delete information on early-formed zoning and thus information on early magmatic history, recorded in olivine during its growth, is often largely lost [8-11]. In the last years many studies [8-11] have shown that natural olivine, terrestrial and extraterrestrial, from several localities and rock types can preserve a complex zoning in P (sometimes associated with Cr and Al). Simple crystallization experiments conducted by [10] and [11] were able to replicate these features (i.e., sector and oscillatory zoning). Here, we describe P, Cr and Al zoning in olivine from the 1981 drilling of Kilauea Iki lava lake hole #1 (KI81-1) [6]. K? X-ray intensity maps and major and minor element quantitative analyses were obtained using the Caltech JEOL JXA-8200 electron microprobe. We acquired P, Cr, Al, Fe and Ti X-ray maps simultaneously at 15 kV and 400 nA, a beam diameter of 1 ?m, pixel spacing of 1-2 ?m, and count times of 420-1500 msec/step were used depending on the dimension of the crystal. 15 kV and 40 nA with a beam diameter of 1 ?m were used to collect quantitative analyses. P2O5 contents of the Iki olivines range from below detection limit to 0.30 wt%. Zoning in phosphorus, based on X-ray intensity maps, was observed in all olivines we examined. The P zoning patterns of the olivines display several styles. P shows oscillatory zoning comparable to that seen in terrestrial and extraterrestrial igneous olivines and in experimentally grown olivine [8-11]; high P regions, inside the crystals, outline low P chambers and P enriched zones were also observed; near the margins of the crystals is possible to find the presence of discontinuous sets of P-enriched bands that generally outline euhedral crystal forms; some crystals are characterized by P-enriched ghosts of relict crystals in their interior that are associated with probable undercooling and/or with an initial pulse of rapid crystal growth [8, 10]. Phenocrysts and microphenocrysts are frequently unzoned in major and minor divalent cations (Fe, Mg, Mn, Ca, Ni), but all are zoned in P. Variations in Cr and Al correlate spatially with P but are much fainter or absents, in some crystal the P-enriched bands are superimposed with small crystals of chromite (?1 ?m) aligned along the P zoning. Probably these chromites were formed by precipitation from the original Cr and Al bands. In no case was observed Ti zoning. [1] Richter D.H. et al. (1970) US Geol Surv Prof Pap 537-E, 73 p. [2] Richter D.H., Moore J.G. (1966) US Geol Surv Prof Pap 537-B, 26 p. [3] Helz R.T. (1980) Bull Volcanol 43-4, 675-701. [4] Helz R.T. et al. (1984) US Geol Surv Open File Rep 84-484, 72 p. [5] Hardee H.C. et al. (1981) Geophys Res Lett 8, 1211-1214. [6] Helz R.T., Wright T.L. (1983) US Geol Surv Open File Rep 83-326, 66 p. [7] Helz R.T. (1987) Geochem Soc Spec Pub 1, 241-258. [8] Beckett J.R. et al. (2008) LPSC abs. 1726. [9] Mccanta M.C. et al. (2008) LPSC abs. 1807. [10] Milmann-Barris M.S. et al. (2008) CMP 155, 739-765. [11] Mccanta M.C. et al. (2008) GCA 72-12, S1, A610.

  3. Chondrule Formation and Protoplanetary Disk Heating by Current Sheets in Non-Ideal Magnetohydrodynamic Turbulence

    E-print Network

    M. K. Ryan Joung; Mordecai-Mark Mac Low; Denton S. Ebel

    2003-09-05

    We study magnetic field steepening due to ambipolar diffusion (Brandenburg & Zweibel 1994) in protoplanetary disk environments and draw the following conclusions. Current sheets are generated in magnetically active regions of the disk where the ionization fraction is high enough for the magnetorotational instability to operate. In late stages of solar nebula evolution, the surface density is expected to have lowered and dust grains to have gravitationally settled to the midplane. If the local dust-to-gas mass ratio near the midplane is increased above cosmic abundances by factors > 10^3, current sheets reach high enough temperatures to melt millimeter-sized dust grains, and hence may provide the mechanism to form meteoritic chondrules. In addition, these current sheets possibly explain the near-infrared excesses observed in spectral energy distributions (SEDs) of young stellar objects. Direct imaging of protoplanetary disks via a nulling interferometer or, in the future, a multi-band, adaptive optics coronagraph can test this hypothesis.

  4. Olivine-rich exposures at Bellicia and Arruntia craters on (4) Vesta from Dawn FC

    NASA Astrophysics Data System (ADS)

    Thangjam, Guneshwar; Nathues, Andreas; Mengel, Kurt; Hoffmann, Martin; Schäfer, Michael; Reddy, Vishnu; Cloutis, Edward A.; Christensen, Ulrich; Sierks, Holger; Corre, Lucille Le; Vincent, Jean-Baptiste; Russell, Christopher T.

    2014-10-01

    We present an analysis of olivine-rich exposures at Bellicia and Arruntia craters using Dawn Framing Camera (FC) color data. Our results confirm the existence of olivine-rich materials at these localities as described by Ammannito et al. using Visual Infrared Spectrometer (VIR) data. Analyzing laboratory spectra of various howardite-eucrite-diogenite meteorites, high-Ca pyroxenes, olivines, and olivine-orthopyroxene mixtures, we derive three FC spectral band parameters that are indicators of olivine-rich materials. Combining the three band parameters allows us, for the first time, to reliably identify sites showing modal olivine contents >40%. The olivine-rich exposures at Bellicia and Arruntia are mapped using higher spatial resolution FC data. The exposures are located on the slopes of outer/inner crater walls, on the floor of Arruntia, in the ejecta, as well as in nearby fresh small impact craters. The spatial extent of the exposures ranges from a few hundred meters to few kilometers. The olivine-rich exposures are in accordance with both the magma ocean and the serial magmatism model (e.g., Righter and Drake; Yamaguchi et al.). However, it remains unsolved why the olivine-rich materials are mainly concentrated in the northern hemisphere (approximately 36-42°N, 46-74°E) and are almost absent in the Rheasilvia basin.

  5. Origin of graphitic carbon and pentlandite in matrix olivines in the Allende meteorite.

    PubMed

    Brearley, A J

    1999-08-27

    Matrix olivines in the Allende carbonaceous chondrite are believed to have formed by condensation processes in the primitive solar nebula. However, transmission electron microscope observations of numerous matrix olivines show that they contain abundant, previously unrecognized, nanometer-sized inclusions of pentlandite and poorly graphitized carbon. Neither of these phases would have been stable at the high-temperature conditions required to condense iron-rich olivine in the solar nebula. The presence of these inclusions is consistent with formation of the olivines by parent body processes that involved overgrowth of fine-grained organic materials and sulfides in the precursor matrix materials. PMID:10464092

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

    USGS Publications Warehouse

    King, T.V.V.; Ridley, W.I.

    1987-01-01

    Using high-resolution visible and near-infrared diffuse spectral reflectance, systematically investigates apparent wavelength shifts as a function of mineral chemistry in the Fe/Mg olivine series from Fo11 to Fo91. The study also shows that trace amounts of nickel can be spectrally detected in the olivine structure. Significant spectral variation as a function of grain size is also demonstrated, adding a further complication to the interpretation of remotely sensed data from olivine-rich surfaces. Some permutations of Fe-Mg-Ni relations in olivines are discussed as they apply to the interpretation of asteroid surfaces and other extraterrestrial bodies. -from Authors

  7. Bar-Halo Interaction and Bar Growth

    E-print Network

    E. Athanassoula

    2002-03-21

    I show that strong bars can grow in galactic discs, even when the latter are immersed in haloes whose mass within the disc radius is comparable to, or larger than, the mass of the disc. I argue that this is due to the response of the halo and in particular to the destabilising influence of the halo resonant stars. Via this instability mechanism the halo can stimulate, rather than restrain, the growth of the bar.

  8. 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.

  9. Destabilization of olivine by 10kV electron irradiation

    NASA Astrophysics Data System (ADS)

    Lemelle, L.; Beaunier, L.; Borensztajn, S.; Fialin, M.; Guyot, F.

    2003-04-01

    Mineral phases in the interplanetary medium are subjected to the solar wind irradiation. Irradiation induces fractional volatilization of chemical elements in silicates; if large scale directional flow occurs, such as predicted by numerous models in the early solar system, then large scale chemical fractionnations occur. Electron irradiation experiments were performed using a 30 keV electron beam on single crystals of olivine in a scanning electron microscope (SEM) and in an electron microprobe (EMP) (Lemelle et al. 2003). Structural damage is caused to the irradiated surface of the iron-bearing olivines. The irradiated areas comprise spherules with sizes of hundreds of nanometers and micrometer-sized holes observed on Focused Ion Beam cuts. In the immediate vicinities of the irradiated areas, droplets with sizes of tens of nanometers and tracks are observed. With increasing total charge, the hundreds of nanometer-sized spherules become larger and more irregular in shape. The size and shape of the nanometer-sized droplets remain almost constant, but their surface density increases (in cm-2). Compared to the initial olivine, irradiated areas are slightly enriched in MgO, whereas the deposits are enriched in SiO_2. This destabilization of olivine results most probably from electrostatic discharges leading to the breakdown of the dielectric lattice. The possibility that such processes could be responsible for significant space weathering of interplanetary dust particles and regoliths of planetary surfaces should be taken into account. In the interplanetary medium, 10 keV-range electrons are carried by the solar wind, whereas at 1 AU from the Sun, the lifetime of cometary dust and the exposure time of lunar regolith are, at least, 10 to 100 times greater than the duration required to accumulate the damaging electronic doses applied in this study. Moreover, the comparison of the microstructures of samples irradiated in the present study with features of lunar regolith grains reveals several chemical and structural similarities. Interestingly, experiments carried out in transmission EM, with 100 keV-range electrons (Carrez et al. 2002) showed different mechanism of destabilization and chemical fractionation elemental loss from the silicate matrix. Lemelle et al. (2003) to be printed in Geochimica Cosmochimica Acta. Carrez P., Leroux H., Cordier P. and Guyot F. (2001) Philos. Mag. A 81, 2823-2840.

  10. Olivine-type NaCd(AsO4)

    PubMed Central

    Weil, Matthias

    2013-01-01

    The title compound, sodium cadmium orthoarsenate, adopts the olivine [Mg2(SiO4)] structure type in space group Pnma, with Na (site symmetry -1) and Cd (.m.) replacing the two Mg positions, and the AsO4 tetra­hedron (.m.) the SiO4 tetra­hedron. The crystal structure is made up of a nearly hexa­gonal closed-packed arrangement of O atoms stacked along [001]. The Na and Cd atoms occupy one half of the octa­hedral voids in alternate layers stacked along [100], and one eighth of the tetra­hedral voids are occupied by As atoms. PMID:24454011

  11. Argon Diffusion in Shocked Pyroxene, Feldspar, and Olivine

    NASA Astrophysics Data System (ADS)

    Weirich, J.; Isachsen, C. E.; Johnson, J. R.; Swindle, T.

    2010-12-01

    Background: The diffusion rate of argon (Ar) in unshocked feldspar has been well studied, but studies on pyroxene and olivine are limited or non-existent. Likewise, the effects of shock on these mineral groups is also limited or non-existent. Understanding how shock affects these mineral groups is important for determining the thermal history of shocked meteorites and collisional impact craters. We have analyzed the Ar diffusion rate of an albitite and a pyroxenite at various experimental shock pressures up to ~60GPa, unshocked high-Ca pyroxene, and an olivine mineral separate from the Springwater meteorite. A previous study of shocked feldspar has shown that Ar diffusion in plagioclase (An67) is unaffected by experimental shock [1]. Re-reduction of data from another study [2] suggests naturally shocked K-rich feldspar is affected, though experimentally shocked oligoclase feldspar (An10-30) is not affected. However, previous shock experiments on feldspar were performed with low temperature resolution and only a single extraction at each temperature. This makes determining the diffusion parameters difficult because the presence of multiple grain sizes can compromise the data. By performing our experiments with a higher temperature resolution and with two extractions at each temperature, we can attain higher quality and more reliable data. The effects of shock on pyroxene and olivine have never been studied. Results: We have found that experimental shock undoubtedly raises the diffusivity of albite (Ab97), and lowers the activation energy required for diffusion. Comparison with previous data indicates that the Ca content may be controlling the response to shock. Pyroxene seems to be somewhat variable regardless of shock pressure, even within the same sample. Shock may have an effect on the diffusion rate of pyroxene, but given the variability it is difficult to delineate. The range of pyroxene diffusion rates is similar to previous studies. Olivine is found to have a low activation energy, somewhat similar to that of unshocked alkali feldspar, despite remaining a high temperature mineral due to a much lower frequency factor. References: [1]Jessberger E. K. and Ostertag R. (1982). GCA 46:1465-1471. [2]Stephan T. and Jessberger E. K. (1992). GCA 56:1591-1605.

  12. Serpentinization of sintered olivine during seawater percolation experiments

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    The mantle exposed at slow to ultra-slow spreading ridges is pervasively and variably serpentinized down to depth of 4-8km according to available geophysical data. The onset and durability of this hydration process require efficient penetration and renewal of fluids at the mineral-fluid interface. Moreover, serpentinization is exovolumic if a mass-conservative system is assumed, or chemical elements have to be leached out to conserve rock volume. Thus, the extent of serpentinization depends of the system capacity to create space and/or to drive mass transfers. In order to investigate these coupled hydrodynamic and chemical mechanisms, we did a laboratory experiment during which seawater was injected in a sintered San Carlos olivine sample at conditions representative of low temperature, ultramafic-hosted, hydrothermal systems. The percolation-reaction experiment was carried out at 19 MPa and 190°C; the initial water flow was set at 0.2 mL/h then decreased down to 0.06 mL/h after 8 days. During experiment, 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 expanse of olivine. Mass balance calculations indicate that, ca. 8 wt. % olivine was dissolved while the same mass of serpentine (+/- brucite) was formed finally resulting in a porosity decrease 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. We observed that the outlet fluid composition is not modified by changes in the fluid flow. These experimental results are used better understand the scale and efficiency of serpentinization at the onset of the alteration reactions (effective reaction rates in porous/fractured media).

  13. 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.

  14. The origin of non-porphyritic pyroxene chondrules in UOCs: Liquid solar nebula condensates?

    Microsoft Academic Search

    Almut Engler; Maria Eugenia Varela; Gero Kurat; Denton Ebel; Paul Sylvester

    2007-01-01

    A total of 56 non-porphyritic pyroxene and pyroxene\\/olivine micro-objects from different unequilibrated ordinary chondrites were selected for detailed studies to test the existing formation models. Our studies imply that the non-porphyritic objects represent quickly quenched liquids with each object reflecting a very complex and unique evolutionary history. Bulk major element analyses, obtained with EMPA and ASEM, as well as bulk

  15. Extremely Na and Cl-rich chondrule from the CV3 carbonaceous chondrite Allende

    Microsoft Academic Search

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

    2011-01-01

    We report on a study of Al3509, a large Na- and Cl-rich, radially-zoned object from the oxidized CV carbonaceous chondrite Allende. Al3509 consists of fine-grained ferroan olivine, ferroan Al-diopside, nepheline, sodalite, and andradite, and is crosscut by numerous veins of nepheline, sodalite, and ferroan Al-diopside. Some poorly-characterized phases of fine-grained material are also present; these phases contain no significant H2O.

  16. 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.

  17. An experimental investigation into the metastable formation of phosphoran olivine and pyroxene

    NASA Astrophysics Data System (ADS)

    Boesenberg, Joseph S.; Hewins, Roger H.

    2010-03-01

    The formation of phosphoran olivine by crystallization from a melt was investigated experimentally using a one atmosphere furnace, using San Carlos olivine [(Mg,Fe) 2SiO 4] mixed with either iron phosphide (FeP) or magnesium pyrophosphate (Mg 2P 2O 7). Both dynamic crystallization and isothermal experiments produced phosphoran olivine as zoned single crystals and as overgrowths surrounding normal, phosphorus-free olivine grains. The crystallization pathways that form phosphoran olivine were traced and confirm that it is a metastable phase that can crystallize from a phosphorus-rich melt over timescales of hours to days. Removal of the P and equilibration of the olivine however requires weeks to months in the presence of silicate melt. Phosphoran olivine with up to 27 wt% P 2O 5 was generated and up to 69% of the Si tetrahedral sites were replaced by P. The substitution of Si by P into olivine was confirmed as 4 VIM +2 + 2 IVSi +4 ? 3 VIM +2 + 2 IVP +5 + VI[]. Phosphoran olivine compositions that vary from (Mg,Fe) 2SiO 4 to (Mg,Fe) 1.65[] 0.35Si 0.3P 0.7O 4 have been produced in these experiments. Phosphoran pyroxene was also generated in a few experiments and forms when phosphoran olivine reacts with either tridymite or melt. It has compositions compatible with protopyroxene, orthopyroxene, pigeonite and sub-calcic augite, and can contain up to 31.5 wt% P 2O 5. Like phosphoran olivine, it is also a metastable phase. Phosphorus replaces Si in pyroxene by the following substitution methods: 8 IVSi +4 ? 3 IVSi +4 + 4 IVP +5 + IV[] with Al entering the structure by the exchange 2 IVSi +4 ? IVAl +3 + IVP +5. Phosphoran pyroxene compositions vary from (Mg,Fe) 8Si 8O 24 to (Mg,Fe) 8Si 3P 4[]O 24.

  18. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  20. 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.

  1. Composite carrier bar device

    SciTech Connect

    Felder, D.W.

    1981-09-01

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

  2. 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.

  3. 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.

  4. Serpentinization of Olivine by Seawater: A Flow-Through Experiment

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    The mantle exposed at slow spreading ridges is pervasively serpentinized, down to ca. 5km according to geophysical data. The onset and durability of this hydration process require efficient penetration and renewal of fluids at the mineral-fluid interface. However, the mechanisms 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 extent of serpentinization 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 laboratory experiment during which seawater was injected in a sintered San Carlos olivine sample at conditions representative of low temperature ultramafic hydrothermal systems. The percolation-reaction experiment was carried out at 19 MPa and 190°C; the initial water flow was set at 0.2 mL/h then decreased down to 0.06 mL/h after 8 days. During the experiment (23 days), permeability decreased continuously. The composition of the outlet fluid varied strongly during the first 24h of the experiment, then reached equilibrium values. The high Si concentrations in outlet fluids indicated steady olivine dissolution, while their low Fe and Mg concentrations suggested precipitation of Fe- and Mg-rich mineral phases. The reacted sample acquired a reddish brown color, indicating oxidation reactions occurred. Optical observation and SEM imaging revealed the presence of a soft white material filling the pores of the reacted sample. It was identified as a poorly crystallized serpentine type material by AEM/TEM analyses. This proto-serpentine is intimately associated to <100 nm Fe-oxide patches (probably hematite) growing on the olivine surface. We interpret the precipitation of this proto-serpentine together with Fe-oxides throughout the sample as marking the early stages of serpentinization. The fluid composition not being modified by changes in fluid flow, we posit that olivine serpentinization is not controlled by elemental transport and/or by chemical kinetics, but takes place at-equilibrium; the reaction velocity is very fast and independent on the changes in the reaction surface area. Indeed, mass balance calculations indicate that more than 15 wt. % olivine was dissolved while the same mass of proto-serpentine was formed; concurrently, porosity decreased from ˜ 12% to 5 %. We infer that the structure of the newly formed proto-serpentine resulted in the clogging of fluid paths and explain the decrease of permeability during experiments. Yet the loose structure of the proto-serpentine allows maintaining a connected pore structure ensuring the perennial renewing (diffusion and/or advection) of the reactants at the reaction surfaces. 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.

  5. Olivine-rich exposures at Bellicia and Arruntia craters on (4) Vesta from Dawn FC

    E-print Network

    Thangjam, Guneshwar; Mengel, Kurt; Hoffmann, Martin; Schäfer, Michael; Reddy, Vishnu; Cloutis, Edward A; Christensen, Ulrich; Sierks, Holger; Corre, Lucille Le; Vincent, Jean-Baptiste; Russell, Christopher T

    2014-01-01

    We present an analysis of the olivine-rich exposures at Bellicia and Arruntia craters using Dawn Framing Camera (FC) color data. Our results confirm the existence of olivine-rich materials at these localities as described by Ammannito et al. (2013a) using Visual Infrared Spectrometer (VIR) data. Analyzing laboratory spectra of various Howardite-Eucrite-Diogenite meteorites, high-Ca pyroxenes, olivines and olivine-orthopyroxene mixtures, we derive three FC spectral band parameters that are indicators of olivine-rich materials. Combining the three band parameters allows us, for the first time, to reliably identify sites showing modal olivine contents >40%. The olivine-rich exposures at Bellicia and Arruntia are mapped using higher spatial resolution FC data. The exposures are located on the slopes of outer/inner crater walls, on the floor of Arruntia, in the ejecta, as well as in nearby fresh small impact craters. The spatial extent of the exposures ranges from a few hundred meters to few kilometers. The olivin...

  6. 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.

  7. Shear wave attenuation and dispersion in melt-bearing olivine polycrystals

    E-print Network

    Shear wave attenuation and dispersion in melt-bearing olivine polycrystals: 1. Specimen fabrication 2003; accepted 7 January 2004; published 23 June 2004. [1] Five melt-bearing polycrystalline olivine behavior of melt-free materials, a broad dissipation peak is observed for each of the melt-bearing

  8. Shear wave attenuation and dispersion in melt-bearing olivine polycrystals

    E-print Network

    Shear wave attenuation and dispersion in melt-bearing olivine polycrystals: 2. Microstructural forced oscillation tests of melt-bearing olivine aggregates reported by Jackson et al. [2004. While the nanometer scale grain boundary structure in the melt-bearing aggregates is essentially

  9. Possible mantle origin of olivine around lunar impact basins detected by SELENE

    Microsoft Academic Search

    Satoru Yamamoto; Ryosuke Nakamura; Tsuneo Matsunaga; Yoshiko Ogawa; Yoshiaki Ishihara; Tomokatsu Morota; Naru Hirata; Makiko Ohtake; Takahiro Hiroi; Yasuhiro Yokota; Junichi Haruyama

    2010-01-01

    The composition, structure and evolution of the Moon's mantle is poorly constrained. The mineral olivine, one of the main constituents of Earth's mantle, has been identified by Earth-based telescopic observations at two craters on the near side of the Moon, Aristarchus and Copernicus. Global reflectance spectra in five discrete spectral bands produced by the spacecraft Clementine suggested several possible olivine-bearing

  10. High-temperature condensation of iron-rich olivine in the solar nebula

    Microsoft Academic Search

    Herbert Palme; Bruce Fegley Jr.

    1990-01-01

    The origin of oxidized iron in chondritic meteorites is a fundamental problem in meteoritics. Conventional models of meteorite formation assume FeO incorporation into olivine and pyroxene at around 500 K. There is evidence that at least some fayalitic olivine in Allende must have formed by condensation. Thermodynamic equilibrium calculations presented here define the nebular conditions that would enable condensation of

  11. Experimental modeling of the cooling history of Apollo 12 olivine basalts

    NASA Technical Reports Server (NTRS)

    Donaldson, C. H.; Usselman, T. M.; Williams, R. J.; Lofgren, G. E.

    1975-01-01

    An analog of the Apollo 12 olivine vitrophyres has been crystallized in a 1-atm gas-mixing furnace at cooling rates ranging between 1250 and 0.7 C/hr and isothermally at degrees of supercooling ranging from 10 C to 325 C. Mineral chemistry, crystal shapes, grain sizes and textures are systematically related to cooling rate and degree of supercooling. At linear cooling rates not exceeding 40 C/hr the texture is porphyritic - large olivine crystals are set in a groundmass of finer-grained pyroxene, plagioclase, and ilmenite; a later generation of olivine never crystallizes. There are three shapes of olivine crystals in the Apollo 12 olivine vitrophyres: glomerocrysts of subhedral crystals, large subequant skeletons, and highly elongate skeletons. These result from three generations of nucleation and a two-stage cooling history - a slow preeruption stage and a rapid continuously increasing posteruption stage. It seems likely that the Apollo 12 olivine basalt magmas were erupted with olivine crystals in suspension. The nucleation temperature of olivine in cooling-rate experiments is dependent on the experimental technique, and hence results of cooling experiments should be applied with caution.

  12. Upper mantle tectonics: three-dimensional deformation, olivine crystallographic fabrics and seismic properties

    Microsoft Academic Search

    Andréa Tommasi; Basil Tikoff; Alain Vauchez

    1999-01-01

    Forward numerical models are used to investigate the effect of deformation regime on the development of olivine lattice-preferred orientations (LPO) and associated seismic anisotropy within continental deformation zones. LPO predicted to form by pure shear, simple shear, transpression, or transtension are compared to a database comprising ca. 200 olivine LPO from naturally deformed upper mantle rocks. This comparison suggests that

  13. Li Conductivity in LixMPO4 ,,M Mn, Fe, Co, Ni... Olivine Materials

    E-print Network

    Ceder, Gerbrand

    Li Conductivity in LixMPO4 ,,M Ä Mn, Fe, Co, Ni... Olivine Materials D. Morgan,z A. Van der Ven. Materials with M Mn, Fe, Co, Ni are considered. Li diffuses through one-dimensional channels with high than those of LixCoO2 .2 The olivines represent a whole class of potential cathode materials

  14. The Mn-Fe negative correlation in olivines in ALHA 77257 ureilite

    NASA Technical Reports Server (NTRS)

    Miyamoto, M.; Furuta, T.; Fujii, N.; Mckay, D. S.; Lofgren, G. E.; Duke, M. B.

    1993-01-01

    An electron probe microanalyzer is used to measure the Mn, Fe, and oxygen zoning profiles of olivines in the ALHA 77257 ureilite. This is done to study the effects of reduction on the Mn-Fe value, as ureilite olivines exhibit thin reduced rims. Since the Mn content gradually increases toward the rim of ureilite olivines, while the Fa (= 100 x Fe/(Mg + Fe), mol percent) component decreases, the Mn-Fe content of olivine is likely related to redox conditions. The results of melting experiments suggest that the Mn-Fe positive correlation is related to temperature and that the negative correlation of Mn-Fe in olivine and low-Ca pyroxene is related to reduction.

  15. The Mn-Fe negative correlation in olivines in ALHA 77257 ureilite

    NASA Astrophysics Data System (ADS)

    Miyamoto, M.; Furuta, T.; Fujii, N.; McKay, D. S.; Lofgren, G. E.; Duke, M. B.

    1993-03-01

    An electron probe microanalyzer is used to measure the Mn, Fe, and oxygen zoning profiles of olivines in the ALHA 77257 ureilite. This is done to study the effects of reduction on the Mn-Fe value, as ureilite olivines exhibit thin reduced rims. Since the Mn content gradually increases toward the rim of ureilite olivines, while the Fa (= 100 x Fe/(Mg + Fe), mol percent) component decreases, the Mn-Fe content of olivine is likely related to redox conditions. The results of melting experiments suggest that the Mn-Fe positive correlation is related to temperature and that the negative correlation of Mn-Fe in olivine and low-Ca pyroxene is related to reduction.

  16. 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.

  17. 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.

  18. Extended planar defects and the rapid incorporation of Ti4+ into olivine

    NASA Astrophysics Data System (ADS)

    Burgess, Katherine D.; Cooper, Reid F.

    2013-10-01

    The formation of extended planar defects in minerals such as olivine is related to high point defect concentration and can be driven by large gradients in chemical potential, where the energy of the system is lowered by the ordering of defects along specific planes in the crystal. The presence of extended defects has the potential to create the (apparently) anomalous ionic diffusion in olivine as reported recently (Spandler and O'Neill in Contrib Mineral Petrol 159(6):791-818, 2010). High-resolution transmission electron microscopy and energy-filtered imaging were done using experimental samples designed to examine the impact of a TiO2 and f O2 on the potential to form such defects in ferromagnesian olivine. Doped basalt (5 wt% TiO2)-olivine reaction couple experiments were run at 1 atm and 1,310 and 1,410 °C for 50 h at various f O2, ranging from 102 below to 102 above the quartz-fayalite-magnetite buffer. Our results show that extended planar defects in olivine, parallel to {101}ol and occurring in ordered "clusters" with a prolate spheroid geometry 5-25 nm across and extending up to 150 nm into the olivine, are present near the olivine-glass interfaces in all of our experimental high-TiO2 basalt-olivine samples. Increased Ti content in the olivine is associated with the defects; ordering of Ti4+ and octahedral site vacancies leads to a two- or three-layer superstructure in the olivine. Defect nucleation and growth is driven by the large TiO2 chemical potential gradient across the phase boundary at the start of the experiments, which provides access to microstructures not otherwise present.

  19. Multi Bar Graph

    NSDL National Science Digital Library

    2011-05-27

    In this activity, students enter in data to be represented in a double bar graph. Multi bar graphs allow the student to compare multiple characteristics of different subjects like population for different continents over time. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

  20. Building Brilliant Bar Graphs

    NSDL National Science Digital Library

    Briana Bower

    2005-01-01

    In this series of three lesson plans, students create bar graphs, double bar graphs, and determine appropriate intervals for scale. Each lesson incorporates teacher modeling, student practice (students have an opportunity to label and create the scale for their own graphs), assessment (including rubrics), and reteaching or extension options.

  1. Bar Graph Sorter

    NSDL National Science Digital Library

    2011-03-09

    In this activity, students make bar graphs by sorting shapes either by shape or by color. This activity allows students to explore how to sort data to make bar graphs. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

  2. 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.

  3. 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.

  4. 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.

  5. Additional Sr Isotopic Heterogeneity in Zagami Olivine-Rich Lithology

    NASA Technical Reports Server (NTRS)

    Misawa, K.; Niihara, T.; Shih, C.-Y; Reese, Y. D.; Nyquist, L. E.; Yoneda, S.; Yamashita, H.

    2012-01-01

    Prior isotopic analyses of Zagami have established differing initial Sr-87/Sr-86 (ISr) ratios of among Zagami lithologies, fine-grained (FG), coarse-grained (CG), and dark mottled lithologies (DML)]. The Zagami sample (KPM-NLH000057) newly allocated from the Kanagawa Prefectural Museum of Natural History contained DML and the Ol-rich lithology which included more ferroan olivines (Ol-rich: Fa(sub 97- 99) vs late-stage melt pockets: Fa(sub 90-97)]). We have combined mineralogy-petrology and Rb-Sr isotopic studies on the Kanagawa Zagami sample, which will provide additional clues to the genesis of enriched shergottites and to the evolution of Martian crust and mantle

  6. 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.

  7. The composition of mesosiderite olivine clasts and implications for the origin of pallasites

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, D. W.

    1980-01-01

    The composition of olivine clasts from the mesosiderites Emery, Mincy and Pinnaroo is investigated, and implications of the results for the origin of the pallasites, which, although chemically distinct, may be related to the diogenites, eucrites, howardites and mesosiderites, are discussed. Centimeter-sized olivines were analyzed by electron microprobe, and instrumental neutron activation analysis was performed on one olivine each from Emery and Pinnaroo and an olivine separate from the Brenham pallasite. The olivine compositions are found to range from Fa8 to Fa28, with Emery samples having values from Fa18 to Fa28, and to require essentially total melting of a source composition rich enough in FeO to produce basaltic clasts. It is argued that the mesosiderite olivines were formed in the outer few kilometers of their parent body, as were those of the pallasites, which have the same compositions as the mesosiderite olivines. A model is then developed for the origin of the pallasites as a by-product of igneous differentiation in the external heating of a chondritic parent body.

  8. 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.

  9. Detections and geologic context of local enrichments in olivine on Vesta with VIR/Dawn data

    NASA Astrophysics Data System (ADS)

    Ruesch, Ottaviano; Hiesinger, Harald; De Sanctis, Maria Cristina; Ammannito, Eleonora; Palomba, Ernesto; Longobardo, Andrea; Zambon, Francesca; Tosi, Federico; Capria, Maria Teresa; Capaccioni, Fabrizio; Frigeri, Alessandro; Fonte, Sergio; Magni, Gianfranco; Raymond, Carol A.; Russell, Christopher T.

    2014-09-01

    The magmatism characterizing the early history of the asteroid Vesta has long been investigated with the mafic and ultramafic meteorites howardite, eucrite, and diogenite (HED). The lack of geologic context for the meteorites, however, has limited its understanding. Here we use the visible to near-IR (VIR) orbital observations of Vesta's surface to detect relative enrichments in olivine and to study the associated geologic features. Because the near-IR signature of olivine on Vesta's surface is subtle relative to the widespread pyroxene absorption bands, a method was developed to distinguish olivine enrichments from admixture of pyroxenes with high Fe2+/M1, dark material, and potential Fe-bearing glass. Relative enrichment of olivine (~<50-60 vol %) is found in 2-5 km wide, morphologically fresh areas. Our global survey reveals a dozen of these areas clustering in the eastern hemisphere of Vesta. The hemispherical coincidence with a widespread, low enrichment in diogenite-like pyroxene suggests the presence of a distinct compositional terrain. On the central mound of the Rheasilvia impact basin, no olivine enrichment was found, suggesting the absence of an olivine-dominated mantle above the basin's excavation depth or, alternatively, a low amount of olivine homogeneously mixed with diogenite-like pyroxenes. Rare olivine-enriched areas in close proximity to diogenite-like pyroxene are found as part of material ejected by the Rheasilvia impact. Such cooccurrence is reminiscent of local, ultramafic lithologies within the crust. The possible formation of such lithologies on Vesta is supported by some HED meteorites dominated by olivine and orthopyroxene.

  10. 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.

  11. New insights into the formation of fayalitic olivine from Allende dark inclusions

    NASA Astrophysics Data System (ADS)

    Varela, Maria E.; Zinner, Ernst; Kurat, Gero; Chu, Hao-Tsu; Hoppe, Peter

    2012-05-01

    Although considerable progress has been made in unraveling the origin(s) of fayalitic olivines in dark inclusions (DIs), many questions remain still unresolved and/or controversial. We combine a chemical and petrographic study of the Allende dark inclusion 4884-2B (AMNH, New York) and ATEM studies of a fragment of the dark inclusion Allende AF (NHM, Vienna) and discuss an alternative way in which fayalitic olivines could have formed. Allende dark inclusion 4884-2B contains a few aggregates with variable proportions of transparent and feathery olivine. Two such objects (aggregates A and B) are the focus of this study as they preserve glasses that can help in deciphering the nature of the processes involved during olivine growth and subsequent olivine transformation. The petrographic and chemical characteristics of aggregates A and B indicate that the forsteritic stack olivines may be pseudomorphs of clear olivine crystals. The ATEM studies in All-AF suggest that fayalitic olivines may be the result of secondary processes (e.g., metasomatic exchange reactions) operating in the solar nebula. Transformation may have occurred through the mediation of a dry gas phase involving nonvolatile major elements, such as Mg and Fe (e.g., Dohmen et al. 1998). This mechanism could reveal olivine growth patterns (e.g., stacked platelets due to a rapid growth regime) and may have contributed to the development of their fibrous aspect while preserving the shape (i.e., volume) of the crystals. This highly selective process did completely or partially transform ferromagnesian minerals, but affected the fine-grained mesostasis only slightly.

  12. 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.

  13. Fe-Mg-Mn relations of ureilite olivines and pyroxenes and the genesis of ureilites

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, D. W.

    1986-01-01

    Microprobe analyses of ureilite and pigeonite cores are studied. The Fe/Mn-Fe/Mg relationship in the olivine core is examined. It is observed that magnetic processs such as fractional crystallization and partial melting, and FeO reduction contribute to the olivine core composition. The study of the Mg/Mn and Fe/Mn distributions reveals that these two distributions are not in equilibrium in the olivine and pigeonite cores. The effect of a reducing agent, carbon, on the ureilite genesis is investigated. It is concluded that fractional crystallization and FeO reduction are the major processes of ureilite genesis.

  14. Olivine CPO in non-deformed peridotite due to topotactic replacement of antigorite

    NASA Astrophysics Data System (ADS)

    Nagaya, Takayoshi; Wallis, Simon; Kobayashi, Hiroaki; Michibayashi, Katsuyoshi; Mizukami, Tomoyuki; Seto, Yusuke; Miyake, Akira; Matsumoto, Megumi

    2014-05-01

    Olivine crystallographic preferred orientation (CPO) is thought to be the main cause of seismic anisotropy in the mantle, and its formation is generally considered to be the result of plastic deformation of mantle by dislocation creep. Olivine CPO has been reproduced in laboratory deformation experiments and considerable success has been achieved in understanding the deformation conditions (e.g. stress, temperature and water content) under which different olivine CPO patterns develop. This opens the possibility of mapping conditions in the mantle using seismic anisotropy and has been the subject of considerable study. Here we report an alternative mechanism for olivine CPO without the need for deformation. This process may be important in understanding the seismic properties of mantle in convergent margins. Metamorphic studies show peridotite in the Happo area, central Japan, formed by the dehydration of antigorite-schist related to contact metamorphism around a granite intrusion. Both field and microstructural observations suggest the olivine has not undergone strong plastic deformation. This was confirmed by TEM work that shows the olivine has very low dislocation densities and lacks low angle tilt boundaries. Such tilt boundaries are general stable even after annealing. These features show that peridotite in the Happo area formed in the absence of solid-state deformation. The olivine of the Happo peridotite formed dominantly by the dehydration breakdown of antigorite schist. We propose that the olivine CPO formed as a result of topotactic replacement of antigorite by the newly formed olivine. EBSD measurements in samples where both antigorite and new olivine are present and in contact show a very close crystallographic relationship between the two minerals: the a-axes are parallel, and the b- and c-axes are perpendicular. We conclude the strong olivine CPO in the Happo area was inherited from the original CPO of the antigorite. Such a process is likely to also occur in subduction zones where serpentinite is dragged down by plate movement. Topotactic growth of olivine may be an important cause of mantle anisotropy in convergent margins.

  15. 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.

  16. 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.

  17. Bahasa Indonesia Kfir Bar

    E-print Network

    Dershowitz, Nachum

    Bahasa Indonesia Kfir Bar #12;Malay Archipelago · During Islam era: Malay) · Dutch and Portuguese traders arrived during the 15th century · Indonesia became a Dutch colony · Indonesia independent - 1945 #12;#12;Indonesian · Formed ­ 15th

  18. 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.

  19. Gas flow in barred galaxies

    E-print Network

    E. Athanassoula

    2000-06-28

    I briefly review the properties of the gas flow in and around the region of the bar in a disc galaxy and discuss the corresponding inflow and the loci of star formation. I then review the flow of gas in barred galaxies which have an additional secondary bar. Finally I discuss the signatures of bars in edge-on galaxies.

  20. LETTER doi:10.1038/nature12665 Olivine in an unexpected location on Vesta's surface

    E-print Network

    Cai, Long

    Earth. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower is not associated with diogenite but seems to be mixed with howardite, the most common7,9 surface material. Olivine

  1. 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 ...

  2. Raman Spectroscopy of Olivine in Dunite Experimentally Shocked to Pressures Between 5 and 59 GPa

    NASA Astrophysics Data System (ADS)

    Turner, S.; Reimold, W. U.; Niewoudt, M.; Erasmus, R.

    2004-03-01

    Raman spectroscopic analysis of olivine in dunite samples experimentally shock-loaded to pressures between 5 and 59 GPa showed no significant shift of the 824 and 856 cm^ 1 Raman bands with increasing shock pressure.

  3. 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.

  4. 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

  5. Phase diagram and electrochemical properties of mixed olivines from first-principles calculations

    E-print Network

    Malik, Rahul

    Using first-principles calculations, we study the effect of cation substitution on the transition-metal sublattice in phospho-olivines, with special attention given to the Li[subscript x](Fe[subscript 1?y]Mn[subscript ...

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

    E-print Network

    Grossman, Lawrence

    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

  7. Evidence for Microimpact in an Olivine-Dominated Hayabusa Dust Particle

    NASA Astrophysics Data System (ADS)

    Langenhorst, F.; Harries, D.; Pollok, K.; van Aken, P. A.

    2014-09-01

    We report the results of a TEM study on a dust particle returned by the Hayabusa space mission. The particle consists of olivine, tetrataenite, troilite, and diopside. Dislocations, microtwins and stacking faults in minerals point to a microimpact.

  8. Olivine and Ca-Phosphate in the Diogenites Manegaon and Roda

    NASA Astrophysics Data System (ADS)

    Domanik, K. J.; Sideras, L. C.; Drake, M. J.

    2005-03-01

    This abstract describes igneous contacts in Manegaon and Roda that involve olivine and orthopyroxene (plus other phases), as well as contacts involving orthopyroxene and Ca-phosphate minerals (both F-apatite and REE-bearing whitlockite).

  9. 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.

  10. Raman spectroscopy of olivine in dunite experimentally shocked to pressures between 5 and 59 GPa

    NASA Astrophysics Data System (ADS)

    Farrell-Turner, S.; Reimold, W. U.; Nieuwoudt, M.; Erasmus, R. M.

    2005-10-01

    Previous Raman investigations on experimentally shocked ingle-crystal olivine indicated that the olivine Raman bands seemingly shift to a higher wave number with increasing shock pressure. If this effect could be confirmed, Raman analysis of natural shock-metamorphosed minerals could potentially provide an important shock barometric tool. We carried out a Raman spectroscopic study on olivine in a series of natural dunite samples experimentally shocked to pressures between 5 and 59 GPa. In addition, we analyzed olivine grains in a sample of the Cold Bokkeveld C1 meteorite. We studied samples of several dunites with olivine of 90.64-92.00 mole% Fo to determine Raman effects in the region from 200 to 900 cm-1. Several olivine grains per sample/shock pressure stage were analyzed. Raman analysis, however, showed little or no shift with increasing shock pressure. The shifts to higher or lower frequencies observed were not specific for a given pressure stage, with some grains within a sample showing more shift than others. This finding is unrelated to the crystallographic orientation of analyzed grains and cannot be related systematically to the different degrees of optically determined shock metamorphism of the analyzed grains. We identified an increase in full width at half maximum (FWHM) for the 824 cm-1 band with increased shock pressure in the shocked Åheim samples above 45 GPa and, to a lesser extent, for the 856 cm-1 band. Evaluation of band broadening of olivine in the Cold Bokkeveld meteorite showed FWHM values that were much greater (9-20 cm-1) than those of olivine in the shocked dunite samples (7-12 cm-1). We concluded that these differences in FWHM are due to differences in chemical composition between the meteoritic and the experimentally shocked olivine. Therefore, using Raman spectroscopy to detect small shifts in wave numbers to higher frequencies with increased shock pressure does not yield consistent effects for polycrystalline dunite. An extra band at 650 cm-1 was identified in the Raman spectra of the unshocked Mooihoek dunite and the Åheim dunite samples shocked to 5, 29.3, and 59 GPa, as well as another at 696 cm-1 in all the spectra of the 59 GPa Åheim sample. The cause of these extra bands is not known. Comparison of these results with Raman spectra of olivine from the Cold Bokkeveld C1 meteorite did not allow us to determine shock pressures for the meteoritic olivine.

  11. A Tale of Two Olivines: Magma Ascent in the Auckland Volcanic Field, New Zealand

    NASA Astrophysics Data System (ADS)

    Smid, E. R.; McGee, L. E.; Smith, I. E.; Lindsay, J. M.

    2013-12-01

    The Auckland Volcanic Field (AVF) is a nephelinitic to subalkali basaltic monogenetic field centered on the city of Auckland, New Zealand. Lavas are olivine-phyric, and the deposits of several volcanoes in the field contain olivine crystals with chrome spinel (Cr-spinel) inclusions. Microprobe analyses show at least two populations of olivine, categorised by their Mg# and their spinel inclusion compositions: the first has olivines that are euhedral, have compositions slightly less forsteritic than expected for whole rock Mg#, and have Cr-spinel inclusions with relatively low Cr2O3 contents of ~20%. These are interpreted as antecrysts inherited from the mantle source that yielded their host magma. The second population is characterised by olivines that are sub- to euhedral, are significantly more forsteritic than expected from their host whole rock Mg#, and have Cr-spinel inclusons with relatively high Cr2O3 contents of ~50%. These are interpreted as xenocrysts. The composition of these high Cr2O3 spinels very closely resembles the composition of spinels within olivines in dunite sampled from the Dun Mountain Ophiolite on the South Island of New Zealand. The northward extension of the Dun Mountain complex beneath the North Island is defined by the Junction Magnetic Anomaly, marking a crustal terrane boundary that underlies the Auckland Volcanic Field. These data indicate that the magmas that have risen to produce the volcanoes of the Auckland Volcanic Field have carried crystals from an underlying ultramafic crust as well as from their asthenospheric source. Euhedral olivine crystals which do not contain Cr-spinel are also present in AVF lavas and these are interpreted as true phenocrysts that crystallised directly from their host magmas. The lack of reaction textures at crystal margins suggests rapid ascent rates. A crustal origin for the xenocrysts not only has large implications for ascent rate modelling of olivines, but also for the crustal structure of the Auckland area and possible magma ascent paths under the AVF.

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

    Microsoft Academic Search

    Allan H. Treiman; M. Darby Dyar; Molly McCanta; Sarah K. Noble; Carle M. Pieters

    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

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

    Microsoft Academic Search

    Allan H. Treiman; M. Darby Dyar; Molly McCanta; Sarah K. Noble; Carle M. Pieters

    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

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

    Microsoft Academic Search

    Allan H. Treiman; M. Darby Dyar; Molly McCanta; Sarah K. Noble; Carle M. Pieters

    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

  15. 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.

  16. 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.

  17. 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.

  18. Charge Localization and Transport in Lithiated Olivine Phosphate Materials

    SciTech Connect

    Yu, Jianguo; Rosso, Kevin M.; Liu, Jun

    2011-11-10

    We report density functional theory (DFT) calculations for olivine-type LiTMPO4 and TMPO4 (TM=Mn, Fe, Co, Ni) structures, using GGA+U and the B3LYP hybrid density functional that includes nonlocal Fock exchange. TM is typically characterized in terms of the formal oxide states of 2+ or 3+, corresponding to TM with localized charge in LiTMPO4 and TMPO4 structures, respectively, in which electron transport would take place by thermally activated hopping of electrons strongly localized on the transition metal (small polarons). In this work, we assess the validity of the concept of formal TM oxidation states in these materials, and conclude that the valence depends in large part on the strength of d-p hybridization. Stable small polaron formation, i.e., mixed 2+ and 3+ valence states, appears to require that the ratio of differences in the metal and oxygen ionic charges (dQTM/dQO) of the two end member phases is larger than 2, corresponding to the mixed-valence TM system. If the ratio of dQTM/dQO is smaller than 2, excess electrons prefer delocalization and the system behaves more single-valence like with charge transport more akin to metallic conduction. The critical ratio emerging from our analysis may turn out to be relevant to other transition metal systems as well, as a criterion to discriminate single-valence or mixed-valence characteristics and hence the predominant conduction mechanism.

  19. Bar code scanning

    NASA Astrophysics Data System (ADS)

    Bravman, Richard

    1990-05-01

    Good afternoon. And thanks, Gary very much again for giving ne a chance to come and spend some time with you. Again, ray name is Richard Bravman, vice president of marketing with Symbol Technologies. For those of you who may not be familiar with the bar coding market, I'll give just a brief word on Symbol. Symbol is today, we find our selves the leader in that business. Our original activity in bar coding went all the way back to the business of creating the film images that are the genesis point for the placement of bar codes on all the consumer items. That was what we did back in mid l970s, moved through several stages, in 1980, we made a significant breakthrough inventing the first laser based bar code scanning device that was portable enough that you could hold it in your hand. That development proved to be the engine of some very significant growth over the last eight or nine years. During the period of the last six years, we've had our compound average growth for our company at something in the range of 80% or so. So we've been fortunate enough to have seen some real growth. Today our businesses included bar code scanning, and as a result of an acquisition we did last year, portable data capture devices, which are handheld computers that are specifically used for remote data capture.

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

    NASA Astrophysics Data System (ADS)

    Basu Sarbadhikari, Amit; Day, James M. D.; Liu, Yang; Rumble, Douglas, III; Taylor, Lawrence A.

    2009-04-01

    We report on the petrography and geochemistry of the newly discovered olivine-phyric shergottite Larkman Nunatak (LAR) 06319. The meteorite is porphyritic, consisting of megacrysts of olivine (?2.5 mm in length, Fo 77-52) and prismatic zoned pyroxene crystals with Wo 3En 71 in the cores to Wo 8-30En 23-45 at the rims. The groundmass is composed of finer grained olivine (<0.25 mm, Fo 62-46), Fe-rich augite and pigeonite, maskelynite and minor quantities of chromite, ulvöspinel, magnetite, ilmenite, phosphates, sulfides and glass. Oxygen fugacity estimates, derived from the olivine-pyroxene-spinel geo-barometer, indicate that LAR 06319 formed under more oxidizing conditions (QFM -1.7) than for depleted shergottites. The whole-rock composition of LAR 06319 is also enriched in incompatible trace elements relative to depleted shergottites, with a trace-element pattern that is nearly identical to that of olivine-phyric shergottite NWA 1068. The oxygen isotope composition of LAR 06319 (? 17O = 0.29 ±0.03) confirms its martian origin. Olivine megacrysts in LAR 06319 are phenocrystic, with the most Mg-rich megacryst olivine being close to equilibrium with the bulk rock. A notable feature of LAR 06319 is that its olivine megacryst grains contain abundant melt inclusions hosted within the forsterite cores. These early-trapped melt inclusions have similar trace element abundances and patterns to that of the whole-rock, providing powerful evidence for closed-system magmatic behavior for LAR 06319. Calculation of the parental melt trace element composition indicates a whole-rock composition for LAR 06319 that was controlled by pigeonite and augite during the earliest stages of crystallization and by apatite in the latest stages. Crystal size distribution and spatial distribution pattern analyses of olivine indicate at least two different crystal populations. This is most simply interpreted as crystallization of megacryst olivine in magma conduits, followed by eruption and subsequent crystallization of groundmass olivine. LAR 06319 shows close affinity in mineral and whole-rock chemistry to olivine-phyric shergottite, NWA 1068 and the basaltic shergottite NWA 4468. The remarkable features of these meteorites are that they have relatively similar quantities of mafic minerals compared with olivine-phyric shergottites (e.g., Y-980459, Dho 019), but flat and elevated rare earth element patterns more consistent with the LREE-enriched basaltic shergottites (e.g., Shergotty, Los Angeles). This relationship can be interpreted as arising from partial melting of an enriched mantle source and subsequent crystal-liquid fractionation to form the enriched olivine-phyric and basaltic shergottites, or by assimilation of incompatible-element enriched martian crust. The similarity in the composition of early-trapped melt inclusions and the whole-rock for LAR 06319 indicates that any crustal assimilation must have occurred prior to crystallization of megacryst olivine, restricting such processes to the deeper portions of the crust. Thus, we favor LAR06319 forming from partial melting of an "enriched" and oxidized mantle reservoir, with fractional crystallization of the parent melt upon leaving the mantle.

  1. Experimental Partitioning of Cr(3+) and Sc(3+) into Olivine: Mechanisms and Implications

    NASA Technical Reports Server (NTRS)

    Jones, John; Mackwell, S. J.

    2006-01-01

    Olivine (Mg, Fe)Si2O4 does not, by stoichiometry, accept cations such as Sc(3+) or Cr(3+). However, the partition coefficients of Sc and Cr between olivine and liquid are significant 0.2-1.0. We have measured Cr(3+) partition coefficients of near unity and have grown olivines with nearly 3 wt.% Sc2O3. Therefore, there must be a simple means of charge balancing 3+ ions in a crystal structure that was obviously not designed to receive other than 2+ ions on the olivine M sites. The simplest explanation is that two 3+ ions enter the olivine structure by displacing three 2+ ions and creating an M site vacancy. Even this explanation has difficulties. For minor elements in our experiments (1 wt.%) the odds of a minor element 3+ ion finding a second 3+ for charge balance are of the order of 100:1 against. Because of the reducing conditions of our experiments, Fe(3+) will not suffice; and Al(3+) is not in sufficient quantity in olivine for charge balance. Therefore, Cr or Sc must, in effect, charge balance itself. For true trace elements, the problem is compounded many times. For an ion at the 10 ppm level the chances of finding a second (for example) Sc ion is approx.10(exp 5):1 against. Of course, any other 3+ ion would suffice but comparisons between percent level doping experiments and trace level partitioning indicate that Henry s law is obeyed. This implies that the same substitution mechanism occurs at both the percent and tens of ppm levels. There are two simple solutions to this problem: (i) The electrical conductivity of olivine is such that charge balance need not be local. This requires substantial domains within the olivine crystal in electrical contact by migration of vacancies or electronic defects. (ii) The 3+ cation brings along its own charge-balancing ion because it existed as a dimer in the silicate liquid. Olivine is not a true insulator but is actually a p-type semiconductor. Even so, electrical communication by this means is unlikely over the tens or hundreds of unit cells that would be required for charge balance to be local. Therefore, we cautiously favor the idea that melt speciation is the means by which 3+ ions enter the olivine structure. Possibly this model might be tested by in situ XAFS measurements or by molecular dynamical calculations.

  2. Role of olivine cumulates in destabilizing the flanks of Hawaiian volcanoes

    USGS Publications Warehouse

    Clague, D.A.; Denlinger, R.P.

    1994-01-01

    The south flank of Kilauea Volcano is unstable and has the structure of a huge landslide; it is one of at least 17 enormous catastrophic landslides shed from the Hawaiian Islands. Mechanisms previously proposed for movement of the south flank invoke slip of the volcanic pile over seafloor sediments. Slip on a low friction de??collement alone cannot explain why the thickest and widest sector of the flank moves more rapidly than the rest, or why this section contains a 300 km3 aseismic volume above the seismically defined de??collement. It is proposed that this aseismic volume, adjacent to the caldera in the direction of flank slip, consists of olivine cumulates that creep outward, pushing the south flank seawards. Average primary Kilauea tholeiitic magma contains about 16.5 wt.% MgO compared with an average 10 wt.% MgO for erupted subaerial and submarine basalts. This difference requires fractionation of 17 wt.% (14 vol.%) olivine phenocrysts that accumulate near the base of the magma reservoir where they form cumulates. Submarine-erupted Kilauea lavas contain abundant deformed olivine xenocrysts derived from these cumulates. Deformed dunite formed during the tholeiitic shield stage is also erupted as xenoliths in subsequent alkalic lavas. The deformation structures in olivine xenocrysts suggest that the cumulus olivine was densely packed, probably with as little as 5-10 vol.% intercumulus liquid, before entrainment of the xenocrysts. The olivine cumulates were at magmatic temperatures (>1100??C) when the xenocrysts were entrained. Olivine at 1100??C has a rheology similar to ice, and the olivine cumulates should flow down and away from the summit of the volcano. Flow of the olivine cumulates places constant pressure on the unbuttressed seaward flank, leading to an extensional region that localizes deep intrusions behind the flank; these intrusions add to the seaward push. This mechanism ties the source of gravitational instability to the caldera complex and deep rift systems and, therefore, limits catastrophic sector failure of Hawaiian volcanoes to their active growth phase, when the core of olivine cumulates is still hot enough to flow. ?? 1994 Springer-Verlag.

  3. CO2-induced small water solubility in olivine and implications for properties of the shallow mantle

    NASA Astrophysics Data System (ADS)

    Yang, Xiaozhi; Liu, Dingding; Xia, Qunke

    2014-10-01

    H2O and CO2 are important components of fluids in the mantle at ?30-150 km depth, and may affect strongly water dissolution in nominally anhydrous olivine; however, available experimental hydrogenation of olivine has been nearly exclusively carried out in coexistence with H2O (CO2-free). In this study, the effect of CO2 on water solubility in olivine has been investigated by H-annealing natural olivine under peridotite- and fluid-saturated conditions. Experiments were conducted at 1.5-5 GPa and 1100-1300 °C, with oxygen fugacity controlled by Ni-NiO and with either H2O or H2O-CO2 as buffering fluid. The olivine shows no change in composition during the experiments. The infrared spectra of the hydrated olivine are characterized by prominent OH bands from ?3650 to 3000 cm in all the runs, at both high frequency (>3450 cm) and low frequency (<3450 cm), and the H2O solubility is ?120-370 ppm for the olivine in coexisting with H2O, and ?65-180 ppm for the olivine in coexisting with H2O-CO2. When CO2 is present in the buffering fluid, the H2O solubility of olivine is reduced by a factor of ?2, due to effect on the partitioning of water between minerals and coexisting fluid, and the measured H2O solubility shows independence on fluid composition (the molar ratio of CO2 to CO2 + H2O at ?0.2-0.5) given pressure, temperature and oxygen fugacity. Olivine equilibrated in the shallow mantle is probably dominated by OH groups in the wavenumber ?3650-3000 cm, and the intensity of OH bands at low frequency may be higher than or comparable to those at higher frequencies. The storage capacity of water in the shallow mantle in previous estimates may have been overestimated by a factor of at least ?4 if the observed effect of CO2 on water solubility is correct. Our results have profound influence on understanding partial melting, electrical conductivity anomalies and metasomatism in the shallow mantle.

  4. 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.

  5. 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 > _{Hem} [100]_{Ol} , < 10{-}10> _{Hem} //[001]_{Ol} , < 11{-}20> _{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.

  6. Influence of FeO and H on the electrical conductivity of olivine

    NASA Astrophysics Data System (ADS)

    Dai, Lidong; Karato, Shun-ichiro

    2014-12-01

    The influence of Fe (iron) and H (hydrogen) on the electrical conductivity of olivine was investigated. Synthetic olivine aggregates with the XFe = Fe/(Fe + Mg) (molar ratio) = 21-64% with the water content of 84-620 ppm wt (Paterson calibration) were prepared and their electrical conductivity was measured at P = 4 GPa and T = 873-1473 K. The impedance spectroscopy was used to calculate the DC electrical conductivity. We found that electrical conductivity of samples increases with increasing FeO content in both anhydrous and hydrous olivine. However, the way in which FeO enhances electrical conductivity is different between anhydrous and hydrous olivine. In anhydrous sample, the activation energy is reduced with FeO content and hence the effect of FeO content is large at low temperatures, but its effect is small at mantle temperatures. In contrast, FeO content does not affect the activation energy in hydrous olivine, and consequently, the magnitude of FeO effect is nearly independent of temperature. For both anhydrous and hydrous olivine, the influence of FeO is only modest at high temperatures (increase in conductivity by a factor of ?2 for the increase in FeO by 20% (e.g., from 10 to 30%)). In contrast, the FeO content has relatively large effects at low temperatures for anhydrous olivine. However, the role of hydrogen is large at low temperatures and hydrogen mechanism dominates under most cases. Therefore the influence of FeO on electrical conductivity is small at all temperatures for a plausible range of water content. We conclude that the water (hydrogen) content in a terrestrial planet can be inferred from observed conductivity without substantial influence of FeO if the temperature is constrained. The present results provide a basis for the interpretation of electrical conductivity model of other planets with different FeO contents.

  7. Partitioning of Ni between olivine and siliceous eclogite partial melt: experimental constraints on the mantle source of Hawaiian basalts

    Microsoft Academic Search

    Zhengrong Wang; Glenn A. Gaetani

    2008-01-01

    Olivine is abundant in Earth’s upper mantle and ubiquitous in basaltic lavas, but rarely occurs in eclogite. Partial melts\\u000a of eclogite are, therefore, not in equilibrium with olivine, and will react with peridotite as they migrate through the upper\\u000a mantle. If such melts erupt at Earth’s surface, their compositions will be highly modified and they may be olivine-saturated.\\u000a We investigated

  8. 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…

  9. Permanent Bar Magnets

    NSDL National Science Digital Library

    2012-08-03

    This is an activity about the basic properties of magnets and magnetism. Learners explore concepts such as magnetic fields and polarity, which form the basic ingredients of a study of Earth's magnetic field and the technology of magnetometers. Materials needed include bar magnets and paper clips. This is Activity 1 of Exploring Magnetism: A Teacher's Magnetism Activity Guide.

  10. Investigation into the Effect of H2O on Olivine-Ringwoodite Transformation Kinetics

    NASA Astrophysics Data System (ADS)

    Diedrich, T. R.; Sharp, T.; Leinenweber, K.; Hervig, R.

    2004-12-01

    The rapid transformation of metastable olivine subducted into the transition zone has been proposed as a mechanism leading to deep focus earthquakes, as well as general rheological weakening of the subducting slab. In evaluation of this hypothesis, several experimental studies have derived olivine-ringwoodite transformation rates for dry systems. However, double-seismic zones in subducting slabs suggest significant hydration and serpentinization. This likely presence of H2O could be expected to significantly enhance the kinetics of the olivine-ringwoodite transformation, reducing the depth to which metastable olivine would persist in the transition zone. We have initiated a series of experiments to systematically investigate the effect of dissolved water on the transformation kinetics of olivine to its high-pressure polymorphs, ringwoodite and wadsleyite. Single crystals of San Carlos olivine were milled and sieved to produce spheres with a diameter of 450-500 microns. These crystals were then hot-pressed in a matrix of olivine and enstatite powder, and deuterated by welding liquid D2O inside the sample capsule during piston-cylinder experiments. The use of D2O as a proxy for H22O was made to ease SIMS analysis because of the high background for H2O. All deuteration experiments were conducted with a nickel/nickel oxide oxygen fugacity buffer. Run conditions ranged from 2-3.2 GPa and 1000-1050 oC. The single-crystal San Carlos olivine spheres in the run products were found to contain 150-400 ppm D2O by weight. The deuterated olivine spheres and hot-pressed matrix were cut into 1.5 mm cubes and are being used as starting material in experiments conducted in the wadsleyite and ringwoodite stability fields. These experiments are being performed in a multi-anvil apparatus for durations ranging from 30-240 minutes. Run products will be prepared as thin sections and the thickness of the reaction rims will be measured and related to run duration to infer transformation rates as a function of temperature, pressure, and water content. TEM analysis will be used to determine the effect of D2O on the transformation mechanisms.

  11. Oxygen Isotopic Diversity in Olivine and Glass within the Volcanic Record of Klyuchevskoy Volcano, Kamchatka, Russia.

    NASA Astrophysics Data System (ADS)

    Auer, S. L.; Bindeman, I.; Ponomareva, V.

    2006-12-01

    Klyuchevskoy volcano, Kamchatka, Russia, is one of the most active volcanoes in the world. Its 4750m edifice has formed in the last 7000 years. We present an oxygen isotope and major element study of glass, as well as individual and bulk phenocrysts of olivine in 16 samples of 14C and tephrochronologically-dated layers and lavas spanning the eruptive history of Klyuchevskoy. Whole rock analysis of these layers demonstrate that high-Mg (8-11 wt% MgO) and high-Al (17-19 wt% Al2O3, 3-6 wt% MgO) basalts and intermediate products erupted coevally over the course of Klyuchevskoy's eruptive history from both flank and central cones. The oxygen isotope record of Klyuchevskoy glass and olivine is also varied throughout its history. The ?18O individual and bulk olivine values range from a normal mantle 5.25 permil to a heavy 7.2 permil. Likewise, tephra and lava matrix glass gives a heavy 5.8 permil to 7.75 permil range. These values exhibit no systematic variation through time suggesting coeval eruption and mixing of normal, moderately-high, and ultra high-?18O melts. Glass ?18O values are heavier in high-Al basalts (6.9-7.6 permil) than in high-Mg basalts (6.2-6.6 permil), but even these high-Mg basalts are distinctly heavier than a normal mantle-derived basalts of 5.5-5.9 permil. These high and more normal olivines occur in both high-Mg and high-Al samples. However, olivines are not in oxygen isotopic equilibrium with their host glass and olivine-glass ?18O values range by 1 permil off equilibrium values. Olivines are also out of Fe-Mg equilibrium with the host glass, but to a lesser extent. In summary, oxygen isotope values indicate that complex olivine recycling and re-equilibration processes involving a multi-component non-primitive magma are involved at Klyuchevskoy Volcano. Further work will focus on establishing the role of oxygen and magnesium diffusion and solution re-precipitation in olivine and glass in order to put constraints on magma storage time and crustal recycling.

  12. 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.

  13. Modal mineralogy of the surface of Vesta: Evidence for ubiquitous olivine and identification of meteorite analogue

    NASA Astrophysics Data System (ADS)

    Poulet, F.; Ruesch, O.; Langevin, Y.; Hiesinger, H.

    2015-06-01

    The observations of the surface of 4 Vesta by the Visible and Infrared Mapping Spectrometer (VIR) onboard the Dawn spacecraft reveals that its composition is dominated by pyroxenes with olivine in very localized spots. To derive new constraints on the surface composition of the asteroid, we apply a scattering model to VIR reflectance spectra. The model is first calibrated by performing a non-linear deconvolution of laboratory spectra of mineral mixtures and howardite, eucrite, diogenite (HED) meteorites. Abundance estimates of minerals are accurate to within 15-25% for the analyzed samples, while the estimated particle sizes are within the intervals of actual sizes. Grain size effects complicate spectral deconvolution and estimation of modal abundances of samples (both HED and mineral mixtures) that contain olivine. The magnesium-rich olivine detection threshold is 10-20% for large grain sizes (100s ?m) and several 10s% for small grain sizes (<50 ?m). Major expected minerals (low-calcium pyroxenes, high-calcium pyroxenes, plagioclase and olivine) can provide satisfactory fits of VIR spectra with excellent residuals ?1%. Terrains with the strongest low-calcium pyroxene signatures are well representative of diogenites. The best fits of any unit are obtained by including Fo70 olivine at an abundance level of 10-20%, with an uncertainty of ?10%. Olivine is therefore likely to be ubiquitous over the whole surface of Vesta. Olivine is coarser grained (a few hundred ?m) than other minerals such as orthopyroxene and clinopyroxene (grain sizes typically smaller than 100 ?m). Both the grain size variance and the modal mineralogy are consistent with the lithologic size and mineral distributions of howardites containing olivine phenocryst-bearing melt. These howardites are the best petrologic analogues of Vesta. Such a surface assemblage could be the result of successive melting and mixing processes due to impacts. The compositional view confirms that Vesta underwent major homogenization processes, resulting in a relatively uniform modal mineralogy and explaining the lack of specific olivine enrichment in the Rheasilvia ejecta.

  14. Seismic Properties and Acoustic Emission of Olivine and Molten Basalt: A Laboratory Study

    NASA Astrophysics Data System (ADS)

    Burlini, L.; Vinciguerra, S.; Meredith, P. G.; Zappone, A. S.; di Toro, G.

    2004-12-01

    Here, we present the first results of petrophysical investigations on the system olivine + MORB up to 1473K and 300MPa confining pressure using an internally-heated Paterson gas apparatus especially designed for the measurements of physical properties of rocks. Both Vp and acoustic emissions were measured during heating and cooling of cold pressed synthetic aggregate of both San Carlos olivine and MORB powder (in the latter case till complete melting). The same measurements were also made on a layered sample comprising an olivine-MORB-olivine sandwich. Vp was measured using the pulse transmission technique, with 1 MHz piezoelectric transducers mounted on the end of ceramic buffer rods. The buffer rods were calibrated using a single crystal of sapphire cut parallel to the c-axis. The acoustic emissions were recorded using the same transducers. A significant decrease of both velocity and of the amplitude of the seismic signal were observed during experiments involving MORB at temperatures above 1273 K. BSE imaged that melt from the MORB layer had intruded into the olivine matrix, even under hydrostatic conditions. Higher acoustic activity recorded after the melting onset, characterized by short durations and very low amplitudes, confirms the melt migration, and suggests a brittle intrusive mechanism such as hydrofracturing. Importantly, this provides a unique experimental insight into magma migration in the lithosphere and the mechanism of dyke emplacement. The results support the presence of a low but distinguishable seismic output during this process.

  15. 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.

  16. 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.

  17. In-situ XRD study of the olivine - ringwoodite transformation kinetics: application for effects of water on its growth kinetics

    NASA Astrophysics Data System (ADS)

    Ning, J.; Wang, S.; Kubo, T.; Higo, Y.; Funakoshi, K.

    2012-12-01

    Dependence of water on the growth kinetics in San Carlos olivine phase transformation to ringwoodite was investigated with time-reserved X-ray diffraction method on BL04B1 station at SPring 8. The starting material is San Carlos olivine powder. Water is added by a mixture of Mg(OH)2 and SiO2. Single crystalline diamond or Ag-Pd is used as the sample capsule to prevent the escape of water. Pressure is generated by the double stage method in the SPEED 1500 system and measured by the gold pressure maker. After the annealing of the sample in the olivine stability field, we observed the olivine-ringwoodite transformation kinetics by time-reserved X-ray diffraction measurements with energy dispersive method using a solid-state detector. Kinetic data of the olivine phase transformation to ringwoodite, at about 16-20 GPa, 680-1050 C, and 500-2000 wt. ppm. H2O, were obtained. In previous kinetic studies, in-situ XRD experiments have been limited to the olivine-wadsleyite transformation. However, the kinetic data on the olivine-ringwoodite transformation is also indispensable to discuss the presence of the metastable olivine seismologically detected in some slabs. The kinetic data newly obtained here, combined with the previous published data, are used to study the effect of water on the olivine transformation to ringwoodite.. We will discuss the difference of the olivine transformation to ringwoodite and to wadsleyite, and the extent of metastable olivine in subduction zone under complicated water environment.

  18. 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.

  19. 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.

  20. Near-infrared spectral reflectance of mineral mixtures - Systematic combinations of pyroxenes, olivine, and iron oxides

    NASA Technical Reports Server (NTRS)

    Singer, R. B.

    1981-01-01

    Near-infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesium and iron oxide minerals used to study the dark materials on Mars. Olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents. Clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 microns. Limonite greatly modifies pyroxene and olivine reflectance, but does not fully eliminate distinctive spectral characteristics. Using only spectral data in the 1 micron region, it is difficult to differentiate orthopyroxene and limonite in a mixture. All composite mineral absorptions were either weaker than or intermediate in strength to the end-member absorptions and have bandwidths greater than or equal to those for the end members. In general, spectral properties in an intimate mixture combine in a complex, nonadditive manner, with features demonstrating a regular but usually nonlinear variation as a function of end-member phase proportions.

  1. Kinetics of evaporation of forsterite and Fe-Mg olivine in vacuum

    NASA Astrophysics Data System (ADS)

    Ozawa, K.; Nagahara, H.

    2009-04-01

    Evaporation of forsterite, which plays an important role in chemical and isotope fractionation in the early solar nebula, is governed by surface kinetics strongly affected by surface conditions, such as surface roughness as well as density and orientation of dislocation outcrops. We have revealed anisotropies in evaporation rate and surface microstructure of forsterite and Fe-Mg olivine [1-3]. In order to better understand the kinetics of evaporation of forsteriete and olivine, we carried out experiments in a wider range of temperature and examined evaporation mode on the basis of temperature dependence of evaporation rates and surface microstructures. Experiments were carried out in a vacuum chamber internally heated by W mesh heater. Starting materials are single crystals of synthetic forsterite and natural Fe-Mg olivine (Fo~90), which are cut into crystallographically oriented rectangular parallelepipeds. The experimental temperature in the present and our previous studies ranged from 1300 to 1600 °C for Fe-Mg olivine and from 1500 to 1800 °C for forsterite. Surface microstructures of experimental residues were observed with SEM and EBSD, and face-specific evaporation rates were calculated from sample sizes and weight losses on at least three parallelepipeds with different [001]:[010]:[001] ratios. Development of Fe-Mg zoning due to preferential evaporation of Fe and Fe-Mg lattice diffusion in the sample was taken into consideration in rate estimation for olivine evaporation. The experimental results for both forsterite and olivine experiments demonstrated systematic temperature dependence of anisotropy in evaporation rate: (010)>(001)>(010) above ~1750°C, (001)>(100)>(010) at temperatures between ~1750 and ~1500°C, and (001)>(010)>(100) below ~1500°C. The maximum anistoropy in the evaporation rate is factor of 5 below ~1750°C, but the anisotropy is significantly suppressed above ~1750°C, where the differences among three evaporation rates are within 70% at ~1800°C. These crossovers in evaporation rate were intimately associated with changes in surface microstructures not directly related to surface morphologies originated from dislocation outcrops. Facets of (010) disappear on the (010) surface above ~1750°C, and (100) facets appear on the (100) surface below ~1500°C, which is consistently observed both for forsterite and olivine. The facets observed in SEM were confirmed to be atomistically flat consisting of stacking of layers with one or few unit-cells height through STM observations. On the contrary, non-facetted surfaces were confirmed to be atomistically rough. Therefore, the rate crossovers are attributed to rough-smooth transitions [4-5] at ~1500°C for (100) and at ~1750°C for (010). Such rough-smooth transition for the (001) surface is expected to exist below ~1500°C. The anisotropy in the rough-smooth transition temperature identified for forsterite and olivine cannot be explained solely by the differences in slice energy or attachment energy (anisotropy in bond stength) for the three crystallographic faces [6], which predicts that the transition temperture decreases in the order of (010), (001), and (100). The presence of Fe notably enhances stoichiometric evaporation of Fe-Mg olivine at 1500°C without forming any reaction product [3]. This suggests that stoichiometric evaporation from olivine or congruent evaporation from forsterite is controlled by removal of Mg2+ and Fe2+ from either the M1 or M2 site followed by spontaneous destruction of SiO4 tetrahedron at least above 1500°C, which is required not to result in incongruent evaporation forming enstatite layer. On the contrary, Fe-Mg olivine evaporates nonstoichiometrically to form enstatite at the forsterite surface at ~1300°C (Ozawa and Nagahara, 2002), where removal of Fe2+ or Mg2+ is not the rate-controlling process but Si removal or breaking Si-O bonds governs the overall reaction. The slow removal of Si results in nonstoichiometric evaporation via reaction with olivine residue to produce enstatite on the sur

  2. Peridotite and pyroxenite components in the sources of Grande Comore lavas: evidence from olivine compositions

    NASA Astrophysics Data System (ADS)

    Weiss, Y.; Class, C.; Goldstein, S. L.

    2013-12-01

    Grande Comore (Ngazidja) is the youngest Island of the Comores Archipelego in the Indian Ocean, located in the Somali Basin between Africa and Madagascar. The island formed by two volcanoes. Karthala is an active shield volcano, and La Grille is composed mainly of monogenetic cinder cones. The island represents interaction between a mantle plume and oceanic lithosphere and previous studies suggested, based on the major, trace elements and Sr-Nd-Pb-Os isotopic relationships of the lavas, that the alkali basalts of Karthala reflect mainly plume derived melts, while the basanites of La Grille are the products of interaction of plume melts with the metasomatized oceanic lithosphere. Here we report the chemical composition of olivine phenocrysts of Karthala lavas (5 samples), old Karthala (1) and La Grille (3) that were previously analyzed for their major, trace elements and Sr, Nd, Pb, Os and He isotopic compositions. Olivine phenocrysts from Karthala lavas have higher Mn and Ca, lower Al and slightly lower Ni content compared to olivines from La Grille at similar Mg#. Olivines from ';Old Karthala'are close in composition to those from La Grille and the content of Cr is similar between all three groups. The average Mn/Fe and Ca/Fe ratios of olivines of the samples positive correlate with the Sr-Pb-Os isotope ratios of the corresponding whole rocks, and Karthala has higher values than La Grille. These ratios negatively correlate with Nd-He isotope ratios, as well as with the La/Gd, Gd/Yb and Nb/K of the host lavas. The average Ni/Mg and Al/Mg ratios of the olivines correlate with the isotopic and trace element ratios of the whole rocks as well, but display trends in the opposite direction to the ones observed for Mn/Ca over Fe. Previous studies have proposed that the minor element (Ni, Mn and Ca) composition in olivine can be used to infer the proportions of peridotite vs pyroxenite and thus, the amount of recycled ocean crust in the source lithologies of magmas (Sobolev et al., 2007. The amount of recycled crust in sources of mantle-derived melts. Science, 306, 412-417). The Karthala olivines have high Mn/Fe and Ca/Fe and are similar in composition to olivines in MORB, suggesting 10-35% melt contribution from a pyroxenite source. La Grille and old Karthala olivines, on the other hand, are closer in composition to olivines from the Makapuu stage of the Koolau Island in Hawaii and represent 50-75% pyroxenite-derived melt. However, the Ni/Mg ratios in the Grande Comore lavas are relatively constant, unlike MORB, Koolau and other OIBs. Indeed the pyroxenite, which melts within the lithosphere to contribute to the La Grille and old Karthala lavas, most probably, due to metasomatic processes, differs from asthenospheric pyroxenite, which has been suggested to form by the interaction of recycled oceanic crust and peridotite in a rising plume. Thus, our data indicate that lithospheric pyroxenite formed by metasomatism of the lithospheric mantle can be distinguished from pyroxenite from mantle recycling from olivine phenocryst compositions in OIBs.

  3. Elasticity of the olivine and spinel polymorphs of Ni 2 SiO 4

    Microsoft Academic Search

    Jay D. Bass; Donald J. Weidner; N. Hamaya; M. Ozima; S. Akimoto

    1984-01-01

    The single-crystal elastic moduli, cij x, of the olivine (a) and spinel (?) polymorphs of nickel orthosilicate have been measured at atmospheric pressure and 20° C by Brillouin spectroscopy. The results are (Mbar), Ni2SiO4 olivine: c11=3.40(2), c22=2.38(2), c33=2.53(2), c44=0.71(1), c55=0.87(1), c66=0.78(1), c12=1.09(2), c13=1.10(4), c23=1.13(3), Ni2SiO4 spinel: c11=3.66(3), c44=1.06(1), c12=1.55(3). In comparing these results with extant elasticity data for olivine- and

  4. Breaking through the Bar

    ERIC Educational Resources Information Center

    Gray, Katti

    2011-01-01

    Howard University School of Law had a problem, and school officials knew it. Over a 20-year period, 40 percent of its graduates who took the Maryland bar exam failed it on their first try. During the next 24 months--the time frame required to determine its "eventual pass rate"--almost 90 percent of the students did pass. What they did not know was…

  5. Bar coded retroreflective target

    SciTech Connect

    Vann, C.S.

    2000-01-25

    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.

  6. Pressure dependence on partition coefficients for trace elements between olivine and the coexisting melts

    NASA Astrophysics Data System (ADS)

    Taura, Hiroshi; Yurimoto, Hisayoshi; Kurita, Kei; Sueno, Shigeho

    Partition coefficients between olivine and melt at upper mantle conditions, 3 to 14 GPa, have been determined for 27 trace elements (Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Rb, Sr, Y, Zr, Cs, Ba, La and Ce) using secondary-ion mass-spectrometry (SIMS) and electron-probe microanalysis (EPMA). The general pattern of olivine/melt partitioning on Onuma diagrams resembles those reported previously for natural systems. This agreement strongly supports the argument that partitioning is under structural control of olivine even at high pressure. The partition coefficients for mono- and tri-valent cations show significant pressure dependence, both becoming larger with pressure, and are strongly correlated with coupled substitution into cation sites in the olivine structure. The dominant type of trace element substitution for mono- and tri-valent cations into olivine changes gradually from (Si, Mg)<-->(Al, Cr) at low pressure to (Si, Mg)<-->(Al, Al) and (Mg, Mg)<-->(Na, Al) at high pressure. The change in substitution type results in an increase in partition coefficients of Al and Na with pressure. An inverse correlation between the partition coefficients for divalent cations and pressure has been observed, especially for Ni, Co and Fe. The order of decreasing rate of partition coefficient with pressure correlates to strength of crystal field effect of the cation. The pressure dependence of olivine/melt partitioning can be attributed to the compression of cation polyhedra induced by pressure and the compensation of electrostatic valence by cation substitution.

  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. Water disequilibrium in olivines from Hawaiian peridotites: Recent metasomatism, H diffusion and magma ascent rates

    NASA Astrophysics Data System (ADS)

    Peslier, Anne H.; Bizimis, Michael; Matney, Mark

    2015-04-01

    Constraining the distribution and mobility of H in olivine, the main mineral of the upper mantle, is crucial to our understanding of Earth's geodynamics because this trace element influences melting, rheology, and electrical and thermal conductivities of peridotite. For this purpose, the olivines from fresh and well-characterized peridotite xenoliths from Salt Lake Crater and Pali (Oahu, Hawaii), representing samples of the oceanic mantle lithosphere, were analyzed by FTIR. Water concentrations decrease from core to edge and near fractures of olivine grains, and are best interpreted as H loss during xenolith ascent to the surface in its host magma. Diffusion modeling of these profiles allowed the calculation of diffusion times, which were in turn used to estimate the average ascent rates of the xenolith host nephelinite at 0.2-25.3 m s-1. These rates are similar to those of continental basaltic magmas. Diffusion modeling further shows that the water contents at the core of olivines are preserved mantle values and are heterogeneous within each xenolith. In addition, the discrepant behavior of the 3225 cm-1 OH band (due to H in a Mg vacancy) relative to the other OH bands (in particular the Ti-H defect) along profiles evidences that H is heterogeneously distributed amongst olivine defects. These defect profiles are modeled to calculate that the diffusion rate of the Mg-H defect is about 1.3-6.8 times faster than that of the Ti-H defect. The heterogeneous distribution of H in the mantle between olivine cores in single xenoliths and within olivine grains testifies of a state of disequilibrium for water in these samples. The Salt Lake Crater peridotite olivines record two processes; recent metasomatism by a melt bringing water followed by water loss during ascent in the host magma, neither having lasted long enough for water to reach equilibrium. The observed decoupling between the heterogeneous distribution of H and the homogeneous distribution of lithophile elements suggests that the process of water addition to the peridotite via incipient melt metasomatism was likely interrupted by the host nephelinite removing the samples from the mantle and bringing them to the surface.

  9. Bulk Diffusion and Isotopic Fractionation of Lithium in Olivine: an Experimental Study

    NASA Astrophysics Data System (ADS)

    Singletary, S.; Bell, D. R.

    2007-12-01

    Lithium is the lightest of the lithophile elements, with high solid-state diffusivity (e.g. Giletti and Shanahan, 1997). Recent studies in synthetic and natural systems suggest that isotopic fractionation of lithium accompanies diffusion (Richter et al., 2003; Lundstrom et al., 2005; Beck et al., 2006; Teng et al., 2007; Jeffcoate et al., 2007). Lithium isotope variations therefore have the potential to constrain time scales of geological processes. We have performed a series of experiments to quantitatively assess the bulk diffusion of lithium in olivine and the degree of isotopic fractionation that can occur during diffusive transport. Single crystals of San Carlos olivine were surrounded by LiF and then held at temperature (800°C to 1000°C) for variable lengths of times (up to 20 hours at 800°C and as short as 2 hours at 1000°C). Measurements of the lithium concentration and isotopic composition of the experimental charges were conducted using the Cameca IMS 3f at Arizona State University. The lowest temperature experiments show no discernable diffusion of lithium into the olivine crystal, while in the highest temperature experiment, up to 650 ppm lithium is incorporated into the olivine. The lithium content in all experiments above 1000°C decreases smoothly from the crystal rim to the core; indicating diffusive transport of Li into the crystal. Lithium concentrations in the crystal cores range from background in the lowest temperature experiment, to ~100 ppm in the highest temperature experiment. Rim values, in contrast, vary from 650 ppm in the high temperature experiments to core concentrations in the low temperature experiment. All experiments in which diffusive transport into the olivine crystal occurred also display a fractionation of 6Li from 7Li. In the most extreme case, a variation of 50‰ in ?7Li was observed across the diffusion profile, which was generated in just under 2 hours. As lithium content decreases toward the crystal center, the ?7Li values become increasingly negative, reaching values of -45‰ in one experiment. These results confirm that solid state Li diffusion can be a major influence on the isotopic composition of Li in olivine, as shown previously for silicate melts (Richter et al., 2003). In one experiment, low ?7Li values were observed ahead of detectable changes in Li concentration, suggesting that isotopic exchange of Li in olivine may be more rapid than bulk Li diffusion. With experimentally determined values of Li diffusivity, it should be possible to place strict time constraints on geochemical processes that affect the lithium abundance and isotopic ratios in olivine.

  10. Seismic evidence for olivine phase changes at the 410- and 660-kilometer discontinuities.

    PubMed

    Lebedev, Sergei; Chevrot, Sébastien; van der Hilst, Rob D

    2002-05-17

    The view that the seismic discontinuities bounding the mantle transition zone at 410- and 660-kilometer depths are caused by isochemical phase transformations of the olivine structure is debated. Combining converted-wave measurements in East Asia and Australia with seismic velocities from regional tomography studies, we observe a correlation of the thickness of, and wavespeed variations within, the transition zone that is consistent with olivine structural transformations. Moreover, the seismologically inferred Clapeyron slopes are in agreement with the mineralogical Clapeyron slopes of the (Mg,Fe)2SiO4 spinel and postspinel transformations. PMID:12016311

  11. Shock-Induced Transformation Exsolution Lamellae in Olivine in Black Veins of the Mbale Meteorite

    NASA Astrophysics Data System (ADS)

    Chen, M.; Wopenka, B.; El Goresy, A.

    1995-09-01

    Mbale is a shocked L6 chondrite [1]. Some shock-induced veins of 0.1 to 2 mm width intersect the meteorite. The veins consist of diaplectic plagioclase glass, unmelted silicate fragments including olivines and pyroxenes, and the shock-induced melt materials consisting of metal-troilite intergrowths, microcrystalline pyroxene and olivine, and silicate glass. Here we report the first finding of shock-induced exsolutions in olivine that appear as compositionally different lamellae which presumably formed at high pressure by inversion of olivine (alpha) to the beta+gamma polymorphs. Olivine compositions in the chondritic part of Mbale range from Fa(sub)22.5 to Fa(sub)26 (average Fa(sub)24). In contrast, the exsolved olivines in the shock-induced veins (30 to 100 mm in diameter) consist of alternating Fe-rich (Fa(sub)22-32) and Fe-poor (Fa(sub)9.9-18.5) lamellae that range in width from less than 0.5 micrometers to up to 10 micrometers. Each individual lamella actually consists of microcrystals of less than 0.5 micrometers in diameter with rather diffuse borders within the lamella. The lamellae occur in ~30 micrometer segments which were formed by faulting and displacement. Micro-Raman spectroscopy confirms that both types of exsolution lamellae currently have the olivine (alpha) structure. The partially melted veins of Mbale may have reached a post-shock peak temperature of 1473 K >= T <= 1873 K. Based on the phase diagrams of the olivine(alpha)-wadsleyite(beta)-ringwoodite(gamma) transformations in the system Mg(sub)2SiO(sub)4-Fe(sub)2SiO(sub)4 at 1473 K [2], olivine of composition ~Fa(sub)24 should exsolve at equilibrium conditionsins to beta- + gamma-phases at P >12.7 GPa, and transform to a single gamma-phase at >15 GPa. Figure 1 shows that the determined compositions of the Fe-rich and Fe-poor lamellae in Mbale match perfectly the compositions at the beta + gamma/gamma and the beta + gamma/beta phase boundaries, respectively. Since these grains depict well ordered lamellar structure displaced by several faults, the exsolution lamellae of olivine must have nucleated before faulting. TEM studies of ringwoodite in black veins in other shocked chondrites indicate that the original olivine has transformed into a mosaic of ringwoodite grains in nano-meter size range [3,4]. The observed lamellar structure in Mbale olivines is indicative of exsolution transformation from single grains before faulting of the olivines and definitely before solidification of the silicate melt to glass in the vein. We therefore consider it unlikely that the shock-induced olivine lamellae were produced via retrograde exsolution from gamma to gamma + beta. Our findings strongly suggest that the exsolutions were produced from an originally homogeneous olivine (alpha) by the following mechanism: Original homogenous olivine exsolved at P>12.7 GPa and 1473 K >=T <= 1873 K into Fe-poor beta- and Fe-rich gamma-phases possibly along [001] which is the predominant dislocation orientation in olivine during deformation [4,5]. The dislocations in olivine may have provided the nucleation sites for the beta- and gamma-phases due to their reduced activation barrier to nucleation. The grains were then faulted to several segments of 30 micrometers in diameter. A cooling rate of >= 260 K/s during the solidification of the shock-induced melt was estimated in the interval of 1223-1673 K, based on the metallic dendrite arm spacing or cell width of ~14 micrometers [6]. The cooling of the veins after the solidification of metal and silicate melts should have been much slower than 260 K/s because of the homogeneous Ni-concentration within the metallic dendrites. We interpret the survival of the lamellar structure as due to a nonlinear cooling rate: (1) very fast cooling after pressure release thus inhibiting obliteration of the lamellae by diffusion; followed by (2) slow cooling <1223 K thus leading to inversion of gamma and beta lamellae to alpha without chemical homogenization. References: [1] Jenniskens P. et al. (1994) Meteoritics ,

  12. Dehydration breakdown of antigorite and the formation of B-type olivine CPO

    NASA Astrophysics Data System (ADS)

    Nagaya, Takayoshi; Wallis, Simon R.; Kobayashi, Hiroaki; Michibayashi, Katsuyoshi; Mizukami, Tomoyuki; Seto, Yusuke; Miyake, Akira; Matsumoto, Megumi

    2014-02-01

    Peridotite formed by contact metamorphism and dehydration breakdown of an antigorite schist from the Happo area, central Japan shows a strong olivine crystallographic preferred orientation (Ol CPO). The lack of mesoscale deformation structures associated with the intrusion and the lack of microstructural evidence for plastic deformation of neoblastic grains suggest that olivine CPO in this area did not form as a result of solid-state deformation. Instead, the good correspondence between the original antigorite orientation and the orientation of the newly formed olivine implies the CPO formed by topotactic growth of the olivine after antigorite. Ol CPO is likely to develop by a similar process in subduction zone environments where foliated serpentinite is dragged down to depths where antigorite is no longer stable. The Happo Ol CPO has a strong a-axis concentration perpendicular to the lineation and within the foliation-commonly referred to as B-type Ol CPO. Seismic fast directions parallel to the ocean trench are observed in many convergent margins and are consistent with the presence of B-type Ol CPO in the mantle wedge of these regions. Experimental work has shown that B-type CPO can form by dislocation creep under hydrous conditions at relatively high stresses. There are, however, several discrepancies between the characteristics of natural and laboratory samples with B-type Ol CPO. (1) The formation conditions (stress and temperature) of some natural examples with B-type CPO fall outside those predicted by experiments. (2) In deformation experiments, slip in the crystallographic c-axis direction is important but has not been observed in natural examples of B-type CPO. (3) Experimental work suggests the presence of H2O and either high shear stress or relatively low temperatures are essential for the formation of B-type CPO. These conditions are most likely to be achieved close to subduction boundaries, but these regions are also associated with serpentinization, which prevents strong olivine CPO patterns from forming. We show B-type Ol CPO can form as a result of static topotactic growth of olivine after high-temperature breakdown of foliated serpentinite. These results resolve the discrepancies between experimental and natural examples of B-type CPO and show the need to rethink the formation process of olivine CPO in convergent margins. Topotactic growth of olivine after antigorite can account for the inferred distribution of B-type Ol CPO in the mantle wedge more successfully than dislocation creep.

  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. Kinetics of synthesis olivine LiFePO 4 by using a precipitated-sintering method

    Microsoft Academic Search

    Peixin Zhang; Xinyang Li; Zhongkuan Luo; Xiaoqian Huang; Jianhong Liu; Qiming Xu; Xiangzhong Ren; Xun Liang

    2009-01-01

    The LiFePO4 precursor was synthesized using a precipitation with raw materials LiOH·H2O, (NH4)2HPO4 and FeSO4·7H2O. The kinetics of synthesis olivine LiFePO4 was studied by using a differential thermal analysis (DTA) at different heating rates. The average activation energy of the reaction where the precursor form olivine LiFePO4 was 239.39kJmol?1, calculated by Doyle–Ozawa and Kissinger methods. The reaction order, frequency factor,

  15. Open-circuit voltage study on LiFePO 4 olivine cathode

    Microsoft Academic Search

    Hiroki Matsui; Tatsuya Nakamura; Yo Kobayashi; Mitsuharu Tabuchi; Yoshihiro Yamada

    2010-01-01

    Olivine LiFePO4 particles were prepared by solid-state reaction using Li2CO3, (NH4)2HPO4 and FeC2O42H2O as raw materials, and they were coated with an appropriate amount of carbon through thermal decomposition of C16H10 pyrene. Cathodes using the olivine particles were subjected to an open-circuit voltage measurement under the relaxation condition of 24h at each SOC and DOD states. The electrochemical reaction in

  16. 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.

  17. 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.

  18. BROWN AND CLEAR OLIVINE IN CHASSIGNITE NWA 2737: WATER AND DEFORMATION. A.H. , M. McCanta1

    E-print Network

    Hiroi, Takahiro

    of vc lenses at right angles to each other and symmetric to the grains' optical extinction directions] chassignite is brown, with visually colorless (vc) lenses and ribbons of the same composition. VC olivine in thin section, not zoned in composition or color [3], and includes ribbons and lenses of vc olivine

  19. STRUCTURE ET ENREGISTREMENT DES TRACES LATENTES D'IONS ARGON ET FER DANS L'OLIVINE ET LE MICA MUSCOVITE

    E-print Network

    Boyer, Edmond

    939 STRUCTURE ET ENREGISTREMENT DES TRACES LATENTES D'IONS ARGON ET FER DANS L'OLIVINE ET LE MICA le mica muscovite. Dans les deux cas, il se forme des zones endommagées qu'on caractérise par leur and Ar ions (energy range : 1-7 MeV/a.m.u.) in olivine and muscovite mica. In both cases, zones

  20. Lithium isotope analysis of olivine by SIMS: Calibration of a matrix effect and application to magmatic phenocrysts

    E-print Network

    Mcdonough, William F.

    Lithium isotope analysis of olivine by SIMS: Calibration of a matrix effect and application-spatial resolution analysis of light element isotope variations by secondary-ion mass spectrometry (SIMS) has of this calibration to a suite of olivines separated from basaltic lavas from Ko'olau, Hawai'i demonstrates

  1. Shock-compressed MgSiO3 glass, enstatite, olivine, and quartz: Optical emission, temperatures, and melting

    E-print Network

    Stewart, Sarah T.

    Shock-compressed MgSiO3 glass, enstatite, olivine, and quartz: Optical emission, temperatures, enstatite, olivine, and quartz under shock wave compression was investigated with optical pyrometry coefficients (a) and blackbody spectral radiances (Llb) of shocked and unshocked materials were obtained

  2. Sound velocities of hydrous olivine and the effects of water on the equation of state of nominally anhydrous minerals

    Microsoft Academic Search

    S. D. Jacobsen; F. Jiang; J. R. Smyth; T. S. Duffy; Z. Mao; C. M. Holl; D. J. Frost

    2006-01-01

    Here we report the sound velocities and elastic constants of olivine containing 0.8 wt% H2O. We will also summarize some emerging trends on the effects of water on the equation of state of nominally anhydrous mantle minerals as they pertain to seismological observation. Olivine is thought to be the most abundant mineral in the mantle to a depth of 410

  3. Simultaneous precipitation of magnesite and lizardite from1 hydrothermal alteration of olivine under high-carbonate alkalinity2

    E-print Network

    Paris-Sud XI, Université de

    under high-carbonate alkalinity2 3 Romain Lafaya, b , German Montes-Hernandeza, *, Emilie Janotsb alkalinity 1M NaHCO3). Under these conditions, competitive precipitation olivine, the alteration reaction for olivine under high-carbonate alkalinity can be expressed as33 follows

  4. Olivine LiCoPO4 phase grown LiCoO2 cathode material for high density Li batteries

    E-print Network

    Cho, Jaephil

    Olivine LiCoPO4 phase grown LiCoO2 cathode material for high density Li batteries Hyunjung Lee olivine LiCoPO4, grown in LiCoO2 at 4.4 V, did not exhibit thermal runaway with a cell surface temperature

  5. 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.

  6. Olivine Weathering and Sulfate Formation Under Cryogenic Conditions

    NASA Astrophysics Data System (ADS)

    Niles, P. B.; Golden, D. C.; Michalski, J. R.

    2013-12-01

    High resolution photography and spectroscopy of the martian surface (MOC, HiRISE) from orbit has revolutionized our view of Mars with one of the most important discoveries being wide-spread layered sedimentary deposits associated with sulfate minerals across the low to mid latitude regions of Mars. The mechanism for sulfate formation on Mars has been frequently attributed to playa-like evaporative environments under prolonged warm conditions. An alternate view of the ancient martian climate contends that prolonged warm temperatures were never present and that the atmosphere and climate has been similar to modern conditions throughout most of its history. This view has had a difficult time explaining the sedimentary history of Mars and in particular the presence of sulfate minerals which seemingly need more water. We suggest here that mixtures of atmospheric aerosols, ice, and dust have the potential for creating small films of cryo-concentrated acidic solutions that may represent an important unexamined environment for understanding weathering processes on Mars. This study seeks to test whether sulfate formation may be possible at temperatures well below 0°C in water limited environments removing the need for prolonged warm periods to form sulfates on early Mars. To test this idea we performed laboratory experiments to simulate weathering of mafic minerals under Mars-like conditions. The weathering rates measured in this study suggest that fine grained olivine on Mars would weather into sulfate minerals in short time periods if they are exposed to H2SO4 aerosols at temperatures at or above -40°C. In this system, the strength of the acidic solution is maximized through eutectic freezing in an environment where the silicate minerals are extremely fine grained and have high surface areas. This provides an ideal environment despite the very low temperatures. On Mars the presence of large deposits of mixed ice and dust is undisputed. The presence of substantial sulfur-rich volcanism, and sulfur-rich surface deposits also makes it very likely that sul-fate aerosols have also been an important component of the martian atmosphere. Thus mixtures of ice, dust, and sulfate aerosols are likely to have been common on the martian surface. Given the fact that it is not difficult to achieve surface temperatures above -40°C on Mars throughout its history, it seems likely that sulfate formation on Mars is controlled by the availability of sulfate aerosols and not by the martian climate. The current polar regions of Mars and Earth provide interesting analogs. Large regions of sulfate-rich material have been detected on and around the modern north polar region of Mars. The prevalence of ice-dust mixtures in this region and the existence of sulfates within the ice cap itself are strong evidence for the origin of the sulfates from inside the ice deposits. In addition sulfates have been found in ice deposits in Greenland and Mount Fuji on Earth that have been attributed to forming within the ice deposit. These sulfates can form either through interaction with dust particles in the atmosphere or through weathering inside the ice itself.

  7. American Mineralogist, Volume 81, pages 327-334, 1996 High-pressure crystal chemistry of LiScSi04: An olivine with

    E-print Network

    Downs, Robert T.

    to the high-pressure behavior of olivine. INTRODUcrION The high-pressure behavior of olivine has been studied displays a significant decrease in polyhedral distortions with pressure, a behavior not observed in other. The behavior ofM~+SiH04 olivines contrasts with that of isostructural chrysoberyl AH+Be2+04,which is more

  8. Cooling of Dense Gas by H2O Line Emission and an Assessment of its Effects in Chondrule-Forming Shocks

    E-print Network

    M. A. Morris; S. J. Desch; F. J. Ciesla

    2008-09-29

    We consider gas at densities appropriate to protoplanetary disks and calculate its ability to cool due to line radiation emitted by H2O molecules within the gas. Our work follows that of Neufeld & Kaufman (1993; ApJ, 418, 263), expanding on their work in several key aspects, including use of a much expanded line database, an improved escape probability formulism, and the inclusion of dust grains, which can absorb line photons. Although the escape probabilities formally depend on a complicated combination of optical depth in the lines and in the dust grains, we show that the cooling rate including dust is well approximated by the dust-free cooling rate multiplied by a simple function of the dust optical depth. We apply the resultant cooling rate of a dust-gas mixture to the case of a solar nebula shock pertinent to the formation of chondrules, millimeter-sized melt droplets found in meteorites. Our aim is to assess whether line cooling can be neglected in chondrule-forming shocks or if it must be included. We find that for typical parameters, H2O line cooling shuts off a few minutes past the shock front; line photons that might otherwise escape the shocked region and cool the gas will be absorbed by dust grains. During the first minute or so past the shock, however, line photons will cool the gas at rates ~ 10,000 K/hr, dropping the temperature of the gas (and most likely the chondrules within the gas) by several hundred K. Inclusion of H2O line cooling therefore must be included in models of chondrule formation by nebular shocks.

  9. Buckling Bars and Boxy Bulges

    E-print Network

    Michael R. Merrifield

    1995-08-08

    It has been suggested that the peanut-shaped bulges seen in some edge-on disk galaxies are produced when bars in these galaxies buckle. This paper reviews the modelling which seeks to show how bars buckle, and I present a very simple new model which captures the essential physics of this process. I then discuss the problems in establishing observationally the connection between peanut-shaped bulges and bars: confirmation of the link has proved difficult because boxy bulges are only apparent in edge-on galaxies whereas bars are only easily detectable in more face-on systems. Finally, I present a new technique which avoids this difficulty by searching for the distinctive kinematic signature of an edge-on bar; application of this method to spectra of peanut-shaped bulges reveals that they are, indeed, associated with hidden bars.

  10. Deformation mechanisms of olivine single crystals compressed at 300 MPa and 800-1100°C

    NASA Astrophysics Data System (ADS)

    Cordier, Patrick; Demouchy, Sylvie; Mussi, Alexandre; Tommasi, Andrea

    2013-04-01

    Rheology of mantle rocks at lithospheric temperatures remains poorly constrained, since most experimental studies on creep mechanisms of olivine single crystals ((MgFe)2SiO4, Pbnm) and polycrystalline olivine aggregates were performed at high-temperatures (T >> 1200oC). In this study, we have performed deformation experiments on oriented single crystals of San Carlos olivine and polycrystalline olivine aggregate at temperatures relevant of the uppermost mantle (ranging from 800o to 1090oC) in tri-axial compression. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at various constant strain rates (from 7 × 10-6 s-1 to 1 × 10-4 s-1). Mechanical tests yield differential stresses ranging from 88 to 1076 MPa. All samples were deformed at constant displacement rate and for finite strains ranging from 4 to 23 %, to provide insight into possible effects of hardening, softening or stick-and-slip. The single crystals were compressed along several crystallographic directions to test the possibility of activating different slip systems (e.g. [100](001), [001](100), [001](010) and [100](010)). We will present the characterization of the dislocation microstructures performed in the TEM.

  11. Pyroxenes and olivines: Structural implications of shock-wave data for high pressure phases

    NASA Technical Reports Server (NTRS)

    Jeanloz, R.; Ahrens, T. J.

    1975-01-01

    The nature of the shock-induced, high-pressure phases of olivine and pyroxene rocks is examined in the light of data for the densities of a new class of perovskite-related silicate structures. Also examined are some new Hugoniot and release adiabat data for bronzite. Reexamining available shock data for magnesian pyroxenes and olivines leads to the conclusion that they define a mixed phase (or disequilibrium) region to about the 100 GPa range, related to the kinetics of phase transformation in these silicates. By recognizing this point, certain discrepancies in previous interpretations of shock data can be explained. A set of theoretical Hugonoits for pyroxene and olivine stoichiometry, perovskite-bearing assemblages was constructed based on their properties deduced from high-pressure work, showing that the shock data is compatible with transformations to perovskites in the 45-7GPa region. Finally, the shock data indicate very similar properties for olivine and pyroxene at high pressures making them both equally likely candidates for the lower mantle.

  12. The elasticity of the upper mantle orthosilicates olivine and garnet to 3 GPa

    Microsoft Academic Search

    Sharon L. Webb

    1989-01-01

    The elastic moduli of single crystals of pyrope-rich garnet and San Carlos olivine have been measured over a 3 GPa pressure range at room temperature. The combination of improved ultrasonic techniques and this large pressure range provide for more reliable characterization of the pressure dependence of acoustic wave velocities than has previously been possible. First and second pressure derivatives of

  13. The fate of fluid inclusions during high-temperature experimental deformation of olivine aggregates

    NASA Astrophysics Data System (ADS)

    Carter, Matthew J.; Zimmerman, Mark E.; Teyssier, Christian

    2015-05-01

    Torsion experiments on initially wet and dry olivine aggregates at equivalent deformation conditions investigated the fate of fluid inclusions (FIs) during high-temperature deformation. Wet samples were produced by adding water to San Carlos olivine powders before hot pressing; those hot pressed without water are considered dry. After hot pressing, wet and dry aggregates have comparable grain sizes, but wet aggregates have more abundant primary FIs. Talc jackets were fitted around some wet and dry samples prior to deformation to hydrate samples during deformation via talc dehydration at elevated temperature, whereas other samples were deformed without talc. At similar strain rates (~1.0 × 10-4 s-1), the peak shear stress for the dry sample (no talc) was 190-220 MPa, whereas all other samples reached 180 MPa; the strengths of wet (± talc) and dry (+ talc) specimens appear similar. Deformed samples reveal abundant FIs, reduced grain size, shape preferred orientation of olivine, and a pervasive low-angle fabric (C') to the shear plane defined by aligned FIs. Samples deformed with talc have FI-rich and FI-depleted domains; where FIs are abundant, the C' fabric is better developed and grain size is smaller. Electron backscatter diffraction pole figures suggest that olivine deformed in the dislocation creep regime via the (010)[100] slip system. Results of these experiments suggest that FIs are redistributed during dislocation creep, leading to the development of grain-scale, high-diffusivity pathways.

  14. Effect of composition on adsorption of water on perfect olivine surfaces

    E-print Network

    Deymier, Pierre

    Effect of composition on adsorption of water on perfect olivine surfaces M. STIMPFL 1 , M.J. DRAKE's water. We are investigating if adsorption of water onto mineral surfaces in the accretion disk could with radii gas and dust with high surface area, points

  15. Spinel from Apollo 12 Olivine Mare Basalts: Chemical Systematics of Selected Major, Minor, and Trace Elements

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    Spinels from Apollo 12 Olivine basalts have been studied by Electron and Ion microprobe techniques. The zoning trends of major, minor and trace elements provide new insights into the conditions under which planetary basalts form. Additional information is contained in the original extended abstract.

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

    E-print Network

    Perfect, Ed

    components in martian basalts Amit Basu Sarbadhikari a , James M.D. Day b,*, Yang Liu a , Douglas Rumble III in mineral and whole-rock chemistry to olivine-phyric shergottite, NWA 1068 and the basaltic shergottite NWA and elevated rare earth element patterns more consistent with the LREE-enriched basaltic shergottites (e

  17. Lithium isotopic signatures of peridotite xenoliths and isotopic fractionation at high temperature between olivine and pyroxenes

    Microsoft Academic Search

    Hans-Michael Seitz; Gerhard P. Brey; Yann Lahaye; Soodabeh Durali; Stefan Weyer

    2004-01-01

    We determined the Li isotopic composition of coexisting olivine, clinopyroxene, and orthopyroxene from spinel- and garnet-bearing peridotite xenoliths from San Carlos (Arizona), Vitim (Siberia), Dreiser Weiher (Eifel, Germany), and Kapfenstein (Austria). These samples represent the upper mantle that experienced varying degrees of partial melting followed by different metamorphic and metasomatic histories. Ultrasonic cleaning of handpicked mineral separates with Milli-Q water

  18. Gochimie des olivines plantaires : une approche micro-analytique par EPMA et LA-ICPMS

    E-print Network

    Demouchy, Sylvie

    Géochimie des olivines planétaires : une approche micro-analytique par EPMA et LA-ICPMS Directeur-louis BODINIER(Géochimie, Modélisation, DR) + Andrea TOMMASI (texture et petrophysique), Claude MERLET (Sonde électronique et ionique, IR), Olivier BRUGUIER (LA-(HR)ICP-MS, IR) Thématique : Sciences de la Terre et des

  19. Onset and Progression of Serpentinization and Magnetite Formation in Olivine-richTroctolite

    E-print Network

    Demouchy, Sylvie

    are a reflection of Fe^Mg exchange between olivine and the brucite þserpentine formed during early serpentini by oxidation of the Fe in brucite and serpentine, whereas addition of silica to the system converted the Mg-component of the brucite to serpentine. Magnetite forms one or more distinct bands in the interior of the vein and is never

  20. Olivine hydration in the deep upper mantle: Effects of temperature and silica activity

    Microsoft Academic Search

    J. R. Smyth; D. J. Frost; F. Nestola; C. M. Holl; G. Bromiley

    2006-01-01

    Although water controls the biology and geology of the surface, hydrogen is perhaps the most poorly constrained compositional variable in the bulk Earth. Its concentration in the upper mantle appears to be controlled by its solubility as hydroxyl in the nominally anhydrous silicate phases, olivine, pyroxene, garnet, wadsleyite, and ringwoodite. Here we describe a series of experiments showing that the

  1. Elasticity of Hydrous Olivine Polymorphs: Implications for Seismic Structure of the Transition Zone

    Microsoft Academic Search

    T. S. Duffy; Z. Mao; S. D. Jacobsen; F. Jiang; J. R. Smyth; C. M. Holl; D. J. Frost

    2007-01-01

    The presence of water in the upper mantle and transition zone has the potential to explain various phenomena such as shear velocity anomalies or uplift and broadening of the 410-km discontinuity. The presence of H2O in the transition zone has also been frequently invoked to reconcile laboratory elasticity data on olivine polymorphs with seismic data for the amplitude of the

  2. Formation of H2 on an olivine surface: a computational study

    Microsoft Academic Search

    T. P. M. Goumans; C. Richard; A. Catlow; Wendy A. Brown

    2009-01-01

    The formation of H2 on a pristine olivine surface [forsterite (010)] is investigated computationally. Calculations show that the forsterite surface catalyzes H2 formation by providing chemisorption sites for H atoms. The chemisorption route allows for stepwise release of the reaction exothermicity and stronger coupling to the surface, which increases the efficiency of energy dissipation. This suggests that H2 formed on

  3. INVITED REVIEW Thermal infrared (vibrational) spectroscopy of MgFe olivines: A review and

    E-print Network

    Hamilton, Victoria E.

    in the minerals. Although band positions move to lower wavenumbers (longer wavelengths) across the forsterite common cations in olivine are Mg2 + and Fe2 + , forming a solid solution between forsterite (Mg2SiO4 of forsterite (Fo) and fayalite (Fa) (e.g., Fo90Fa10), or in shortened form, by just their forsterite number

  4. Midinfrared spectroscopy of synthetic olivines: Thermal emission, specular and diffuse reflectance, and attenuated total reflectance

    E-print Network

    Glotch, Timothy D.

    , and attenuated total reflectance studies of forsterite to fayalite Melissa D. Lane,1 Timothy D. Glotch,2 M. Darby] Synthetic olivine samples ranging in composition from forsterite to fayalite are analyzed in the midinfrared is identified of a specific emissivity maximum/reflectivity minimum (the flection position). From forsterite

  5. Effects of hydration on the elastic properties of olivine Steven D. Jacobsen,1

    E-print Network

    Jacobsen, Steven D.

    and single-crystal elastic constants of hydrous forsterite (hy-Fo100) and hydrous olivine (hy-Fo97 obtain KS0 = 124.4(±0.4) GPa and G0 = 75.3(±0.3) GPa. Compared with anhydrous forsterite, the combined

  6. Iron Partitioning in the Lower Mantle: New Experimental Data from Al-Enriched Olivine

    NASA Astrophysics Data System (ADS)

    Piet, H.; Nabiei, F.; Gillet, P.; Badro, J.

    2014-12-01

    The partitioning of iron between the major phases of the lower mantle has an important impact on their physical and chemical properties. A series of experimental studies of Fe-Mg exchange between bridgemanite (magnesium silicate perovskite) and ferropericlase have shown that stark differences in partitioning are observed if olivine [1, 2] or a pyrolitic [3, 4] starting composition are used. The discrepancy has been attributed to the presence of alumina, to that of ferric iron, to multiphase equilibria and even to the activity of FeO in the system. In order to mitigate the discrepancy, we synthesized a sample with San Carlos olivine composition that was doped in alumina. We then used this as starting material for experiments in the laser-heated diamond anvil cell at lower mantle (P,T) conditions along the geotherm. Samples were pressurized, heated, transformed to bridgemanite and ferropericlase, equilibrated, quenched, and decompressed. Thin sections were recovered from the hotspot using a focused ion beam microscope and the composition of the two phases was analyzed using analytical transmission electron microscopy. Iron partitioning in Al-rich olivine will be discussed through a detailed comparison with the Al-rich pyrolitic trend and the Al-free olivine trend. References [1] A-L. Auzende et al., Earth Planet. Sci. Lett., 2008. [2] R. Sinmyo et al., J. Geophys. Res., 2008.[3] R. Irifune et al., Science, 2010. [4] R. Sinmyo et al., Phys. Chem. Minerals, 2013.

  7. Crystal orientation results in different amorphization of olivine during solar wind implantation

    NASA Astrophysics Data System (ADS)

    Li, Yang; Li, Xiongyao; Wang, Shijie; Li, Shijie; Tang, Hong; Coulson, Ian M.

    2013-10-01

    Crystal orientation plays an important role in mineral amorphization during solar wind implantation. To discuss these effects, ion implantation experiments were carried out to irradiate natural olivine grains by 1 × 1017 cm-2 50 keV He+. Based on the olivine grains irradiated in our experiment, residual crystal planes have been identified by reference to the crystal plane's spacing shown in diffraction images. It is found that He+ ions injected along [010] damages the olivine structure more effectively than with other orientations and that this possibly relates to the higher atomic density and the vertical impact of the flux on MO6 (where M commonly represents Fe2+ and Mg2+) octahedra chains. Crystal planes perpendicular or approximately perpendicular to [010] may be destroyed easily during the early stages of irradiation, particularly for (040). However, crystal planes, such as (041), (021), (022), (120), and (140), parallel to [100] or [001] may survive until the final stages of olivine amorphization. These different characteristics affected by crystal orientation in ion implantation might help researchers to better understand the process of solar wind weathering and in dating the exposure time of lunar and asteroidal soil grains as well as interplanetary dust particles affected by the solar wind.

  8. In situ observation of texture development in olivine, ringwoodite, magnesiowqstite and silicate perovskite at high pressure

    E-print Network

    Shen, Guoyin

    perovskite at high pressure H.-R. Wenka,*, I. Lonardellia , J. Pehla , J. Devineb , V. Prakapenkac , G. Shenc, perovskite and magnesiowqstite display transformation textures that are then modified by continuing towards h001i with increasing deformation. Perovskite, transforming from olivine, has a pronounced (100

  9. IMPORTANCE OF OLIVINE IN S-ASTEROID SPACE WEATHERING. T. Hiroi1 and S. Sasaki2

    E-print Network

    Hiroi, Takahiro

    IMPORTANCE OF OLIVINE IN S-ASTEROID SPACE WEATHERING. T. Hiroi1 and S. Sasaki2 , 1 Dept: Existence, cause, and process of space weathering on the S asteroids have been often discussed that S asteroids larger than about 120 km show much shallower absorption bands than the others [1], which could

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

    E-print Network

    Montes-Hernandez, German

    high-carbonate alkalinity Romain Lafay a,b , German Montes-Hernandez a, , Emilie Janots b , Rodica alteration High-carbonate alkalinity Magnesite Lizardite Crystal growth Hydrothermal systems The present = 15, olivine grain size b 30 m and high-carbonate alkalinity 1 M NaHCO3). Under these conditions

  11. The role of olivine in the crystallization of the prehistoric Makaopuhi tholeiitic lava lake, Hawaii

    Microsoft Academic Search

    James G. Moore; Bernard W. Evans

    1967-01-01

    On eruption, the tholeiitic basalt lava of the prehistoric Makaopuhi lake contained nearly seven percent euhedral olivine phenocrysts of approximately Fa14 composition. In the center of the 225 foot vertical section of the lake, the lava became more than 90 percent solid at 1000° C after about 30 years. At the surface the lava was quenched to air temperature, whereas,

  12. Phosphorus-rich olivine overgrowths: Evidence for additional impact to the Main Group pallasite parent body

    NASA Astrophysics Data System (ADS)

    Fowler-Gerace, Neva; Tait, Kimberly

    2015-04-01

    Phosphorus-rich olivine (1-7 wt% P2O5) is a metastable phase known from fewer than a dozen meteoritic or terrestrial occurrences. We have thoroughly examined P-rich olivine in the Springwater pallasite to characterise its distribution, textural relationships, and geochemical signature. P-rich olivine is abundant in Springwater as randomly distributed millimetre-scale partial overgrowths on the nominally P-free forsterite crystals. Geochemical analyses support the substitution mechanism of P into the tetrahedral Si site with octahedral site vacancies for charge balance; observed trace element variations, on the other hand, are not related to P substitution. Element mapping reveals fine-scale oscillatory P zoning in unusual serrate patterns, indicating rapid crystal nucleation from a melt and a subsequently variable rate of crystallisation. We constrain P-rich olivine formation in Springwater to at least 10-100 Myr subsequent to the introduction of the metal but before cooling below 700°C. Because the P-rich overgrowths overprint specific host grain boundary modifications, we suggest an impact to the Main Group pallasite parent body may have triggered the episode of extremely rapid cooling necessary to crystallise and preserve this rare phase.

  13. Crystallographic preferred orientations and melt-rock interactions : olivine-rich troctolites from IODP Hole U1309D

    NASA Astrophysics Data System (ADS)

    Drouin, M.; Ildefonse, B.; Hirth, G.; Waters, C. L.; Godard, M.

    2010-12-01

    IODP Expeditions 304-305 sampled the Atlantis Massif, an oceanic core complex located at 30°N in the inside corner of the intersection of the Mid-Atlantic Ridge with the Atlantis Fracture Zone. The most primitive end-members of the recovered gabbroic sequence, olivine-rich troctolites (ol > ~70%), have textures and geochemical compositions intermediate between those of mantle peridotites and primitive cumulates, indicative of melt impregnation processes (Drouin et al., 2009). Olivine-rich troctolites from Hole U1309D (about 5% of recovered rocks) display poikilitic textures, with olivine ranging from coarse-grained subhedral crystals, commonly containing well-developed subgrains, to medium-grained rounded crystals with fewer or no substructures. Olivine substructures reveal dislocation creep that is consistent with activation of the main high-temperature slip systems, dominantly (010)[100]. Olivine crystallographic preferred orientation is very weak, but generally shows a relatively stronger, uncommon [001] concentration (Drouin et al., 2010). These unusual olivine fabrics are interpreted as resulting from dunitisation and melt impregnation of a previously deformed olivine matrix; the solid olivine framework is eventually disrupted by olivine corrosion along grain and subgrain boundaries, and the high-temperature plastic fabric is modified in a liquid-dominated regime. Similar fabrics are described in impregnated peridotites from the mantle/crust transition zone in the Oman ophiolite. A reduction of fabric strength in the presence of melt is also documented in deformation experiments performed in a gas-medium high-pressure high-temperature vessel. Experiments were conducted with olivine + melt (10 to 30 wt%) isostatically hot-pressed initial material. The olivine crystallographic preferred orientation is weaker in deformed sampled than in the undeformed hot pressed material. We propose that very weak fabrics such as those measured in the Atlantis Massif olivine-rich troctolites, in this case with unusual preferred [001] maxima, are a common result of melt-rock interactions in melt-impregnated peridotites or ultramafic cumulates in mid-ocean ridge environments. The joint study of in situ crystal geochemistry and microstructures is needed to characterize complex crystallization histories in open system with percolation of large volume of MORB-type melt that postdate olivine crystal-plastic deformation. - Drouin, M., Godard, M., Ildefonse, B., Bruguier, O., and Garrido, C., 2009. Chem. Geol., doi:10.1016/j.chemgeo.2009.02.013 - Drouin, M., B. Ildefonse, and M. Godard, 2010. Geochem. Geophys. Geosyst., doi:10.1029/2009GC002995

  14. Olivine Oxygen Isotope Evidence for Intracontinental Recycling of Continental Crust in the North China Craton

    NASA Astrophysics Data System (ADS)

    Xu, W.; Yang, D.; Pei, F.; Gao, S.

    2012-12-01

    A suite of peridotite and pyroxenite xenoliths entrained by the Early Cretaceous high-Mg diorites and Feixian basalts in the eastern North China Craton provide direct evidence for recycling of dense lower continental crust in an intracontinental setting. Petrographic observations indicate that peridotite xenoliths include spinel-lherzolite, spinel-harzburgite, chromite-bearing dunite and wehrlite, and that pyroxenite xenoliths are olivine pyroxenite and websterite. The replacement of olivines by orthopyroxenes and in turn orthopyroxenes by clinopyroxenes can be found within the pyroxenite xenoliths. The ?18O values of olivines from the harzburgite and lherzolite xenoliths with Archean and Paleoproterozoic Re-depletion model ages (TRD) vary from 5.1 ± 0.1 ‰ to 5.8 ± 0.1 ‰ (average: 5.4 ± 0.2 ‰, error = 2SD), which is typical of mantle values, whereas olivines from dunites and wehrlite xenoliths have ?18O ranging from 6.1 ± 0.2 ‰ to 7.7 ± 0.2 ‰ (averaging 6.45 ‰), the latter are consistent with high incompatible element abundance (such as Ca, Ti, and Sc) in olivines and high initial 187Os/188Os ratios (0.16221-0.72715) of dunite xenoliths. The olivines from websterite xenoliths in Feixian basalts vary from 7.1 ‰ to 7.6 ‰. These data, combined with positive correlations among Sr, Nd, and Os isotope ratios, Cr content of peridotite xenoliths, and the ?18O values of olivines, provide compelling evidence for the recycling of continental crust in an intracontinental setting. Therefore, our study shows that the intracontinental recycling of lower continental crust is a key factor not only to result in chemical and isotopic enrichment in the subcontinental lithospheric mantle (Xu et al., 2008), but also to result in compositonal variations of intracontinental basalts (Gao et al., 2008; Liu et al., 2008). This research was financially supported by National Basic Research Program of China (2009CB825005) and the NSFC (90814003 and 90714010). References Gao S. et al. (2008) Earth Planet. Sci. Lett. 270, 41-53. Liu Y S. et al. (2008) Geochim Cosmochim Acta 72, 2349-2376. Xu et al. (2008) Earth Planet. Sci. Lett. 265, 123-137.

  15. Deformation mechanism maps of olivine and rheology of the continental upper mantle

    NASA Astrophysics Data System (ADS)

    Wang, Q.

    2009-12-01

    The reliability of straightforward extrapolation of the laboratory-determined constitutive equations to the upper mantle depends on good quality of experimental data as well as the activation of same deformation mechanism at the much lower natural strain rates and stress. Recent laboratory studies have provided more accurate flow law parameters for olivine under both dry and wet conditions, which allow us to investigate deformation mechanisms of olivine and the mantle rheology more confidently. To compare rheology of the continental upper mantle in different geological settings, the western Superior Province (Canada), the Dabie Mountains and the North Jiangsu basin (China) are selected to represent an Archean craton, a Triassic continental collision zone and a Cenozoic intracratonic rift basin, respectively. Deformation mechanism maps of olivine were constructed under P-T conditions of the three tectonic units, and in a continental subduction zone characterized by P=6.28 GPa and T=900 °C. For dry olivine, diffusion creep is the dominant mechanism in all the cases, which is contrary to the widely observed lattice-preferred orientation of olivine in peridotite xenoliths and tectonites. For wet olivine, a small amount of water (50 H/106Si) can remarkably decrease the stress of dislocation creep and increase contribution of dislocation creep to the deformation of olivine in the upper mantle. In contrast, the effect of water to diffusion creep is ignorable when water content is less than 100 H/106Si. Combined with a compilation of water contents of natural olivine, rheology of the continental upper mantle is controlled by power law creep of wet olivine, and diffusion creep is the dominant deformation mechanism in the asthenosphere, especially for fine-grained peridotites. The Lehmann discontinuity characterized by the rapid decrease in seismic anisotropy at depth of ~220 km can be attributed to the transition from dislocation creep to diffusion creep in most regions, or to the pressure-induced olivine fabric transition from [100] slip to [001] slip in cold subduction zones. The effective viscosity (?) profiles indicate remarkable rheological contrast among the three units at depth <120 km and a decreasing viscosity difference with depth. At depth >250 km, the values of effective viscosity are very similar in different units, implying that changes in water contents and composition will control rheological contrast of the deep upper mantle. The mechanical lithosphere-asthenosphere boundary (LAB) can be defined as the depth where d?/dP changes from the negative to positive (e.g., a sharp LAB beneath the Dabie Mountains and the North Jiangsu basin) or the absolute value of d?/dP is less than 5×1012 s (e.g., a diffuse LAB beneath the western Superior Province). The LAB is about 250 km, 140 km and 75 km beneath the western Superior Province, the Dabie Mountains and the North Jiangsu basin, respectively. The sharp LAB (5-10 km thick) favors the lithosphere-asthenosphere decoupling beneath orogenic belts and rifts, while the diffuse LAB (~30 km thick) will lead to coherent deformation of the upper mantle and protect the continental roots from convective erosion. Hence the small pressure derivative of viscosity caused by cold and thick thermal lithosphere is the key to preserve continental roots.

  16. Stellar bar in NGC 1068

    SciTech Connect

    Scoville, N.Z.; Matthews, K.; Carico, D.P.; Sanders, D.B.

    1988-04-01

    High-resolution 2-micron mapping of the inner disk of NGC 1068 reveals a bar extending to + or - 16 arcsec from the nucleus at position angle 48 deg. The stellar mass distribution, presumably traced by the near-infrared light, is therefore strongly nonaxisymmetric with a contrast of approximately 3:1 between the major and minor axes of the bar. This large-scale galactic structure is probably responsible for the concentration of molecular clouds in a ring just outside the bar. The massive bar may also drive noncircular motions in the inner disk of the galaxy as possibly seen in the gaseous emission lines. 21 references.

  17. Timing characteristics of scintillator bars

    NASA Astrophysics Data System (ADS)

    Denisov, S.; Dzierba, A.; Heinz, R.; Klimenko, A.; Samoylenko, V.; Scott, E.; Shchukin, A.; Smith, P.; Steffen, C.; Teige, S.

    2002-02-01

    The proposed Hall D detector at Jefferson Lab will have a time-of-flight detector composed of long and narrow scintillator bars. We have evaluated the time resolution of two bar prototypes in particle beams at the Institute for High Energy Physics in Protvino, Russia. The bars are 2.0 m long and have square cross-sections of size 2.5 and 5.0 cm2. In this paper, we present results on how the time resolution of each of these bars depends on the entry position of the beam into the scintillator, on the material used for scintillator wrapping and on the phototube used for the readout.

  18. Microstructural development in olivine aggregates during dislocation creep under hydrous conditions

    NASA Astrophysics Data System (ADS)

    Tasaka, M.; Zimmerman, M. E.; Kohlstedt, D. L.

    2014-12-01

    Since hydrogen plays an important role in dynamic processes in the mantle, we conducted high-strain torsion experiments on aggregates of Fe-bearing olivine [(Mg,Fe)2SiO4; Fo50] under hydrous condition. Olivine with a composition of Fo50 was used because of its enhanced grain growth kinetics and low strength relative to Fo90. Two pieces of an oriented San Carlos olivine crystal were embedded in the aggregates to monitor water fugacity both before and after deformation. We deformed samples to high enough strain, ? ? 4, to achieve a steady-state microstructure. A non-linear, least-squares fit to the stress versus strain rate data yielded a stress exponent, n ? 3.5, indicative of deformation involving dislocations. The water content determined from Fourier transform infrared (FTIR) spectroscopy analyses of the single crystals demonstrate that the samples are water saturated after deformation. Fabric analyses of the polycrystalline olivine samples, determined using electron backscatter diffraction (EBSD), indicate that the strength of the lattice preferred orientation (LPO) increases with increasing strain. Further, at low strain, ? < 2, two slip systems contribute to deformation: (i) [100] axes parallel to the shear direction with the [001] axes normal to the shear plane, indicative of the (001)[100] slip system, plus (ii) [001] axes are parallel to the shear direction with the [100] axes normal to the shear plane, suggestive of the (100)[001] slip system. With increasing strain, the LPO evolves until (100)[001] becomes the dominant slip system at ? > 3. We interpret the observed fabric evolution to represent the competition between the two easiest slip systems in olivine, (100)[001] and (001)[100]. The evolution of fabric can be applied to investigations of upper mantle seismic anisotropy especially in a mantle wedge or in a shear zone, locations in which hydrous conditions prevail.

  19. Solubility of hydrogen in olivine: dependence on temperature and iron content

    NASA Astrophysics Data System (ADS)

    Zhao, Yong-Hong; Ginsberg, S. B.; Kohlstedt, D. L.

    The solubility of hydrogen in Mg-Fe olivines as a function of temperature and iron concentration was investigated by hydrothermally annealing single crystals of synthetic forsterite and San Carlos olivine. Experiments were performed at temperatures between 1,273 and 1,573 K on samples with compositions between Fa0 and Fa16.9 under a confining pressure of 300 MPa in a gas-medium apparatus with oxygen fugacity, fO_2, buffered by the Ni:NiO solid-state reaction and silica activity, aSiO_2, buffered by the presence of enstatite. Hydroxyl concentrations were determined from infrared spectra obtained from polished thin sections in crack-free regions <=50 µm in diameter. Hydroxyl solubility increases systematically with increasing temperature and with increasing iron content. Combined with published results on the dependence of hydroxyl solubility on water fugacity and pressure, the present results can be summarized by the relation COH = Af1H_2O [-(? Eo + P? Vo] (? XFa ) with A=90+/-10 H/106Si/MPa, ?=97+/-4 kJ/mol, ? Eo=50+/-2 kJ/mol, and ? Vo =(10.0+/-0.1)×10-6 m3/mol. The subscript {} indicates that hydroxyl ions are incorporated primarily as defect pairs, probably of the type ( OH )O - V''Me - ( OH )3Ox ? ( 2H )x_Me. Under similar thermodynamic conditions, the water content in olivine in the martian mantle and in olivine from gabbros may be as much as 5 to 25 times larger than in the less iron-rich olivine dominant in Earth's mantle.

  20. Microstructures, textures, and deformation mechanisms in highly sheared 2-phase aggregates: olivine - plagioclase

    NASA Astrophysics Data System (ADS)

    Stunitz, H.; Heilbronner, R.; Deronde, A.; Oesterling, N.

    2003-04-01

    In the laboratory, processes of deformation of polyphase rocks were studied in synthetic olivine - plagioclase aggregates. Depending on the composition of the feldspar, the deforming aggregates undergo chemical reaction. The presence of metamorphic reaction greatly influences the deformation. Powders composed of olivine and labradorite (An60) or anorthite (An92) were placed between forcing blocks of dunite, pre-cut at 45 °, and hot-pressed, yielding approx. 0.5 mm thick layers of solid material (porosity < 1%). Deformation was effected in a Griggs apparatus at 900°C, 1.0 or 1.5 GPa confining pressure, and a shear strain rate of 5·10-5 s-1. The deformed samples were cut parallel to the compression axis and the shape change of elongated intraclasts ("xenoliths" of fine grained fractions of the powder) was used to ascertain homogeneous and pervasive deformation (at the 100µm-scale). Localization of deformation (at the µm scale) within the matrix of the shear zones was studied using tesselations of the autocorrelation function (ACF). On SEM back scatter images, complete transects across the shear zone were recorded, with the olivine appearing grey, plagioclase dark and the reaction products white. The anisotropy and preferred orientation of the ACF of the olivine or olivine aggregates (thresholded at a specified level) was used as a measure of the deformation intensity. Calibrating the variations of the aspect ratio of the ACF against the applied shear strain revealed that there is a strain and strain rate ratio of up to 4:1 This variation closely correlates with the reaction progress, being highest where the reaction is complete.

  1. Cross pressure and temperature derivatives of selected elastic moduli for olivine from gigahertz ultrasonic interferometry

    NASA Astrophysics Data System (ADS)

    Chen, Ganglin; Yoneda, Akira; Getting, Ivan C.; Spetzler, Hartmut A.

    1996-11-01

    Techniques have been developed to measure the cross pressure and temperature dependence of elastic moduli of olivine using the gigahertz ultrasonic interferometric method in a gas pressure vessel (to 500 MPa) equipped with an internal heater (to 500 K). Special attention has been drawn to the effect of the bond which couples the sample to the buffer rod. We obtained ?2C22/?P?T = (2.8 ± 0.9) × 10-3 K-1 for a San Carlos olivine sample with a lapped contact. Selective values of ?2KT/?P?T (0, 0.5 × 10-3, 1.0 × 10-3 K-1) are used to calculate their effect on cell volume, bulk modulus, and bulk sound velocity for olivine at pressures to 14 GPa and temperatures to 1800 K (410-km depth), using the high-temperature form of the Birch-Murnaghan equation of state. The largest difference between the cell volumes for ?2KT/?P?T = 1 × 10-3 K-1 and for ?2KT/?P?T = 0 is about 0.6% at the highest pressure and the highest temperature (14 GPa, 1800 K). Therefore PVT data with precision at least better than 0.6% are required to distinguish between the extreme values of ?2KT/?P?T for olivine if the pressure and temperature data are free of errors. If the cross pressure and temperature derivative term is neglected (?2KT/?P?T = 0) in extrapolating laboratory elasticity data to mantle pressure and temperature conditions, the bulk modulus of olivine can be underestimated by as much as 10% and the bulk sound velocity by 3% at the 410-km seismic discontinuity. Thus the present study highlights the need to measure elastic properties of mantle candidate minerals at the P-T conditions of the mantle transition zone in order to establish a more precise model of the mantle mineralogy.

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  3. Transformer bar connector and pedestal bar connector cover

    SciTech Connect

    McGrane, E. W.

    1985-10-15

    A protective cover is provided for a standard rectangular transformer connector bar and for pedestal bar connector having ports for cable installation and threaded boreholes in adjacent ninety degree planes. The cover comprises a translucent housing open at one end and closed at the other when used with the transformer bar connector, and closed at both ends when used as a pedestal bar connector. The cover has a plurality of internal aligning ribs having apertures therein which allow longitudinal passage of the connector bar therethrough. A plurality of parallel access ports through the housing extend longitudinally and are spaced from each other ninety degrees so as to be alignable with the installation ports and boreholes of the bar connector. Opposed flexible tines extend across each of the access ports from the edges thereof. The apertures in the ribs are geometrically configured so as to align the access ports with the installation ports and boreholes of the transformer connector bar for either a right-hand or left-hand installation of the connector bar on the transformer stud.

  4. Distinguishing between Apollo 14 impact melt and pristine mare basalt samples by geochemical and textural analyses of olivine

    NASA Astrophysics Data System (ADS)

    Fagan, A. L.; Neal, C. R.; Simonetti, A.; Donohue, P. H.; O'Sullivan, K. M.

    2013-04-01

    Apollo 14 (A-14) impact melt olivine vitrophyres (OVs), composed of olivine phenocrysts in an opaque glass matrix with minor amounts of pyroxene and plagioclase, are petrographically similar to pristine quenched A-14 high-alumina (high-Al) and Apollo 12 (A-12) basalts. Textural and chemical analyses have been conducted on olivines within impact melt and pristine mare basalt clasts from A-14 breccia 14321 as well as various olivine-phyric Apollo 12 and 17 basalts to be able to distinguish between the petrographically similar samples. The A-14 high-Al basalts examined here represent samples from each of the three chemical groups (A, B, C). Examples from the three A-12 basalt suites (Ilmenite, Olivine, Pigeonite) and olivine-rich Apollo 17 (A-17) Type C basalt, 74275, have also been analyzed. As a complement to the chemical analyses, crystal size distributions (CSDs) were determined for approximately half of the samples investigated here (due to a small number of olivine crystals that did not produce statistically meaningful CSDs on half of the samples), and confirm that although similar, the basalts and impact melts are texturally distinct. Olivines from A-14 impact melts have the highest average forsterite contents (average Fo ˜0.82) and generally the lowest average Co (37 ppm) and Mn (1544 ppm) abundances, thus chemically distinguishing them from the pristine basalts. In addition, chemical compositions obtained for olivine from 14321,1486 are most likely representative of an impact melt and thus contradict its previous classification as a high-Al basalt (Neal et al., 1988); olivine from, 1486 have similar average forsterite (average Fo ˜0.82) and Ti/V-ratio to the OVs. Furthermore, on the basis of their chemical compositions, olivines have been identified within the impact melts that are likely inherited from basalts; these olivines are chemically distinct from the rest of the impact melt olivine population with lower forsterite (0.67-0.80) and low Ti/V (˜10), which are similar to olivine compositions from the A-14 high-Al basalts. In addition to distinguishing between sample types from A-14, olivine compositions can also be used to distinguish between pristine mare basalts from various missions. Olivine within the selected samples from the individual A-12 basalt suites can also be distinguished chemically from one another using the Ti/V ratio, where Olivine suite basalts have Ti/V <3 and Ilmenite suite basalts have Ti/V >3.5. The results indicate that combined use of CSDs and chemical analyses of olivine can be used to reliably distinguish between (1) impact melts and pristine Apollo 14 basalts, (2) basalts from different landing sites, and (3) individual basalt suites from a single site.

  5. Low-pressure fractionation of strongly undersaturated alkaline ultrabasic magma: the olivine-melilite-nephelinite at Moiliili, Oahu, Hawaii

    NASA Astrophysics Data System (ADS)

    Wilkinson, J. F. G.; Stolz, A. J.

    1983-09-01

    The olivine-melilite-nephelinite at Moiliili, a representative of the Honolulu Volcanic Series, experienced post-eruptive fractional crystallization which resulted in the formation of pegmatoids of restricted volume. The pegmatoids can be equated in composition with melilite-bearing nephelinite (?melilite-bearing titanaugite melteigite and titanaugite ijolite). Pegmatoid olivine, titaniferous Ca-rich pyroxene and melilite display mild decreases in their 100 Mg/(Mg + Fe) ratios, largely in response to olivine fractionation. Titanomagnetite Fe2TiO4 components increased with fractionation, mainly at the expense of Fe3O4. Nepheline and sodalite show only restricted compositional variation, although sodalite solid solution is more extensive than in plutonic analogues. Compared with the host olivine-melilite-nephelinite, the pegmatoids are highly depleted in Cr and Ni and enriched in Rb, Sr, Y, Zr, Nb and Ba. The Moiliili fractionation sequence confirms the low-pressure trend olivine-melilite-nephelinite?melilite-bearing nephelinite, previously defined on the basis of relationships in the synthetic system diopside-akermanite-nepheline, but it provides no support for the proposal that olivine-melilite-nephelinite ultimately may fractionate to phonolite. Phonolitic differentiates can be generated by the low-pressure fractionation of alkali feldspar-bearing olivine nephelinites but the relative volumes of the salic derivatives are minor. These volumetric and other constraints inherent in low-pressure fractionation models employing nephelinitic parents suggest that at least some phonolites may be the products of deep crustal or upper mantle anatexis.

  6. Petrogenesis of Apollo 12 mare basalts. Part 1: Multiple melts and fractional crystallization to explain olivine and ilmenite basalt compositions

    NASA Technical Reports Server (NTRS)

    Neal, Clive R.; Taylor, Lawrence A.

    1993-01-01

    Mare basalts returned by the Apollo 12 mission have been divided into 4 groups on the basis of mineralogy and whole-rock chemistry: olivine basalts; pigeonite basalts; ilmenite basalts; and feldspathic basalts. James and Wright and Rhodes et al. concluded that the olivine and pigeonite groups were co-magmatic and that the within group variations are due to fractional crystallization of olivine and minor Cr-spinel, with pigeonite replacing olivine in the pigeonite basalts. Rhodes et al. concluded that the parental compositions for these suites were probably represented by the vitrophyres, and the olivine basalts are comprised essentially of cumulates and the pigeonites of evolved end-members. However, Neal et al. have demonstrated, using trace-element considerations, that the Apollo 12 olivine and pigeonite suites are not related. The ilmenite basalts were studied extensively by Dungan and Brown who noted that both cumulates and evolved fractionates were present within this group. In their modeling, Dungan and Brown used the vitrophyre compositions as parents. Neal et al. demonstrated that the feldspathic suite was probably comprised of only one member - 12038. Herein, the ilmenite and olivine basalts are demonstrated to be the products of several non-modal partial melting events of a single source followed by closed-system fractional crystallization.

  7. Olivine weathering in soil, and its effects on growth and nutrient uptake in Ryegrass (Lolium perenne L.): a pot experiment.

    PubMed

    ten Berge, Hein F M; van der Meer, Hugo G; Steenhuizen, Johan W; Goedhart, Paul W; Knops, Pol; Verhagen, Jan

    2012-01-01

    Mineral carbonation of basic silicate minerals regulates atmospheric CO(2) on geological time scales by locking up carbon. Mining and spreading onto the earth's surface of fast-weathering silicates, such as olivine, has been proposed to speed up this natural CO(2) sequestration ('enhanced weathering'). While agriculture may offer an existing infrastructure, weathering rate and impacts on soil and plant are largely unknown. Our objectives were to assess weathering of olivine in soil, and its effects on plant growth and nutrient uptake. In a pot experiment with perennial ryegrass (Lolium perenne L.), weathering during 32 weeks was inferred from bioavailability of magnesium (Mg) in soil and plant. Olivine doses were equivalent to 1630 (OLIV1), 8150, 40700 and 204000 (OLIV4) kg ha(-1). Alternatively, the soluble Mg salt kieserite was applied for reference. Olivine increased plant growth (+15.6%) and plant K concentration (+16.5%) in OLIV4. At all doses, olivine increased bioavailability of Mg and Ni in soil, as well as uptake of Mg, Si and Ni in plants. Olivine suppressed Ca uptake. Weathering estimated from a Mg balance was equivalent to 240 kg ha(-1) (14.8% of dose, OLIV1) to 2240 kg ha(-1) (1.1%, OLIV4). This corresponds to gross CO(2) sequestration of 290 to 2690 kg ha(-1) (29 10(3) to 269 10(3) kg km(-2).) Alternatively, weathering estimated from similarity with kieserite treatments ranged from 13% to 58% for OLIV1. The Olsen model for olivine carbonation predicted 4.0% to 9.0% weathering for our case, independent of olivine dose. Our % values observed at high doses were smaller than this, suggesting negative feedbacks in soil. Yet, weathering appears fast enough to support the 'enhanced weathering' concept. In agriculture, olivine doses must remain within limits to avoid imbalances in plant nutrition, notably at low Ca availability; and to avoid Ni accumulation in soil and crop. PMID:22912685

  8. A review of water contents and ductile deformation mechanisms of olivine: Implications for the lithosphere-asthenosphere boundary of continents

    NASA Astrophysics Data System (ADS)

    Wang, Qin

    2010-11-01

    Water plays an important role in the ductile deformation and evolution of the upper mantle. Water contents of natural olivine from 240 samples reveal a wide variation of 0-170 ppm H 2O, suggesting heterogeneous water distribution in the continental upper mantle. The average water contents (17 ± 13 ppm H 2O) in kimberlite nodules provide the best estimation of water concentrations in olivine in the lithosphere beneath cratons. The very low water contents (7 ± 9 ppm H 2O) of olivine from basalt xenoliths are caused by significant hydrogen loss during transport, while the high values (44 ± 34 ppm H 2O) in olivine megacrysts from kimberlites reflect restricted fluid-rich conditions in the upper mantle. To compare deformation in different tectonic environments, the western Superior Province (Canada), the Dabie Mountains and the North Jiangsu basin (China) are selected to represent an Archean craton, an orogenic belt and a rift basin, respectively. Using recent flow laws of olivine, deformation maps of dry and wet olivine are constructed under P- T conditions of the three tectonic units and in a continental subduction zone characterized by P = 6.28 GPa and T = 900 °C. For dry olivine, diffusion creep is the dominant mechanism in all the cases, which is contrary to the widely observed crystal preferred orientation of olivine in peridotites and seismic anisotropy observations. For wet olivine, only a small amount of water (50 H/10 6 Si) can remarkably decrease the stress of dislocation creep and increase contribution of dislocation creep to the deformation of olivine. The strain rate profiles of olivine indicate a transition from dislocation creep to diffusion creep at a depth of ˜ 220 km, which can be related with the Lehmann discontinuity characterized by a rapid decrease in seismic anisotropy. However, the pressure-induced fabric transition from [100] slip to [001] slip may be responsible for the Lehmann discontinuity in subduction zones. Therefore rheology of the continental upper mantle is controlled by power-law creep of wet olivine, and diffusion creep is the dominant deformation mechanism in the deep upper mantle, especially for fine-grained peridotites. The mechanical lithosphere-asthenosphere boundary (LAB) can be defined by the characteristic pressure derivative of effective viscosity. The sharp LAB beneath the Dabie Mountains and the Sulu terrane favors the lithosphere-asthenosphere decoupling, while the diffuse LAB beneath the western Superior Province will protect the continental root from convective erosion and mantle metasomatism. The long-term preservation of the continental roots can be attributed to a large viscosity contrast (temperature contrast) at a depth of < 150 km, and a thick and diffuse LAB at a depth of > 150 km.

  9. Dynamical Evolution of Barred Galaxies

    E-print Network

    E. Athanassoula

    2005-01-11

    Angular momentum redistribution within barred galaxies drives their dynamical evolution. Angular momentum is emitted mainly by near-resonant material in the bar region and absorbed by resonant material mainly in the outer disc and in the halo. This exchange determines the strength of the bar, the decrease of its pattern speed, as well as its morphology. If the galaxy has also a gaseous component and/or a companion or satellite, then these also take part in the angular momentum exchange. During the evolution a bar structure forms in the inner parts of the halo as well. This bar is shorter and fatter than the disc bar and stays so all through the simulation, although its length grows considerably with time. Viewed edge-on, the bar in the disc component acquires a boxy or peanut shape. I describe the families of periodic orbits that explain such structures and review the observations showing that boxy/peanut `bulges' are in fact just bars seen edge-on.

  10. Bar Dissolution in Prolate Halos.

    PubMed

    Ideta; Hozumi

    2000-06-01

    The time evolution of barred structures is examined under the influence of the external forces exerted by a spherical halo and by prolate halos. In particular, galaxy disks are placed in the plane including the major axis of prolate halos, whose configuration is often found in cosmological simulations. N-body disks in fixed external halo fields are simulated, so that bars are formed via dynamical instability. In the subsequent evolution, the bars in prolate halos dissolve gradually with time, while the bar pattern in a spherical halo remains almost unchanged to the end of the simulation. The decay times of the bars suggest that they can be destroyed in a time smaller than a Hubble time. Our results indicate that this dissolution process could occur in real barred galaxies, if they are surrounded by massive dark prolate halos, and the configuration adopted here is not unusual from the viewpoint of galaxy formation. For a prolate halo model, an additional simulation that is restricted to two-dimensional in-plane motions has also ended up with similar bar dissolution. This means that the vertical motions of disk stars do not play an essential role in the bar dissolution demonstrated here. PMID:10835306

  11. Chemical zonation in olivine-hosted melt inclusions: A record of syn-eruptive cooling

    NASA Astrophysics Data System (ADS)

    Newcombe, M. E.; Fabbrizio, A.; Zhang, Y.; Ma, C.; Le Voyer, M.; Guan, Y.; Eiler, J. M.; Saal, A. E.; Stolper, E. M.

    2013-12-01

    During the last few minutes to hours of a volcanic eruption, olivine-hosted melt inclusions (MIs) cool and crystallize olivine on their walls, producing olivine-depleted boundary layers in the melt adjacent to their olivine hosts. Competition between diffusive relaxation of these boundary layers into the centers of the MIs and replenishment of the boundary layers by continued olivine crystallization produces concentration profiles that are preserved in glassy MIs. The concentration profile of a given element in a single MI depends on the diffusion coefficient of the element in the melt, its partition coefficient between melt and olivine, and the growth rate of the olivine. Concentration profiles thus differ from element to element in a single MI, and also from inclusion to inclusion depending on the size of the MI and its thermal history. An implication of this chemical zonation is that analyses of zoned MIs, even if made near the centers of the MIs, will be diffusively fractionated relative to a simple olivine extraction path (i.e., the diffusion of fast-diffusing elements such as Ca can extend to the center of a ~150 ?m radius MI). We have developed a model that uses measured MgO concentration profiles across compositionally zoned, naturally glassy, olivine-hosted MIs to constrain the thermal histories of the MIs in the last few minutes to hours of an eruption. We have applied this model to MIs sampled from three different magmatic settings: (1) glassy rims of pillow basalts sampled from the Siqueiros transform fault; (2) a hornito on Santiago Island, (Galapagos); (3) a lava flow on a submarine flank of Fernandina Island (Galapagos). Cooling rates of five MIs from the Siqueiros transform fault range from ~0.08-3 K/s. Most MIs from this sample suite require two-stage, linear cooling histories from liquidus temperatures to ~1000°C with a slower-cooling first stage followed by a faster-cooling second stage, over a time period of a few minutes to just over one hour. MgO profiles in eight MIs from the subaerial hornito on Santiago Island are well described by single-stage linear cooling histories, with cooling rates ranging from ~1-4 K/s and durations of < 2 mins. MgO profiles in the two MIs so far studied from the submarine Fernandina flow show different behaviors, with one being well described by a single-stage linear cooling history with a cooling rate of ~1 K/s and the other requiring a two-stage cooling history with the lowest recorded cooling rates of the entire sample set (0.02 K/s for ~1 hr, then 0.09 K/s for ~20 mins). The differences in thermal histories determined for the three different magmatic settings may reflect differences in their eruptive styles: The two-stage cooling histories required by most of the submarine MIs could reflect slow cooling of the MIs as they travel through a lava flow or pillow interior followed by rapid quenching of the MIs as the host phenocrysts near the melt-water interface. The short, single-stage cooling histories determined by the model for MIs from a subaerial hornito are consistent with the efficient fragmentation observed during this style of volcanic eruption.

  12. GASEOUS STRUCTURES IN BARRED GALAXIES: EFFECTS OF THE BAR STRENGTH

    SciTech Connect

    Kim, Woong-Tae; Seo, Woo-Young; Kim, Yonghwi, E-mail: wkim@astro.snu.ac.kr [Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of)

    2012-10-10

    Using hydrodynamic simulations, we investigate the physical properties of gaseous substructures in barred galaxies and their relationships with the bar strength. The gaseous medium is assumed to be isothermal and unmagnetized. The bar potential is modeled as a Ferrers prolate with index n. To explore situations with differing bar strength, we vary the bar mass f{sub bar} relative to the spheroidal component as well as its aspect ratio R. We derive expressions as functions of f{sub bar} and R for the bar strength Q{sub b} and the radius r(Q{sub b} ) where the maximum bar torque occurs. When applied to observations, these expressions suggest that bars in real galaxies are most likely to have f{sub bar} {approx} 0.25-0.50 and n {approx}< 1. Dust lanes approximately follow one of the x{sub 1}-orbits and tend to be straighter under a stronger and more elongated bar, but are insensitive to the presence of self-gravity. A nuclear ring of a conventional x{sub 2} type forms only when the bar is not so massive or elongated. The radius of an x{sub 2}-type ring is generally smaller than the inner Lindblad resonance, decreases systematically with increasing Q{sub b} , and is slightly larger when self-gravity is included. This is evidence that the ring position is not determined by the resonance, but instead by the amount of angular momentum loss at dust-lane shocks. Nuclear spirals exist only when the ring is of the x{sub 2} type and is sufficiently large in size. Unlike the other features, nuclear spirals are transient in that they start out being tightly wound and weak, and then, due to the nonlinear effect, unwind and become stronger until they turn into shocks, with an unwinding rate that is higher for larger Q{sub b} . The mass inflow rate to the galaxy center is found to be less than 0.01 M{sub Sun} yr{sup -1} for models with Q{sub b} {approx}< 0.2, while becoming larger than 0.1 M{sub Sun} yr{sup -1} when Q{sub b} {approx}> 0.2 and self-gravity is included.

  13. Gaseous Structures in Barred Galaxies: Effects of the Bar Strength

    NASA Astrophysics Data System (ADS)

    Kim, Woong-Tae; Seo, Woo-Young; Kim, Yonghwi

    2012-10-01

    Using hydrodynamic simulations, we investigate the physical properties of gaseous substructures in barred galaxies and their relationships with the bar strength. The gaseous medium is assumed to be isothermal and unmagnetized. The bar potential is modeled as a Ferrers prolate with index n. To explore situations with differing bar strength, we vary the bar mass f bar relative to the spheroidal component as well as its aspect ratio { R}. We derive expressions as functions of f bar and { R} for the bar strength Qb and the radius r(Qb ) where the maximum bar torque occurs. When applied to observations, these expressions suggest that bars in real galaxies are most likely to have f bar ~ 0.25-0.50 and n <~ 1. Dust lanes approximately follow one of the x 1-orbits and tend to be straighter under a stronger and more elongated bar, but are insensitive to the presence of self-gravity. A nuclear ring of a conventional x 2 type forms only when the bar is not so massive or elongated. The radius of an x 2-type ring is generally smaller than the inner Lindblad resonance, decreases systematically with increasing Qb , and is slightly larger when self-gravity is included. This is evidence that the ring position is not determined by the resonance, but instead by the amount of angular momentum loss at dust-lane shocks. Nuclear spirals exist only when the ring is of the x 2 type and is sufficiently large in size. Unlike the other features, nuclear spirals are transient in that they start out being tightly wound and weak, and then, due to the nonlinear effect, unwind and become stronger until they turn into shocks, with an unwinding rate that is higher for larger Qb . The mass inflow rate to the galaxy center is found to be less than 0.01 M ? yr-1 for models with Qb <~ 0.2, while becoming larger than 0.1 M ? yr-1 when Qb >~ 0.2 and self-gravity is included.

  14. Galaxy Zoo: CANDELS Barred Disks and Bar Fractions

    E-print Network

    Simmons, B D; Lintott, Chris; Masters, Karen L; Willett, Kyle W; Keel, William C; Smethurst, R J; Cheung, Edmond; Nichol, Robert C; Schawinski, Kevin; Rutkowski, Michael; Kartaltepe, Jeyhan S; Bell, Eric F; Casteels, Kevin R V; Conselice, Christopher J; Almaini, Omar; Ferguson, Henry C; Fortson, Lucy; Hartley, William; Kocevski, Dale; Koekemoer, Anton M; McIntosh, Daniel H; Mortlock, Alice; Newman, Jeffrey A; Ownsworth, Jamie; Bamford, Steven; Dahlen, Tomas; Faber, Sandra M; Finkelstein, Steven L; Fontana, Adriano; Galametz, Audrey; Grogin, N A; Grutzbauch, Ruth; Guo, Yicheng; Haussler, Boris; Jek, Kian J; Kaviraj, Sugata; Lucas, Ray A; Peth, Michael; Salvato, Mara; Wiklind, Tommy; Wuyts, Stijn

    2014-01-01

    The formation of bars in disk galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in disks decreases from the local Universe to z ~ 1, and by z > 1 simulations predict that bar features in dynamically mature disks should be extremely rare. Here we report the discovery of strong barred structures in massive disk galaxies at z ~ 1.5 in deep rest-frame optical images from CANDELS. From within a sample of 876 disk galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a sub-sample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5< z < 2 (f_bar = 10.7 +6.3 -3.5% after correcting for incompleteness) does not significantly evolve. We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disk galaxies have evolved over the last 11 bil...

  15. Galaxy Zoo: CANDELS barred discs and bar fractions

    NASA Astrophysics Data System (ADS)

    Simmons, B. D.; Melvin, Thomas; Lintott, Chris; Masters, Karen L.; Willett, Kyle W.; Keel, William C.; Smethurst, R. J.; Cheung, Edmond; Nichol, Robert C.; Schawinski, Kevin; Rutkowski, Michael; Kartaltepe, Jeyhan S.; Bell, Eric F.; Casteels, Kevin R. V.; Conselice, Christopher J.; Almaini, Omar; Ferguson, Henry C.; Fortson, Lucy; Hartley, William; Kocevski, Dale; Koekemoer, Anton M.; McIntosh, Daniel H.; Mortlock, Alice; Newman, Jeffrey A.; Ownsworth, Jamie; Bamford, Steven; Dahlen, Tomas; Faber, Sandra M.; Finkelstein, Steven L.; Fontana, Adriano; Galametz, Audrey; Grogin, N. A.; Grützbauch, Ruth; Guo, Yicheng; Häußler, Boris; Jek, Kian J.; Kaviraj, Sugata; Lucas, Ray A.; Peth, Michael; Salvato, Mara; Wiklind, Tommy; Wuyts, Stijn

    2014-12-01

    The formation of bars in disc galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in discs decreases from the local Universe to z ˜ 1, and by z > 1 simulations predict that bar features in dynamically mature discs should be extremely rare. Here, we report the discovery of strong barred structures in massive disc galaxies at z ˜ 1.5 in deep rest-frame optical images from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. From within a sample of 876 disc galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a subsample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5 ? z ? 2 ( f_{bar} = 10.7^{+6.3}_{-3.5} per cent after correcting for incompleteness) does not significantly evolve. We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disc galaxies have evolved over the last 11 billion years.

  16. Developing a Game Plan for the Bar

    E-print Network

    Marsh, David

    · Stress management · Your likelihood of success on your bar exam will increase you with some 8me management strategies for your bar review period · Share students who pass? · A firm intent to take and pass your bar exam

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

    NASA Astrophysics Data System (ADS)

    Nagahara, H.; Kushiro, I.

    1987-10-01

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

  18. Olivine flotation and settling experiments on the join Mg2SiO4-Fe2SiO4

    NASA Technical Reports Server (NTRS)

    Herzberg, C. T.; Baker, M. B.; Wendlandt, R. F.

    1982-01-01

    Results are presented of a study of some unusual density relations between olivine and coexisting liquid in the system fosterite-fayalite. At 1 atmosphere pressure it is found that olivine floats on its coexisting liquid for intermediate compositions on this binary because of extreme partitioning of Fe into the melt phase. At 20 kilobars, the usual behavior of olivine settling is found to occur because the partitioning of Fe in the melt is reduced, aided possibly by the dissolution of CO2 in the melt from the use of a graphite container. It is determined that olivine flotation and settling are rapid in a time period of only a few hours because viscosities are slightly greater than that of paraffin oil at room temperature. Some adcumulate textures with good triple junction grain boundaries are found to be developed. Observations of differentiated magmatic systems suggest that the mechanisms by which magmas can differentiate vary considerably in the ultramafic to tholeiitic compositional range.

  19. Photometric Decomposition of Barred Galaxies

    E-print Network

    A. S. Reese; T. B. Williams; J. A. Sellwood; Eric I. Barnes; Brian A. Powell

    2007-02-27

    We present a non-parametric method for decomposition of the light of disk galaxies into disk, bulge and bar components. We have developed and tested the method on a sample of 68 disk galaxies for which we have acquired I-band photometry. The separation of disk and bar light relies on the single assumption that the bar is a straight feature with a different ellipticity and position angle from that of the projected disk. We here present the basic method, but recognise that it can be significantly refined. We identify bars in only 47% of the more nearly face-on galaxies in our sample. The fraction of light in the bar has a broad range from 1.3% to 40% of the total galaxy light. If low-luminosity galaxies have more dominant halos, and if halos contribute to bar stability, the luminosity functions of barred and unbarred galaxies should differ markedly; while our sample is small, we find only a slight difference of low significance.

  20. An Fe isotope study of ordinary chondrites

    NASA Astrophysics Data System (ADS)

    Needham, A. W.; Porcelli, D.; Russell, S. S.

    2009-12-01

    The Fe isotope composition of ordinary chondrites and their constituent chondrules, metal and sulphide grains have been systematically investigated. Bulk chondrites fall within a restricted isotopic range of <0.2‰ ? 56Fe, and chondrules define a larger range of >1‰ (-0.84‰ to 0.21‰ relative to the IRMM-14 Fe standard). Fe isotope compositions do not vary systematically with the very large differences in total Fe concentration, or oxidation state, of the H, L, and LL chondrite classes. Similarly, the Fe isotope compositions of chondrules do not appear to be determined by the H, L or LL classification of their host chondrite. This may support an origin of the three ordinary chondrite groups from variable accretion of identical Fe-bearing precursors. A close relationship between isotopic composition and redistribution of Fe during metamorphism on ordinary chondrite parent bodies was identified; the largest variations in chondrule compositions were found in chondrites of the lowest petrologic types. The clear link between element redistribution and isotopic composition has implications for many other non-traditional isotope systems (e.g. Mg, Si, Ca, Cr). Isotopic compositions of chondrules may also be determined by their melting history; porphyritic chondrules exhibit a wide range in isotope compositions whereas barred olivine and radial pyroxene chondrules are generally isotopically heavier than the ordinary chondrite mean. Very large chondrules preserve the greatest heterogeneity of Fe isotopes. The mean Fe isotope composition of bulk ordinary chondrites was found to be -0.06‰ (±0.12‰ 2 SD); this is isotopically lighter than the terrestrial mean composition and all other published non-chondritic meteorite suites e.g. lunar and Martian samples, eucrites, pallasites, and irons. Ordinary chondrites, though the most common meteorites found on Earth today, were not the sole building blocks of the terrestrial planets.

  1. Aggregation of grains in a turbulent pre-solar disk. [meteoritic inclusion and chondrule subcentimeter maximum size argument

    NASA Technical Reports Server (NTRS)

    Wieneke, B.; Clayton, D. D.

    1983-01-01

    The growth and evolution of grains in the protostellar nebula are investigated within the context of turbulent low-mass disk models developed by previous investigators. Because of grain collisions promoted by the turbulent velocities, particles aggregate to millimeter size in times of the order of 1000 yrs. During the growth the particles acquire a large inward radial velocity due to gas drag (Weidenschilling, 1977) and spiral into the sun. The calculations indicate that the final size of the particles does not exceed a few centimeters. This result is not very sensitive to the specific nebula parameters. For all conditions investigated it seems impossible to grow meter- or kilometer-sized bodies that could decouple from the gas motion. An additional argument is given that shows that only particles smaller than centimeter size can survive drift into the growing sun by being transported radially outward by turbulent mixing. This agrees well with the maximum size of inclusions and chondrules. Since sedimentation of grains and subsequent dust disk instability is effectively inhibited by turbulent stirring, the formation of planetesimals and planets cannot be explained in the above scenario without further assumptions.

  2. Phospho-olivines as cathode materials for lithium ion battery: trends on microwave synthesis

    NASA Astrophysics Data System (ADS)

    Alarcón-Suesca, C. E.; Nilges, T.

    2014-04-01

    In recently years, scientific research has been focused on finding new sources of efficient energy storage and lithium batteries are one of the most outstanding alternatives. Nowadays, investigation on cathode materials constitute one of the key factors of lithium rechargeable batteries studies. Recently, oxides with olivine structures has triggered the battery field, due to its excellent electrochemical properties, crystal stability, energy density, power capacity and are not expensive. However, the demand and development of more enhanced cathode materials can be achieved by the use of sophisticated synthetic methods. The purpose of this article is to provide a perspective to the materials community on the opportunities and limitations of nanostructured materials by highlighting examples in synthesis, fundamental studies and applications on microwave synthesis as novel route to obtain high voltage phospho-olivines.

  3. Ar-Ar and Rb-Sr Ages of the Tissint Olivine-phyric Martian Shergottite

    NASA Technical Reports Server (NTRS)

    Park, J.; Herzog, G. F.; Nyquist, L. E.; Shih, C.-Y.; Turin, B.; Lindsay, F. N.; Delaney, J. S.; Swisher, C. C., III; Agee, C.

    2013-01-01

    The fifth martian meteorite fall, Tissint, is an olivine-phyric shergottite that contains olivine macrocrysts (approximately 1.5 mm) [1]. [2] reported the Sm-Nd age of Tissint as 596 plus or minus 23 Ma along with Rb-Sr data that defined no isochron. [3] reported Lu-Hf and Sm-Nd ages of 583 plus or minus 86 Ma and 616 plus or minus 67 Ma, respectively. The cosmic-ray exposure ages of Tissint are 1.10 plus or minus 0.15 Ma based on 10Be [4], and 1.0-1.1 Ma, based on 3He, 21Ne, and 38Ar [5,6].We report Ar-Ar ages and Rb-Sr data.

  4. Partition of Ni between olivine and sulfide: equilibria with sulfide-oxide liquids

    Microsoft Academic Search

    M. E. Fleet; N. D. MacRae

    1988-01-01

    The partition of Ni between olivine and monosulfide-oxide liquid has been investigated at 1300–1395° C, \\u000a$$f_{O_2 }$$\\u000a=10-8-9-10-6.8, and \\u000a$$f_{S_2 }$$\\u000a=10-2.0-10-0.9, over the composition range 20–79 mol. % NiS. The product olivine compositions varied from Fo98 to Fo59 and from 0.06 to 3.11 wt% NiO. The metal\\/sulfur ratio of the sulfide-oxide liquid increases with increase in \\u000a$$f_{O_2 }$$\\u000a,

  5. Magnetic petrology of eastern North America diabases. I - Olivine-normative dikes from western South Carolina

    NASA Technical Reports Server (NTRS)

    Warner, Richard D.; Wasilewski, Peter J.

    1990-01-01

    The oxide mineralogy and the magnetic behavior of 15 olivine-normative samples obtained from South-Caroline diabase dikes were investigated using electron microprobe and SEM analyses and measurements of natural remanence magnetization (NRM), saturation isothermal remanence magnetization (SIRM), and anhysteritic remanence magnetization. It was found that chromite (which for these olivine-normative diabases is a sensitive petrologic indicator) constitutes up to 0.5 vol pct and that its abundance and composition correlate with bulk rock Cr. Microscopic analyses showed that titanomagnetite compositions were mostly between 0.4 and 0.55. The values of NRM and the NRM/SIRM ratios varied between 4 and 0.01 A sq m/kg and 0.0019 and 0.032, respectively. These properties inversely correlate with Cr content and demonstrably contrast Cr-rich and Cr-poor samples.

  6. Olivine clasts from mesosiderites and howardites - Clues to the nature of achondritic parent bodies

    NASA Technical Reports Server (NTRS)

    Delaney, J. S.; Prinz, M.; Nehru, C. E.

    1980-01-01

    The compositional ranges of olivine clasts from mesosiderites and most clasts from howardites (FO90-55 and FO89-45 respectively) overlap. Only one clast in howardite Allan Hills A78006,9 (FO16) differs significantly. Differences in FeO/MnO in olivines from the two groups may be explained by different redox states of their source regions. Whether the two meteorite groups were derived from the same parent body is not clear, but the lack of Fe-rich eucritic clasts in mesosiderites together with the lack of tridymite-phosphate rich gabbros and basalts in howardites, suggests that different bodies are required since both meteorite groups are near-surface polymict breccias, which have probably sampled significant portions of their parent body surfaces.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  8. Unusual spin fluctuations and magnetic frustration in olivine and non-olivine LiCoPO4 detected by P31 and Li7 nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Baek, S.-H.; Klingeler, R.; Neef, C.; Koo, C.; Büchner, B.; Grafe, H.-J.

    2014-04-01

    We report P31 and Li7 nuclear magnetic resonance (NMR) studies in new non-olivine LiZnPO4-type LiCoPO4tetra microcrystals, where the Co2+ ions are tetrahedrally coordinated. Olivine LiCoPO4, which was directly transformed from LiCoPO4tetra by an annealing process, was also studied and compared. The uniform bulk magnetic susceptibility and the P31 Knight shift obey the Curie-Weiss law for both materials with a high spin Co2+ (3d7, S =3/2), but the Weiss temperature ? and the effective magnetic moment ?eff are considerably smaller in LiCoPO4tetra. The spin-lattice relaxation rate T1-1 reveals a quite different nature of the spin dynamics in the paramagnetic state of both materials. Our NMR results imply that strong geometrical spin frustration occurs in tetrahedrally coordinated LiCoPO4, which may lead to the incommensurate magnetic ordering.

  9. Observation of $?_{c}$ decay into $?^{+}\\bar?^{-}$ and $?^{-}\\bar?^{+}$ final states

    E-print Network

    The BESIII Collaboration; M. Ablikim; M. N. Achasov; O. Albayrak; D. J. Ambrose; F. F. An; Q. An; J. Z. Bai; Y. Ban; J. Becker; J. V. Bennett; M. Bertani; J. M. Bian; E. Boger; O. Bondarenko; I. Boyko; R. A. Briere; V. Bytev; X. Cai; O. Cakir; A. Calcaterra; G. F. Cao; S. A. Cetin; J. F. Chang; G. Chelkov; G. Chen; H. S. Chen; J. C. Chen; M. L. Chen; S. J. Chen; X. Chen; Y. B. Chen; H. P. Cheng; Y. P. Chu; F. Coccetti; D. Cronin-Hennessy; H. L. Dai; J. P. Dai; D. Dedovich; Z. Y. Deng; A. Denig; I. Denysenko; M. Destefanis; W. M. Ding; Y. Ding; L. Y. Dong; M. Y. Dong; S. X. Du; J. Fang; S. S. Fang; L. Fava; F. Feldbauer; C. Q. Feng; R. B. Ferroli; C. D. Fu; J. L. Fu; Y. Gao; C. Geng; K. Goetzen; W. X. Gong; W. Gradl; M. Greco; M. H. Gu; Y. T. Gu; Y. H. Guan; A. Q. Guo; L. B. Guo; Y. P. Guo; Y. L. Han; F. A. Harris; K. L. He; M. He; Z. Y. He; T. Held; Y. K. Heng; Z. L. Hou; H. M. Hu; J. F. Hu; T. Hu; G. M. Huang; G. S. Huang; J. S. Huang; X. T. Huang; Y. P. Huang; T. Hussain; C. S. Ji; Q. Ji; Q. P. Ji; X. B. Ji; X. L. Ji; L. L. Jiang; X. S. Jiang; J. B. Jiao; Z. Jiao; D. P. Jin; S. Jin; F. F. Jing; N. Kalantar-Nayestanaki; M. Kavatsyuk; M. Kornicer; W. Kuehn; W. Lai; J. S. Lange; C. H. Li; Cheng Li; Cui Li; D. M. Li; F. Li; G. Li; H. B. Li; J. C. Li; K. Li; Lei Li; Q. J. Li; S. L. Li; W. D. Li; W. G. Li; X. L. Li; X. N. Li; X. Q. Li; X. R. Li; Z. B. Li; H. Liang; Y. F. Liang; Y. T. Liang; G. R. Liao; X. T. Liao; B. J. Liu; C. L. Liu; C. X. Liu; C. Y. Liu; F. H. Liu; Fang Liu; Feng Liu; H. Liu; H. H. Liu; H. M. Liu; H. W. Liu; J. P. Liu; K. Y. Liu; Kai Liu; P. L. Liu; Q. Liu; S. B. Liu; X. Liu; Y. B. Liu; Z. A. Liu; Zhiqiang Liu; Zhiqing Liu; H. Loehner; G. R. Lu; H. J. Lu; J. G. Lu; Q. W. Lu; X. R. Lu; Y. P. Lu; C. L. Luo; M. X. Luo; T. Luo; X. L. Luo; M. Lv; C. L. Ma; F. C. Ma; H. L. Ma; Q. M. Ma; S. Ma; T. Ma; X. Y. Ma; Y. Ma; F. E. Maas; M. Maggiora; Q. A. Malik; Y. J. Mao; Z. P. Mao; J. G. Messchendorp; J. Min; T. J. Min; R. E. Mitchell; X. H. Mo; C. Morales Morales; C. Motzko; N. Yu. Muchnoi; H. Muramatsu; Y. Nefedov; C. Nicholson; I. B. Nikolaev; Z. Ning; S. L. Olsen; Q. Ouyang; S. Pacetti; J. W. Park; M. Pelizaeus; H. P. Peng; K. Peters; J. L. Ping; R. G. Ping; R. Poling; E. Prencipe; M. Qi; S. Qian; C. F. Qiao; X. S. Qin; Y. Qin; Z. H. Qin; J. F. Qiu; K. H. Rashid; G. Rong; X. D. Ruan; A. Sarantsev; B. D. Schaefer; J. Schulze; M. Shao; C. P. Shen; X. Y. Shen; H. Y. Sheng; M. R. Shepherd; X. Y. Song; S. Spataro; B. Spruck; D. H. Sun; G. X. Sun; J. F. Sun; S. S. Sun; Y. J. Sun; Y. Z. Sun; Z. J. Sun; Z. T. Sun; C. J. Tang; X. Tang; I. Tapan; E. H. Thorndike; D. Toth; M. Ullrich; G. S. Varner; B. Wang; B. Q. Wang; D. Wang; D. Y. Wang; K. Wang; L. L. Wang; L. S. Wang; M. Wang; P. Wang; P. L. Wang; Q. Wang; Q. J. Wang; S. G. Wang; X. L. Wang; Y. D. Wang; Y. F. Wang; Y. Q. Wang; Z. Wang; Z. G. Wang; Z. Y. Wang; D. H. Wei; J. B. Wei; P. Weidenkaff; Q. G. Wen; S. P. Wen; M. Werner; U. Wiedner; L. H. Wu; N. Wu; S. X. Wu; W. Wu; Z. Wu; L. G. Xia; Z. J. Xiao; Y. G. Xie; Q. L. Xiu; G. F. Xu; G. M. Xu; H. Xu; Q. J. Xu; X. P. Xu; Z. R. Xu; F. Xue; Z. Xue; L. Yan; W. B. Yan; Y. H. Yan; H. X. Yang; Y. Yang; Y. X. Yang; H. Ye; M. Ye; M. H. Ye; B. X. Yu; C. X. Yu; H. W. Yu; J. S. Yu; S. P. Yu; C. Z. Yuan; Y. Yuan; A. A. Zafar; A. Zallo; Y. Zeng; B. X. Zhang; B. Y. Zhang; C. Zhang; C. C. Zhang; D. H. Zhang; H. H. Zhang; H. Y. Zhang; J. Q. Zhang; J. W. Zhang; J. Y. Zhang; J. Z. Zhang; S. H. Zhang; X. J. Zhang; X. Y. Zhang; Y. Zhang; Y. H. Zhang; Y. S. Zhang; Z. P. Zhang; Z. Y. Zhang; G. Zhao; H. S. Zhao; J. W. Zhao; K. X. Zhao; Lei Zhao; Ling Zhao; M. G. Zhao; Q. Zhao; Q. Z. Zhao; S. J. Zhao; T. C. Zhao; X. H. Zhao; Y. B. Zhao; Z. G. Zhao; A. Zhemchugov; B. Zheng; J. P. Zheng; Y. H. Zheng; B. Zhong; J. Zhong; Z. Zhong; L. Zhou; X. K. Zhou; X. R. Zhou; C. Zhu; K. Zhu; K. J. Zhu; S. H. Zhu; X. L. Zhu; Y. C. Zhu; Y. M. Zhu; Y. S. Zhu; Z. A. Zhu; J. Zhuang; B. S. Zou; J. H. Zou

    2012-12-19

    Using a data sample of $2.25\\times10^{8}$ $J/\\psi$ events collected with the BESIII detector, we present the first observation of the decays of $\\eta_{c}$ mesons to $\\Sigma^{+}\\bar{\\Sigma}^{-}$ and $\\Xi^{-}\\bar{\\Xi}^{+}$. The branching fractions are measured to be $(2.11\\pm0.28_{\\rm stat.}\\pm0.18_{\\rm syst.}\\pm0.50_{\\rm PDG})\\times10^{-3}$ and $(0.89\\pm0.16_{\\rm stat.}\\pm0.08_{\\rm syst.}\\pm0.21_{\\rm PDG})\\times10^{-3}$ for $\\eta_{c} \\to \\Sigma^{+}\\bar{\\Sigma}^{-}$ and $\\Xi^{-}\\bar{\\Xi}^{+}$, respectively. These branching fractions provide important information on the helicity selection rule in charmonium-decay processes.

  10. Characterization of olivine fabrics and mylonite in the presence of fluid and implications for seismic anisotropy and shear localization

    NASA Astrophysics Data System (ADS)

    Jung, Sejin; Jung, Haemyeong; Austrheim, Håkon

    2015-04-01

    The Lindås Nappe, Bergen Arc, is located in western Norway and displays two high-grade metamorphic structures. A Precambrian granulite facies foliation is transected by Caledonian fluid-induced eclogite-facies shear zones and pseudotachylytes. To understand how a superimposed tectonic event may influence olivine fabric and change seismic anisotropy, two lenses of spinel lherzolite were studied by SEM and EBSD techniques. The granulite foliation 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 by thin (<1 cm) garnet-bearing ultramylonite zones. The olivine fabrics in the spinel bearing assemblage were E-type and B-type and a combination of A- and B-type LPOs. There was a change in olivine fabric from a combination of A- and B-type LPOs in the spinel bearing assemblage to B- and E-type LPOs in the garnet lherzolite mylonite zones. FTIR analyses reveal that the water content of olivine in mylonite is much higher (~600 ppm H/Si) than that in spinel lherzolite (~350 ppm H/Si), indicating that water caused the difference in olivine fabric. Fabric strength of olivine gets weaker as the grain size reduced, and as a result calculated seismic properties for the two deformation stages reveal that P- and S-velocity anisotropies are significantly weaker in the mylonite. Microtextures and LPO data indicate that the deformation mechanism changed from dominant dislocation creep in spinel lherzolite to dislocation creep accompanied by grain-boundary sliding in mylonite. Shear localization in the mylonite appears to be originated from the grain size reduction through (1) enhanced dynamic recrystallization of olivine in the presence of water and (2) Zener pinning of clinopyroxene, or (3) by ultracommunition during the pseudotachylyte stage.

  11. Characterization of olivine fabrics and mylonite in the presence of fluid and implications for seismic anisotropy and shear localization

    NASA Astrophysics Data System (ADS)

    Jung, Sejin; Jung, Haemyeong; Austrheim, Håkon

    2014-12-01

    The Lindås Nappe, Bergen Arc, is located in western Norway and displays two high-grade metamorphic structures. A Precambrian granulite facies foliation is transected by Caledonian fluid-induced eclogite-facies shear zones and pseudotachylytes. To understand how a superimposed tectonic event may influence olivine fabric and change seismic anisotropy, two lenses of spinel lherzolite were studied by scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD) techniques. The granulite foliation 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 by thin (<1 cm) garnet-bearing ultramylonite zones. The olivine fabrics in the spinel bearing assemblage were E-type and B-type and a combination of A- and B-type lattice preferred orientations (LPOs). There was a change in olivine fabric from a combination of A- and B-type LPOs in the spinel bearing assemblage to B- and E-type LPOs in the garnet lherzolite mylonite zones. Fourier transform infrared (FTIR) spectroscopy analyses reveal that the water content of olivine in mylonite is much higher (approximately 600 ppm H/Si) than that in spinel lherzolite (approximately 350 ppm H/Si), indicating that water caused the difference in olivine fabric. Fabric strength of olivine gets weaker as the grain size reduced, and as a result, calculated seismic properties for the two deformation stages reveal that P- and S-velocity anisotropies are significantly weaker in the mylonite. Microtextures and LPO data indicate that the deformation mechanism changed from dominant dislocation creep in spinel lherzolite to dislocation creep accompanied by grain-boundary sliding in mylonite. Shear localization in the mylonite appears to be originated from the grain size reduction through (1) enhanced dynamic recrystallization of olivine in the presence of water and (2) Zener pinning of clinopyroxene or (3) by ultracomminution during the pseudotachylyte stage.

  12. Mineralogy and petrology of the diabasic rocks in a differentiated olivine diabase sill complex, Sierra Ancha, Arizona

    Microsoft Academic Search

    Douglas Smith

    1970-01-01

    The Precambrian Sierra Ancha sill complex, more than 700 feet thick, is a multiple intrusion with a central layer of feldspathic olivine-rich diabase, and upper and lower layers of olivine diabase derived from a high-alumina basalt magma. Minor rock types include albite diabase and albite-diabase pegmatite. Deuteric alteration was extensive. Principal primary minerals are plagioclase (An72 to An16), augite (Wo43En44Fs13

  13. Grafted NiO on natural olivine for dry reforming of methane

    Microsoft Academic Search

    C. Courson; L Udron; C Petit; A Kiennemann

    2002-01-01

    Natural olivine is used for gasification of biomass in a fluidised bed. Characterisations by X-ray diffraction and electron microscopies (SEM and TEM) have proved the presence of a (Mg,Fe)2SiO4 structure (Mg\\/Fe ratio: 9\\/1) with a rather broad distribution in elemental composition. Temperature programmed reduction has revealed equally the presence of iron oxides outside of this structure. The nature of free

  14. Partitioning of phosphorus between olivine, clinopyroxene and silicate glass in a spinel lherzolite xenolith from Yemen

    Microsoft Academic Search

    Fabrice Brunet; Gilles Chazot

    2001-01-01

    The melting reaction: amphibole+apatite=olivine+cpx+spinel+liquid is documented in spinel lherzolite xenoliths found in Plio-Quaternary alkali basalts from Yemen (Ataq Volcano). All the phases involved in this reaction, including the melt, have been preserved within millimeter-size glassy melt pockets. In a previous study, ion microprobe analyses performed on these phases allowed determination of trace-element partition coefficients between apatite, clinopyroxene, amphibole and glass.

  15. Diffusion-driven magnesium and iron isotope fractionation in Hawaiian olivine

    USGS Publications Warehouse

    Teng, F.-Z.; Dauphas, N.; Helz, R.T.; Gao, S.; Huang, S.

    2011-01-01

    Diffusion plays an important role in Earth sciences to estimate the timescales of geological processes such as erosion, sediment burial, and magma cooling. In igneous systems, these diffusive processes are recorded in the form of crystal zoning. However, meaningful interpretation of these signatures is often hampered by the fact that they cannot be unambiguously ascribed to a single process (e.g., magmatic fractionation, diffusion limited transport in the crystal or in the liquid). Here we show that Mg and Fe isotope fractionations in olivine crystals can be used to trace diffusive processes in magmatic systems. Over sixty olivine fragments from Hawaiian basalts show isotopically fractionated Mg and Fe relative to basalts worldwide, with up to 0.4??? variation in 26Mg/24Mg ratios and 1.6??? variation in 56Fe/54Fe ratios. The linearly and negatively correlated Mg and Fe isotopic compositions [i.e., ??56Fe=(??3.3??0.3)????26Mg], co-variations of Mg and Fe isotopic compositions with Fe/Mg ratios of olivine fragments, and modeling results based on Mg and Fe elemental profiles demonstrate the coupled Mg and Fe isotope fractionation to be a manifestation of Mg-Fe inter-diffusion in zoned olivines during magmatic differentiation. This characteristic can be used to constrain the nature of mineral zoning in igneous and metamorphic rocks, and hence determine the residence times of crystals in magmas, the composition of primary melts, and the duration of metamorphic events. With improvements in methodology, in situ isotope mapping will become an essential tool of petrology to identify diffusion in crystals. ?? 2011 Elsevier B.V.

  16. A Plagioclase-Olivine-Spinel-Magnetite Inclusion from Maralinga (CK): A Record of Sequential Condensation

    Microsoft Academic Search

    E. Zinner; F. Brandstatter; G. Kurat

    1995-01-01

    An unusual inclusion of triangular cross section (5 mm x 2.5 mm in size) from the Maralinga CK chondrite has a zonal structure, consisting of core, mantle, and crust. The core (2.5 x 1 mm) consists mainly of plagioclase-olivine intergrowth (troctolite) with ophitic texture, but also contains minor clinopyroxene and Cl-apatite, as well as some calcite, which partially fills pore

  17. On high-temperature formation of iron-rich olivine in the early solar system

    NASA Technical Reports Server (NTRS)

    Dorofeyeva, V. A.; Makalkin, A. B.; Vityazev, A. V.

    1993-01-01

    A kinetic restriction on the formation of fayalite-rich olivine in equilibrium with the cooling solar-composition gas appears to exist at the low temperature of approximately 500 K. We offer a high-temperature formation mechanism (different from simple condensation) which operates at high hydrogen depletion (up to 300 times) relative to solar abundance. We show how the necessary depletion rate decreases with temperature (thermodynamical equilibrium is suggested). The consequences for planet formation are considered.

  18. Optical absorption spectra at high temperatures and radiative thermal conductivity of olivines

    Microsoft Academic Search

    Yoshio Fukao; Hitoshi Mizutani; Seiya Uyeda

    1968-01-01

    The absorption coefficient alpha of olivine crystals was measured in the range of wavelength from 0.3 mu-10 mu at various temperatures up to 1300 °K. It was discovered that alpha in the pass-band (about 1.8 mu-3.0 mu) increases by a factor of about 100 in going from 300 °K to 1300 °K. The radiative thermal conductivity calculated from this result

  19. Crystal melt partitioning of noble gases (helium, neon, argon, krypton, and xenon) for olivine and clinopyroxene

    Microsoft Academic Search

    Veronika S. Heber; Richard A. Brooker; Simon P. Kelley; Bernard J. Wood

    2007-01-01

    Mineral melt partition coefficients of all noble gases (min\\/meltDi) have been obtained for olivine (ol) and clinopyroxene (cpx) by UV laser ablation (213 nm) of individual crystals grown from melts at 0.1 GPa mixed noble gas pressure. Experimental techniques were developed to grow crystals virtually free of melt and fluid inclusions since both have been found to cause profound problems

  20. Orthorhombic perovskite phases observed in olivine, pyroxene and garnet at high pressures and temperatures

    Microsoft Academic Search

    Lin-Gun Liu

    1976-01-01

    Ferromagnesian silicate olivines, pyroxenes and garnets with Mg\\/(Mg + Fe)>~0.3 (molar) have been found to transform to high-pressure phases characterized by the orthorhombic perovskite structure when compressed to pressures above 250 kbar in a diamond-anvil press and heated to temperatures above 1,000°C with a YAG laser. The zero-pressure density of the perovskite phase of (Mg,Fe)SiO3 is about 3-4% greater than

  1. Effects of pressure on high-temperature dislocation creep in olivine

    Microsoft Academic Search

    Shun-Ichiro Karato; Haemyeong Jung

    2003-01-01

    Effects of pressure on high-temperature, dislocation creep in olivine ((Mg, Fe)2SiO4) aggregates have been determined under both water-poor ('dry') and water-saturated ('wet') conditions. New experimental data were obtained at pressures of 1-2 GPa under 'dry' and 'wet' conditions using a newly developed high-resolution dislocation density measurement technique to estimate the creep strength. These data are compared with previous data at

  2. Serpentinization of sintered olivine during seawater percolation experiments AGU abstract N

    E-print Network

    Luquot, Linda

    Serpentinization of sintered olivine during seawater percolation experiments AGU abstract N° OS21C.% of serpentine, 4.3 wt.% of brucite and 0.8 wt.% of hematite were formed. The estimated total hydrogen content as follow: Fe2+ Fe3+ + e- 2H+ + 2e- H2 Log aSiO2 LogaMg2+ Talc Brucite Serpentine Mg[2+] -7 -6 -5 -4 -3 -2

  3. Genesis of ilmenite rods and palisades along humite-type defects in olivine from Alpe Arami

    Microsoft Academic Search

    A.-C. Risold; V. Trommsdorff; B. Grobéty

    2001-01-01

    Rod-shaped ilmenite inclusions in olivine have been observed in numerous peridotite lenses of the Adula-Cima Lunga unit, Central Alps. The rods are elongated parallel to [010]ol and identical in size, shape and concentration to those reported from garnet peridotite at Alpe Arami (AA). TEM investigation of the rods at AA, Cima di Gagnone (CDG) and Monte Duria (MD) demonstrates that

  4. First-principles calculations of equilibrium Mg isotope fractionations between garnet, clinopyroxene, orthopyroxene, and olivine: Implications for Mg isotope thermometry

    NASA Astrophysics Data System (ADS)

    Huang, Fang; Chen, Lijuan; Wu, Zhongqing; Wang, Wei

    2013-04-01

    Equilibrium fractionation factors of Mg isotopes at high temperature and pressure are investigated for pyrope, majorite, clinopyroxene, orthopyroxene, and olivine using density functional theory. The calculated equilibrium fractionation factors are in good agreement with previous study (Schauble, 2011), suggesting that our calculations are reliable and accurate. The results reveal significant inter-mineral Mg isotope fractionations due to different coordination environment of Mg in minerals. Specifically, pyrope, where Mg is in eight-fold coordination, is more enriched in light Mg isotopes than olivine and pyroxene where Mg is in six-fold coordination. The calculated isotope fractionation for Mg isotopes between clinopyroxene and pyrope is consistent with observations from natural eclogites (Li et al., 2011; Wang et al., 2012). Our calculation also reveals substantial pressure effect on Mg isotope fractionations among garnet, pyroxene, and olivine. Equilibrium fractionation of Mg isotopes between pyrope and pyroxene (and olivine) could be used as a novel and independent thermometry with precision much better than the traditional garnet-clinopyroxene Fe-Mg exchange thermometry because such fractionation is significantly greater than the current uncertainties of Mg isotope analyses (˜0.05‰ amu-1). These Mg isotope thermometries could have wide applications in high-temperature mafic igneous and metamorphic rocks where garnet co-exists with pyroxene or olivine. Equations for equilibrium Mg isotope fractionation factors between garnet (pyrope and majorite) and pyroxene and between garnet and olivine as a function of temperature and pressure are also presented in this study.

  5. Extracting Olivine (Fo-Fa) Compositions from Raman Spectral Peak Positions

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

    Olivine and pyroxene are two major basaltic minerals that have been identified at Gusev Crater and Meridiani Planum by the Mars Exploration Rovers. Full petrologic characterization of a sample (rock or soil), however, requires determining the range of mineral compositions, extent of zoning, range of grain sizes, mineral associations, presence of xenocrysts, etc. Information of this sort will aid the interpretation of sample crystallization and differentiation histories and help discriminate between lithologies. In Raman spectroscopic experiments, minerals are identified by their spectral patterns and mineral compositions can be inferred from the peak positions. Instruments currently in use or slated for impending surface exploration missions provide only average elemental compositions for relatively large rock or soil targets or bulk mineral analysis. No techniques currently in use or scheduled for flight can characterize both structure and composition of individual mineral grains, in-situ, like the Mars Microbeam Raman Spectrometer (MMRS). The MMRS is designed to take 100 spectra along a 1 cm linear traverse on the surface of a sample, with contributions from one or a few mineral phases per spectrum. We presented a method to extract structural and compositional information from the Raman spectra of quadrilateral pyroxenes. The pyroxene calibration was applied to a Raman spectroscopic study of Martian meteorite EETA79001 along with a preliminary olivine calibration, where we demonstrated the capability to discriminate related lithologies using Raman point counts. This paper presents an improved olivine calibration that will further aid sample characterization and the study of alteration processes.

  6. Two-Stage Deformation of Olivine Aggregates with Changing Deformation Kinematics

    NASA Astrophysics Data System (ADS)

    Mahan, B. M.; Skemer, P. A.; Griera, A.

    2011-12-01

    Two-stage deformation experiments have been conducted on synthetic olivine aggregates to investigate the influence of pre-existing fabric on the evolution of lattice-preferred orientation (LPO), seismic anisotropy, and grain morphology. This study is motivated by recent work on naturally and experimentally deformed peridotites, which suggest that the alignment of olivine axes with the shear plane requires more strain in samples with a strong pre-existing LPO than in samples with weak or random LPO. In the first stage of deformation, aggregates synthesized from San Carlos olivine are deformed at P = 1 GPa and T = 1500 K in a triaxial geometry to produce axi-symmetric LPOs of varying strength. In a second stage of deformation, the aggregates are re-deformed in simple shear to varying shear strains. Microstructural analyses are performed after each step (synthesis, triaxial deformation, simple shear deformation) using optical microscopy and electron backscatter diffraction (EBSD). These results are compared to numerical models of microstructural evolution. Our results provide constraints on the evolution of LPO and consequent seismic signature as a function of preexisting rock fabric. These data are necessary to interpret seismic anisotropy in settings where kinematics are complex, such as mid-ocean ridges and subduction zones.

  7. In situ observation of texture development in olivine, ringwoodite, magnesiowüstite and silicate perovskite at high pressure

    NASA Astrophysics Data System (ADS)

    Wenk, H.-R.; Lonardeli, I.; Pehl, J.; Devine, J.; Prakapenka, V.; Shen, G.; Mao, H.-K.

    2004-10-01

    Magnesium silicates are the dominant minerals in the earth's mantle. Their preferred orientation is important for understanding the rheology and seismic anisotropy in the deep earth. Here we report results of radial synchrotron diffraction diamond anvil cell (DAC) experiments on San Carlos olivine, axially compressed to 50 GPa. Experiments were performed at room temperature, except for brief laser heating to induce phase transformations. High stresses and development of preferred orientation were observed in diffraction images. Quantitative texture information was obtained by analyzing the images with the Rietveld method. With increasing pressure (between 9 and 43 GPa) olivine develops a texture with [001] axes perpendicular to the compression direction that is compatible with {hk0}[001] pencil glide. Ringwoodite (between 20 and 50 GPa) develops weak preferred orientation with {011} lattice planes perpendicular to the compression direction. After the phase transformation, perovskite and magnesiowüstite display transformation textures that are then modified by continuing deformation. Magnesiowüstite has a weak <111> maximum parallel to the compression direction that changes towards <001> with increasing deformation. Perovskite, transforming from olivine, has a pronounced (100) transformation texture and with increasing deformation a {012} maximum develops. The transformation texture is probably produced by mechanical {110} twinning and nucleation in orientations that minimize elastic strain energy. The deformation texture of perovskite is due to slip.

  8. High brightness laser diode bars

    Microsoft Academic Search

    Norbert Lichtenstein; Yvonne Manz; Jürgen Müller; Jörg Troger; Susanne Pawlik; Achim Thies; Stefan Weiss; Rainer Baettig; Christoph Harder

    2006-01-01

    Based on the most recent generation of Bookham's laser diode bars in the 9xx nm wavelength range which are able to deliver in excess of 250 W of output power from 50% filling factor 2.4 mm cavity length design, we have developed low 20% fill-factor bar devices for high brightness applications. Close to 200 W of output power has been

  9. A high precision EPMA data of olivine: comparison with LA ICP-MS

    NASA Astrophysics Data System (ADS)

    Batanova, V. G.; Sobolev, A. V.; Kuzmin, D.

    2013-12-01

    Composition of olivine provides critical information on the composition and origin of primary mantle derived melts and their sources. Especially informative are minor and trace elements Ni, Mn, Ca, Al, Cr, Co, Ti, Zn, P, Na [1, 2], which being in the concentration range over 10 ppm are assessable by EPMA. The analytical protocol built up on new JEOL JXA 8230 EPMA in ISTerre, UJF, Grenoble, France. Facility has tungsten source gun, is equipped by five WDS and one SDD EDS and placed in the environment with controlled temperature (22+/-0.3 degrees C) and humidity (50+/-3%). The analytical conditions are the following: acceleration voltage 25kV, 900 nA beam current, WDS recording for trace elements (Ni, Mn, Ca, Al, Cr, Co, Ti, Zn, P, Na) and EDS recording for Si, Mg, Fe, total counting time 12 minutes, ZAF correction. Instrumental drift during analytical sessions is monitored by repeated measurements of olivine standards. For trace elements this protocol yields detection limits from 3 to 10 ppm and average precision of individual analysis of 10 ppm (2 standard errors). For Fo of olivine precision is 300 ppm (2 standard errors). Comparison of EPMA and LA ICP-MS data for the large range of olivine compositions suggests that accuracy of EPMA is similar to precision noted above. For elements with concentration over 100 ppm the obtained EPMA precision and accuracy are better than these of LA ICP-MS. For the concentration of elements between 50-100 ppm both methods show similar precision and accuracy; and for concentration between 10-50 ppm LA ICP-MS yields better precision and accuracy. Spatial resolution of EPMA, however, is significantly better: 3-5 micrometres compared to 30-50 for LA ICP-MS. This makes our new EPMA protocol of great advantage for measurement of zoned or small olivine grains. [1] Sobolev et al., 2007. Science 316 (5823), p.412-417. [2] De Hoog et al., 2010. Chemical Geology 270, p. 196-2015

  10. Rheological contrast between serpentines and olivine and weakening of a subducting plate interface

    NASA Astrophysics Data System (ADS)

    Hirauchi, K.; Katayama, I.

    2010-12-01

    Recent seismic observations have suggested that water released by dehydration reactions within a subducting slab is transported through the base of the overlying mantle, thereby causing serpentinization. The degrees of viscous coupling between the serpentinite layer and the overlying mantle wedge might influence the style of mantle convection and the thermal state of a subduction zone (Wada et al., 2008). Serpentine minerals (lizardite, chrysotile, and antigorite) are hydrous phyllosilicates (13 wt% H2O). In subduction zone environments, lizardite and chrysotile seem to form at temperatures below 300-400°C, whereas antigorite is stable at higher temperatures of 300 to 600°C. Previous deformation experiments have revealed that the low- and high-temperature serpentine species display intracrystalline plastic flow in the mantle wedge (e.g., Hilairet et al., 2007; Hirauchi et al., 2010). In particular, Hilairet et al. (2007) indicated that the strength of antigorite is an order of magnitude lower than that of olivine at geological time scales: however, the rheological contrast between lizardite/chrysotile and antigorite under the mantle wedge conditions is not directly constrained. We therefore conducted two-layer shear deformation experiments on serpentines and olivine under P-T conditions (P = 1 GPa, T = 250, 300°C) that correspond to the forearc mantle wedge in subduction zones. The experimental results show that strain rates in lizardite/chrysotile are approximately an order of magnitude higher than those in olivine, whereas strain rates in antigorite is only 1 to 2 times higher than those in olivine. The contrasts in strain rates between lizardite/chrysotile and antigorite is represented by a factor of 5 to 6. Based on the results of our experiments, we suggest that the rheology of lizardite/chrysotile can only explain strong decoupling on the subducting plate interface. Our experiments also show that antigorite is not significantly weaker than olivine in the dislocation-accommodated creep regime, as compared to Hilairet et al. (2007), resulting in weak decoupling at the plate interface. Therefore, we suggest that the degrees of viscous coupling in subduction zones are strongly controlled by the serpentine species stable in the base of the mantle wedge, depending on various parameters (e.g., cool vs. warm subduction zones, change with depth).

  11. The effect of conductive grain boundary impurities on electrical conductivity in polycrystalline olivine

    NASA Astrophysics Data System (ADS)

    Watson, H. C.; Roberts, J. J.; Tyburczy, J. A.

    2009-12-01

    Grain boundaries affect the rheological, mechanical, diffusive, and electrical properties of polycrystalline materials. In crustal and mantle rocks, they may provide a “fast conduction path” explaining areas of anomalously high electrical conductivity without necessitating intra-granular hydrogen or an interconnected melt or fluid phase. Conductive impurities on grain boundaries such as graphite or sulfide have been suggested to explain some field-based high-conductivity anomalies, but direct experimental studies have been few. Studies on grain boundary conductivity in polycrystalline monomineralic, dry olivine exist, but a systematic understanding of impure grain boundary conductivity remains unrealized. Bulk electrical conductivity and impedance spectroscopy of single crystal and polycrystalline San Carlos olivine and polycrystalline olivine with carbon or iron sulfide on grain boundaries were measured at 1GPa and 350o C-1200o C in a piston cylinder apparatus. Sometimes, impedance spectroscopy is the only tool that yields definitive evidence of a secondary (grain boundary) conduction mechanism. We demonstrate that grain boundary conductivity in series with grain interiors is more apparent in the presence of small amounts of carbon grain boundary impurities, whereas the presence of quenched iron sulfide melt on grain boundaries can enhance bulk conductivity even if full melt interconnectivity is not established. Specifically, the addition of 0.1 wt% (~0.16 vol%) C has no significant effect on bulk conductivity. In contrast, the addition of ~1.0 vol% Fe67S33 melt results in conductivity much higher than that of pure olivine, but lower than what is expected for a fully interconnected sulfide phase. We infer that the sulfide is partially connected on the grain boundaries and edges and has reached the electrical percolation threshold, but not the fluid percolation threshold. The effect of the addition of sulfide to the grain boundaries on electrical conductivity is similar to the effect of adding 0.01%-0.1% H to pure olivine. It may not always be necessary to have hydrogen or connected melt or fluid to account for anomalously high conductivity in some parts of the mantle or crust. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  12. Elasticity of Hydrous Olivine Polymorphs: Implications for Seismic Structure of the Transition Zone

    NASA Astrophysics Data System (ADS)

    Duffy, T. S.; Mao, Z.; Jacobsen, S. D.; Jiang, F.; Smyth, J. R.; Holl, C. M.; Frost, D. J.

    2007-12-01

    The presence of water in the upper mantle and transition zone has the potential to explain various phenomena such as shear velocity anomalies or uplift and broadening of the 410-km discontinuity. The presence of H2O in the transition zone has also been frequently invoked to reconcile laboratory elasticity data on olivine polymorphs with seismic data for the amplitude of the 410-km discontinuity (Li et al., 2001; Chambers et al., 2005). Recently, we have measured the single-crystal elastic properties of hydrous olivine (Jacobsen et al., 2006) and a suite of hydrous wadsleyites (Mao et al., 2007a) at ambient conditions and one hydrous wadsleyite composition (0.84 wt% H2O) up to 12 GPa (Mao et al., 2007b). These data provide new constraints on elastic moduli and their pressure derivatives for hydrous olivine and wadsleyite. Using this data, we first examine the effect of H2O on bulk sound velocities under transition zone conditions because anelastic effects can be neglected in this case. At 410 km depth (~13.8 GPa, along a 1400°C adiabat), the bulk sound velocity of wadsleyite with 1 wt% H2O is 3.1% lower than for dry wadsleyite. Comparison of the seismic velocity jump across the 410-km discontinuity with the measured velocity contrast between wadsleyite and olivine provides a means to estimate the olivine abundance at 410-km depth. For mantle wadsleyite with 0.1-0.2 wt% H2O (Huang et al., 2005) and using experimentally determined olivine- wadsleyite H2O partition coefficients, the olivine abundance is found to be 40%, much lower than a pyrolite model. In order for a pyrolite composition to satisfy the seismic data, 1.2 wt. % H2O is needed in wadsleyite- a value greater than its maximum solubility under these conditions. The anomalously steep seismic gradient in the transition zone has been another feature of the region that has long defied explanation. We show that the seismic gradient can be matched if there is a gradient in H2O concentration across the transition zone such that the H2O content drops, for example, from 0.3 wt% at 410 km to 0.1 wt% at 520 km dpeth. For compressional and shear wave velocities, 0.1 wt% H2O in wadsleyite would lead to 0.3% and 0.4% reductions in VP and VS, respectively, neglecting any anelasticity. If the water content of wadsleyite was instead 1.0 wt. %, then the corresponding velocity reductions would be 3.3% and 3.6%. Following the work of Karato and Jung (1998), we have implemented a preliminary model accounting for the effect of H2O on anelasticity. This model indicates that 0.1 wt% H2O in wadsleyite could be responsible for reductions in shear velocities up to 1.0%.

  13. Reaction Progress of Olivine Alteration as a Function of Time and CO2 Supply at 150°C - An Experimental Study

    NASA Astrophysics Data System (ADS)

    Prikryl, J.; Stefansson, A.

    2014-12-01

    Increased anthropogenic CO2 emissions have caused an imbalance in the Earth's carbon cycle causing climate changes. Interaction of CO2 with water and rock plays important role in geochemical cycle of carbon and among potential ways of reducing atmospheric CO2 by sequestration into carbonates. Olivine, among the main constituents of mafic and ultramafic rocks, is rich in Mg and Fe that can react with CO2 to form Mg-Fe carbonates like siderite and magnesite. Laboratory experiments were performed in batch-type titanium reactors to study the interaction between CO2-rich water and olivine under hydrothermal conditions. The experimental were conducted at 150°C, for 1 to 4 weeks, the CO2 concentration was 5 to 30 mmol/kg and the initial pH was around neutral. The olivine used was forsterite 93% from Åheim Olivine Pit-Norway. The alteration products and fluid chemistry were monitored as a function of time. Moreover, the results were supported with reaction path modeling to further constrain the olivine alteration and carbonate mineral formation mechanism. Initially forsterite dissolved releasing elements into solution. During this stage limited alteration products were formed and the solution pH was buffered by H+ uptake by olivine dissolution and CO2 concentration. Upon further reactions secondary phases started to form including chrysotile, brusite and mainly solid solution of iron-containing magnesite. This resulted in decrease of CO2 concentrations and eventually increased solution pH. Experiments with higher initial CO2 concentrations required longer period until CO2was consumed. Furthermore experiments with longer duration had quantitatively larger amount of precipitated minerals. Findings of this research represent platform for kinetic numerical simulations of olivine alteration and therefore provide insight into carbon storage in mafic rocks under in-situ conditions.

  14. Crustal origin for coupled 'ultra-depleted' and 'plagioclase' signatures in MORB olivine-hosted melt inclusions: evidence from the Siqueiros Transform Fault, East Pacific Rise

    Microsoft Academic Search

    Leonid V. Danyushevsky; Michael R. Perfit; Stephen M. Eggins; Trevor J. Falloon

    2003-01-01

    Geochemical data from melt inclusions in olivine phenocrysts in a picritic basalt from the Siqueiros Transform Fault on the northern East Pacific Rise provide insights into the petrogenesis of mid-ocean ridge basalts (MORB). The fresh lava contains ~10% of olivine phenocrysts (Fo89.3-91.2) and rare, small (80-90, An57-63). Melt inclusions in olivine phenocrysts are glassy, generally rounded in shape and vary