Sample records for barred olivine chondrules

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

    NASA Astrophysics Data System (ADS)

    Rubin, Alan E.

    2013-03-01

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

  2. Chondrule reheating experiments and relict olivine

    NASA Astrophysics Data System (ADS)

    Fox, G. E.; Hewins, R. H.

    2005-05-01

    Chondrules contain foreign objects, including some olivine grains that obviously did not crystallize from their silicate melt. The term recycling is usually applied to chondrules with relict grains, implying that the precursor contained relicts of a previous generation of chondrules. This has given rise to the idea that the pervasive melt droplet formation that affected the early solar system involved repeated events in which chondrules or chondrule debris were reheated. We conducted experiments in which synthetic chondrules generated from fine-grained mineral aggregates were heated and cooled a second time to see what the textural consequences of this reheating would be. Charges were heated to peak temperatures for 1 min and were cooled to near-solidus temperatures over 35 min, for both thermal cycles. We first made microporphyritic olivine charges and on reheating and second cooling observed coarser grain sizes and disappearance of relict grains, if the second peak temperature was the same as or higher than the first (but insufficient for destroying all nuclei). The coarsening was due to the dissolution of the smallest first generation crystals and additional growth on the relicts during cooling. Reheated barred olivine spheres generated barred olivine spheres again, no matter how low the peak temperature. This is because the number of remaining olivine grains or nuclei that acted as sites for regrowth was constant. Generating the observed distribution of chondrule textures, dominantly porphyritic, directly from a fine-grained precursor such as nebular or presolar condensates is impossible with a single event. With reheating of chondrules, generating the texture distribution is possible provided that subsequent heating events have higher peak temperatures than the first, so that total dissolution of the smallest grains occurs, with consequent coarsening. For our thermal history and a reasonable distribution of peak temperatures, multiple recycling events might be needed to make most chondrules porphyritic. Alternatively, the predominance of porphyritic textures in chondrules could be explained by heating times hours long for a fine-grained precursor or by heating of a coarse-grained precursor. The presence of relict grains derived from older chondrules or other material suggests that an aggregate has been heated for the first time, because recycling brings an approach to equilibrium. There appears to be no reliable way to use textures to tell just how many chondrules have been heated more than once. The relict grains simply indicate the nature of the precursors, which were at least in part derived from earlier chondrules, and of the peak temperatures too low for total melting and heating times too short for total dissolution. Rim thicknesses on relict grains depend on number density of crystals and melt composition, and are not a reliable guide to the chondrule cooling rate.

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

    SciTech Connect

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

    2011-06-24

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

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

    NASA Technical Reports Server (NTRS)

    Jones, Rhian H.; Lofgren, Gary E.

    1993-01-01

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

  7. Diffusional Modification of Igneous Zoning During Crystal Growth: Analysis of Fe-Mg Zoning of Olivine in Semarkona (LL3.0) Porphyritic Olivine Chondrule

    Microsoft Academic Search

    M. Miyamoto; T. Mikouchi; H. Kaiden

    1999-01-01

    We computed diffusional modification of Fe-Mg zoning of olivine in Semarkona (LL3.0) porphyritic olivine chondrule formed by closed-system fractional crystallization as olivine crystal grows by solving the diffusion equation to study cooling history.

  8. Diffusion Modeling of Cooling Rates of Relict Olivine in Semarkona Chondrules

    NASA Astrophysics Data System (ADS)

    Hewins, R. H.; Ganguly, J.; Mariani, E.

    2009-03-01

    Diffusive exchange profiles between relict olivine and melt-grown olivine in Semarkona Type IIA chondrules were oriented by EBSD to correct D. Results for Fe-Mg (D from Dohmen) and Cr (Ito and Ganguly) are concordant at 300°-400°C/hr.

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

    NASA Astrophysics Data System (ADS)

    Tomeoka, Kazushige; Ohnishi, Ichiro

    2014-07-01

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

  10. A Wide Range of the Cooling Rate of Type II Porphyritic Olivine Chondrules in Semarkona (LL3.0)

    NASA Astrophysics Data System (ADS)

    Miyamoto, M.; Koizumi, E.; Mikouchi, T.

    2008-03-01

    We applied the model on the basis of Fe-Mg diffusion during olivine crystal growth to calculating the cooling rate of olivines in several different PO chondrules in Semarkona and found that PO chondrules show a wide range of the cooling rate.

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

    NASA Technical Reports Server (NTRS)

    Lofgren, Gary E.; Le, L.

    2002-01-01

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

  12. Cooling rates of porphyritic olivine chondrules in the Semarkona (LL3.00) ordinary chondrite: A model for diffusional equilibration of olivine during fractional crystallization

    NASA Astrophysics Data System (ADS)

    Miyamoto, M.; Mikouchi, T.; Jones, R. H.

    2009-05-01

    Cooling rates of chondrules provide important constraints on the formation process of chondrite components at high temperatures. Although many dynamic crystallization experiments have been performed to obtain the cooling rate of chondrules, these only provide a possible range of cooling rates, rather than providing actual measured values from natural chondrules. We have developed a new model to calculate chondrule cooling rates by using the Fe-Mg chemical zoning profile of olivine, considering diffusional modification of zoning profiles as crystals grow by fractional crystallization from a chondrule melt. The model was successfully verified by reproducing the Fe-Mg zoning profiles obtained in dynamic crystallization experiments on analogs for type II chondrules in Semarkona. We applied the model to calculating cooling rates for olivine grains of type II porphyritic olivine chondrules in the Semarkona (LL3.00) ordinary chondrite. Calculated cooling rates show a wide range from 0.7 °C/h to 2400 °C/h and are broadly consistent with those obtained by dynamic crystallization experiments (10-1000 °C/h). Variations in cooling rates in individual chondrules can be attributed to the fact that we modeled grains with different core Fa compositions that are more Fe-rich either because of sectioning effects or because of delayed nucleation. Variations in cooling rates among chondrules suggest that each chondrule formed in different conditions, for example in regions with varying gas density, and assembled in the Semarkona parent body after chondrule formation.

  13. Relict olivine grains, chondrule recycling, and implications for the chemical, thermal, and mechanical processing of nebular materials

    NASA Astrophysics Data System (ADS)

    Ruzicka, Alex; Floss, Christine; Hutson, Melinda

    2008-11-01

    Chondrules and isolated forsterites in five low-subtype ordinary chondrites [NWA 3127 (LL3.1), Sahara 97210 (LL3.2), Wells (LL3.3), Chainpur (LL3.4), and Sahara 98175 (LL3.5)] were studied using petrographic, EMPA, and SIMS techniques to better constrain the origin of chondrules and the olivine grains within them. Our results imply that igneous crystallization, vapor fractionation, redox effects, and open-system behavior were important processes. All olivine grains, including normal, relict, and isolated forsterite grains, show evidence for igneous fractionation under disequilibrium conditions, with olivine crystallizing during rapid cooling (closer to 2000 °C/h than to 100 °C/h). Vapor fractionation is manifested by anti-correlated abundances between refractory elements (Al, Sc, Y, Ti, Ca, V) and volatile elements (Cr, Mn, P, Rb, Fe) in olivine. Redox effects are evidenced in various ways, and imply that Fe, Co, Ni, and P were partitioned more into metal, and V was partitioned more into olivine, under reducing conditions in the most FeO-poor melts. There is no obvious evidence for systematic variations in olivine composition according to meteorite subtype, but shock melting in Sahara 97210 resulted in the injection of glass-derived melt into olivine, resulting in artificially high abundances of Ba, Sr, Na, Ti, and some other incompatible elements in olivine. Terrestrial weathering in a hot desert environment may have mobilized Ba and Sr in some glasses. Our data suggest that chondrules in ordinary chondrites experienced repeated thermal, chemical, and mechanical processing during a "recycling" process over an extended time period, which involved multiple episodes of melting under fluctuating redox and heating conditions, and multiple episodes of chondrule break-up in some cases. Forsterite grains, including normal grains in forsterite-bearing type I chondrules, the cores of isolated forsterites, and relict forsterite in type II chondrules, all crystallized from similar, refractory melts under reducing conditions; relict Mg-olivine and isolated forsterite grains were thus derived from type I chondrules. Olivine in type II chondrules, including normal grains and ferroan overgrowths on relict Mg-olivine, crystallized from more volatile-rich, oxidized, and relatively unfractionated melts. Relict dusty olivine grains in type I chondrules were derived from type II chondrules during incomplete melting episodes involving reduction and some vaporization, with clear (non-dusty) grains in dusty olivine-bearing chondrules crystallizing from the reduced and partly vaporized melts. Melt compositions parental to normal olivine grains in type I and II chondrules are systematically enriched in refractory elements compared to bulk chondrule compositions, implying that chondrules often experienced open-system exchange with more volatile-rich surroundings after some olivine had crystallized, possibly while the chondrules were still partly molten. Type II chondrules could have been derived from type I chondrules by the addition of relatively volatile-rich material, followed by re-melting and little evaporation under oxidizing conditions. In contrast, type I chondrules could have been derived from type II chondrules by re-melting involving more-or-less evaporation under reducing conditions. Chemical, oxygen isotope, and petrographic data are best accommodated by a model in which there were several (>2-3, sometimes ?4-5) melting episodes for most chondrules in ordinary chondrites.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  15. 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

  16. 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

  17. 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.

  18. 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.

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

    NASA Technical Reports Server (NTRS)

    Krot, Alexander N.; Rubin, Alan E.

    1993-01-01

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

  20. Trace element geochemistry of ordinary chondrite chondrules: The type I/type II chondrule dichotomy

    NASA Astrophysics Data System (ADS)

    Jacquet, Emmanuel; Alard, Olivier; Gounelle, Matthieu

    2015-04-01

    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 < pyroxene < mesostasis, and heavy REE (HREE) being enriched by 1-2 orders of magnitude (CI-normalized) relative to light REE (LREE) in ferromagnesian silicates, although no single olivine with very large LREE/HREE fractionation has been found. On average, olivine in type II chondrules is poorer in refractory lithophile incompatible elements (such as REE) than its type I counterpart by a factor of ?2. This suggests that olivine in type I and II chondrules formed by batch and fractional crystallization, respectively, implying that type II chondrules formed under faster cooling rates (>?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.

  1. 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.

  2. Na-, Cl-rich mesostases in Chainpur (LL3) and Parnallee (LL3) chondrules

    NASA Astrophysics Data System (ADS)

    Bridges, J. C.; Alexander, C. M. O'd.; Hutchison, R.; Franchi, I. A.; Pillinger, C. T.

    1997-07-01

    Forty six chondrules from Chainpur (LL3.4) and 39 chondrules and clasts from Parnallee (LL3.6) have been sectioned and searched for Na-, Cl-rich phases by EPMA. Oxygen isotopic compositions, I-Xe ages and ion probe data were also obtained on some of these chondrules. Sodium-, Cl-rich glass and microcrystalline sodalite (Na4Al3Si3O12Cl), nepheline (NaAlSiO4), scapolite (Na4Al3Si9O24Cl) have been identified in 7% of the Chainpur and 8% of the Parnallee samples. These phases are present in chondrule mesostases or, in one case, the plagioclase of a barred-olivine chondrule. None of the chondrules contain more than 5% by volume of Na-, Cl-rich phases. In the Chainpur chondrules, they originated through partial devitrification of silica-undersaturated, REE-, Na- and Cl-rich mesostases. Two processes have been identified which led to the formation of these mesostases. In two of the chondrules, which consist mainly of low-Ca pyroxene, the extended, metastable crystallization of low-Ca pyroxene created silica-undersaturated, REE-rich residua. Ba- and Cl-enrichments in nepheline and scapolite of one chondrule suggest that there was also an influx of alkalis and Cl during crystallization of the low-Ca pyroxene. Similarly, another one of the Chainpur chondrules - mainly composed of olivine phenocrysts - is markedly enriched in Cl (10 x OC). As there is no evidence of corrosive metasomatism in any of the chondrules, Cl- (and alkali) enrichment is believed to have occurred when they were still partially molten. The chondrules were derived from normal oxygen isotopic reservoirs, so the postulated influx of Ba, Na and Cl did not occur on an exotic parent body. Trace amounts of nepheline and sodalite, present in two Parnallee chondrules, crystallized from small Na-, Cl-, REE-rich residua following extended crystallization of anorthite. An I-Xe age of 5.0 Ma. post-Bjurbole obtained on one of these Parnallee chondrules dates the crystallization of feldspathoid and thus formation of the chondrule.

  3. 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.

  4. 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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  7. Correlated Study of Rb-Sr Systematics and Petrologic Properties of Chondrules from Allende (CV): Evidence for Secondary Alteration

    NASA Astrophysics Data System (ADS)

    Nakamura, N.; Kimura, M.; Shimoda, H.; Nohda, S.

    1993-07-01

    In order to clarify when and where the distributions of alkalis in chondrules were established [1-3] we have undertaken a correlated study of Rb-Sr systematics and petrologic properties of chondrules from the Allende (CV) meteorite. We report here the results of Rb-Sr isotopic analyses combined with petrologic examinations for 16 chondrules (19 specimens) from Allende. The whole-rock analyses indicate a model age of 4.5 +/- 0.05 Ga (using ALL [4]), suggesting that the Rb-Sr isotopic system has been closed in bulk Allende for 4.5 yr. For the chondrules, the earlier works [4,5] include a few barred-olivine and many unknown petrographic types (probably mostly porphyritic) chondrules. In this work, we present results for 1 radial pyroxene, 4 porphyritic (7 specimens), and 11 barred olivine chondrules, covering major petrographic types. The results are shown in an 87Rb-87Sr evolution diagram (Fig. 1). Including earlier results [4,5], no systematic differences are found for different textural types, but data points mostly deviate from the 4.5-Ga line to the right, forming a rough linear array. This means that the Rb-Sr isotopic system in chondrules have been disturbed by a late event(s). The slope of the dotted line corresponds to an age of ~4.0 Ga. The meanlng of the linear trend is not clear because of the lack of isotopic equilibrium. Ground masses of chondrules analyzed for Rb-Sr isotopes were examined by optical microscope and EPMA. Some chondrules have primary glassy ground masses enriched in the anorthite component, especially in their central parts. However, as demonstrated previously [6], most of the chondrules analyzed here for Rb-Sr isotopes were also altered. They have abundant nepheline and sodalite components that replace primary glassy ground masses. Sodium was secondarily introduced and Ca was lost from the Allende chondrules. Using abundances of dodalite and nepheline components, the degree of alteration was tentatively classified into three categories: A (least altered), B (middle), and C (most altered). In Fig. 1, the chondrules with higher 87Rb/86Sr are mostly in categories of B or C. On the other hand, the chondrules of category A have the lower 87Rb/86Sr ratio, relatively close to that of bulk Allende. The 87Rb/86Sr ratios are related to the alteration categories but are not directly related to the isotopic deviation. It is thus considered that the general trend of high and low elemental ratios of Rb/Sr had been basically established during the early nebular processes and were then modified significantly more recently. The diffusivities of alkalis in glassy materials [7] at low temperatures (~400 degrees C) suggest a possible migration of Rb as well as Na from matrix to ground masses of chondrules. The old model age for Allende "matrix" [5] is consistent with such a possibility. We therefore strongly suggest that the Allende chondrules were subjected to a low- temperature alteration reaction after consolidation of the chondrules. References: [1] Grossman J. N. and Wasson J. T. (1983) In Chondrules and Their Origins (E. A. King, ed.), 88-121, LPI. [2] Hewins R. H. (1991) GCA, 55, 935-942. [3] Matsuda H. et al. (1990) Meteoritics, 25, 137-143. [4] Gray C. M. et al. (1973) Icarus, 20, 213-239. [5] Tatsumoto M. et al. (1976) GCA, 40, 617-634. [6] Kimura M. and Ikeda Y. (1992) Papers 17th Symp. Antarct. Meteor., 31-33. [7] Jambon A. and Carron J. P. (1976) GCA, 40, 897-903. Fig. 1, which appears here in the hard copy, shows an 87Rb-87Sr evolution diagram for chondrules from the Allende meteorite.

  8. 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.

  9. Mineralogy and Chemistry of Large Chondrules Formed <0.8 Million Years After CAIs

    NASA Astrophysics Data System (ADS)

    Bischoff, A.; Chaussidon, M.; Weyrauch, M.

    2014-09-01

    Macro chondrules appear to be older than normal-sized chondrules and show a different distribution of chondrule types. Barred or radial textures dominate. They are also rich in FeO similar in composition to normal-sized type II chondrules.

  10. Chondrules: Precursors and interactions with the nebular gas

    NASA Astrophysics Data System (ADS)

    Hewins, Roger H.; Zanda, Brigitte

    2012-07-01

    Chondrule compositions suggest either ferroan precursors and evaporation, or magnesian precursors and condensation. Type I chondrule precursors include granoblastic olivine aggregates (planetary or nebular) and fine-grained (dustball) precursors. In carbonaceous chondrites, type I chondrule precursors were S-free, while type II chondrules have higher Fe/Mn than in ordinary chondrites. Many type II chondrules contain diverse forsteritic relicts, consistent with polymict dustball precursors. The relationship between finer and coarser grained type I chondrules in ordinary chondrites suggests more evaporation from more highly melted chondrules. Fe metal in type I, and Na and S in type II chondrules indicate high partial pressures in ambient gas, as they are rapidly evaporated at canonical conditions. The occurrence of metal, sulfide, or low-Ca pyroxene on chondrule rims suggests (re)condensation. In Semarkona type II chondrules, Na-rich olivine cores, Na-poor melt inclusions, and Na-rich mesostases suggest evaporation followed by recondensation. Type II chondrules have correlated FeO and MnO, consistent with condensation onto forsteritic precursors, but with different ratios in carbonaceous chondrites and ordinary chondrites, indicating different redox history. The high partial pressures of lithophile elements require large dense clouds, either clumps in the protoplanetary disk, impact plumes, or bow shocks around protoplanets. In ordinary chondrites, clusters of type I and type II chondrules indicate high number densities and their similar oxygen isotopic compositions suggest recycling together. In carbonaceous chondrites, the much less abundant type II chondrules were probably added late to batches of type I chondrules from different O isotopic reservoirs.

  11. Impact jetting as the origin of chondrules.

    PubMed

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

    2015-01-15

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

  12. Impact jetting as the origin of chondrules

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  13. Coarse-grained chondrule rims in type 3 chondrites

    NASA Astrophysics Data System (ADS)

    Rubin, A. E.

    1984-09-01

    Coarse-grained rims composed of olivine, with or without low-Ca pyroxene, occur around all types of chondrules and compound chondrules in type 3 carbonaceous chondrites and around ordinary chondrites. The dark zoned chondrules and coarse grained rims were formed by the heating of clumps of opaque matrix material to subsolidus-subliquidus temperatures in the solar nebula. The most likely source of the heat that formed the coarse grained rims is the mechanism responsible for chondrule formation. CV chondrites may have formed in a region where the chondrule formation mechanism was less efficient, probably at greater solar distances than the ordinary chondrites. Alternatively, CV chondrules may have suffered fewer particle collisions prior to agglomeration.

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

    SciTech Connect

    Desch, S. J.; Morris, M. A. [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404 (United States); Connolly, H. C. [Kingsborough Community College and the Graduate Center of the City University of New York, 2001 Oriental Boulevard, Brooklyn, NY 11235-2398 (United States); Boss, Alan P., E-mail: steve.desch@asu.ed [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015-1305 (United States)

    2010-12-10

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

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

    NASA Astrophysics Data System (ADS)

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

    1986-02-01

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

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-04-01

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

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

    NASA Technical Reports Server (NTRS)

    2004-01-01

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

  19. Oxygen isotope ratios of FeO-poor chondrules in CR3 chondrites: Influence of dust enrichment and H2O during chondrule formation

    NASA Astrophysics Data System (ADS)

    Tenner, Travis J.; Nakashima, Daisuke; Ushikubo, Takayuki; Kita, Noriko T.; Weisberg, Michael K.

    2015-01-01

    We present detailed electron microprobe analyses and oxygen three-isotope measurements by high precision secondary ion mass spectrometry on 45 type I (FeO-poor) chondrules/fragments and 3 type II (FeO-rich) chondrule fragments from Meteorite Hills 00426 and Queen Alexandra Range 99177, two of the most primitive CR3 chondrites. Type I chondrules/fragments have Mg#'s (defined as the Mg# of constituent olivine and/or low-Ca pyroxene) ranging from 94.2 to 99.2; type II chondrule fragments have Mg#'s of 53-63. Oxygen three-isotope measurements plot on the slope ?1 primitive chondrule mineral (PCM) line. Within chondrules, ?17O (=?17O-0.52 × ?18O) values of coexisting olivine, pyroxene, and plagioclase are homogeneous, with propagated uncertainties of 0.3‰. This indicates each phase crystallized from the final chondrule melt, and that efficient oxygen isotope exchange occurred between ambient gas and chondrule melt. Among type I chondrules there is a well-defined increase in ?17O, from -5.9‰ to ?-1‰, as Mg#'s decrease from 99.2 to ?96; type II chondrule fragments are comparatively 16O-poor (?17O: ?0.2-0.6‰). The relationship between Mg# and ?17O among type I chondrules confirms that addition of a 16O-poor oxidizing agent to the highest Mg# chondrule precursors resulted in forming lower Mg# CR chondrules. Using aspects of existing equilibrium condensation models and a mass balance we estimate that type I CR chondrules formed at dust enrichments of 100-200×, from dusts with 0-0.8 times the atomic abundance of ice, relative to CI dust. The type II chondrule fragments are predicted to have formed at CI dust enrichments near 2500×.

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

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

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

    USGS Publications Warehouse

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

    2000-01-01

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

  2. Compound Chondrules fused Cold

    E-print Network

    Hubbard, Alexander

    2015-01-01

    About 4-5% of chondrules are compound: two separate chondrules stuck together. This is commonly believed to be the result of the two component chondrules having collided shortly after forming, while still molten. This allows high velocity impacts to result in sticking. However, at T ~ 1100K, the temperature below which chondrules collide as solids (and hence usually bounce), coalescence times for droplets of appropriate composition are measured in tens of seconds. Even at 1025K, at which temperature theory predicts that the chondrules must have collided extremely slowly to have stuck together, the coalescence time scale is still less than an hour. These coalescence time scales are too short for the collision of molten chondrules to explain the observed frequency of compound chondrules. We suggest instead a scenario where chondrules stuck together in slow collisions while fully solid; and the resulting chondrule pair was subsequently briefly heated to a temperature in the range of 900-1025K. In that temperatur...

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  4. 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).

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

    NASA Astrophysics Data System (ADS)

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

    1982-06-01

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

  6. Carefully Characterizing Chondrules: A Review

    NASA Astrophysics Data System (ADS)

    Herd, R. K.

    2014-09-01

    Systematic, simple, easily understood, detailed documentation of the mineralogy and textures of chondrules and chondrule-like objects, enables researchers to examine and record chondrule contents to very small scales and to discriminate among them.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  8. 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.

  9. 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.

  10. 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.

  11. Experimental petrology of meteorites: Phosphorus and oxygen isotopes in olivine

    NASA Astrophysics Data System (ADS)

    Boesenberg, Joseph S.

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  15. 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.

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

    SciTech Connect

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

    1990-06-01

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

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1993-05-01

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

  19. Towards a Novel Classification of Chondrules: Examples From the L4 Ordinary Chondrite Saratov

    NASA Astrophysics Data System (ADS)

    Herd, R. K.; Dixon, L.; Samson, C.; Hunt, P. A.

    2009-05-01

    In order to classify and thoroughly investigate the origin of chondrites, the most primitive class of meteorites, exhaustive and systematic textural and mineralogical observations of chondrules are required. Long-standing mineralogical-textural classifications for chondrules obscure relevant data. Accepted classification schemes place chondrules in relatively few categories (e.g. radiating, cryptocrystalline, granular, porphyritic, barred) but ignore abundant micron-scale features within chondrules (relict crystals, overgrowths, zonations, quench textures) that provide invaluable evidence of chondrule history. Chondrule mineralogy and textures in polished thin sections and slabs of Saratov (L4) have been recorded using a scanning electron microscope (SEM). The most detailed work so far, on a single section, has mapped the size, sorting, packing, mineralogy and textures of 370 chondrules greater than 100 microns in diameter. Using back-scatter electron (BSE) images, a photomosaic of the entire thin section was created, and overlain with a grid system to locate and map specific chondrules. Textures and mineral phases were documented with BSE images, energy-dispersive spectrometry (EDS) and cathodoluminescence (CL). Chondrule textures are akin to those of igneous and metamorphic Earth rocks, and the processes forming them can be likewise interpreted. Many different heating, cooling and annealing histories, for chondrules now found associated in the same chondrite, are implied. Groups of chondrules with similar provenance, different from other groups, may be recognized by their analogous textural histories. Each chondrule has had at least a two-stage origin. Many show the effects of multi-stage processing. We anticipate that our conclusions will contribute to a new comprehensive classification scheme for chondrules and chondrites, and encourage others to examine the petrology of these complex and fascinating rocks.

  20. 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.

  1. 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.

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

    USGS Publications Warehouse

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

    1991-01-01

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

  3. 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.

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

    NASA Technical Reports Server (NTRS)

    Jones, Rhian H.; Rubie, David C.

    1991-01-01

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

  5. 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.

  6. 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.

  7. Semarkona: Lessons for chondrule and chondrite formation

    NASA Astrophysics Data System (ADS)

    Hubbard, Alexander; Ebel, Denton S.

    2015-01-01

    We consider the evidence presented by the LL3.0 chondrite Semarkona, including its chondrule fraction, chondrule size distribution and matrix thermal history. We show that no more than a modest fraction of the ambient matrix material in the Solar Nebula could have been melted into chondrules; and that much of the unprocessed matrix material must have been filtered out at some stage of Semarkona's parent body formation process. We conclude that agglomerations of many chondrules must have formed in the Solar Nebula, which implies that chondrules and matrix grains had quite different collisional sticking parameters. Further, we note that the absence of large melted objects in Semarkona means that chondrules must have exited the melting zone rapidly, before the chondrule agglomerations could form. The simplest explanation for this rapid exit is that chondrule melting occurred in surface layers of the disk. The newly formed, compact, chondrules then settled out of those layers on short time scales.

  8. 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

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

    NASA Technical Reports Server (NTRS)

    Treiman, Allan H.; Goodrich, Cyrena Anne

    2001-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  11. The effect of NA vapor on the NA content of chondrules

    NASA Astrophysics Data System (ADS)

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

    1993-12-01

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

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

    NASA Technical Reports Server (NTRS)

    Johnson, M. C.

    1986-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Metzler, K.; Bischoff, A.

    1994-01-01

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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Not All Refractory Spherules in CM2S are Chondrules

    NASA Astrophysics Data System (ADS)

    Greenwood, R. C.

    1992-07-01

    Refractory spherules in CM2 meteorites are small, <300 micrometers in diameter, inclusions composed predominantly of spinel, with accessory hibonite and perovskite (Macdougall 1981). On the basis of their chondrule-like morphology, and the inward-radiating habit of hibonite in some inclusions, it has been suggested that refractory spherules formed from liquid droplets (Macdougall 1981; MacPherson et al. 1983). Since many spherules are composed purely of spinel, Macdougall (1981) estimated that their 1-atm melting temperature might have been as high as 2135 degrees C. Melt temperatures in excess of 1550 degrees C were estimated by MacPherson et al. (1983) for the spinel-hibonite spherule BB1. Refractory spherules are a minor component of the Ca-Al rich inclusions (CAIs) found in CM2s. Of 345 CAIs located in the CM2 Cold Bokkeveld only 4 are refractory spherules (study in collaboration with M. Lee, University of Essex). Textural evidence from Cold Bokkeveld demonstrates that CAIs in CM2s are highly fragmented and must have been derived by disruption of larger objects (Greenwood et al. 1991). That this is also the case for refractory spherules is clearly demonstrated by MSP1, an anhedral, spinel-bearing inclusion (300 mmicrometer longest dimension) located in situ in Murchison (CM2). It comprises a rounded core (110 micrometers in diameter) of Fe-free spinel (V2O3 0.5wt%) surrounded by a rim of pyroxene (15-25 micrometers thick), in turn enclosed by a zone of olivine (Fo 99.7) and Mg-rich phyllosilicate. The spinel core contains 15% void space (estimated). The pyroxene rim is zoned outwards from fassaite to diopside. Blocky crystals of olivine <20 micrometers in diameter form a discontinuous rim to pyroxene and occur as isolated grains enclosed by Mg-phyllosilicate. The inclusion has an irregular outline and a sharp contact with surrounding matrix, indicating that it is a fragment of a larger, now disrupted CAI. In CV3 meteorites refractory spinel-rich spherules, similar to the Murchison example, occur within a number of different inclusion-types. Nodules, 5-300 micrometers in diameter, composed of spinel, melilite, perovskite, and pyroxene are common constituents of amoeboid olivine aggregates (Hashimoto and Grossman 1987). Melilite is also present in some Murchison spherules (MacPherson et al. 1983), and prior to aqueous alteration may have been an important constituent in many of these objects. Spherical clumps of spinel crystals, termed "framboids" by El Goresy et al. (1979) are common constituents of type B2 coarse-grained CAIs (Wark and Lovering 1982). One B2 CAI in Vigarano contains a 160-micrometer-diameter framboid with a 10-20-micrometer-thick rim of spinel enclosing a touching framework of rounded grains (5-15 micrometers in diameter). Melilite, present in the bulk inclusion, forms an outer rind to the framboid 5-10 micrometers thick and may be contiguous with crystals (angstrom k(sub)16.5) interstitial to spinel within the framboid. Individually rimmed spinel nodules, up to 300 micrometers in diameter, are also an important component of "fluffy" type A inclusions (MacPherson and Grossman 1984). The structure of the Murchison inclusion MSP1 indicates that at least some CM2 refractory spherules were components of larger inclusions. In CV3s, experimental evidence suggests that spinel spherules represent residual solid material that acquired a rounded form during partial melting (Wark and Lovering 1982). The comparison made between chondrules and spherules may therefore be misleading and results in erroneously high estimates of the temperatures experienced by these objects. El Goresy A., Nagel K., and Ramdohr P. (1979) Proc. Lunar Planet. Sci. Conf. 10th, 833-850. Greenwood R.C., Hutchison R., and Cressey G. (1991) Meteoritics (abstract) 26, 340. Hashimoto A. and Grossman L. (1987) Geochim. Cosmochim. Acta 51, 1685-1704. Macdougall J.D. (1981) Geophys. Res. Lett. 8, 966-969. MacPherson G.J. and Grossman, L. (1984) Geochim. Cosmochim. Acta 48, 29-46. MacPherson G.J., Bar-Matthews M., Tanak

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Chondrites represent the building blocks of the solar system and the factors controlling their formation have implications for processes within the protoplanetary disk and interactions between the solar nebula and the early Sun. However, the source of the flash heating that formed the constituent chondrules is a subject of debate, with proposed mechanisms including various forms of convection drawing nebular dust towards and ejecting it away from the Sun, or alternatively extra-nebular energy pulses that require no interaction with the young star. Because the Sun was strongly magnetic early in its life, paleointensity measurements of chondrules can be used to determine the distance at which they cooled through their Curie temperature, providing evidence about which formation mechanism caused their melting and potentially shedding light on accretionary processes within the protoplanetary disk. The Bishunpur LL3.1 meteorite is among the most pristine ordinary chondrites, having both limited thermal and aqueous alteration and a known (magnetic) history on Earth. As such, its chondrules have the potential to preserve primary remanence from their formation if the recorders are capable of maintaining a stable magnetic state over timescales greater than 4.6 Ga. Previous work has shown that dusty olivine—iron nanoparticle-bearing silicate that constitutes a proportion of the chondrules of Bishunpur—is an stable recorder over these timescales even at temperatures approaching the Curie temperature of iron. In bulk measurements, however, the paleointensity signal from the chondrules is masked by magnetic phases on chondrule rims and in the matrix, necessitating a technique that allows the contribution of different signals to be distinguished. Scanning SQUID microscopy presents an ideal solution as it produces a map of magnetic field measurements with a spatial resolution of 10s of ?m from which the absolute magnetization can be calculated, allowing the paleointensity and demagnetization behavior of the chondrules to be directly observed. This work presents the demagnetization sequence of a thin section of Bishunpur as well as rock magnetic measurements acquired on the scanning SQUID microscope and a bulk moment magnetometer. Bulk measurements of the NRM are dominated by signal from the matrix and chondrule rim, but the sensitivity of the scanning SQUID technique allows weak signals from individual chondrules to be identified which are stable in alternating-field demagnetization through 290 mT. These signals can be modeled as single dipoles, which means the magnetization of dusty olivine regions can be quantitatively measured. Calibration curves from synthetic analogues will permit the paleointensity of these regions to be determined and combined with SEM observations of the microstructure, used to provide a unique line of evidence about chondrule formation and the process of accretion in the solar nebula.

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

    NASA Astrophysics Data System (ADS)

    Ruzicka, Alex; Floss, Christine; Hutson, Melinda

    2012-02-01

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

  1. Chondrule Destruction in Nebular Shocks

    NASA Astrophysics Data System (ADS)

    Jacquet, Emmanuel; Thompson, Christopher

    2014-12-01

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

  2. MAGNESIUM ISOTOPIC COMPOSITION OF CAIs AND CHONDRULES FROM CR CHONDRITES. B. , M. Gounelle1

    E-print Network

    Technische Universiteit Delft

    MAGNESIUM ISOTOPIC COMPOSITION OF CAIs AND CHONDRULES FROM CR CHONDRITES. B. Mimoun1 , M. Gounelle1. Introduction: The magnesium isotopic composi- tion of primitive extraterrestrial materials is worth measuring.g. 10]. Figure 1: The magnesium isotopic composition of CAIs in CR chondrites. Error bars are 1

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

    NASA Technical Reports Server (NTRS)

    Jones, Rhian H.

    1993-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    Two rare spinel-bearing Al-rich chondrules are identified in chondrite finds from Roosevelt County, New Mexico-RC 071 (L4) and RC 072 (L5). These chondrules have unusual mineralogies dominated by highly and asymmetrically zoned Al-Cr-rich spinels. Two alternatives exist to explain the origin of this zoning-fractional crystallization or metamorphism. Fractional crystallization formed the zoning of the trivalent cations and caused a localized depletion in chromites around the large Al-Cr-rich spinels. Diffusive exchange and partitioning of Fe and Mg between olivine and spinel during parent-body metamorphism can explain the asymmetric zoning of these elements. The bulk compositions of the chondrules suggest affinities with the Na-Al-Cr-rich chondrules, as would be expected from the abundance of Al-Cr-rich spinels. The most important factors are the temperature to which the molten chondrule was heated and the cooling rate during crystallization. These two chondrules cooled rapidly from near the liquidus, as indicated by the zoning, occurrence and sizes of spinels, radiating chondrule textures and localized chromite depletions.

  5. The formation conditions of chondrules and chondrites.

    PubMed

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

    2008-06-20

    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. PMID:18566282

  6. Stardust to Planetesimals: A Chondrule Connection?

    NASA Technical Reports Server (NTRS)

    Paque, Julie; Bunch, Ted

    1997-01-01

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

  7. Formation of Layered Chondrules in CR2 Chondrites: A Petrologic and Oxygen Isotopic Study

    NASA Astrophysics Data System (ADS)

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

    1992-07-01

    Introduction: Spectacular, large (up to 1 cm) concentrically layered chondrules are conspicuous components of the CR2 chondrites [1-5]. To gain a better understanding of the formation of layered chondrules and their implications, we carried out a petrologic investigation of these chondrules in all CR2 chondrites, and a combined petrologic-oxygen isotopic study of the cores and rims of three layered chondrules from El Djouf 001. Study of separated chondrules from other CR2 chondrites is under way. Results: Layered chondrules in CR2 chondrites generally consist of (A) a silicate-rich core, surrounded by (B) a continuous or discontinuous FeNi mantle followed by (C) an anhydrous silicate-rich rim, +- (D) a serpentine-rich layer, +- (E) a matrix-like layer. Cores (A) consist of olivine (ol) and/or pyroxene (pyx) phenocrysts +- blebs of FeNi set in a feldspathic (feld) glassy or altered (chloritic) mesostasis. Core silicates are magnesian (Fa <=6) and, in some cases, zoned with an increase in FeO (up to 3 wt%), MnO and Cr2O3, at grain margins. Margins approach or equal the composition of silicates in the associated rim (C). Metal blebs have up to 14.3% Ni and a solar Ni:Co ratio. The metallic mantle (B) typically has lower Ni (up to 8.2%) and Co, and also has a solar Ni:Co ratio. Rims (C) consist of ol and/or pyx, a feld component +- FeNi metal; Pyx poikilitically encloses ol. Rims (C) have important general characteristics in comparison to their associated cores (A): (1) they are finer grained; (2) ol has higher (or similar) Fe/(Fe+Mg), Mn and Cr; (3) bulk compositions have higher Na, K and lower Al, Ca; (4) FeNi metal has lower Ni and Co, even lower than the associated metallic mantle, and has a solar Ni:Co ratio. Many layered chondrules contain an outermost serpentine-rich (D) and/or a matrix-like (E) layer. The outermost matrix-like layer (E) is petrologically similar to interstitial matrix and dark inclusions [5]. Cores and rims of three layered chondrules separated from El Djouf 001 have layers A, B and C; none have layers D or E. Oxygen isotopic compositions of the cores (A) and associated rims (C) of these chondrules (figure) lie on the CR2 mixing line (slope=0.7) [5], with each rim having heavier oxygen than its core. CR matrix compositions generally have even heavier oxygen than the rims (C). All of this is analogous to layered Allende chondrules [6], which lie on the Allende mixing line, have rims with heavier oxygen, and some rims have lighter oxygen than the cores of other chondrules. Conclusions: Chondrule cores (A) and rims (B-E) are derived from the same reservoir of materials. Rim (C) materials accreted onto solidified cores (A) and were subsequently melted (or partially melted). Since these rims (C) have higher volatile contents than the cores (A), they may have experienced lesser volatile loss or formed from more volatile-rich precursors. CR chondrite formation may be reflected in the CR layered chondrules, and may be a process of progressive accretion (in time and possibly in space) of chondritic materials at continuously lower temperatures, with decreasing volatile loss or increasing volatile enrichment, and evolution of oxygen toward heavier compositions. References: [1] Mason B. and Wiik H.B. (1962), Amer. Mus. Novit. 2106, 11 pp. [2] McSween H.Y. (1977), GCA 41, 1777-1790. [3] Prinz et al. (1985) LPSC XVI, 677-678. [4] Kring (1991) EPSL 105, 65-80. [5] Weisberg et al. (1992) GCA, in press. [6] Rubin et al. (1990) EPSL 96, 247-255.

  8. 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.

  9. 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.

  10. Compositional and genetic relationship between chondrules, chondrule rims, metal, and matrix in the Renazzo chondrite

    NASA Astrophysics Data System (ADS)

    Kong, Ping; Palme, Herbert

    1999-11-01

    Individual chondrules, coarse and fine-grained metal, chondrule rims, and matrix samples were separated from the Renazzo chondrite (CR2) and studied by instrumental neutron activation analysis. Both Renazzo chondrule and matrix fractions have CI Cr/Mg concentration ratios, unlike chondrules from other classes of chondrites, which have fractionated Cr/Mg ratios. This and other arguments suggest that Renazzo chondrules and matrix formed in the same nebular region. In Renazzo, fine-grained metal - the dominant metal component, is mostly located inside chondrules or in chondrule rims. Matrix contains few coarse metal grains. Both types of metal, fine and coarse, exhibit similar chemical signatures, comparatively high in Cr and low in Ni, suggesting a genetic relationship. Although metal is mostly contained in chondrules, chondrules and matrix of Renazzo have similar common siderophile/lithophile abundance ratios. This may imply that Renazzo chondrules and metal were formed by reduction of oxidized precursors compositionally similar to CI chondrites. The CI-like concentrations of Sc, Mg, Se, and Zn in Renazzo matrix are consistent with this inference. The differences in siderophile element pattern between chondrules, chondrule metal, and matrix indicate evaporation and recondensation of volatile elements during chondrule formation. Recondensation of evaporated elements was incomplete and the degree of recondensation correlates with element volatility. The higher-than-CI K/Mg, Na/Mg, and Ga/Fe ratios of Renazzo matrix may reflect recondensation of K, Na, and Ga into the matrix. The CI Se/Sc and Zn/Sc concentration ratios of the matrix, however, reflect very limited degrees of recondensation of Se and Zn into matrix. The presence of abundant phyllosilicates and organic material in Renazzo matrix requires a low background temperature (<200 K) during formation of the Renazzo meteorite. Partial recondensation of volatile elements in a cold nebular environment implies instantaneous agglomeration of the Renazzo chondrite following chondrule formation.

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

    Northwest Africa (NWA) 5717 is a highly primitive ordinary chondrite of petrologic type 3.05 with ubiquitous fine-grained chondrule rims [1, 2]. Rims appear around approximately 60% of chondrules and are comprised of micron-sized mineral and lithic fragments and microchondrules that are embdedded in an FeO-rich submicron groundmass that compositionally resembles fayalitic olivine. Some rim clasts appear overprinted with FeO-rich material, suggesting secondary alteration that postdates rim formation. Here we present a microanalytical (TEM) study of the submicron component (i.e. the groundmass) of the rims in order to determine the crystal structures and compositions of their constituent phases and decipher the accretion and alteration history recorded in rims.

  12. The conditions of chondrule formation, Part I: Closed system

    NASA Astrophysics Data System (ADS)

    Hezel, Dominik C.; Palme, Herbert

    2007-08-01

    Mixing was an important process in the early solar nebula and is often used as an argument to explain the compositional scatter among chondrules—mm-sized, once molten silicate spherules in chondritic meteorites. If it is hypothesized that chondrules only acted as closed systems and the scatter in chondrule bulk chemical compositions is only the result of mixing heterogeneous precursor grains—the basic components of chondrules—, it is in turn possible to determine the sizes of the precursor grains using statistical calculations. In order to reproduce the observed compositional scatter in chondrules not more than ˜10 precursor grains should contribute to a single chondrule, each with a diameter of several 100 ?m. This finding has important implications for the conditions of chondrule formation and replaces the so far widely accepted model that chondrules formed from fine-grained "dust-balls". Chondrules rather formed from coarse-grained precursor aggregates with variable amounts of ?m-fine matrix material. As a consequence, only chondrite matrix or interstellar material winnows as precursor material. Large grains of variable composition serving as precursor grains must have been formed prior to chondrule formation. Chondrules probably have not been their immediate precursors, as only 1-2 chondrule recycling steps would have homogenized bulk chondrule compositions. Chondrule recycling can therefore only have occurred to a limited extent. Chondrule formation needed at least three steps: (1) production of large and heterogeneous chondrule precursor grains, (2) agglomeration of large precursor grains and fine-grained precursors into aggregates, (3) formation of chondrules during transient heating events. Al-rich chondrules can in this context be explained by the admixture of CAIs to either chondrule precursors or a population of existing chondrules.

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

    NASA Technical Reports Server (NTRS)

    Lauretta, Dante S.

    2004-01-01

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

  14. Genetic Relationships Between Chondrules, Rims and Matrix

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    The most primitive chondrites are composed of chondrules and chondrule fragments, various types of inclusions, discrete mineral grains, metal, sulfides, and fine-grained materials that occur as interchondrule matrix and as chondrule/inclusion rims. Understanding how these components are related is essential for understanding how chondrites and their constituents formed and were processed in the solar nebula. For example, were the first generations of chondrules formed by melting of matrix or matrix precursors? Did chondrule formation result in appreciable transfer of chondrule material into the matrix? Here, we consider three types of data: 1) compositional data for bulk chondrites and matrix, 2) mineralogical and textural information, and 3) the abundances and characteristics of presolar materials that reside in the matrix and rims. We use these data to evaluate the roles of evaporation and condensation, chondrule formation, mixing of different nebular components, and secondary processing both in the nebula and on the parent bodies. Our goal is to identify the things that are reasonably well established and to point out the areas that need additional work.

  15. Photophoretic Strength on Chondrules. 1. Modeling

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Photophoresis is a physical process that transports particles in optically thin parts of protoplanetary disks, especially at the inner edge and at the optical surface. To model the transport and resulting effects in detail, it is necessary to quantify the strength of photophoresis for different particle classes as a fundamental input. Here, we explore photophoresis for a set of chondrules. The composition and surface morphology of these chondrules were measured by X-ray tomography. Based on the three-dimensional models, heat transfer through illuminated chondrules was calculated. The resulting surface temperature map was then used to calculate the photophoretic strength. We found that irregularities in particle shape and variations in composition induce variations in the photophoretic force. These depend on the orientation of a particle with respect to the light source. The variation of the absolute value of the photophoretic force on average over all chondrules is 4.17%. The deviation between the direction of the photophoretic force and illumination is 3.°0 ± 1.°5. The average photophoretic force can be well approximated and calculated analytically assuming a homogeneous sphere with a volume equivalent mean radius and an effective thermal conductivity. We found an analytic expression for the effective thermal conductivity. The expression depends on the two main phases of a chondrule and decreases with the amount of fine-grained devitrified, plagioclase-normative mesostasis up to factor of three. For the chondrule sample studied (Bjurböle chondrite), we found a dependence of the photophoretic force on chondrule size.

  16. The origin of chondrules at jovian resonances

    PubMed

    Weidenschilling; Marzari; Hood

    1998-01-30

    Isotopic dating indicates that chondrules were produced a few million years after the solar nebula formed. This timing is incompatible with dynamical lifetimes of small particles in the nebula and short time scales for the formation of planetesimals. Temporal and dynamical constraints can be reconciled if chondrules were produced by heating of debris from disrupted first-generation planetesimals. Jovian resonances can excite planetesimal eccentricities enough to cause collisional disruption and melting of dust by bow shocks in the nebular gas. The ages of chondrules may indicate the times of Jupiter's formation and dissipation of gas from the asteroidal region. PMID:9445468

  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

    E-print Network

    Loesche, Christoph; Teiser, Jens; Friedrich, Jon M; Bischoff, Addi

    2013-01-01

    Photophoresis is a physical process that transports particles in optical thin parts of protoplanetary disks, especially at the inner edge and at the optically 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 was 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 variations of the absolute value of the photophoretic force on average over all chondrules is $4.17\\%$. The deviation between the directio...

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  20. An Evaluation of Microcomputer-Based Strain Analysis Techniques on Meteoritic Chondrules

    NASA Astrophysics Data System (ADS)

    Hill, H. G. M.

    1995-09-01

    Introduction: Chondrule flattening and distinct foliation are preserved in certain chondrites [1] and have been interpreted, by some, as evidence of shock-induced pressure through hypervelocity impacts on parent bodies [2]. Recently, mean aspect ratios of naturally and artificially shocked chondrules, in the Allende (CV3) chondrite, have been correlated with shock intensity [3] using established shock stage criteria [4]. Clearly, quantification of chondrule deformation and appropriate petrographic criteria can be useful tools for constraining parent body shock history and, possibly, post-shock heating [3]. Here, strain analysis techniques (R(sub)(f)/phi and Fry) normally employed in structural geology, have been adapted and evaluated [5], for measuring mean chondrule strain, and orientation. In addition, the possible use of such strain data for partial shock stage classification is considered. R(sub)(f)/phi and Fry Analysis: The relationship between displacement and shape changes in rocks is known as strain [6] and assumes that an initial circle with a unit radius is deformed to form an ellipse, the finite strain ellipse (Rf). The strain ratio (Rs) is an expression of the change of shape. The orientation of the strain ellipse (phi) is the angle subtended between the semi-major axes and the direction of a fixed point of reference. Generally, log mean Rf ~ Rs and, therefore, the approximation Rf = Rs is valid. For chondrules, this is reasonable as they were originally molten, or partially-molten, droplets [7]. Fry's 'center-to-center' geological strain analysis technique [8] is based on the principle that the distribution of particle centers in rocks can sometimes be used to determine the state of finite strain (Rf). Experimental Techniques: The Bovedy (L3) chondrite was chosen for investigation as it contains abundant, oriented, elliptical chondrules [5]. Hardware employed consisted of a Macintosh microcomputer and a flat-bed scanner. Chondrule outlines, obtained from macrophotographic tracings of four complete thin-sections (total area 8.2 cm2) and a sawn slab (49.45cm2), were digitally scanned using application Ofoto v. 1.0.0^(TM). Chondrule outline (pict) files were then exported to a fabric analysis program, Image v. 1.44, and Rf values obtained thereafter exported to a spreadsheet environment for manipulation. Fry analysis was undertaken with an interactive program, Fry v. 5.0 [9] using the same pict files as before. Chondrule central points were manually inserted and center-to-center distances, when calculated, were displayed on screen in a way which echoes mean chondrule strain and orientation. Results and Conclusion. 364 chondrule outlines (three thin-sections and a sawn slab) were analysed by R(sub)(f)/phi and Fry techniques. In its present form, the Fry technique was judged to be unsuited to chondrule shape analysis as it is too dependant on grain size, i.e. the smallest grain, and the need for a planar homogenous sample bearing several hundred grains [8]. Recent developments in the Fry technique [10] may make it more suitable for chondrule analysis. Representative strain (Rf) data obtained for parallel thin-sections Bovedy M5385b and M5385c (total of 158 chondrules) were 1.49 and 1.41 respectively. Corresponding phi values were 115.0 degrees and 114.6 degrees respectively (with respect to a fixed reference point). Rf data together with petrographic shock features noted, mostly in olivine (e.g. planar fractures, undulatory extinction and weak mosaicism), were suggestive of shock stage S3 [4]. The degree of chondrule flattening and the nature of the (S3) shock effects observed are comparable with artifically flattened chondrules belonging to the same shock stage [3, 11]. The R(sub)(f)/phi technique evaluated was found to be more precise and quantitative than other methods previously employed for measuring maximum and minimum chondrule axes and orientation. Furthermore, it can provide reliable strain (axial, orientation) data for material subjected to very low grades of shock which would otherwise be difficult to

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

    NASA Astrophysics Data System (ADS)

    Béjina, Frédéric; Sautter, Violaine; Jaoul, Olivier

    2009-01-01

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

  2. 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:

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

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

    NASA Astrophysics Data System (ADS)

    McSween, H. Y., Jr.

    1985-09-01

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

  5. Artificial meteor ablation studies: Olivine

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

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

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1987-07-01

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

  8. Experimental Reproduction of Type 1B Chondrules

    NASA Technical Reports Server (NTRS)

    Lofgren, G. E.; Le, L.

    2002-01-01

    We have replicated type 1B chondrule textures and compositions with crystallization experiments in which UOC material was melted at 1400 deg.C and cooled at 5-1000 deg.C/hr using graphite crucibles in evacuated silica tubes to provide a reducing environment. Additional information is contained in the original extended abstract.

  9. Revisiting Jovian-resonance Induced Chondrule Formation

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  10. Alkali elemental and potassium isotopic compositions of Semarkona chondrules

    USGS Publications Warehouse

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

    2005-01-01

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

  11. 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.

  12. Evaporation of nebular fines during chondrule formation

    NASA Astrophysics Data System (ADS)

    Wasson, John T.

    2008-06-01

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

  13. The Origin of Silica-Rich Chondrules and Clasts in Ordinary and Carbonaceous Chondrites

    NASA Astrophysics Data System (ADS)

    Ruzicka, A.; Boynton, W. V.

    1992-07-01

    Chondrules and clasts containing a silica mineral or a silica glass are a minor but important constituent in many ordinary (Planner, 1983; Brigham et al., 1986) and some carbonaceous (Olsen, 1983) chondrites, and have been considered somewhat enigmatic. The recent discovery of a large, silica-rich igneous clast in the Bovedy (L3) chondrite (Ruzicka and Boynton, 1992) sheds light on the possible origin of other silica-rich objects. As discussed in Ruzicka and Boynton (1992), the Bovedy clast probably crystallized from an Lchondrite silicate magma in a relatively large magma body that had previously undergone olivine fractionation. The existence of similar fractionating magmas can also account for the origin of other silica-rich objects, as shown below. Pyroxene-silica objects. Chondrules (drop-formed objects) and clasts (irregularly shaped objects) consisting essentially of a mixture of orthopyroxene (opx) and a silica mineral (SiO2) have been found in various ordinary chondrites (Brigham et al., 1986). Brigham and coworkers (1986) proposed that these objects could be condensates. However, fractional crystallization of a liquid similar in composition to the Bovedy clast (Ruzicka and Boynton, 1992) will produce (Morse, 1980) the following solids: (a) orthopyroxenite, (b) an opx + SiO2 rock, and (c) a feldspar, SiO2 and pyroxene rock. Brecciation or remelting of rock (b), which lies on the opx-SiO2 join in the cristobalite primary crystallization field, could have produced the pyroxene-silica objects of Brigham et al. (1986) and Planner (1983). Fayalite-silica clasts. These clasts consist of SiO2, olivine (ol, Fa(sub)63-96), and highly variable amounts of opx and clinopyroxene (Brigham et al., 1986). Brigham et al. (1986) discussed various origins for these objects and concluded that none were entirely satisfactory, but that an accidental mixture of the various phases in them was probably the best hypothesis. However, a rock mainly containing SiO2 and fayalitic ol (Fa(sub)>59) can form as a late-stage differentiate of a melt of any ol + opx or opx + SiO2 mixture (Bowen and Schairer, 1935). The presence of some opx in these objects suggests disequilibrium and incomplete removal of opx from the fractionating liquids. The absence of appreciable feldspar in the fayalite-silica objects may indicate that the parent melt formed from an opx or opx + SiO2 cumulate. Murchison chondrules. Olsen (1983) described two chondrules in Murchison that contain opx (En(sub)99-97Wo(sub)O.5-0.7) set in a groundmass of feldspar or feldspathic glasses, Mgclinopyroxene, and pods of silica glass. Cr-bearing metal also occurs in the chondrules. Olsen (1983) proposed that the two chondrules experienced a nearly equilibrium cooling history from a melt composition projecting in the opx primary crystallization field. These melt compositions are best explained as the result of ol and opx fractionation from a magma of CM-like composition. CM-chondrites have a high bulk CaAl2Si2O7:SiO2 ratio compared to L-chondrites, and this can account for the more feldspathic compositions of the Murchison chondrules compared to that of the Bovedy clast (Ruzicka and Boynton, 1992). Remelting of the differentiate produced by ol and opx fractionation could have formed the two objects. Their Mg-rich pyroxene compositions imply either that the initial magmatic or that the chondrule-forming event was accompanied by reduction. References Bowen N.L. and Schairer J.F. (1935) The system MgO-FeO-SiO2. Am. J. Sci., 5th ser., 29, 151-217. Brigham C.A., H. Yabuki, Z. Ouyang, M.T. Murrell, A. El Goresy and D.S. Burnett (1986) Silica-bearing chondrules and clasts in ordinary chondrites. Geochim. Cosmochim. Acta. 50, 1655-1666. Morse S.A. (1980) Basalts and Phase Diagrams. An Introduction to the Quantitative Use of Phase Diagrams in Igneous Petrology. Springer-Verlag. 493 pp. Olsen E.J. (1983) SiO2-bearing chondrules in the Murchison meteorite. In Chondrules and Their Origins (ed. E.A. King), pp. 223-234. Lunar and Planetary Institute, Houston. Planner H.N. (1983) Phase separation in

  14. 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.

  15. 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. Investigation of the magnesium isotopic compositions of chondrules can place stringent constraints on the timing

  16. In Situ Investigation of Preirradiated Olivines in CM Chondrites

    NASA Astrophysics Data System (ADS)

    Metzler, K.

    1993-07-01

    Most CM chondrites are breccias that contain fragments of primary rock representing densely packed agglomerates of chondrules, CAIs, etc., all of which are mantled by thick layers of fine-grained mineral dust [1]. These dust mantles seem to be the result of dust sampling by the various components during their isolated existence in the solar nebula prior to the formation of the CM parent body [1]. Metzler et al. [1] concluded that these rock fragments are well-preserved remnants of the freshly accreted CM parent body(ies). There is an opposing hypothesis that favors an origin of the dust mantles in an active regolith on the CM parent body [e.g., 2]. A list of arguments against the latter view is given by Metzler et al. [1], including a hint at the absence of solar-wind-implanted gases in dust mantles and in fragments of primary rock. In analogy to brecciated ordinary chondrites and lunar breccias, the most probable residence of the solar gases in CM chondrites is their clastic matrix. The same holds for track-rich olivines that were observed in CM chondrites. The occurrence of these grains in the clastic matrix and their absence in the primary rock would give an additional argument for the idea of a dust mantle origin in the solar nebula rather than in a planetary regolith. To answer this important question, mosaics of backscattered electron images of several large polished thin sections of Murchison and Cold Bokkeveld were prepared. The thin sections (1.5-5 cm^2 each) were etched in a WN solution [3] for about 4 hr to reveal the heavy ion tracks in olivines. Results: The background GCR track density produced during meteoroid transit is on the order of 10^4 tracks/cm^2, as was previously observed by [4]. Following the definition given by Goswami and Lal [4], olivines with track densities >10^5 tracks/cm^2 were classified as preirradiated grains and were found in both meteorites in a very small quantity. In both meteorites, 39 preirradiated isolated olivine grains were found in the clastic matrix, whereas the investigated fragments of primary rock do not contain preirradiated olivines. In Murchison about 1.8% (15 out of 850 investigated grains) of the isolated olivines in the clastic matrix show high track densities in the range between 1.9 x 10^6 and >5 x 10^7, comparable to the results of Goswami and co-workers [4,5]. Both Fe-poor and Fe-rich olivines with grain sizes between 40 and 710 micrometers were found to be preirradiated. Track gradients were found in 33% of these olivines, which is very similar to the values obtained by Goswami and Lal [4] and identical to those obtained by MacDougall and Phinney [6]. About 0.4% (2 out of 530) of the investigated olivine-bearing chondrules and chondrule fragments are preirradiated. In the case of Cold Bokkeveld, 3.7% (24 out of 650) of the isolated olivines show high track densities. Thirteen of these 24 grains were found to be concentrated in a distinct inclusion (1 x 4 mm) that is characterized by its elongated appearence and clastic fabric. The track densities of its preirradiated olivines show a very narrow range, indicating a common irradiation history of these grains. The petrography of this inclusion is currently under investigation. Conclusions: Track-rich (preirradiated) olivines in CM chondrites occur exclusively in the clastic matrix of these meteorites, comparable to observations in brecciated ordinary chondrites. Fragments of primary rock in CM chondrites do not contain solar-wind-implanted gases [1] or preirradiated grains. This confirms the view that the dust mantles around various components of these rocks are the products of dust accretion in the solar nebula rather than of regolith processes on the parent body surface. References: [1] Metzler K. et al. (1992) GCA, 56, 2873. [2] Kerridge J. (1992) personal communication. [3] Krishnaswami S. et al. (1971) Science, 174, 287. [4] Goswami J. N. and Lal D.(1979) Icarus, 40, 510. [5] Goswami J. N. and MacDougall J. D. (1983) Proc. LPSC 13th, in JGR, 88, A755. [6] MacDougall J. D. and Phinney D. (1977) Proc. LS

  17. Porphyritic Olivine-Pyroxene Clast in Kaidun: First Discovery of an Ordinary Chondrite Clast?

    NASA Technical Reports Server (NTRS)

    Mikouchi, T.; Makishima, J.; Koizumi, E.; Zolensky, M. E.

    2005-01-01

    Kaidun is an enigmatic meteorite showing a micro-brecciated texture composed of variable kinds of lithic clasts and mineral fragments. The constituent components range from primitive chondritic materials to differentiated achondritic materials, and thus believed to have originated from a large parent body accumulating materials from many different bodies in the asteroid belt. One of the interesting observations is that no ordinary chondrite component has been found yet, although C and E chondrites components are abundant. In this abstract, we report mineralogy of the clast (Kaidun #15415- 01.3.13a) showing a porphyritic olivine-pyroxene chondrule-like texture similar to those found in unequilibrated ordinary chondrites.

  18. 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.

  19. Chondrules from the Earth and Moon: A Review

    NASA Astrophysics Data System (ADS)

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

    1995-09-01

    Since chondrules are arguably the most important constituent of chondritic meteorites, deciphering their origin would constitute a major step towards understanding early solar system processes. We here draw attention to proposed chondrules found in lunar and terrestrial samples since their existence on these parent bodies would seriously constrain theories for the origin of meteoritic chondrules. Terrestrial chondrules. Graup has reported lithic chondrules in the crater suevite and both fluid drop and lithic chondrules in the fall-out suevite of the Ries Crater [1, see also 2]. He observed 115 fluid drop and 44 lithic chondrules (as well as 10 glass spherules). Fourteen were shown in figures. He argued that textures and sizes, and thus modes of formation, are very similar to those of meteoritic chondrules. The Ries chondrules often have fine-grained rims similar to those found on meteoritic chondrules and similar origins have been proposed for both kinds of rim [1. 3, 4]. There is little available data beyond Graup's initial descriptions and these objects require further study. Lunar chondrules. Chondrules have been found in Apollo 11, 14, 15, 16 and Luna 16 soils and breccias [5-11]. Both fluid drop and lithic chondrules have been reported, many with fine-grained rims. Again, because of the similarity in texture, similar formation details to those of meteoritic chondrules have been proposed for both the chondrules and their rims. Most lunar chondrules have ANT compositions, as opposed to basaltic compositions, either because nucleation of these compositions is favored or because of the more intense impact history of the lunar highlands [e.g. 11]. Lunar agglutinates, which constitute 50 vol% of some soil samples, have histories involving reduction and evaporation similar to those of group A meteoritic chondrules [12]. They differ from the chondrules mainly in size, shape, the presence of unmelted dust particles and abundant vesicles [12]. At the moment there appear to be only two significant differences hetween lunar, terrestrial and meteoritic chondrules, their compositions and their place of origin. Further study, especially of the terrestrial chandrules, is required to confirm this. In many respects, size, texture, the presence of rims and the existence of both droplet and lithic forms, they resemble each other and are distinguishable from simple melt spherules which are relatively common on the Moon. The occurrence of true chondrules on three planetary bodies, especially when associated with impact, and differing only in that their compositions, would suggest that the meteoritic chondrules are impact in origin. The differences in chondrule abundance on the meteorite bodies and other planetary objects could reflect differences in parent body size, impact mechanics, surface processes, and selection effects surrounding the transfer of meteorites to earth and their passage through the atmosphere. References: [1] Graup G. (1981) EPSL, 55, 407-418. [2] Newsom H. E. (1990) GSA Spec. Paper 247, 195-206. [3] Hewins R. H. (1989) Symp. Antarc. Meteorites, 2, 200-220. [4] Huang S. et al. (1995) Icarus, submitted. [5] Fredriksson K. et al. (1970) Science, 167, 664-666. [6] Kurat G. et al. (1972) Proc. LSC 3rd, 707-721. [7] King E. A. et al. (1972) Science, 175, 59-60. [8] King E. A. et al. (1972) Proc. LSC 3rd, 673-686. [9] Bunch T. E. et al. (1972) Nature, 239, 57-59. [10] Holder J. and Ryder G. (1995) Lunar News, 58, 7. [11] Keil K. et al. (1972) EPSL, 13, 243-256. [12] McKay D. S. et al. (1991) in Lunar Sourcebook (Heiken G. H. et al., eds.), 285-356, Cambridge Univ.

  20. 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.

  1. Helium Diffusion in Olivine

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  2. Primary Oxygen Isotope Signatures of Chondrules in R Chondrites

    NASA Astrophysics Data System (ADS)

    Kita, N. T.; Tenner, T. J.; Nakashima, D.; Ushikubo, T.; Bischoff, A.

    2013-09-01

    Chondrules in R3 clast from NWA 753 (R3-5) breccia show oxygen isotope ratios similar to those in LL3 chondrites. ?^17O values of most chondrules distribute between 0‰ and +1.5‰, significantly lower than that of bulk R chondrites (~2.7‰).

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

    NASA Astrophysics Data System (ADS)

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

    1987-11-01

    This paper presents results on neutron activation analyses of the interiors and the abraded surfaces of seven chondrules from Semarkona chondrite. The results showed that six of seven chondrule rims have enhanced contents of siderophiles and chalcophiles relative to chondrule interiors, indicating that, during chondrule formation, metal/sulfide melts migrated to the exterior of the chondrule; later reheating caused this material to spread out into fine-grained rim material. For nonvolatile elements, the lithophile and siderophile element abundance patterns in the surfaces are generally similar to those in the corresponding interiors, indicating that the surface and the interior metal might have originated from a single precursor. The volatile to moderately-volatile elements K, As, and Zn tend to be enriched in the surface, compared with other elements of similar mineral affinity.

  4. Titanium isotopic anomalies in chondrules from carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Niemeyer, S.

    1988-02-01

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

  5. Elemental composition of individual chondrules from ordinary chondrites.

    NASA Technical Reports Server (NTRS)

    Osborn, T. W.; Schmitt, R. A.; Smith, R. H.

    1973-01-01

    Sequential nondestructive neutron activation analysis was used to determine the bulk abundance of Fe, Al, Na, Mn, Cr, Sc, Co, and Ir in approximately 300 individual chondrules from 16 chondrites representing the H(3-5), L4, and LL(3-6) compositional and petrologic classes. The histograms indicate that the most probable abundances for lithophilic elements, except Cr, are enriched in the chondrules, while the siderophilic elements are depleted in the chondrules compared to the whole chondrite. Some of the abundance populations, such as Al and Fe, appear to be multimodal. Systematic variations in the composition of the chondrules with increasing petrologic type were observed; most consistent are an increasing Na-Al and Cr-Al correlation, a decreasing Na-Mn correlation, increasing Na abundance, and decreasing Na and Mn dispersions among chondrules.

  6. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    The effect of oxygen fugacity, f(O2), on the partitioning behavior of Ni and Co between olivine, silicate melt, and metal was investigated in the CaO-MgO-Al2O3-SiO2-FeO-Na2O system, an analogue of a chondrule composition from an ordinary chondrite. The conditions were 1350 C and 1 atm, with values of f(O2) varying between 10 exp -5.5 and 10 exp -12.6 atm (i.e., the f(O2) range relevant for crystal/liquid processes in terrestrial planets and meteorite parent bodies). Results of chemical analysis showed that the values of the Ni and Co partitioning coefficients begin to decrease at values of f(O2) that are about 3.9 log units below the nickel-nickel oxide and cobalt-cobalt oxide buffers, respectively, near the metal saturation for the chondrule analogue composition.

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

    E-print Network

    3127 (LL3.1), Sahara 97210 (LL3.2), Wells (LL3.3), Chainpur (LL3.4), and Sahara 98175 (LL3.5)] were composition according to meteorite subtype, but shock melting in Sahara 97210 resulted in the injection

  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. 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.

  11. Flash heating is required to minimize sodium losses from chondrules

    NASA Technical Reports Server (NTRS)

    Yu, Y.; Hewins, R. H.; Connolly, H. C., Jr.

    1994-01-01

    Chondrules were formed by high-temperature melting events, but do not always show Na depletion compared to CI chondrites, though extensive Na loss has been found in previous isothermal experiments. While Na loss can be prevented by high partial pressure of Na in the nebula, many people favor a flash-heating mechanism to reduce the Na loss from chondrule melts. To examine the validity of the flash-heating hypothesis, we have conducted a series of flash-heating experiments and observed Na loss rate under different conditions. Our results support the flash heating as a plausible heating mechanism to form chondrules.

  12. Ca-Al-rich chondrules and inclusions in ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Bischoff, A.; Keil, K.

    1983-01-01

    Ca-Al-rich objects, hitherto mostly found in carbonaceous chondrites, are shown to be widespread, albeit rare, constituents of type 3 ordinary chondrites. Widespread occurrence and textural similarities of Ca-Al-rich chondrules to common, Mg-Fe-rich chondrules suggest that they formed by related processes. It is suggested in this article that Ca-Al-rich chondrules were formed by total melting and crystallization of heterogeneous, submillimeter- to submillimeter-sized dustballs made up of mixtures of high-temperature, Ca-Al-rich and lower-temperature, Na-K-rich components.

  13. Bulk compositions of Al-rich chondrules in ordinary and carbonaceous chondrites: Variations and similarities

    NASA Technical Reports Server (NTRS)

    Bischoff, A.

    1984-01-01

    An extended study of ordinary chondrites revealed that chondrules exist which are transitional in composition between Al-rich and Mg-Fe-rich types in contrast to the finding of Wlotzka, who inferred a gap in compositions between the Ca-Al-rich and Mg-Fe-rich chondrules. Transitional chondrule bulk compositions are plotted. They show that no compositional gap exists between the Mg-Fe-rich and Al-rich chondrules. Chondrules with Na2O-contents 3.0 wt.% are indicated. Variable CaO/Na2O-ratios for chondrule bulk compositions exist, similar to what was described for the subgroups of Al-rich chondrules. Al-rich and transitional chondrules similar to those described above were found also in carbonaceous chrondrites. Thirty-nine chondrules from the carbonaceous chondrites Leoville, Allende, Vigarano and Colony were investigated. Their bulk compositions in terms of Al2O3 vs. CaO were plotted.

  14. Rates and mechanisms of Fe-Mg interdiffusion in olivine

    Microsoft Academic Search

    Sumit Chakraborty

    1997-01-01

    Fe-Mg interdiffusion rates have been measured in olivine solid solutions using the diffusion couple technique. Measured diffusion rates along (001) at fo2 = 10 -2 bars and between 980øC and 1300øC are found to be slower by about 2 orders of magnitude, compared to previous studies with the exception of some isolated data points of Misener (1974). There is no

  15. 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

  16. Elemental composition of individual chondrules from ordinary chondrites

    Microsoft Academic Search

    T. W. Osborn; R. H. Smith; R. A. Schmitt

    1973-01-01

    Sequential non-destructive neutron activation analysis was used to determine the bulk abundance of Fe, Al, Na, Mn, Or, Sc, Co and Ir in approximately 300 individual chondrules from 16 chondrites representing the H (3-5), L4 and LL(3-6) compositional and petrologic classes. For some of the chondrules, Si, Ni, Ca and V were also determined. The histograms indicate that the most

  17. A critical analysis of shock models for chondrule formation

    NASA Astrophysics Data System (ADS)

    Stammler, Sebastian M.; Dullemond, Cornelis P.

    2014-11-01

    In recent years many models of chondrule formation have been proposed. One of those models is the processing of dust in shock waves in protoplanetary disks. In this model, the dust and the chondrule precursors are overrun by shock waves, which heat them up by frictional heating and thermal exchange with the gas. In this paper we reanalyze the nebular shock model of chondrule formation and focus on the downstream boundary condition. We show that for large-scale plane-parallel chondrule-melting shocks the postshock equilibrium temperature is too high to avoid volatile loss. Even if we include radiative cooling in lateral directions out of the disk plane into our model (thereby breaking strict plane-parallel geometry) we find that for a realistic vertical extent of the solar nebula disk the temperature decline is not fast enough. On the other hand, if we assume that the shock is entirely optically thin so that particles can radiate freely, the cooling rates are too high to produce the observed chondrules textures. Global nebular shocks are therefore problematic as the primary sources of chondrules.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    Petrographic and mineralogic studies of amoeboid olivine inclusions (AOIs) in CO3 carbonaceous chondrites reveal that they are sensitive indicators of parent-body aqueous and thermal alteration. As the petrologic subtype increases from 3.0 to 3.8, forsteritic olivine (Fa(sub 0-1)) is systematically converted into ferroan olivine (Fa(sub 60-75)). We infer that the Fe, Si and O entered the assemblage along grain boundaries, forming ferroan olivine that filled fractures and voids. As temperatures increased, Fe(+2) from the new olivine exchanged with Mg(+2) from the original AOI to form diffusive haloes around low-FeO cores. Cations of Mn(+2), Ca(+2) and Cr(+3) were also mobilized. The systematic changes in AOI textures and olivine compositional distributions can be used to refine the classification of CO3 chondrites into subtypes. In subtype 3.0, olivine occurs as small forsterite grains (Fa(sub 0-1)), free of ferroan olivine. In petrologic subtype 3.2, narrow veins of FeO-rich olivine have formed at forsterite grain boundaries. With increasing alteration, these veins thicken to form zones of ferroan olivine at the outside AOI margin and within the AOI interior. By subtype 3.7, there is a fairly broad olivine compositional distribution in the range Fa(sub 63-70), and by subtype 3.8, no forsterite remains and the high-Fa peak has narrowed, Fa(sub 64-67). Even at this stage, there is incomplete equilibration in the chondrite as a whole (e.g., data for coarse olivine grains in Isna (CO3.8) chondrules and lithic clasts show a peak at Fa(sub39)). We infer that the mineral changes in A01 identified in the low petrologic types required aqueous or hydrothermal fluids whereas those in subtypes greater than or equal to 3.3 largely reflect diffusive exchange within and between mineral grains without the aid of fluids.

  19. 26Al in plagioclase-rich chondrules in carbonaceous chondrites: Evidence for an extended duration of chondrule formation

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

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

  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. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    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' 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 Icelandic 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. First-order reversal curve (FORC) diagrams contain a central ridge with a broad coercivity distribution extending to 600 mT, attributed to non-interacting single-domain (SD) particles. A braod vertically spread positive peak is centred on Hc = 56 ± 14 mT and Hu = -114 ± 41 mT, and is accompanied by a broad horizontaly spread negative peak at Hc = 183 ± 30 mT, just underneath the central ridge. The combination of positive and negative peaks can be attributed to the presence of single-vortex (SV) states. Average SV nucleation and annihilation fields of 58 ± 55 mT and 170 ± 55 mT, respectively, were extracted from the FORC diagrams, indicating that demagnetization to >>170 mT would be required to isolate the stable SD signal. Single-vortex states are likely to be important remanence carriers in dusty olivine. Accounting for their presence will be essential in interpreting the remanence of natural samples. All samples showed uni-directional, single-component demagnetization behaviour. Even after applying the highest possible AF-field of 150 mT it was not possible to fully demagnetize the samples. The REM ratio (NRM/SIRM) shows non-linear behaviour as a function of applied field, saturating at a value of ~0.3. Saturation of REM at a value < 1 is explained by the presence of particles that can adopt either stable SV or metastable SD states depending on the field. Such particles are likely to adopt low-remanence SV states during TRM acquisition and high-remanence SD states after appication of a saturating field, hence artificially lowering the REM value. A calibration factor f = 3000 ?T, relating paleofield to the REM value, was derived from the low-field region of the data, which matches well with literature values. A range of more sophisticated normalisation techniques are assessed for use in paleointensity determination from meteorties, including the newly proposed method based on Preisach analysis of FORC diagrams.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

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

    NASA Technical Reports Server (NTRS)

    Burger, Paul V.; Brearley, Adrian J.

    2004-01-01

    CR2 carbonaceous chondrites are a primitive group of meteorites that preserve evidence of a variety of processes that occurred in the solar nebula as well as on asteroidal parent bodies. CR2 chondrites are distinct from other carbonaceous chondrites by (among other properties) their relatively high abundance of chondrules (50-60 vol. %) and Fe,Ni metal (5-8 vol. %) [1]. Like the CM2 chondrites, the CRs have been affected by aqueous alteration and according to [2] show a range of degrees of alteration. In weakly- altered CR chondrites, fine-grained matrices and chondrule rims have been partially altered and chondrule mesostases show evidence of incipient aqueous alteration. In these meteorites, glassy mesostasis is still common. However, some CR chondrites, (e.g. Renazzo and Al Rais) show evidence of much more extensive alteration with complete replacement of chondrule mesostasis [2] by chlorite and serpentine. Although the general characteristics of alteration of the CR chondrites have been described, the details of alteration reactions in these meteorites remain unclear. In addition, the setting for aqueous alteration is poorly understood: both asteroidal and preaccretionary alteration scenarios have been proposed [2].

  6. Partitioning coefficients between olivine and silicate melts

    Microsoft Academic Search

    J. H. Bédard

    2005-01-01

    Variation of Nernst partition coefficients (D) between olivine and silicate melts cannot be neglected when modeling partial melting and fractional crystallization. Published natural and experimental olivine\\/liquidD data were examined for covariation with pressure, temperature, olivine forsterite content, and melt SiO2, H2O, MgO and MgO\\/MgO+FeOtotal. Values of olivine\\/liquidD generally increase with decreasing temperature and melt MgO content, and with increasing melt

  7. Partitioning coefficients between olivine and silicate melts

    Microsoft Academic Search

    J. H. Bédard

    2005-01-01

    Variation of Nernst partition coefficients (D) between olivine and silicate melts cannot be neglected when modeling partial melting and fractional crystallization. Published natural and experimental olivine\\/liquidD data were examined for covariation with pressure, temperature, olivine forsterite content, and melt SiO2, H2O, MgO and MgO\\/MgO + FeOtotal. Values of olivine\\/liquidD generally increase with decreasing temperature and melt MgO content, and with

  8. 1, 3750, 2006 Olivine in kimberlites

    E-print Network

    Paris-Sud XI, Université de

    eED 1, 37­50, 2006 Olivine in kimberlites N. T. Arndt et al. Title Page Abstract Introduction reviewed discussion forum of eEarth What olivine, the neglected mineral, tells us about kimberlite, 37­50, 2006 Olivine in kimberlites N. T. Arndt et al. Title Page Abstract Introduction Conclusions

  9. 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.

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

    NASA Technical Reports Server (NTRS)

    1994-01-01

    The following topics are covered in the presented papers: (1) producing chondrules; (2) carbons, CAI's, and chondrules; (3) large scale processes in the solar nebula; (4) chondrule-matrix relationships in chondritic meteorites; (5) overview of nebula models; (6) constraints placed on the nature of chondrule precursors; (7) turbulent diffusion and concentration of chondrules in the protoplanetary nebula; (8) heating and cooling in the solar nebula; (9) crystallization trends of precursor pyroxene in ordinary chondrites; (10) precipitation induced vertical lightning in the protoplanetary nebula; (11) the role of chondrules in nebular fractionations of volatiles and other elements; (12) astronomical observations of phenomena in disks; (13) experimental constraints on models for origins of chondrules, and various other topics.

  11. Chondrule-like object from the Indian Ocean cosmic spherules

    NASA Astrophysics Data System (ADS)

    Reshma, K.; Rudraswami, N. G.; Shyam Prasad, M.

    2013-08-01

    Five hundred and eighteen cosmic spherules were identified among the 672 spherules handpicked from deep sea sediments by using Scanning Electron Microscope-Energy Dispersive Spectrometry (SEM-EDS). One of the spherules is found to enclose a spherical chondrule-like object that can be distinguished from the rest of the spherule by its shape, texture and composition and whose petrographic features, size and chemical composition are similar to chondrules from a chondritic meteorite, probably of carbonaceous chondritic nature. The present finding suggests that a small fraction of the particulate extraterrestrial matter enters the earth as fragments of larger meteorites.

  12. Supernova olivine from cometary dust

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  13. Sulfur Isotope Composition of Putative Primary Troilite in Chondrules

    NASA Technical Reports Server (NTRS)

    Tachibana, Shogo; Huss, Gary R.

    2002-01-01

    Sulfur isotope compositions of putative primary troilites in chondrules from Bishunpur were measured by ion probe. These primary troilites have the same S isotope compositions as matrix troilites and thus appear to be isotopically unfractionated. Additional information is contained in the original extended abstract.

  14. The natural occurrence of hydroxide in olivine

    NASA Astrophysics Data System (ADS)

    Miller, Gregory H.; Rossman, George R.; Harlow, George E.

    1987-09-01

    Polarized infrared (IR) spectra of olivine single crystals from 17 different localities show a tremendous variability in both mode and abundance of hydroxide (OH) incorporation. Kimberlitic olivines contain the most total OH at an estimated concentration level of 976 H/106Si, whereas olivines from basalts contain the least at 3 H/106Si. Olivines of metamorphic and hydrothermal origin have widely varying concentration levels intermediate between those of basalts and kimberlites. Over 30 distinct OH absorption bands have been identified. Most of these bands are not unique to individual localities but may be found in samples from several different localities. Pleochroism is consistent among localities, but relative band intensities vary. No evidence is found for molecular H2 in olivine. Hydrous minerals have been identified in olivine by their characteristic OH absorption bands. Serpentine is commonly found and is clearly distinguishable from intrinsic OH. Talc is present in one sample. Prominent OH bands at 3572 and 3525 cm-1 are attributed to humite group minerals. San Carlos, Arizona, olivines annealed in the presence of H2O develop absorption bands which are found in natural samples, however the OH absorption spectra of these annealed olivines are not identical to those of any single natural crystal. Sharp-band OH abundances in annealed samples are an order of magnitude lower than the maximum measured in natural specimens. The mechanical properties determined from these annealed olivines may not be directly applicable to mantle olivine because both the OH sites and concentrations are different.

  15. Amoeboid olivine aggregates from CH carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    Amoeboid olivine aggregates (AOAs) in CH carbonaceous chondrites are texturally and mineralogically similar to those in other carbonaceous chondrite groups. They show no evidence for alteration and thermal metamorphism in an asteroidal setting and consist of nearly pure forsterite (Fa<3; in wt%, CaO = 0.1-0.8, Cr2O3 = 0.04-0.48; MnO < 0.5), anorthite, Al-diopside (in wt%, Al2O3 = 0.7-8.1; TiO2 < 1), Fe,Ni-metal, spinel, and, occasionally, low-Ca pyroxene (Fs1Wo2-3), and calcium-aluminum-rich inclusions (CAIs). The CAIs inside AOAs are composed of hibonite, grossite, melilite (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.

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

    NASA Astrophysics Data System (ADS)

    Plümper, Oliver; King, Helen E.; Vollmer, Christian; Ramasse, Quentin; Jung, Haemyeong; Austrheim, Håkon

    2012-04-01

    Crystal-plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence of asthenospheric mantle flow. Although crystal-plastic deformation and serpentinization are spatio-temporally decoupled, we identified compositional readjustments expressed on the micrometric level as a striped Fe-enriched ( bar{X}_{text{Fe}} = 0.24 ± 0.02 (zones); 0.12 ± 0.02 (bulk)) or Fe-depleted ( bar{X}_{text{Fe}} = 0.10 ± 0.01 (zones); 0.13 ± 0.01 (bulk)) zoning in partly serpentinized olivine grains from two upper mantle sections in Norway. Focused ion beam sample preparation combined with transmission electron microscopy (TEM) and aberration-corrected scanning TEM, enabling atomic-level resolved electron energy-loss spectroscopic line profiling, reveals that every zone is immediately associated with a subgrain boundary. We infer that the zonings are a result of the environmental Fe2+Mg-1 exchange potential during antigorite serpentinization of olivine and the drive toward element exchange equilibrium. This is facilitated by enhanced solid-state diffusion along subgrain boundaries in a system, which otherwise re-equilibrates via dissolution-reprecipitation. Fe enrichment or depletion is controlled by the silica activity imposed on the system by the local olivine/orthopyroxene mass ratio, temperature and the effect of magnetite stability. The Fe-Mg exchange coefficients K_{text{D}}^{{{text{Atg}}/{text{Ol}}}} between both types of zoning and antigorite display coalescence toward exchange equilibrium. With both types of zoning, Mn is enriched and Ni depleted compared with the unaffected bulk composition. Nanometer-sized, heterogeneously distributed antigorite precipitates along olivine subgrain boundaries suggest that water was able to ingress along them. Crystallographic orientation relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations support the hypothesis that serpentinization was initiated along olivine subgrain boundaries.

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  18. 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...

  19. Water-Induced Fabric Transitions in Olivine

    Microsoft Academic Search

    Haemyeong Jung; Shun-ichiro Karato

    2001-01-01

    The interpretation of seismic anisotropy in Earth's upper mantle has traditionally been based on the fabrics (lattice-preferred orientation) of relatively water-poor olivine. Here we show that when a large amount of water is added to olivine, the relation between flow geometry and seismic anisotropy undergoes marked changes. Some of the puzzling observations of seismic anisotropy in the upper mantle, including

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

    E-print Network

    Carrera, Daniel; Davies, Melvyn B

    2015-01-01

    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 $\\sim$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 use a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from sub-millimeter-sized chondrules to meter-sized rocks. We find 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 make a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) which are prone to ...

  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. 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.

  3. Questions, questions: Can the contradictions between the petrologic, isotopic, thermodynamic, and astrophysical constraints on chondrule formation be resolved?

    NASA Astrophysics Data System (ADS)

    Alexander, Conel M. O'D.; Ebel, Denton S.

    2012-07-01

    Here, we show that several geochemical indicators point to number densities during chondrule formation that were far higher than can be accounted for by known nebula processes. The number densities implied by compound chondrules and nonspherical chondrules are shown to be significantly higher than estimated in previous studies. At the implied chondrule number densities, if a chondrule formation region survived a formation event it would have been gravitationally bound and would have collapsed quite rapidly to form an asteroidal-sized body. The diversity of chondrule compositions and textures in a chondrite group could have formed in a single event in subvolumes of a formation region that were chemically isolated from one another because of slow diffusion in the gas. Within these subvolumes, equilibration between chondrules with different compositions would have been fairly rapid, although small isotopic mass fractionations in elements like Fe, Si, Mg, and O may persist. This could explain the existence of the small isotopic mass fractionations in these elements that have been observed in chondrules. However, the evidence for recycling of chondrules requires that there was more than one chondrule formation event prior to formation of a parent asteroid. Finally, we argue that OC and CO chondrule Mg-Al systematics are both consistent with single ages or narrow ranges of ages, and that the CO, and possibly the OC, ages date parent body alteration. This would resolve the conundrum of needing to preserve in a turbulent nebula physically and chemically distinct CO and OC chondrule populations for 1-2 Myr.

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

    NASA Astrophysics Data System (ADS)

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

    1996-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Hezel, D. C.; Palme, H.

    2007-03-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

    The paper discusses element bulk compositions of 373 chondrules from 18 H3 to H6 chondrites determined by broad-beam electron probe analysis. Bulk chondrule FeO and Al2O3 amounts increase and TiO2 and Cr2O3 decrease with increasing petrologic type; normative faylite, albite, and plagioclase amounts increase through the petrologic sequence. Chondrule diameters correlate with phenocryst sizes in porphyritic chondrules of type 3 chondrites, but this correlation is diminished in the higher petrologic types. The compositional trends in chondrules through the petrologic sequence are attributed to diffusion and equilibration among chondrules, and between chondrules and matrix in response to increasing degrees of thermal metamorphism. It is suggested that H-group chondrites are formed by accretion of high-temperature (chondrules) and low-temperature (matrix) materials. Internal reheating of the parent materials to different temperatures caused compositional equilibration, grain coarsening, and reduction of FeO to Fe(0) by carbon.

  7. Crystallization kinetics of olivine-phyric shergottites

    NASA Astrophysics Data System (ADS)

    Ennis, Megan E.; McSween, Harry Y.

    2014-08-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  9. 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.

  10. Rates and mechanisms of Fe-Mg interdiffusion in olivine at 980°-1300°C

    Microsoft Academic Search

    Sumit Chakraborty

    1997-01-01

    Fe-Mg interdiffusion rates have been measured in olivine solid solutions using the diffusion couple technique. Measured diffusion rates along [001] at f02=10-12 bars and between 980°C and 1300°C are found to be slower by about 2 orders of magnitude, compared to previous studies with the exception of some isolated data points of Misener [1974]. There is no change in temperature

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  12. Exsolved kirschsteinite in angrite LEW86010 olivine

    NASA Technical Reports Server (NTRS)

    Mikouchi, Takashi; Takeda, Hiroshi; Mori, Hiroshi; Miyamoto, Masamichi; Mckay, Gordon

    1993-01-01

    Mineralogy of kirschsteinite exsolution in olivine from Antarctic meteorite LEW86010 has been studied by single crustal X-ray diffraction technique. The LEW86010 olivine crystals have exsolution lamellae of kirschteinite about 15 microns wide. Determination of crystallographic orientation of exsolved kirschsteinite in an olivine grain has been made. Weak reflections of exsolved kirschsteinite share common crystallographic orientation with the host olivine. The cell dimensions of the exsolved phase (a - 4.87 plus or minus 0.05A, b - 11.14 plus or minus 0.10A, c - 6.36 plus or minus 0.05A) and intensities were in well accord with those of kirschsteinite previously reported. Oriented section perpendicular to the a axis shows exsolution lamellae in two directions parallel to (031) and (031). The lamellae are up to 10 microns in width and spacings between them are usually 50-100 microns.

  13. 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

  14. Atom Probe Tomography of Olivine

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Here we present atom probe tomographic (APT) analyses of natural olivine. APT provides three-dimensional trace element and isotopic analysis with sub-nanometer spatial resolution. It has been used for many years in engineering and materials science, but has not been applied to geological materials because traditional APT can only be used on conducting (usually metal) samples. The recent development of laser assisted APT has changed this situation, and now semi-conductors and insulators can be analyzed (Marquis et al., 2009, Kelly et al 2007). Potentially, this opens APT to extensive use in geoscience as many Fe-bearing silicates are semi-conductors. In this study, we explore the capability of the new class of APT instrumentation to analyze geological materials. APT involves the controlled evaporation of small, cylindrical specimens (100's nm in diameter) within an electric field. Specimens are typically prepared using in-situ focused-ion-beam (FIB) liftout and shaping techniques. Evaporated atoms are accelerated to a detector plate that records the position of the atom with sub-nm precision. Evaporated atoms are measured using time-of-flight mass spectrometry, allowing both elemental and isotopic determination. Since the method progressively ablates into the needle, the final analytical result is a nm-scale 3-dimensional image in which the position and identity of each detected atom is known. Typical mass resolution is between 200 and 1200 (full-width at half maximum) and typical concentration detection limits are 10 ppm. The number of potential applications of APT to igneous, metamorphic and sedimentary materials is large, ranging from studies of mineral and melt inclusions, to fine scale layering in minerals, to reaction surfaces and diffusion profiles. Much recent progress in the geochemical and petrologic fields has been driven by the increasing spatial resolution of the ion probe and laser ablation ICPMS. The ability of APT to provide atom-scale mass spectrometry should continue this trend. The main limitations to atom probe analysis of geological materials are the ability to control heat flow during laser pulsing and the associated ability to control clustering during field evaporation. Both of these factors can be controlled through specimen preparation and varying the atom probe experimental factors. Olivine specimens were properly analyzed using laser pulsed APT through the use of shallow (nominally 1mm) FIB liftouts and wide shank angle specimen apices. APT settings were found to give the best mass resolution using low specimen temperatures, 0.2 nJ laser energy, and 50 kHz pulse repetition rate. Increasing any of these values increases the amount of thermal tails due to excessive heat buildup, reducing the mass spectrum resolution, and ultimately affecting the spatial resolution of the reconstruction. Marquis EA, Miller MK, Blavette D, Ringer SP, Sudbrack CK and Smith DW (2009). MRS Bulletin 34: 725-730. Thomas F. Kelly, David J. Larson, Keith Thompson, Roger L. Alvis, Joseph H. Bunton, Jesse D. Olson, Brian P. Gorman, Ann. Rev. Mat. Res. 37: 681-727.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    We investigate the plausibility of a planetary embryo bow shock as a mechanism for chondrule formation in the early solar system. A Mars-size planetary embryo traveling on a moderately excited orbit through the dusty early environment of the solar system will experience supersonic velocities relative to the circularly orbiting gas and dust. The resulting bow shock can thermally process solids that pass through it, with a wide range of possible conditions depending on impact radius. Volatile outgassing by the embryo along with some gas capture from the surrounding nebula can produce temporary atmospheres. We use radiation hydrodynamics simulations with direct particle integration to model the consequences of solids that encounter a bow shock produced by a 3000 km embryo with relative speeds to the gas of 5, 6, and 7 km/s. The embryos are envisaged to be surrounded by low- and high-mass atmospheres (0.75 and 6.25 Martian-mass atmospheres, respectively), and we explore different opacities for the gas. We find that a high-mass atmosphere and low dust opacity can produce peak temperatures and cooling rates that are most consistent with constraints set by chondrule furnace studies for plausible shock speeds.

  16. Chondrule-like objects and brown glasses in howardites

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Matsunami, S.; El Goresy, A.

    1992-07-01

    In order to understand the origin of oxidized components in enstatite chondrites, matrix reduced olivine (RO) (<~60 micrometers in diameter) in Yamato-691 (EH3) chondrite has been examined in detail using EPMA. It commonly shows a lamellar structure, composed of alternation (with the spacing of about 1 micrometer) of "reduced olivine," which is a mixture of forsterite, metallic Fe, and probably unreacted olivine (relict), and sub-grain boundaries (SB) partly filled with decomposition products (Fe-metal, troilite, enstatite, and siliceous melt) due to reduction, strongly suggesting that the reduction of high-FeO olivine took place along SB (Boland and Duba, 1986). The presence of RO with bended SB is also suggestive of plastic deformation of the olivine before reduction. We estimated the rate of reduction of (Mg,Fe)-olivine as a function of temperature, composition of olivine (X(sub)Fe) and PO(sub)2 of reducing gas. We assumed that PO(sub)2 of the reducing gas was buffered by Si-bearing Fe-Ni metal + quartz assemblage. A mean Si- and Ni-contents of kamacite in Y-691 (Si=2.09 wt%; Ni=2.90 wt%) was adopted (El Goresy et al., 1988). To form RO with the SB spacing of 1 micrometer within 10^6-7 yr, which is a typical time-scale of thermal metamorphism at shallow parts of meteorite parent bodies (Wood, 1979), the temperature during reduction must have exceeded 700 K. From these results, the formational history of matrix RO and other coexisting phases in Y-691 could be summarized as follows: (1) High-FeO chondrule olivines crystallized in chondrule melts enriched in oxidized components. (2a) A severe impact process deformed them plastically and generated numerous dislocations (>10^9/cm^2) in them. (2b) Post-shock high-T (>~1100 K) annealing process formed SB in them due to dislocation climb. (3) The olivine grains were then mixed with E-chondritic materials containing at least both Si-bearing Fe- Ni metals and silica. (4) During metamorphism and/or impact heating process (T>~700 K), reduction of the olivine proceeded along SB to precipitate reduction products. (5) After reduction, the ROs were comminuted to grain sizes less than ~60 micrometers. (6) Finally, the fine- grained ROs were assembled with other E-chondritic components (e.g., sulfides) to form Y-691 chondrite at temperatures lower than ~500 degrees C (Nagel, 1991). Boland J.N. and Duba A.G. (1986) Jour. Geophys. Res. 91, 4711- 4722. El Goresy A. et al. (1988) Proc. NIPR Symp. Antarct. Meteorites 13th, 65-101. Nagel H.-J. (1991) Ph.D. Thesis, Univ. of Heidelberg, 117 pp. Wood J.A. (1979) In Asteroids (ed. T. Gehrels), pp. 849-891. Univ. Arizona Press, Tucson, Arizona.

  18. Bar Graphs!

    NSDL National Science Digital Library

    Mrs. Pocock

    2006-10-26

    Mrs. Kohlar has been working with you on bar graphs. Here are a couple of games for you to play to help you practice using them. Catch all the Bugs in the system and put them in the correct column of the bar graph. Answer the questions about the bugs in the graph. You can play the game twice if you wish. Do these bar graph activities and have some bar graph fun! Don\\'t worry about the last question, just answer ...

  19. Bar Graph

    NSDL National Science Digital Library

    Shodor

    2012-04-02

    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.

  20. Diffusion of highly charged cations in olivine

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  1. Olivines: revelation of tracks of charged particles.

    PubMed

    Krishnaswami, S; Lal, D; Prabhu, N; Tamhane, A S

    1971-10-15

    A one-step, three-component aqueous etchant was developed for revealing the tracks of charged particles in olivine. The etchant reveals tracks of small cone angle, which are equally well developed in all the crystallographic directions. The scope of fossil cosmic-ray track studies in extraterrestrial samples has thus been increased, because olivine is often an abundant constituent and because it has a higher threshold ionization for track registration and has lower uranium, thorium, and trace element concentrations as compared with pyroxenes and feldspars. The etchant does not attack any of the principal rock-forming minerals in normal etching time, which allows a nondestructive study of fossil tracks in thin-section mounts. The study of fossil cosmic-ray tracks in olivine is particularly valuable for investigations of very, very heavy cosmic-ray nuclei and for highly irradiated samples such as those found in the lunar regolith. PMID:17778062

  2. Shock-produced olivine glass - First observation

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  3. Fe-Mg Diffusion Processes in Compound Chondrules in the NWA 505 Chondrite

    NASA Astrophysics Data System (ADS)

    Sierchio, J. M.; Lauretta, D. S.; Davidson, J.

    2011-03-01

    We present the results of numerically modeling isothermal Fe-Mg diffusion processes in the NWA 505 chondrite. We also discuss the implications of these results for the thermal history and formation of compound chondrules in NWA 505.

  4. Fe-Mg Diffusion Processes in Compound Chondrules in the NWA 505 Chondrite

    Microsoft Academic Search

    J. M. Sierchio; D. S. Lauretta; J. Davidson

    2011-01-01

    We present the results of numerically modeling isothermal Fe-Mg diffusion processes in the NWA 505 chondrite. We also discuss the implications of these results for the thermal history and formation of compound chondrules in NWA 505.

  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. 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.

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

    E-print Network

    Hitoshi Miura; Taishi Nakamoto

    2006-07-03

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

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

    PubMed

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

    2014-05-20

    Batch experiments were conducted in water at 150 °C and PCO2 = 280 bar on a Mg-rich tholeiitic basalt (9.3 wt % MgO and 12.2 wt % CaO) composed of olivine, Ti-magnetite, plagioclase, and clinopyroxene. After 45 days of reaction, 56 wt % of the initial MgO had reacted with CO2 to form Fe-bearing magnesite, (Mg0.8Fe0.2)CO3, along with minor calcium carbonates. The substantial decrease in olivine content upon carbonation supports the idea that ferroan magnesite formation mainly follows from olivine dissolution. In contrast, in experiments performed under similar run durations and P/T conditions with a San Carlos olivine separate (47.8 wt % MgO) of similar grain size, only 5 wt % of the initial MgO content reacted to form Fe-bearing magnesite. The overall carbonation kinetics of the basalt was enhanced by a factor of ca. 40. This could be explained by differences in the chemical and textural properties of the secondary silica layer that covers reacted olivine grains in both types of sample. Consequently, laboratory data obtained on olivine separates might yield a conservative estimate of the true carbonation potential of olivine-bearing basaltic rocks. PMID:24735106

  9. 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: Magnesium isotopic analyses were performed at the Isotope Geochemistry Labora- tory of the Field Museum

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

    E-print Network

    Tommasi, Andrea

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

  11. 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.

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

    USGS Publications Warehouse

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

    2000-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

  14. Chondrule Magnetizations in the Allende CV Chondrite and Implications for the Dynamo of the CV Parent Body

    NASA Astrophysics Data System (ADS)

    Weiss, B. P.; Fu, R. R.

    2012-12-01

    Many early-accreting planetesimals larger than several tens of km in diameter underwent extensive interior melting and differentiation. Advection in the molten metallic cores of these planetesimals may have generated magnetic dynamos. Remanent magnetization preserved in meteorites can reveal the past presence of core dynamo fields and therefore a metallic core on their parent bodies. Furthermore, the meteoritic magnetic record can constrain the duration of the dynamo, providing insight into the thermal evolution of the parent planetesimal. Carporzen et al. (2011) argued that bulk samples of the Allende CV carbonaceous chondrite carry a unidirectional partial thermoremanent magnetization (pTRM) blocked up to ~290C. They interpreted this magnetization as recording a magnetic core dynamo on the CV parent body. However, the previous study provided no constraints on the duration of the dynamo and did not characterize the magnetic recording in each component of the Allende meteorite. We conducted paleomagnetic experiments on 23 mutually oriented individual Allende chondrules and matrix samples. We also studied mutually oriented subsamples of 9 of these chondrules. We found that Allende chondrules can be divided into two distinct classes based on their natural remanent magnetization (NRM). Class A chondrules carry a strong low temperature overprint parallel to that of bulk Allende and matrix material that also unblocks at ~290C. Class B chondrules do not carry this low temperature overprint and exhibit randomly oriented NRMs. Electron microprobe analysis and thermal demagnetization of saturation remanence showed that magnetic phases in both Class A and Class B chondrules are likely products of parent body metasomatism. We infer that the random magnetization of Class B chondrules as well as the magnetization blocked above 290C in Class A chondrules and matrix material is a chemical remanent magnetization that resulted in randomly oriented remanence at the sub-millimeter scale. Allende chondrules therefore do not carry pre-accretional magnetization. The presence of a unidirectional pTRM overprint in Class A chondrules and matrix material but not in Class B chondrules requires a process that removed the pTRM overprint in Class B chondrules after its acquisition. We infer that, while all Allende components experienced metasomatic recrystallization of their magnetic phases, Class A chondrules completed this process before the pTRM event while Class B chondrules underwent metasomatism after the pTRM event. Furthermore, the random magnetization directions of Class B chondrules may suggest that a stable dynamo field no longer existed during the period of aqueous alteration, thereby constraining the lifetime of the CV parent body dynamo to less than several tens of My.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2001-05-01

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

  17. 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).

  18. H in olivine: How much and where?

    NASA Astrophysics Data System (ADS)

    Withers, A. C.; Umemoto, K.; Hirschmann, M. M.

    2011-12-01

    Hydrous defects in nominally anhydrous minerals are known to play a fundamental role in influencing the mechanisms and extent of deformation in mantle rocks. The extent of water weakening in olivine, in particular, may dictate the nature of upper mantle deformation, thereby controlling the very processes of tectonism. Infrared spectroscopy (IR) is a powerful tool commonly used to analyze these extrinsic defects. In addition to determining defect concentrations, and in contrast to other analytical techniques such as secondary ion mass spectroscopy (SIMS), IR offers the possibility of determining the location of H atoms in the crystal structure. In the case of olivine, however, the relationships between the IR spectrum and the concentrations and locations of hydrous defects are widely disputed, with recent estimates of calibration coefficients varying by more than a factor of 3, and the same absorption bands being thought variously to represent substitutions on tetrahedral or on octahedral crystallographic sites. New analytical and theoretical results will be used to refine our view of the location and concentration of H in olivine. Elastic recoil detection analysis (ERDA) measurements are used to determine the infrared absorption coefficient (k) for OH bands in Fo90 olivines with 240-2000 ppm H2O, synthesised at 3-10 GPa in multianvil experiments that were optimised for growth of large, homogeneous crystals. On the basis of 20 ERDA and >200 FTIR analyses of olivines from 7 experiments, the H content (in ppm H2O) is given by 0.120±0.008×total integral absorption, corresponding to an integral extinction coefficient of 45,000 L/(mol cm2), i.e. k is ~35% smaller than the value previously derived by Bell et al. (2003)[1] for natural olivines. This implies that the H contents of experimental olivines have been generally overestimated. The samples that were analysed using ERDA are used as SIMS standards, thereby providing a direct calibration that avoids the baseline uncertainties that are inherent to FTIR. Direct calibration of SIMS using high pressure experimental samples allows for improved high accuracy analysis at high spatial resolution. In addition, first principles investigation of hydrous defects in forsterite provides new constraints on the crystallographic locations of hydrous defects. The lowest energy configuration for a hydrous substitution is found for a hydrogarnet type defect. Relaxation of the defect increases O-O distances in the tetrahedral site, thus reconciling the assignment of the more intense, high frequency IR peaks to H substitution on this site. This leaves us with the problem of explaining the mechanism for water weakening in olivine, which is thought to involve metal, rather than Si, vacancies. It may be that hydrolytic weakening is facilitated by hydrous defects of a less abundant type. [1] JGR 108:2105 doi:10.1029/2001JB000679

  19. Formation of chondrules in radiative shock waves I. First results, spherical dust particles, stationary shocks

    E-print Network

    Joham, H; 10.1051/0004-6361/201118467

    2013-01-01

    The formation of chondrules in the protoplanetary nebulae causes many questions concerning the formation process, the source of energy for melting the rims, and the composition of the origin material. The aim of this work is to explore the heating of the chondrule in a single precursor as is typical for radiation hydrodynamical shock waves. We take into account the gas-particle friction for the duration of the shock transition and calculate the heat conduction into the chondrules. These processes are located in the protoplanetary nebulae at a region around 2.5 AU, which is considered to be the most likely place of chondrule formation. The present models are a first step towards computing radiative shock waves occurring in a particle-rich environment. We calculated the shock waves using one-dimensional, time-independent equations of radiation hydrodynamics involving realistic gas and dust opacities and gas-particle friction. The evolution of spherical chondrules was followed by solving the heat conduction equa...

  20. Mechanisms and Timescales for Reequilibration of Water in Olivine-Hosted Melt Inclusions

    NASA Astrophysics Data System (ADS)

    Gaetani, G. A.; O'Leary, J. A.; Shimizu, N.

    2009-12-01

    Water solubility in silicate melts drops substantially with decreasing pressure. A magma containing several weight % dissolved H2O in the shallow crust is left with only a few thousand ppm following eruption. Olivine-hosted melt inclusions provide information on the pre-eruptive H2O contents of degassed magmas because the strength of the host crystal protects the melt inclusion from the decompression experienced by the entraining magma. The principal uncertainty involved with interpreting pre-eruptive H2O concentrations from melt inclusions is the potential for diffusive loss or gain of H+ (protons) through the host olivine. It has been proposed that Fe redox reactions severely limit the proton flux, and that episodes of H2O loss/gain are easily identifiable through changes in oxidation state of the inclusion [1,2]. Results from hydration and dehydration experiments carried out on natural inclusion-bearing olivines and analyzed by SIMS confirm that H2O re-equilibratrion occurs rapidly via proton diffusion through the host olivine, and demonstrate that re-equilibration of oxygen fugacity within the inclusions occurs on comparable timescales via diffusion of point defects. Therefore, an olivine-hosted melt inclusion only provides a reliable record for the H2O content of the external melt with which it most recently equilibrated. Hydration experiments were performed on olivines from Puu Wahi, a scoria cone on the NE rift zone of Mauna Loa volcano. Melt inclusions initially containing 0.36±0.05 wt% H2O were held at 1 GPa and 1250°C in water enriched in 18O (18O/?O = 0.977) and D (2H/?H = 0.998) to map the transport of protons and oxygen during equilibration of melt inclusions with an external fluid. Dehydration experiments were carried out for 1 to 18 hrs at 1 bar and 1250 °C on inclusion-bearing olivines in scoria erupted from Cerro Negro volcano, Nicaragua, in 1999. The initial concentration of H2O in these melt inclusions is uniformly high (3.6±0.6 wt%). All run products were analyzed by SIMS on the Cameca 1280 ion microprobe at WHOI. Results from our experiments confirm that the mechanism for loss or gain of H2O from olivine-hosted melt inclusions is lattice diffusion of protons. This process leaves behind an O2- for every 2 protons lost, and scavenges an O2- for every 2 protons gained, producing an increase or decrease, respectively, of the fugacity of oxygen within the inclusion. However, H2O loss/gain for olivine-hosted melt inclusions is coupled with point defect-mediated oxygen fugacity re-equilibration. Therefore, Fe redox reactions do not limit either the amount or rate of water loss or gain by the inclusion. The H2O concentration of an olivine-hosted melt inclusion can change rapidly, and that change is not recorded by the oxygen fugacity of the melt. References: [1] A. V. Sobolev, L. V. Danyushevsky, J Petrol 35, 1183 (1994); [2] L. V. Danyushevsky, A. W. McNeill, A. V. Sobolev, Chem Geol 183, 5 (2002).

  1. Shock-Produced Olivine Glass: First Observation

    Microsoft Academic Search

    Raymond Jeanloz; Thomas J. Ahrens; J. S. Lally; G. L. Nord Jr.; J. M. Christie; A. H. Heuer

    1977-01-01

    Transmission electron microscope (TEM) observations of an experimentally shock-deformed single crystal of natural peridot, (Mg0.88Fe0.12)2SiO4, 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 of olivine glass. The shocked sample exhibits a wide variation in the

  2. Evaluation of olivine refractories for TES

    NASA Astrophysics Data System (ADS)

    Gay, B. M.; Cochrane, R. L.; Palmour, H., III; Paisley, M. J.

    1982-02-01

    The principal objectives of this program are to (1) experimentally determine the degree of improvement in thermal and mechanical performance that can be obtained with an olivine thermal storage brick made of domestic materials using advanced processing techniques compared with state-of-the-art as represented by commercial European bricks, (2) conduct an assessment of existing German ceramic process technology and determine its adaptability to domestic raw materials and manufacturing practices, and (3) investigate, on a limited basis, method for further improvement of domestic-olivine brick. To date, accomplishments include (1) installation of improved, computer-based instrumentation, (2) the use of this system to determine performance characteristics of a set of heat storage refractories under cyclic use conditions, (3) acquisition of the services of a knowledgeable European consultant, (4) continued lab-scale process/property optimization studies, and (5) comparative testing of olivine-based and magnesite-based heat storage refractories in the calorimetric test facility at Purdue University.

  3. Bar Graph

    NSDL National Science Digital Library

    2010-01-01

    In this activity, students use preset data or input their own data to be represented by a bar graph. This activity allows students to explore bar graphs and how changing scales will alter how their data is represented. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

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

    NASA Astrophysics Data System (ADS)

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

    1993-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  6. Water and Carbon Dioxide Adsorption at Olivine Surfaces

    SciTech Connect

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

    2013-11-14

    Plane-wave density functional theory (DFT) calculations were performed to simulate water and carbon dioxide adsorption at the (010) surface of five olivine minerals, namely, forsterite (Mg2SiO4), calcio-olivine (Ca2SiO4), tephroite (Mn2SiO4), fayalite (Fe2SiO4), and Co-olivine (Co2SiO4). Adsorption energies per water molecule obtained from energy minimizations varied from -78 kJ mol-1 for fayalite to -128 kJ mol-1 for calcio-olivine at sub-monolayer coverage and became less exothermic as coverage increased. In contrast, carbon dioxide adsorption energies at sub-monolayer coverage ranged from -20 kJ mol-1 for fayalite to -59 kJ mol-1 for calcio-olivine. Therefore, the DFT calculations show a strong driving force for carbon dioxide displacement by water at the surface of all olivine minerals in a competitive adsorption scenario. Additionally, adsorption energies for both water and carbon dioxide were found to be more exothermic for the alkaline-earth (AE) olivines than for the transition-metal (TM) olivines and to not correlate with the solvation enthalpies of the corresponding divalent cations. However, a correlation was obtained with the charge of the surface divalent cation indicating that the more ionic character of the AE cations in the olivine structure relative to the TM cations leads to greater interactions with adsorbed water and carbon dioxide molecules at the surface and thus more exothermic adsorption energies for the AE olivines. For calcio-olivine, which exhibits the highest divalent cation charge of the five olivines, ab initio molecular dynamics simulations showed that this effect leads both water and carbon dioxide to react with the surface and form hydroxyl groups and a carbonate-like species, respectively.

  7. 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.

  8. 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.

  9. 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.

  10. Vaporization Studies of Olivine via Knudsen Effusion Mass Spectrometry

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  11. Olivine-based heat storage refractories

    NASA Astrophysics Data System (ADS)

    Gay, B. M.; Palmour, H., III; Cochrane, R. L.

    1981-03-01

    The processing properties and performance of special refractory shapes produced from olivine for prototype evaluations in heat storage furnaces are investigated. Heat storage furnaces and related consumer owned thermal storage units are energy conversion/storage devices of the sensible heat type. Their primary purpose is to permit electrical load leveling of large generating/distributing systems. Load-leveling enables power generating plants to operate more efficiency thus contributing to better overall energy utilization. The principal application for these ceramic thermal energy reservoirs is in home or business heating (furnaces, space heaters).

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

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

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

    USGS Publications Warehouse

    Roedder, E.

    1983-01-01

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

  14. The Origin of Silica-Rich Chondrules and Clasts in Ordinary and Carbonaceous Chondrites

    Microsoft Academic Search

    A. Ruzicka; W. V. Boynton

    1992-01-01

    Chondrules and clasts containing a silica mineral or a silica glass are a minor but important constituent in many ordinary (Planner, 1983; Brigham et al., 1986) and some carbonaceous (Olsen, 1983) chondrites, and have been considered somewhat enigmatic. The recent discovery of a large, silica-rich igneous clast in the Bovedy (L3) chondrite (Ruzicka and Boynton, 1992) sheds light on the

  15. 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.

  16. Gamma-ray bursts and X-ray melting of material to form chondrules and planets

    E-print Network

    P. Duggan; B. McBreen; A. J. Carr; E. Winston; G. Vaughan; L. Hanlon; S. McBreen; L. Metcalfe; A. Kvick; A. E. Terry

    2004-07-15

    Chondrules are millimeter sized objects of spherical to irregular shape that constitute the major component of chondritic meteorites that originate in the region between Mars and Jupiter and which fall to Earth. They appear to have solidified rapidly from molten or partially molten drops. The heat source that melted the chondrules remains uncertain. The intense radiation from a gamma-ray burst (GRB) is capable of melting material at distances up to 300 light years. These conditions were created in the laboratory for the first time when millimeter sized pellets were placed in a vacuum chamber in the white synchrotron beam at the European Synchrotron Radiation Facility. The pellets were rapidly heated in the X-ray and gamma-ray furnace to above 1400C melted and cooled. This process heats from the inside unlike normal furnaces. The melted spherical samples were examined with a range of techniques and found to have microstructural properties similar to the chondrules that come from meteorites. This experiment demonstrates that GRBs can melt precursor material to form chondrules that may subsequently influence the formation of planets. This work extends the field of laboratory astrophysics to include high power synchrotron sources.

  17. Chemical energy in cold-cloud aggregates - The origin of meteoritic chondrules

    Microsoft Academic Search

    D. D. Clayton

    1980-01-01

    If interstellar particles and molecules accumulate into larger particles during the collapse of a cold cloud, the resulting aggregates contain a large store of internal chemical energy. It is here proposed that subsequent warming of these accumulates leads to a thermal runaway when exothermic chemical reactions begin within the aggregate. These, after cooling, are the crystalline chondrules found so abundantly

  18. An olivine-free mantle source of Hawaiian shield basalts

    Microsoft Academic Search

    Albrecht W. Hofmann; Stephan V. Sobolev; Igor K. Nikogosian; Alexander V. Sobolev

    2005-01-01

    More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both

  19. Diffusion kinetics of Cr in olivine and 53 Cr thermochronology

    E-print Network

    Ganguly, Jibamitra

    Diffusion kinetics of Cr in olivine and 53 Mn­53 Cr thermochronology of early solar system objects Motoo Ito a,b , Jibamitra Ganguly a,* a Department of Geosciences, University of Arizona, Tucson, AZ, which showed 53 Mn­53 Cr bulk age of olivine that is 10 Myr younger than the age of the solar system

  20. Martian dunite NWA 2737: Integrated spectroscopic analyses of brown olivine

    Microsoft Academic Search

    Carle M. Pieters; Rachel L. Klima; Takahiro Hiroi; M. Darby Dyar; Allan H. Treiman; Sarah K. Noble; Jessica M. Sunshine; Janice L. Bishop

    2008-01-01

    A second Martian meteorite has been identified that is composed primarily of heavily shocked dunite, Northwest Africa (NWA) 2737. This meteorite has several similarities to the Chassigny dunite cumulate, but the olivine is more Mg rich and, most notably, is very dark and visually brown. Carefully coordinated analyses of NWA 2737 whole-rock and olivine separates were undertaken using visible and

  1. 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

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Jurewicz, Amy J. G.; Watson, E. Bruce

    1988-06-01

    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 diffusion of calcium, iron, magnesium and manganese. This anisotropy is a weak function of temperature, but strongly dependent upon oxygen fugacity. Because diffusion is independent of olivine composition over the small range of compositions used in this study, it could be shown that the absolute values of the diffusion coefficients were also functions of temperature and fO2. At near-atmospheric total pressure and an oxygen fugacity of 10-8atm, D Fe> D Mn> D Ca and D Mg? D Mn for a range of geologically reasonable temperatures. These relative diffusivities were shown to change with oxygen fugacity. The power-law dependence of diffusion on oxygen partial-pressure was determined for each cation and the results are consistent with the range of values given by Stocker (1978) and by other workers. For Ca and Fe, the effect of hydrostatic pressure on diffusion appears to be weak, at least for transport parallel to the c crystallographic direction. Unfortunately, no true activation volumes (or other pressure-related parameters) could be computed because the oxygen fugacity was not held constant over changes in pressure, and because accurate post-experiment reconstruction of sample orientation was not possible. Al was found to enter high-pressure olivines at concentrations of up to 0.14 weight percent, thus allowing aluminum diffusion to be characterized. The diffusivity of aluminum is, within error, the same as iron at 20 kb at 1430° C at the ambient fO2 of our piston-cylinder cells. This correspondence suggests that diffusion of Al may depend on transport of either Fe or of Fe +3 defects. While the results of these experiments are generally consistent with results published elsewhere, there are important inconsistencies. Tracer diffusion and interdiffusion in pure, ordered, olivine endmembers (e.g., tephroite and forsterite) showed significantly higher activation energies. This discrepancy could reflect the role of Fe+3 defects in diffusion; however, it may also suggest that order-disorder phenomena may be significant factors influencing diffusion in analog systems. The results of this study are applied to four petrologic problems: (1) calculation of rates of equilibration for olivine xenocrysts; (2) calculation of closure temperatures for the CaO/MgO olivine/basalt geothermometer (Jurewicz and Watson 1988); (3) delineation of an intrinsic-/O2 geobarometer; and (4) investigation of the dependence of olivine dissolution upon crystallographic orientation. In addition, it is demonstrated that diffusion-exchange experiments are useful for studying the dominant point-defect mechanisms for cation diffusion.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  5. 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.

  6. 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.

  7. Did Ordinary Chondrite Impactors Deliver Olivine to Vesta?

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    USGS Publications Warehouse

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

    2006-01-01

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

  9. Fraction Bars

    NSDL National Science Digital Library

    2005-01-01

    This virtual manipulative is a Java applet that allows students to explore concepts in whole number operations and fractions, just as they would with a physical manipulative such as Cuisinaire Rods. The user can add bars of length 1 to 10 to the workspace, change their color, and move, duplicate, or remove them. Instructions for using the applet and teaching ideas for parents/teachers are available through the links at the top of the page.

  10. Olivine in the Southern Isidis Basin

    NASA Technical Reports Server (NTRS)

    2007-01-01

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

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

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

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

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

  12. Chondrites: The Compaction of Fine Matrix and Matrix-like Chondrule Rims

    NASA Astrophysics Data System (ADS)

    Wasson, J. T.

    1995-09-01

    Primitive chondritic meteorites mainly consist of chondrules, sulfide+/-metal, and fine-grained matrix. The most unequilibrated chondrites preserve in their phase compositions and, to a lesser degree, their textures, many details about processes that occurred in the solar nebula. On the other hand, much of the textural evidence records processes that occurred in or on the parent body. I suggest that the low-porosity of chondrule matrix and matrix-like rims reflects compaction processes that occurred in asteroid-size bodies, and that neither matrix lumps nor compact matrix-like rims on chondrules could have achieved their observed low porosities in the solar nebula. Recent theoretical studies by Donn and Meakin (1) and Chokshi et al. (2) have concluded that grain-grain sticking in the solar nebula mainly produces fluffy structures having very high porosities (probably >>50%). If these structures grow large enough, they can provide an aerogel-like matrix that can trap chondrules as well as metal and sulfide grains, and thus form suitable precursors of chondritic meteorites. However, the strength of any such structure formed in the solar nebula must be a trivial fraction of that required to survive passage through the Earth's atmosphere in order to fall as a meteorite. The best evidence of accretionary structures appears to be that reported by Metzler et al. (3). They made SEM images of entire thin sections of CM chondrites, and showed that, in the best preserved chondrites, rims are present on all entitities--on chondrules, chondrule fragments, refractory inclusions, etc. A study by Krot and Wasson (4) shows a more complex situation in ordinary chondrites. Although matrix is common, a sizable fraction of chondrules are not surrounded by matrix-like rims. As summarized by Rubin and Krot (1995), there are reports of small textural and compositional differences between matrix lumps and mean matrix-like chondrule rims, but there is so much overlap in properties between these two classes that I will assume that they can be treated as parts of a single statistical population. Published SEM images of matrix lumps and matrix-like rims show them to be relatively compact. Although some porosity is surely present as indicated by broad-beam electron-probe analysis totals <100%, it never reaches values comparable to those expected from low-velocity collisions in the solar nebula. Most chondrite researchers seem to hold that the low porosities reflect efficient packing of each grain as it accreted to the assemblage (i.e., as micrometer-size grains gradually covered the surface of a chondrule to form the matrix-like rim). I find this process very difficult to envision. If the velocities are low, the fluffy structures of Dodd and Meakin (1) should result; if the velocities are high, then rim erosion would seem to be more probable than growth. A possible scenario that avoids this dilemma is to form cm to m-size fluffy structures in low-turbulence regions of the nebular midplane. During accretion of these larger objects these experienced enough compaction to form tough, low-porosity (but unequilibrated) chondrites. If no chondrules were in a region, matrix lumps formed; if chondrules were widely separated, a matrix-like rim resulted. And, if chondrules were close to other chondrules or chondrule fragments, only small amounts of intervening fine-grained materials now separate them from their neighbors. During the compaction event, gas and dust migration occurred, and matrix filled all interstices, as now observed in the most primitive chondrites. According to this picture there could have been more diversity in the fine-grained nebular component before compaction occurred. These differences would be best preserved in matrix-like rims and matrix lumps. Much of the interchondrule matrix should consist of homogenized dust that was mixed during compaction-induced transport. References: [1] Donn B. and Meakin P. (1989) Proc. LPSC 19th, 577-580. [2] Chokshi A. et al. (1993) Astrophys. J., 407, 806-819. [3] Metzler K. et al. (1992) GCA,

  13. Exploring Exogenic Sources for the Olivine on Asteroid (4) Vesta

    E-print Network

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

    2015-01-01

    The detection of olivine on Vesta is interesting because it may provide critical insights into planetary differentiation early in our Solar System's history. Ground-based and Hubble Space Telescope (HST) observations of asteroid (4) Vesta have suggested the presence of olivine on the surface. These observations were reinforced by the discovery of olivine-rich HED meteorites from Vesta in recent years. However, analysis of data from NASA's Dawn spacecraft has shown that this olivine-bearing unit is actually impact melt in the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed during the formation of the 19 km deep Rheasilvia basin on Vesta's South Pole, further complicated this picture. Ammannito et al., (2013a) reported the discovery of local scale olivine-rich units in the form of excavated material from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. Here we explore alternative sources for the olivine in the northern hemisphere of Vesta by reanalyzing the data from ...

  14. Sushi Bar

    NSDL National Science Digital Library

    An innovative website where customers order from a realistic sushi bar menu to learn about international fisheries resources and impacts. Select shrimp, tuna, squid, octopus, or sea urchin to learn where resources are harvested, current fisheries methods, population status and concerns. This on-line activity also demonstrates how global our use of resources has become, with a single country dependent on seafood imports from around the world. The site also contains lesson plans on natural resources and resource management. Appropriate for grades 6 and up.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  16. Olivines from Kimberlites and Diamonds: Problem of Origin

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Mg-rich olivine Fo [100Mg/(Mg + Fe)] 85-94 is the principal mineral of kimberlites, peridotite xenoliths and diamond inclusions. It is completely altered in common kimberlites, however, it is absolutely fresh in a huge block from Udachnaya-East kimberlite in Yakutia (Russia). Pioneering studies of this unaltered kimberlite resulted in a discovery of high role of a mantle chlorine along with very low water content (Kamenetsky et al., 2004, Geology, 32: 845-848). Two olivine populations are distinguished, which are represented by oval-rounded unzoned or partly zoned xenocrysts of olivine I (more than 1 mm) and well defined zoned phenocrysts ( 0.05-1.0 mm) of olivine II (e.g. Kamenetsky et al., 2008, J.Petrol., 49: 823-839). The cores of olivine II are compositionally similar to olivine I with Mg# 86-94, but rims of olivine II and partly preserved rims of olivine I have constant Fo values about 89-90. We report here the results of major and minor elements analyses by EPMA of more than 300 grains of olivine I and olivine II, both of cores and rims by high precision approach (Sobolev et al., 2007, Science, 316: 412-417) to minor elements including Ti, Al, Cr, Ca, Mn, Ni, Co using the high sample current and high counting time, which was found optimal to obtain limit of detection about 10 ppm. Several grains of analyzed olivines contain clinopyroxene (cpx) and pyrope (prp) inclusions confirming their high pressure origin. One large olivine I grain contains clusters of cpx ( 33 grains) and prp ( 6 grains) inclusions., having a range in Cr2O3 (1.52- 2.36 wt%) , Al2O3 (0.99-5.53 wt%) and Na2O (1.45-5.96 wt%) for cpx and Cr2O3 (3.51-4.42 wt%) and CaO (5.64-6.61 wt%) for prp, showing disequilibrium in olivine I core, containing 200 ppm Ti. This is completely different from any peridotite xenoliths, confirming the uniqueness of this assemblage. The systematic high Ti ( more than 150 ppm) of all studied cores of olivine grains containing low T (Ca# 43.3-48) cpx and prp inclusions confirm the listed differences from all olivines from peridotites and diamonds (e.g. Sobolev et al., 2009, Lithos, 112S: 701-713.). Earlier, similar Ti abundance was reported only for olivines from dunite nodules in Greenland kimberlites (e.g. Arndt et al., 2010, J. Petrol., 51: 573-602).We suggest that Ti-bearing olivine, represented more that 70% of studied samples, is a part of high pressure pyrope lherzolite assemblage, which was formed and grew during the formation and early evolution of kimberlites

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  18. Systematics of Vanadium in Olivine from Planetary Basalts

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    The systematics of vanadium in olivines from the Earth, Moon and Mars allows for the comparison of planetary basalt origin and igneous setting and process. Additional information is contained in the original extended abstract.

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

    NASA Technical Reports Server (NTRS)

    Zolensky, Michael E.; Frank, D.

    2011-01-01

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

  20. Refractory precursor components of Semarkona chondrules and the fractionation of refractory elements among chondrites

    NASA Astrophysics Data System (ADS)

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

    1983-04-01

    Instrumental neutron activation analysis has been used to measure about 20 of the lithophile elements in 30 chondrules from the Semarkona chondrite. The amounts of oxidized iron were calculated from other compositional parameters, and Si concentrations are estimated from mass-balance considerations. It is suggested that the refractory component probably forms from fine grained materials that were able to equilibrate down to lower nebular temperatures. The chondrite matrix may have had an origin similar to that of the nonrefractory material. The low abundance of refractories and Mg in ordinary and enstatite chondrites was produced by the loss of materials having a higher refractory element/Mg ratio than that of the refractory element of the chondrules.

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

    E-print Network

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

    2007-12-04

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

  2. Aluminum speeds up the hydrothermal alteration of olivine

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The reactivity of ultramafic rocks toward hydrothermal fluids controls chemical fluxes at the interface between the internal and external reservoirs of silicate planets. On Earth, hydration of ultramafic rocks is ubiquitous and operates from deep subduction zones to shallow lithospheric environments where it considerably affects the physical and chemical properties of rocks and can interact with the biosphere. This process also has key emerging societal implications, such as the production of hydrogen as a source of carbon-free energy. To date, the chemical model systems used to reproduce olivine hydrothermal alteration lead to the formation of serpentine with sluggish reaction rates. Although aluminum is common in geological environments and in hydrothermal systems in particular, its role in serpentinization or olivine dissolution has not been investigated under hydrothermal conditions. Nevertheless, abundant Al supply is expected in fluids released from dehydration of metapelites in subduction zones as well as during the hydrothermal alteration of gabbros at mid-ocean ridges. Aluminum was also abundant in primitive environments of both the Earth and Mars, stored in either Al-rich minerals like plagioclase or Al-enriched ultramafic lavas. We have investigated the role of Al on the hydrothermal alteration of olivine in a series of experiments performed in a low-pressure diamond anvil cell while following the reaction progress in situ by optical imaging and Raman spectroscopy. Experiments were run for 4.5 to 7.5 days with two olivine grains reacted in saline water (0.5 molal NaCl) at 200°C and 300°C, and P=200 MPa. After two days, olivine crystals were fully transformed to an aluminous serpentine, also enriched in iron. The presence of Al in the hydrothermal fluid increases the rate of olivine serpentinization by more than one order of magnitude by enhancing olivine solubility and serpentine precipitation. The mechanism responsible for this increased solubility has to be further investigated but this result motivates a re-evaluation of the natural rates of olivine serpentinization and of olivine hydrolysis in general in a wide range of settings where olivines or peridotites are intimately associated with Al-providers. Such a fast reaction rate may affect the contribution of reaction-enhanced processes at the micrometer-scale, such as reaction-driven cracking, already proposed for enhancing serpentinization or carbonation of olivine. The effect of Al on lower crust and upper mantle metasomatism is expected to be even stronger at higher pressure in subduction zones where those reactions control the rheology and physical properties of the subducting plate and mantle wedge.

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

    Microsoft Academic Search

    J. Drennan; Z. Liu; P. Kelly

    2002-01-01

    High-resolution transmission electron microscopy (HRTEM) of partially transformed samples of Mg2GeO4 have revealed a clear picture of the atomic re-arrangements that take place when the olivine form of the compound transforms to the spinel type under the influence of high pressure and temperatures. This important transformation is an anolog of the olivine-spinel transition in mantle silicates and has been the

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

    Microsoft Academic Search

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

    2009-01-01

    Though solid solution of iron and magnesium between forsterite (Mg2SiO4) and fayalite (Fe2SiO4) is possible in the olivine crystal structure, the high oxygen fugacity condition of the terrestrial mantle inhibits the widespread crystallization of intermediate (Fo40-Fo60) composition olivine. This limitation is not the same for some other inner solar system bodies (e.g. the Moon and Mars), where conditions are reducing

  5. 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

  6. Effect of Water on Fe-Mg Interdiffusion in Olivine

    Microsoft Academic Search

    Z. Wang; T. Hiraga; S. Mei; D. L. Kohlstedt

    2001-01-01

    To quantify the effect of water on the kinetics of Fe-Mg interdiffusion in olivine, diffusion couples composed of two single crystals of San Carlos olivine were hydrothermally annealed in a Paterson gas-medium high-pressure apparatus. Crystals were oriented using a micro-diffractometer with an orientation accuracy of approximately 1° . Samples with approximate dimensions 6x5x1 mm were cut with their large surfaces

  7. Influence of Protons on Fe-Mg Interdiffusion in Olivine

    Microsoft Academic Search

    S. Hier-Majumder; I. M. Anderson; D. L. Kohlstedt

    2004-01-01

    In this work, we present experimental quantification of the influence of water-derived protons on Fe-Mg interdiffusion in olivine. We carried out interdiffusion experiments on diffusion couples consisting of oriented single crystals of olivine of composition {Fo90} and {Fo80}. The diffusion anneals were performed between pressures 0.1 and 6 GPa at temperatures of 1373 to 1450 K. The oxygen fugacity during

  8. Influence of protons on Fe-Mg interdiffusion in olivine

    Microsoft Academic Search

    S. Hier-Majumder; I. M. Anderson; D. L. Kohlstedt

    2005-01-01

    We report the experimental measurement of Fe-Mg interdiffusivity in olivine along the [001] crystallographic direction in a water-saturated environment at pressures of 0.1 to 6 GPa and temperatures between 1373 and 1450 K. The concentration of water-derived protons in olivine was controlled by varying the water fugacity. The oxygen fugacity was set by the Ni-NiO solid state reaction, while the

  9. 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.

  10. New shock-induced transformations of olivines in Martian meteorites

    NASA Astrophysics Data System (ADS)

    Reynard, B.; van de Moortele, B.; Beck, P.; Gillet, P.; McMillan, P. F.

    2006-12-01

    Transient high pressures and temperatures generated during the impact of meteors or asteroids on planetary surfaces can induce phase transformations in low-pressure minerals that mimic those occurring at depth within the silicate mantle of terrestrial planets. For olivine, phase transitions to the high-pressure polymorphs wadsleyite and ringwoodite are observed in shocked chondrites. Melting transitions have also been reported in some samples. We have investigated the transformations of the olivine presenting an unusually black color in two newly-described Martian meteorites NWA2737 and NWA1950. The shock conditions were not sufficient to cause melting or transformation into the high-pressure polymorphs. The black color of the olivines is due to the presence of Fe-Ni metallic nanoparticles that result from loss of oxygen during the shock event. Raman spectroscopy and high-resolution transmission electron microscopy indicate that the shocked "olivines" have a hexagonal close-packed (hcp) structure similar to that observed in the metastable transformations of olivine at high pressure and low temperature, and of wadsleyite at low pressure and moderate temperatures. We propose a metastable phase diagram of olivine including a new hcp phase that accounts for the observations in natural samples and the experimental results.

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

    PubMed Central

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

    2005-01-01

    Bulk chondritic meteorites and terrestrial planets show a monotonic depletion in moderately volatile and volatile elements relative to the Sun's photosphere and CI carbonaceous chondrites. Although volatile depletion was the most fundamental chemical process affecting the inner solar nebula, debate continues as to its cause. Carbonaceous chondrites are the most primitive rocks available to us, and fine-grained, volatile-rich matrix is the most primitive component in these rocks. Several volatile depletion models posit a pristine matrix, with uniform CI-like chemistry across the different chondrite groups. To understand the nature of volatile fractionation, we studied minor and trace element abundances in fine-grained matrices of a variety of carbonaceous chondrites. We find that matrix trace element abundances are characteristic for a given chondrite group; they are depleted relative to CI chondrites, but are enriched relative to bulk compositions of their parent meteorites, particularly in volatile siderophile and chalcophile elements. This enrichment produces a highly nonmonotonic trace element pattern that requires a complementary depletion in chondrule compositions to achieve a monotonic bulk. We infer that carbonaceous chondrite matrices are not pristine: they formed from a material reservoir that was already depleted in volatile and moderately volatile elements. Additional thermal processing occurred during chondrule formation, with exchange of volatile siderophile and chalcophile elements between chondrules and matrix. This chemical complementarity shows that these chondritic components formed in the same nebula region. PMID:16174733

  12. Verification of a Model to Calculate Cooling Rates in Olivine by Consideration of Fe-Mg Diffusion and Olivine Crystal Growth

    Microsoft Academic Search

    M. Miyamoto; R. H. Jones; E. Koizumi; T. Mikouchi

    2005-01-01

    We developed a model to analyze chemical zoning in olivine based on Fe-Mg diffusion during olivine crystal growth to obtain the cooling rate. We verify this model by using Fe-Mg zoning in olivine produced by dynamic crystallization experiments.

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

    E-print Network

    Geist, Dennis

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  15. Chemical and physical studies of chondrites. X - Cathodoluminescence and phase composition studies of metamorphism and nebular processes in chondrules of type 3 ordinary chondrites

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    The cathodoluminescence (CL) characteristics of eight type-3 ordinary chondrites and one L5 chondrite were investigated with particular emphasis on detailed compositions of the relevant phases in four of these chondrites: Semarkona (type-3.0); Krymka (3.1); Allan Hills A77214 (3.5); and Dhajala (3.8). By sorting the chondrules into eight groups according to the CL of mesostasis and to certain compositional criteria and by determining the number of chondrules in these groups as a function of petrological type, it was possible to deduce genetic/evolutionary sequences of the chondrules. It is shown that there are major compositional differences in chondrules, which account for their CL properties and the chondrule groups.

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

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

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

  17. Extraction of in situ cosmogenic 14C from olivine

    USGS Publications Warehouse

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

    2010-01-01

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

  18. Weathering of olivine under CO2 atmosphere: A martian perspective

    NASA Astrophysics Data System (ADS)

    Dehouck, E.; Gaudin, A.; Mangold, N.; Lajaunie, L.; Dauzères, A.; Grauby, O.; Le Menn, E.

    2014-06-01

    Recent analyses from the Curiosity rover at Yellowknife Bay (Gale crater, Mars) show sedimentary rocks deposited in a lacustrine environment and containing smectite clays thought to derive from the alteration of olivine. However, little is known about the weathering processes of olivine under early martian conditions, and about the stability of smectite clays in particular. Here, we present a 3-month experiment investigating the weathering of forsteritic olivine powders (Fo90) under a dense CO2 atmosphere, and under present-day terrestrial conditions for comparison. The experiment also evaluates the potential effects of hydrogen peroxide (H2O2), as a representation of the highly oxidizing compounds produced by photochemical reactions throughout martian history. The weathered samples were characterized by means of near-infrared spectroscopy (NIR), X-ray diffraction (XRD), transmission electron microscopy with energy dispersive X-ray spectrometry (TEM-EDX), Mössbauer spectroscopy and thermogravimetry. The results show that a Mg-rich smectite phase formed from the weathering of olivine under CO2 conditions, although in lower abundance than under terrestrial conditions. The main secondary phase formed under CO2 turns out to be a silica-rich phase (possibly acting as a “passivating” layer) with a non-diagnostic near-infrared spectral signature. The use of H2O2 highlights the critical importance of both the redox conditions and Fe content of the initial olivine on the nature of the secondary phases.

  19. Minor elements in lunar olivine as a petrologic indicator

    NASA Technical Reports Server (NTRS)

    Steele, I. M.; Smith, J. V.

    1975-01-01

    Accurate electron microprobe analyses (approximately 50 ppm) were made for Al, Ca, Ti, Cr, Mn, and Ni in Mg-rich olivines which may derive from early lunar crust or deeper environments. Low-Ca contents consistently occur only in olivines from dunitic and troctolitic breccia: spinel troctolite and other rock types have high-Ca olivines suggesting derivation by near-surface processes. Rock 15445 has olivine with distinctly low CaO (approximately 0.01 wt.%). Chromium ranges to higher values (max.0.2 oxide wt.%) than for terrestrial harzburgites and lherzolites but is similar to the range in terrestrial komatiites. Divalent chromium may be indicated over trivalent Cr because olivines lack sufficient other elements for charge balance of the latter. NiO values in lunar specimens range from 0.00 to 0.07 wt.% and a weak anticorrelation with Cr2O3 suggests an oxidation state effect. Al2O3 values are mostly below 0.04-wt.% and show no obvious correlation with fragment type. TiO2 values lie below 0.13-wt.% and seem to correlate best with crystallization rate and plagioclase content of the host rock. High values of Al2O3 and TiO2 reported by other workers have not been confirmed, and are probably wrong.

  20. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

    Olivine absorptions are known to dominate telescopic spectra of several asteroids. Among the meteorite collection, three groups (excluding Martian meteorites), the pallasites, brachinites, and R group chondrites are plausible analogs to olivine-rich asteroids in that they are dominated by olivine. These meteorite groups have distinct petrologic origins. The primitive achondrite brachinites (which include both depleted and undeleted subgroups) are products of relatively minor differentiation and evolved in oxidizing environments. R chondrites are also thought to have formed in high oxygen states, but are closely related to ordinary chondrites (yet with their own distinct compositions and oxygen isotopic signatures). In contrast, pallasites, widely thought to be mantle components from much more evolved bodies, formed in more reducing environments. Petrologic indicators that are identifiable in spectral data must be used in order to infer the petrologic history of asteroids from surveys of their actual population. As discussed below, olivine composition (e.g. Fa#) can provide key constraints in exploring the origin and significance of olivine dominated asteroids.

  2. Experiments on the Photophoretic Motion of Chondrules and Dust Aggregates - Indications for the Transport of Matter in Protoplanetary Disks

    E-print Network

    Wurm, Gerhard; Bischoff, Addi; Haack, Henning; Roszjar, Julia; 10.1016/j.icarus.2010.01.033

    2010-01-01

    In a set of 16 drop tower experiments the motion of sub-mm to mm-sized particles under microgravity was observed. Illumination by a halogen lamp induced acceleration of the particles due to photophoresis. Photophoresis on dust-free chondrules, on chondrules, glass spheres and metal spheres covered with SiC dust and on pure SiC dust aggregates was studied. This is the first time that photophoretic motion of mm-sized particles has been studied experimentally. The absolute values for the photophoretic force are consistent with theoretical expectations for spherical particles. The strength of the photophoretic force varies for chondrules, dust covered particles and pure dust from low to strong, respectively. The measurements support the idea that photophoresis in the early Solar System can be efficient to transport solid particles outward.

  3. 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.

  4. Exotic Olivine in Antarctic Angrites LEW 87051 and Asuka 881371

    NASA Astrophysics Data System (ADS)

    McKay, G.; Crozaz, G.; Mikouchi, T.; Miyamoto, M.

    1995-09-01

    Angrites are basaltic meteorites with very early formation ages [e.g., 1] suggesting magrnatic activity on their parent body shortly after accretion. To constrain the nature of this magmatism, it is necessary to determine the composition of the melts parental to the angrite meteorites so that these melts can be compared with known phase relationships. Of the four known angrites, Angra dos Reis is highly differentiated and has had a complex history [e.g.,2]. LEW 86010 is probably a low-temperature partial melt containing minor accumulated plagioclase [3]. LEW 87051 (LEW 87) contains porphyritic olivine in a fine-grained groundmass, and the olivine crystals have variously been interpreted as phenocrysts [e.g., 4], xenocrysts [e.g., 5], and compound crystals in which exotic xenocryst cores have been overgrown by olivine that crystallized from the melt [e.g 6]. Asuka 881371 (Asuka 88) contains large olivine crystals in a medium-grained groundmass [7 and these large olivines are unambiguously xenocrysts that are not directly related to the melt in which they now reside [9], and may shed light on the olivines in LEW 87. Several lines of evidence point towards the exotic nature of the large olivines in Asuka 88. Despite being internally homogeneous, these crystals show large variations in composition from one crystal to another. Such variations are shown for Ca and Mg/Mg+Fe in Fig. 1, but are also observed for Cr, Al, and Y. Moreover, the concentrations of these elements in the large olivines are different from the concentrations in the cores of the groundmass olivines that were obviously the first minerals to crystallize from the Asuka 88 melt (Fig 1). Thus the large olivines could not have been in equilibrium with one another nor with the host melt. Furthermore, along healed fractures the the large olivines have been altered towards the groundmass olivine composition either through physical invasion of melt or by enhanced surface diffusion along the fractures. However, despite the clear exotic relationship to the Asuka 88 melt, the O isotopic composition of one olivine xenocryst falls within the angrite group [9], so the xenocrysts are probably not completely exotic to the angrite parent body. By analogy with Asuka 88, we infer that the Mg-rich cores of some porphyritic olivines in LEW 87 are xenocrysts (Fig. 1), but the main portions of these crystals surrounding the cores (labeled LEW 87 phenos in Fig. 1) grew from the LEW 87 melt. Agreement in minor elements between the main portions of LEW 87 olivines and synthetic olivines from LEW 87 experiments supports this interpretation (Fig. 1). We plan to use elemental mapping to locate more cores in LEW 87, to look for core-to-core variation and to measure additional profiles to test for diffusive equilibration between xenocrysts and the outer part of the olivine or groundmass. Using the compositions of first olivines to crystallize from the parent melts of both meteorites and K(sub)(DFe/Mg) of 0.29 from LEW 87 crystallization experiments, we calculate that the bulk compositions reported for Asuka 88 by [9] and LEW 87 by [12] have about 11% and 20% excess olivine (exotic or accumulated) of Fo(sub)83 and Fo(sub)81 respectively. References: [1] Nyquist L. et al. (1994) Meteoritics, 29, 872-885. [2] Mittlefehldt D. and Lindstrom M. (1990) GCA, 54, 3209-3218. [3] McKay G. et al. (1988) LPS XIX, 762-763. [4] McKay G. et al. (1990) LPS XXI, 771-772. [5] Prinz et al. (1990) LPS XXI, 979. [6] Mikouchi T. et al. (1995) LPS XXVI, 973-974. [7] Yanai K. (1994) Proc. NIPR Symp. Antarc. Meteorites, 7, 30-41. [8] McKay G. et al. (1995) Antarc. Meteorites, XX, 155-158. [9] Warren P. et al. (1995) Antarc. Meteorites, XX, 261-264. [10] Warren P. and Kallemeyn G. (1990) LPS XXI, 1295-1296.

  5. An olivine-free mantle source of Hawaiian shield basalts.

    PubMed

    Sobolev, Alexander V; Hofmann, Albrecht W; Sobolev, Stephan V; Nikogosian, Igor K

    2005-03-31

    More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both nickel and silicon at lower levels. This can be resolved if the olivine of the mantle peridotite is consumed by reaction with melts derived from recycled oceanic crust, to form a secondary pyroxenitic source. Our modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from this source. In addition, we estimate that the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plume edge. These results are also consistent with volcano volumes, magma volume flux and seismological observations. PMID:15800614

  6. Iddingzitized olivine in mantle xenoliths: evidence for (really) early alteration

    NASA Astrophysics Data System (ADS)

    Low, P. C.; Schultz, L.; Stier, N.

    2011-12-01

    Iddingsite is an alteration product of olivine (or pyroxene) that contains goethite and some combination of maghemite, hematite, orthopyroxene, Mg-rich phyllosilicates, amorphous silica, and a temperature and a pressure-appropriate SiO2 polymorph and lacks the definite structure or chemical composition requisite of classification as a mineral. The process of iddingsitization is most commonly discussed as a low-temperature, near-surface phenomenon involving the oxidation and inorganic hydroxylation of olivine during weathering. High-temperature iddingsite (sometimes referred to as magmatic iddingsite) is also discussed in the literature and is generally attributed to reactions that occur at low pressure in response unusually high water content and/or high oxygen fugacity in pre-eruptive mafic magmas or during the process of extrusion and cooling or to hydrothermal metasomatism. Xenoliths from the Ponderosa flow of the Uinkaret Volcanic Field located along the Colorado River just downstream from Lava Falls in the Western Grand Canyon include spinel-bearing dunite, harzburgite, and olivine-rich lherzolite samples that exhibit geochemical characteristics that are consistent with residues of 5-17% partial melting. Olivine from xenoliths collected from this flow contain olivine that is either entirely fresh (no evidence of alteration) or olivine that has been ubiquitously partially iddingzitized with some samples containing both the green-colored fresh samples and the red-colored altered samples mere centimeters apart. Preliminary in situ FTIR mapping of water peaks in the region of 3700-3000 cm-1 indicate notable peak near 3680 cm-1 (a region of the spectrum associated with the presences of serpentine minerals) in altered samples. Iddingsite exhibits two distinct morphologies in these samples, one thicker (about 1 micrometer across) occurring mostly along fractures in the olivine grains, and the other much thinner occurring along crystallographically-oriented planes in olivine. Some of the partially altered olivine crystals exhibiting the later texture contain deformational kink bands that, given that the young eruption age of the host basalt, post-dates any crustal activity that could be responsible for such a fabric at this location, much have occurred in the lithospheric mantle. Textural evidence that the iddingzitized areas of these olivine crystals pre-date the kink banding suggests that the alteration of these olivines occurred in the mantle. Post-entrainment alteration is unlikely particularly given the close proximity of altered and unaltered samples with similar post-entrainment history and the fact that the host basalts are not particularly hydrous. The variety of alteration in xenoliths at this location suggest that the entraining flows are either sampling small regions of the mantle that contains very high gradients with regard to water content or oxygen fugacity or are sampling relatively large areas. Quantitative analysis of volatiles in altered and unaltered olivine crystals planned in order to better constrain these gradients.

  7. 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.

  8. 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.

  9. Diffusion of REE, Hf and Sr in Olivine

    NASA Astrophysics Data System (ADS)

    Remmert, P.; Dohmen, R.; Chakraborty, S.

    2008-12-01

    We have determined diffusion coefficients of the rare earth elements Ce, Nd, Sm, Eu, Lu, and also of Sr and Hf, in single crystals of natural olivine at atmospheric pressure, at an oxygen fugacity of 10-5 Pa and a temperature of 1275 °C. Sources of diffusants were thin films of olivine composition doped with the relevant elements. Thin films were produced by PLD (pulsed laser deposition) and RBS (Rutherford backscattering) was used to measure thickness and stoichiometry of the films as well as to analyze the concentration profiles. The concentration profiles were numerically fitted to yield the following diffusion coefficients (D, in m2/s): log DCe: -19.61 ± 0.21; log DNd: -19.54 ± 0.11; log DSm: -19.15 ± 0.05; log DEu: -19.10; log DLu: -19.00, log DHf: -20.23 ± 0.07; log DSr: -18.7. Diffusion coefficients of the rare-earth elements increase from Ce to Lu, demonstrating the role of ionic radius in controlling diffusion because all REE are trivalent. The tetravalent and divalent cations hafnium and strontium diffuse an order of magnitude slower and faster, respectively, than the REE in olivine. This highlights the important influence of ionic charge on diffusion rates. The diffusion coefficients of the REE are slower by a few orders of magnitudes than the diffusion rate of Cr in olivine [1]. The rates found in this study are slower than those assumed by a model [2] for compositional modification of melt inclusions in olivine. Use of our data in their calculations indicates that it will take longer to modify the composition of melt inclusions in olivine (millions of years rather than thousands of years) but the fractionation of HREE from LREE will be larger. [1] Ganguly J, Ito M (2006) Geochim Cosmochim Acta, 70, 799-809. [2] Cottrell E, Spiegelman M, Langmuir CH (2002) Geochem Geophys Geosyst, doi:10.1029/2001GC000205

  10. 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).

  11. Nickel enrichment in mantle olivine beneath a volcanic front

    Microsoft Academic Search

    Satoko Ishimaru; Shoji Arai

    2008-01-01

    We found abnormally Ni-rich olivine (Fo = 93) with up to 5.3 wt% of NiO, ten times higher than the ordinary mantle value (0.4 wt%),\\u000a in a highly metasomatized mantle peridotite xenolith from Avacha volcano, the Kamchatka arc, Russia. The Ni enrichment displays\\u000a outward diffuse circular domains (<1 mm across) in fine-grained (mostly <100 ?m) olivine-rich parts. Associated metasomatic\\u000a orthopyroxene also shows high NiO (<1.1 wt%). Such

  12. Grinding methods to enhance the reactivity of olivine

    SciTech Connect

    Summers, Cathy A.; Dahlin, David C.; Rush, Gilbert E.; O'Connor, William K.; Gerdemann, Stephen J.

    2004-01-01

    The Albany Research Center (ARC) conducted studies of mechanical activation by conventional and ultra-fine grinding techniques to enhance olivine reactivity in mineral carbonation reactions. Activated olivine is one of several solid feed materials used at ARC in reactions with carbon dioxide to form carbonate minerals. This paper compares grinding techniques via energy demand data and product characteristics, including particle size distributions, surface areas, full width at half maximum (FWHM) XRD analyses, and particle morphology by SEM analyses. Reactivity was gauged by percent conversion to carbonate in subsequent carbonation tests.

  13. Trace Element Distribution Between Olivine and Kirschsteinite in Angra Dos Reis

    NASA Astrophysics Data System (ADS)

    Fittipaldo, M. M.; Jones, R. H.; Shearer, C. K.

    2003-03-01

    Kirschsteinite occurs interstitially to olivine grains in olivine aggregates in the Angra dos Reis angrite. Trace element abundances in these two phases in Angra dos Reis are similar to trace element abundances in these phases in LEW86010.

  14. Influence of aluminum on the hydrothermal alteration rate of olivine

    NASA Astrophysics Data System (ADS)

    Andreani, M.; Daniel, I.; Pollet-Villard, M.

    2013-12-01

    The reactivity of ultramafic rocks under hydrothermal conditions controls chemical fluxes at the interface between the internal and external reservoirs of silicate planets. On Earth, hydration of ultramafic rocks is ubiquitous and operates from deep subduction zones to shallow lithospheric environments where it considerably affects the physical and chemical properties of rocks and can interact with the biosphere. This process also has key emerging societal implications, such as the production of hydrogen as a source of carbon-free energy. To date, the chemical model systems used to reproduce olivine hydrothermal alteration lead to the formation of serpentine with sluggish reaction rates. Although aluminum is common in geological environments and in hydrothermal systems in particular, its role in serpentinization or olivine dissolution has not been investigated under hydrothermal conditions. Nevertheless, abundant Al supply is expected in fluids released from dehydration of metapelites in subduction zones as well as during the hydrothermal alteration of gabbros at mid-ocean ridges. Aluminum was also abundant in primitive environments of both the Earth and Mars, stored in either Al-rich minerals like plagioclase or Al-enriched ultramafic lavas. We have investigated the role of Al on the hydrothermal alteration of olivine in a series of experiments performed in a low-pressure diamond anvil cell while following the reaction progress in situ by optical imaging and by confocal Raman spectroscopy. Experiments were run for 4.5 to 7.5 days with two olivine grains reacted in saline water (0.5 molal NaCl) at 200°C and 300°C, and P=200 MPa. After two days, olivine crystals were fully transformed to an aluminous serpentine, also enriched in iron. The very fast precipitation of serpentine may inhibit magnetite nucleation here. However, this does not rule out an H2 production since serpentines classically incorporate non negligible amount of ferric iron in their structure. The presence of Al in the hydrothermal fluid increases the rate of olivine serpentinization by more than one order of magnitude by increasing olivine solubility and enhancing serpentine precipitation. The mechanism responsible for this increased solubility has to be investigated further but this result motivates a re-evaluation of the natural rates of olivine serpentinization and of olivine hydrolysis in general in a wide range of settings where olivines or peridotites are intimately associated with Al-providers. Such a fast reaction rate may affect the contribution of reaction-enhanced processes at the micrometer-scale, such as reaction-driven cracking, already proposed for enhancing serpentinization or carbonation of olivine. The effect of Al on lower crust and upper mantle metasomatism is expected to be even stronger at higher pressure in subduction zones where those reactions control the rheology and physical properties of the subducting plate and mantle wedge. Finally, this study also provides a way to accelerate serpentinization reactions towards economically feasible time-scale and temperature for industrial H2 production and/or CO2 remediation.

  15. 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 3.1016/j.jcrysgro.2012.02.040 #12;2 Abstract16 Olivine mineral replacement by serpentine is one major between olivine and chrysotile-brucite minerals. Coupled dissolution-precipitation21 led to the alteration

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

    E-print Network

    Treiman, Allan H.

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

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

    Microsoft Academic Search

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

    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

  18. NEBULAR FORMATION OF FAYALITIC OLIVINE: INEFFECTIVENESS OF DUST ENRICHMENT. A. V. Fedkin1

    E-print Network

    Grossman, Lawrence

    is predicted to reach the level found in UOCs only below 600K, where Fe-Mg interdiffusion rates in olivine abundances of C and O [3], making the nebula more reducing; and Fe-Mg interdif- fusion rates in olivine [4,5], making diffusion slower; as well as recognition of non-ideality in olivine solid solutions, lowering

  19. Slip-system and EBSD analysis on compressively deformed fine-grained polycrystalline olivine

    E-print Network

    pre- ferred orientations (CPO) develop under upper mantle conditions due to prevailing plate tectonic and silica (in the case of olivine) and `water'. The type-A CPO typically develops in low-OH natural olivine of water concentrations in olivine

  20. Martian dunite NWA 2737: Integrated spectroscopic analyses of brown olivine

    Microsoft Academic Search

    Carle M. Pieters; Rachel L. Klima; Takahiro Hiroi; M. Darby Dyar; Allan H. Treiman; Sarah K. Noble; Jessica M. Sunshine; Janice L. Bishop

    2008-01-01

    Received 5 October 2007; revised 13 December 2007; accepted 6 March 2008; published 18 June 2008. (1) A second Martian meteorite has been identified that is composed primarily of heavily shocked dunite, Northwest Africa (NWA) 2737. This meteorite has several similarities to the Chassigny dunite cumulate, but the olivine is more Mg rich and, most notably, is very dark and

  1. Spinel-olivine geothermometry in peridotites from ultramafic complexes

    Microsoft Academic Search

    Jacques Fabriès

    1979-01-01

    An empirical calibration of the spinel-olivine geothermometer (Evans and Frost, 1975) is attempted and applied to parageneses of lherzolitic rocks. In ultramafic complexes, most of the derived temperature estimates range between 700 ° and 850 °C, and appear generally lower than those given by other geothermometers, based upon Ca or Al contents of coexisting pyroxenes. A comparison of the different

  2. Temperature dependence of Fe,Mg partitioning in Acapulco olivine

    Microsoft Academic Search

    ROLF HEINEMANN; VERONIKA STAACK; ARNE FISCHER; HERBERT KROLL; THOMAS VAD; ARMIN KIRFEL

    The temperature dependence of the intracrystalline Fe,Mg partitioning ( KD) in two olivine crys- tals (Fa11) separated from the Acapulco meteorite was determined by single-crystal X-ray structure analysis. The independent atom model (IAM) was compared with a \\

  3. Micromechanical modeling of the viscoplastic behavior of olivine

    NASA Astrophysics Data System (ADS)

    Castelnau, O.; Blackman, D. K.; Lebensohn, R. A.; Ponte CastañEda, P.

    2008-09-01

    Efforts to couple mantle flow models with rheological theories of mineral deformation typically ignore the effect of texture development on flow evolution. The fact that there are only three easy slip systems for dislocation glide in olivine crystals leads to strong mechanical interactions between the grains as the deformation proceeds, and subsequent development of large viscoplastic anisotropy in polycrystals exhibiting pronounced Lattice Preferred Orientations. Using full-field simulations for creep in dry polycrystalline olivine at high temperature and low pressure, it is shown that very large stress and strain rate intragranular heterogeneities can build up with deformation, which increase dramatically with the strength of the hard slip system (included for the purpose of enabling general deformations). Compared with earlier nonlinear extensions of the Self-Consistent mean-field theory to simulate polycrystal deformation, the "Second-Order" method is the only one capable of accurately describing the effect of intraphase stress heterogeneities on the macroscopic flow stress, as well as on the local stress- and strain rate fluctuations in the material. In particular, this approach correctly predicts that olivine polycrystals can deform with only four independent slip systems. The resistance of the fourth system (or accommodation mechanism), which is likely provided by dislocation climb or grain boundary processes as has been observed experimentally, may essentially determine the flow stress of olivine polycrystals. We further show that the "tangent" model, which had been used extensively in prior geophysical studies of the mantle, departs significantly from the full-field reference solutions.

  4. The geoengineering potential of artificially enhanced silicate weathering of olivine

    Microsoft Academic Search

    Peter Köhler; Jens Hartmann; Dieter A. Wolf-Gladrow

    2010-01-01

    Geoengineering is a proposed action to manipulate Earth's climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate in more detail the potential of a specific geoengineering technique, the carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification,

  5. Olivine dissolution in basaltic melt Yang Chen *, Youxue Zhang

    E-print Network

    Zhang, Youxue

    reaction and mass transfer. Heat transfer is often considered not the rate-controlling mecha- nism because. Therefore, diffusion, not interface reaction, is the rate-controlling step for non-convective olivine that enhances mass transport. Such convective dissolution and growth rates have not been quantified before. Mg

  6. Olivine in kimberlites: metasomatism of the deep lithospheric mantle

    NASA Astrophysics Data System (ADS)

    Cordier, Carole; Sauzeat, Lucie; Arndt, Nicholas; Boullier, Anne-Marie

    2014-05-01

    Most kimberlites contain abundant mantle microxenoliths (nodules) and xenocrysts, mainly composed of olivine. We present here a geochemical and microstructural study of nodules from well-preserved type-I kimberlites from Kangamiut region in Greenland, the sequel of a preliminary study of Arndt et al. (2010). A striking feature of these and many other kimberlites is the wide range of olivine composition (Fo83 to Fo94) from nodule to nodule in a single kimberlite sample, contrasting with the olivine homogeneity within a single nodule (variation of less than 0.5 mol. %). We defined three chemical zones within normally zoned nodules based on Fo and Ni variations. Xenocrystic cores have high and constant Fo and Ni contents. Outer rims crystallized from the kimberlitic magma have constant Fo content (Fo88) coupled with significant decrease in Ni content (from 2500 to 500 ppm). Transition zones between cores and rims, along grain boundaries and along fluid inclusion trails have variable Fo content (Fo93 to Fo88) but roughly constant Ni content (from 3000 to 25000 ppm) and their composition mimics that defined by the nodules. Microstructural study of transition zones associated with curvilinear grain boundaries suggests these zones are produced during fluid-assisted plastic deformation. We propose that the transition zones formed during reaction of mantle peridotite with CO2-rich fluid, a process that removes the pyroxene and garnet components. The compositional variations of the transition zones monitor at the fine scale the processes that produce the chemical variability of olivine from nodule to nodule. We propose that the range of olivine composition records the position of sample relative to fluid-rich zones, grain boundaries for transition zones and larger conduits for broader scale variations registered in the nodules. This conclusion implies that metasomatic processes that produced the range of olivine composition and removed pyroxene and garnet from the initial peridotite occurred within the lithospheric mantle and not within the kimberlite magma during it ascent toward the surface. Arndt, N. T.; Guitreau, M.; Boullier, A. M.; Le Roex, A.; Tommasi, A.; Cordier, P. & Sobolev, A. V. (2010): Olivine, and the origin of kimberlite. Journal of Petrology, 51, 573-602.

  7. 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.

  8. 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.

  9. Copper and Zinc Stable Isotope Compositions of Chondrules and CAIs: Method Development and Possible Implications for Early Solar System Processes

    NASA Astrophysics Data System (ADS)

    Mullane, E.; Mason, T. F. D.; Russell, S. S.; Weiss, D.; Hortswood, M.; Parrish, R. R.

    2001-03-01

    Using MC-ICP-MS to measure Cu-Zn isotope fractionation, we aim to determine their chondrule and CAI systematics, to delineate early solar system processes. We introduce a new method using Ga, to monitor mass-bias, enabling concurrent Cu-Zn analyses.

  10. 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.

  11. February 21, 2012 ---Isotopic measurements of a chondrule in a Comet Wild 2 grain tell the story of

    E-print Network

    February 21, 2012 --- Isotopic measurements of a chondrule in a Comet Wild 2 grain tell the story's Stardust spacecraft provide crucial information not only about the mission's target, comet 81P/Wild 2, but also about the dynamics in the solar nebula that brought the comet's materials together. Ryan Ogliore

  12. The role of Fe and redox conditions in olivine carbonation rates: An experimental study of the rate limiting reactions at 90 and 150 °C in open and closed systems

    NASA Astrophysics Data System (ADS)

    Saldi, Giuseppe D.; Daval, Damien; Morvan, Gilles; Knauss, Kevin G.

    2013-10-01

    The mechanisms and rates of olivine carbonation reactions have been the object of a number of studies, but the thermodynamic limitations and the kinetics of the elementary processes that control the overall reaction are still poorly understood and characterized. The main objective of this study is to probe the effect of Fe on the measured rates of olivine carbonation and its role in the formation of Si-rich surface layers, which can significantly inhibit olivine dissolution and limit the extent of the carbonation reaction. A series of batch and flow-through reactor experiments was conducted in pure water at 90 and 150 °C and under a CO2 partial pressure of 100 and 200 bar, using both a natural sample of Fe-bearing olivine (Fo88) and a synthetic sample of pure forsterite (Fo100). Experimental results show that Fe plays an ambivalent role in the carbonation rates of olivine. On one hand, the presence of Fe favors the formation of Fe-Si-rich protective layers at the interface between olivine and aqueous solution, slowing down the dissolution reaction and limiting the extent of carbonation, whereas pure silica coatings have little to no inhibiting effect on measured carbonation rates. On the other hand, Fe enhances olivine to carbonate conversion rates at low degrees of supersaturation, by promoting the formation of fast precipitating Mg-Fe carbonate solid solutions. The passivating properties of Fe-Si-rich layers originate from the strong Fe(III)-Si interaction and are linked to the permanence of oxidizing conditions in the aqueous fluid. As a consequence, under reducing conditions, olivine carbonation rates can be significantly increased by higher extents of dissolution and by the formation of ferroan magnesites (Mg,Fe)CO3, which nucleate faster than the pure Mg end-member. Forsterite and olivine carbonation reactions can be hindered by the formation of secondary Mg sheet-silicates but, at the conditions studied, the formation of such silicate phases was observed to be transitional and not affecting significantly the rates of carbonation at the end of one-month long experimental runs. This work presents new measurements of olivine carbonation rates and delivers relevant information that suggest new reference criteria for the assessment of the sequestration potential of CO2 repositories and the optimization of the mineral carbonation process in mafic and ultramafic rocks.

  13. Geoengineering potential of artificially enhanced silicate weathering of olivine

    PubMed Central

    Köhler, Peter; Hartmann, Jens; Wolf-Gladrow, Dieter A.

    2010-01-01

    Geoengineering is a proposed action to manipulate Earth’s climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate the potential of a specific geoengineering technique, carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. If important details of the marine chemistry are taken into consideration, a new mass ratio of CO2 sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1 Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments, a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg of C per year, but these upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2. Open water dissolution of fine-grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1–5 Pg of C per year for the 21st century by this technique. PMID:21059941

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

    PubMed

    Köhler, Peter; Hartmann, Jens; Wolf-Gladrow, Dieter A

    2010-11-23

    Geoengineering is a proposed action to manipulate Earth's climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate the potential of a specific geoengineering technique, carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. If important details of the marine chemistry are taken into consideration, a new mass ratio of CO(2) sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1 Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments, a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg of C per year, but these upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2. Open water dissolution of fine-grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1-5 Pg of C per year for the 21st century by this technique. PMID:21059941

  15. Olivine vitrophyres - A nonpristine high-Mg component in lunar breccia 14321

    NASA Technical Reports Server (NTRS)

    Shervais, John W.; Taylor, Lawrence A.; Lindstrom, Marilyn M.

    1988-01-01

    The presence of olivine vitrophyres in breccia 14321 is discussed, suggesting that olivine vitrophyres could account for the high-Mg component of soils and breccias in the lunar highlands. The olivine vitrophyre clasts from 14321 have high bulk MgO and the Mg/(Mg+Fe) ratio is 78 percent. The olivine vitrophyres are impact melt rocks and are rich in KREEP. The high MgO concentration is manifest by skeletal quench crystals of olivine that constitute about 30 percent of the mode.

  16. Olivine and Carbonate Globules in ALH84001: A Terrestrial Analog, and Implications for Water on Mars

    NASA Technical Reports Server (NTRS)

    Treiman, A. H.

    2005-01-01

    Carbonate globules in ALH84001 are associated with small olivine grains an unexpected finding because the olivines equilibrated at high T while the carbonate is chemically zoned and unequilibrated. A possible explanation comes from a terrestrial analog on Spitsbergen (Norway), where some carbonate globules grew in cavities left by aqueous dissolution of olivine. For ALH84001, the same process may have acted, with larger olivines dissolved out and smaller ones shielded inside orthopyroxene. Carbonate would have been deposited in holes where the olivine had been. Later shocks crushed remaining void space, and mobilized feldspathic glass around the carbonates.

  17. Cosmogenic 3He and 21Ne Production in Olivine and Pyroxene From a Pleistocene Basalt Flow, Western Grand Canyon, AZ, USA

    NASA Astrophysics Data System (ADS)

    Fenton, C. R.; Niedermann, S.; Goethals, M. M.; Schneider, B.; Wijbrans, J.

    2008-12-01

    Using a combination of 3Hec and 21Nec measurements on both pyroxene and olivine from two basalt flows (80-114 kyr) greatly increases the ability to evaluate the accuracy of cosmogenic 3Hec and 21Nec production rates and corresponding exposure ages. In this study, samples were collected from two flows, once mapped as the single Bar Ten lava flow, which is located between 1180 to 1820 m above sea level and 36.2239° to 36.2417° N. Comparison of 3Hec and 21Nec age-pairs calculated from experimental production rate determinations and composition-based model calculations indicates that the former yield more accurate exposure ages than the latter. Calibrated production rates, however, should be normalized to the composition of the specific minerals being analyzed to obtain the best agreement between 3Hec and 21Nec ages. Measuring both He and Ne in olivine and/or pyroxene samples allows for the identification of samples with 3Hec and 21Nec anomalies, particularly when 21Nec/3Hec data for a sample are not in agreement with expected values. 21Nec/3Hecvalues are 0.400 ± 0.034 and 0.200 ± 0.020 for olivine and pyroxene in Bar Ten lava flows, in agreement with previously published values, and indicate that 21Nec/3Hec in olivine and pyroxenes remains constant with latitude, elevation, and time (up to 10 Myr). The neon three-isotope diagram can also indicate whether or not all excess neon in mineral separates comes from cosmogenic or non-cosmogenic sources. An error-weighted regression defines a spallation line [y = (1.0834 ± 0.0348)x + (0.09835 ± 0.00037)], which is similar to that for pyroxene (Schäfer et al., 1999). Based on an 40Ar/39Ar age of the younger Bar Ten lava flow (80 ± 25 ka), we approximate a new calibrated production rate of 25 ± 8 at/g/yr for 21Nec in clinopyroxene [(Ca0.46Mg0.42Fe0.09)(Si0.92Al0.08)O3]. Cosmogenic noble gas data indicate that Ca may play a greater role in the production of 21Nec than previously established. Cosmogenic 3He and 21Ne remain extremely useful, particularly when paired, in determining accurate eruption ages of young olivine- and pyroxene-rich basaltic lava flows.

  18. Bar Graph Mania

    NSDL National Science Digital Library

    Ms. Thurlow

    2005-10-26

    Use these activities to build and interpret data on bar graphs. Catch all the bugs in the system and put them in the correct column of the bar graph. Answer the questions about the bugs in the graph. Catch bugs in six rooms. Bugs in the system Do these bar graphing activities. You don\\'t have to do the last question ...

  19. Lattice preferred orientations of olivine in the schistosed antigorite serpentinite

    NASA Astrophysics Data System (ADS)

    Soda, Y.; Ando, J.; Mizukami, T.; Morishita, T.

    2011-12-01

    The lattice preferred orientation (LPO) of the schistosed antigorite serpentinite is considered as causes of the seismic anisotropy observed at the subduction zones (Katayama et al., 2009; Jung, 2011) and the natural examples are reported by several researchers (Bezacier et al., 2010; Hirauchi et al., 2010; Soda and Takagi, 2010). Formation process of the antigorite LPO is unclear, especially at primary serpentinized stage. To understand the development of micro-structures of antigorite serpentinite, we made structural analyses of serpentinite schist and the former peridotite fabric. Samples were taken from lenticular serpentinite bodies (< 1km) stack in Jurassic accretionary complex, Toba area, Southwest Japan. The serpentinite consist of olivine, antigorite, meta-clinopyroxene and Cr-spinel. The foliation and lineation of serpentinite is defined by parallel alignment of elongated olivine grain and antigorite blades, which make up mylonitic textures, such as a porphyroclast system and composite planar fabric. Antigorite blades show syn-kinematic growth in pressure shadows and pull-apart of olivine porphyroclast. In the less serpentinized part, antigorite blades are crystallized along the grain boundary of olivine. We measure the LPOs of coarse olivine grains in the serpentinite schist using a u-stage. The X, Y and Z directions represent directions of lineation, normal to lineation within the foliation and normal to foliation, respectively. The LPOs of olivine show point maximum or partial girdle distribution, and these concentrated crystal axes are incongruous with X, Y and Z direction. The a[100] axes of olivine are parallel to the serpentinite foliation, and form a point maximum several degrees away from the Y direction. The b[010] axes and the c[001] axes are concentrated Z and X direction forming a partial girdle normal to Y direction, respectively. Boudier et al. (2010) have reported the topotactic relationship between olivine and antigorite. They show that the (100)ol is parallel to the (001)atg or the (010)ol is parallel to the (001)atg. And, the a[100] axes of olivine are normal to serpentinite foliation with point maximum in the thin section scale. However, in the case of this study, the simple topotactic relationship does not connect the fabric in the thin section scale of serpentinite schist. Although, more detail analysis need to discuss the formation of antigorite LPO, the other mechanisms, such as crystal plastic deformation or diffusion-precipitation, might cause rearrangement of antigorite fabric. References Bezacier, L. et al., 2010, Earth and Planetary Science Letters, 289, 198-208. Boudier, F. et al., 2010, Journal of Petrology 51, 495-512. Hirauchi et al., 2010, Earth and Planetary Science Letters, 299, 196-206. Jung, H., 2011, Earth and Planetary Science Letters, 307, 535-543. Katayama, I., et al., 2009, Nature, 461, 1114-1118. Soda, Y. and Takagi, H., 2010, Journal of Structural Geology, 32, 792-802.

  20. Non-nebular origin of dark mantles around chondrules and inclusions in CM chondrites

    NASA Astrophysics Data System (ADS)

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

    2006-03-01

    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. Acta56, 1992, 2873-2897]. 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 791198 we find no correlation when all sizes of central objects and dark lumps are included but a significant correlation ( r2 = 0.44) if we limit consideration to central objects with radii >35 ?m; 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).

  1. 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).

  2. The solubility of olivine in basaltic liquids - An ionic model

    NASA Technical Reports Server (NTRS)

    Herzberg, C. T.

    1979-01-01

    A model is presented which enables the temperature at which olivine is in equilibrium with any alkali-depleted basaltic compound to be calculated to within + or - 30 C. It is noted that the error increases substantially when applied to terrestrial basalts which contain several weight percent alkalis. In addition the model predicts and quantifies the reduced activity of SiO4(4-) monomers due to increasing SiO2 concentrations in the melt. It is shown that the coordination of alumina in melts which precipitate olivine only appears to be dominantly octahedral, while titanium acts as a polmerizing agent by interconnecting previously isolated SiO4(4-) monomers. It is concluded that the model is sufficiently sensitive to show that there are small repulsive forces between Mg(2+) and calcium ions which are in association with normative diopside in the melt.

  3. Grinding methods to enhance the reactivity of olivine

    SciTech Connect

    Summers, Cathy A.; Dahlin, David C.; Rush, Gilbert E.; O'Connor, William K.; Gerdemann, Stephen J.

    2005-08-01

    The Albany Research Center (ARC) conducted studies of mechanical activation by conventional and ultrafine grinding techniques to enhance olivine reactivity in mineral carbonation reactions. Activated olivine is one of several solid feed materials used at ARC in reactions with carbon dioxide to form carbonate minerals. This paper compares grinding techniques via energy demand data and product characteristics, including particle size distributions, surface areas, full-width-at-half-maximum (FWHM) XRD analyses, and particle morphology by SEM analyses. Reactivity was calculated by percent conversion to carbonate in subsequent carbonation tests. Particle size reduction has the greatest impact on reactivity, and wet grinding is more energy efficient than dry grinding. Large additional inputs of energy to increase surface area or reduce crystallinity do not result in proportional improvements in reactivity.

  4. First-principles studies of native defects in olivine phosphates

    NASA Astrophysics Data System (ADS)

    Hoang, Khang; Johannes, Michelle

    2011-03-01

    Olivine phosphates LiMPO4 (M=Mn, Fe, Co, Ni) are promising candidates for rechargeable Li-ion battery electrodes because of their energy storage capacity and electrochemical and thermal stability. It is known that native defects have strong effects on the performance of olivine phosphates. Yet, the formation and migration of these defects are not fully understood, and we expect that once such understanding has been established, one can envisage a solution for improving the materials' performance. In this talk, we present our first-principles density-functional theory studies of native point defects and defect complexes in LiMPO4, and discuss the implications of these defects on the performance of the materials. Our results also provide guidelines for obtaining different native defects in experiments.

  5. Si-rich layer formation on olivine surfaces during reaction with water and supercritical carbon dioxide under conditions relevant for geologic carbon storage

    NASA Astrophysics Data System (ADS)

    Johnson, N. C.; Jackson, A.; Maher, K.; Bird, D. K.; Brown, G. E.

    2013-12-01

    The reaction of Mg-silicate minerals (i.e. olivine) with carbon dioxide (CO2) is a promising method for secure, long-term, geologic carbon storage. Several technical challenges must be overcome before implementing mineral carbonation technology on a large scale, one of which is slow reaction kinetics. This study probes surface reaction limitations of olivine carbonation, specifically the formation of a passivating, Si-rich layer on olivine surfaces upon exposure to water and CO2 under sequestration conditions (elevated temperature and pressure). A series of batch reactions were performed at 60°C and 100 bar CO2 pressure in Dickson-style rocker bombs, varying the length of reaction and the amount of mixing (rocking). The initial aqueous phase was spiked with 29Si. Fluid samples were taken periodically and analyzed for cation content, alkalinity, and dissolved inorganic carbon. At the end of each experiment, the solid products were analyzed with a Sensitive High Resolution Ion Microprobe Reverse Geometry (SHRIMP-RG) in order to measure the amount of 29Si incorporated into the Si-rich layer on reacted olivine grains. We also cut cross sections of reacted grains from each experiment using a Focused Ion Beam (FIB) which were thinned to <100nm and imaged using Transmission Electron Microscopy (TEM). SHRIMP-RG results show incorporation of 29Si on olivine grain surfaces reacted for 19 days with no mixing, and TEM images of olivine grains from the same experiment show an amorphous, Si-rich layer that is 30nm thick. Similarly, SHRIMP-RG results for olivine grains reacted for 19 days with mixing indicate 29SiO2 precipitation and TEM images reveal a Si-rich layer 60nm thick. In both experiments, EDS (energy dispersive spectroscopy) data show a step change in composition from the bulk rock to the surface layer in addition to the sharp crystalline/amorphous interface visible in the TEM images. Olivine from the unmixed experiment also has a slow decrease in Mg relative to Si before the step change, suggesting that, at least in this experiment, a Si-rich layer precipitated on top of a Mg-depleted layer that formed via a leaching process. SHRIMP-RG data also imply the presence of a precipitated Si-rich layer on top of a leached Si-rich layer, as the 29Si penetration depth is only 25-65% of the total Si-rich layer thickness. The combination of SHRIMP-RG and FIB/TEM analysis leads us to hypothesize that a Si-rich layer forms quickly on olivine surfaces due to preferential Mg removal from the surface (the traditional 'leached' layer), and as the reaction proceeds, amorphous silica reaches saturation in the fluid and precipitates on surfaces inside the reactor (including olivine grains).

  6. A re-evaluation of the olivine-spinel geothermometer

    Microsoft Academic Search

    Peter L. Roeder; Ian H. Campbell; Heather E. Jamieson

    1979-01-01

    The Irvine olivine-spinel geothermometer, as formulated by Jackson (1969), appears to yield magmatic temperatures when applied\\u000a to plutonic rocks such as the Stillwater Complex but Evans and Wright (1972) have demonstrated that it gives temperatures\\u000a in excess of 2,000 ° C when applied to volcanic assemblages. A re-evaluation of the geothermometer has shown that more realistic\\u000a temperatures can be obtained

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

    Microsoft Academic Search

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

    2007-01-01

    Despite considerable effort to measure the activation volume V* of creep of olivine using a new generation of high-pressure deformation machines, namely the Rotational Drickamer Apparatus (RDA) and the Deformation- DIA (D-DIA) in conjunction with synchrotron x-ray sources, progress has been marred by a combination of an apparently weak signal (i.e., low V*) and measurement noise. The latter has a

  8. Water dissolved in Olivine: A single-crystal infrared study

    Microsoft Academic Search

    Friedemann Freund; Gert Oberheuser

    1986-01-01

    Polarized infrared spectra of the hydrogen impurities in an olivine single crystal, approximately (Mg0.9Fe0.1)2SiO4, from the Zargabad Island, Red Sea, are reported in the range 4200-3000 cm-1. In the O-H stretching frequency region, two groups of IR absorption bands occur which show the same pleochroism and the same temperature-induced shift between room temperature and 80 K. Each of these IR

  9. New measurements of activation volume in olivine under anhydrous conditions

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

    A new cell assembly for the deformation-DIA (D-DIA) shows promise for limiting the water content of samples and providing a more mechanically stable environment for deformation. The 6-mm cubic cell consists of a 6-mm diameter mullite sphere cradled in a web of unfired pyrophyllite. The pyrophyllite flows during initial compression of the D-DIA to form gaskets between the six anvils while the mullite flows to become a nearly cubic-shaped pressure medium. Measurements on olivine indicate more than one order of magnitude drop in water content to <40 ppm H/Si compared with the boron-epoxy medium. Improved mechanical stability is achieved by elimination of the thermocouple from the assembly and determination of temperature from calibration curves of furnace power vs. temperature. Three samples of polycrystalline orthopyroxene-buffer San Carlos olivine have been deformed in high-temperature creep in the new cell, at pressures of 2.7-4.9 GPa and temperatures near 1473 K. Strength is consistent with that measured in the gas-apparatus at lower pressures. Over the pressure range investigated we resolve an activation volume for creep of dry olivine of V* = 9.5 ± 7 × 10 -6 m 3/mol.

  10. Polaron formation and transport in olivine cathode materials

    NASA Astrophysics Data System (ADS)

    Johannes, Michelle; Hoang, Khang

    2011-03-01

    One of the critical factors limiting Li ion battery performance is electronic conduction through the cathode material. In the olivine structure type materials, such as LiFePO4, the parent materials are insulators with a gap of approximately 4 (or more) eV. The withdrawal of an electron results not in a band-type hole state, but rather a localized polaronic state. Transport then occurs via hopping of the polaron through the crystal. The measured electronic conduction in olivine materials depends on the transition metal cation type. In this study, we use density functional theory to compare formation of polarons in olivine materials with different transition metal cations: Mn, Fe, Co, and Ni. We show that the underlying electronic structure of the fully lithiated material (or fully delithiated material) essentially determines whether or not polaron formation is possible in localized d-states or whether the holes that result from adding or removing an electron reside in oxygen-derived states. We also investigate the facility of polaronic hopping by calculating the barrier between adjacent polaron sites in each of the four materials.

  11. Chemical energy in cold-cloud aggregates - The origin of meteoritic chondrules

    NASA Astrophysics Data System (ADS)

    Clayton, D. D.

    1980-07-01

    If interstellar particles and molecules accumulate into larger particles during the collapse of a cold cloud, the resulting aggregates contain a large store of internal chemical energy. It is here proposed that subsequent warming of these accumulates leads to a thermal runaway when exothermic chemical reactions begin within the aggregate. These, after cooling, are the crystalline chondrules found so abundantly within chondritic meteorites. Chemical energy can also heat meteoritic parent bodies of any size, and both thermal metamorphism and certain molten meteorites are proposed to have occurred in this way. If this new theory is correct, (1) the model of chemical condensation in a hot gaseous solar system is eliminated, and (2) a new way of studying the chemical evolution of the interstellar medium has been found. A simple dust experiment on a comet flyby is proposed to test some features of this controversy.

  12. 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.

  13. LA-ICP-MS mapping of olivine from the Brahin and Brenham meteorites: Complex elemental distributions in the pallasite olivine precursor

    NASA Astrophysics Data System (ADS)

    McKibbin, Seann J.; O'Neill, Hugh St. C.; Mallmann, Guilherme; Halfpenny, Angela

    2013-10-01

    To investigate the early history of olivine from the Main-Group pallasites Brahin and Brenham, we have spatially mapped their trace-element distributions using laser-ablation inductively-coupled-plasma mass spectrometry (LA-ICP-MS). Brahin olivine interiors contain ˜100-200 ?m patches enriched in Cr, Al, Ti, V, Sc and Ga, separated by linear enrichments of P; these structures bear no relation to current crystal morphologies. Rather, cross-cutting relationships suggest they predate olivine-metal mixing. Brenham olivine also has internal variations for these elements. By contrast, Ni and Co concentrations in olivine from both meteorites decrease near crystal margins, as expected for freezing-in of profiles formed during diffusive re-equilibration with metal during cooling. Brenham olivine also has decreasing Al, Cr and Ti near the margin. Correlations between concentrations of Cr and Al exist for individual Brahin olivine grains, but do not hold over multiple grains, indicating a heterogeneous precursor. Al and Ti are correlated over multiple grains in Brahin, interpreted as Ti cations decorating pre-existing Al-defects. In Brenham olivine, similar geochemical trends exist, but the Cr-Al relationship probably represents both grain margin effects and pre-existing internal heterogeneity. The preservation of structure for elements which are normally fast diffusers in olivine hinges on coupled substitutions involving Al, which along with P diffuses much more slowly than most other elements under some conditions. Al concentrations in olivine are low and variable (3-33 ppm) which is inconsistent with crystallisation from a normal silicate melt; Al-in-olivine thermometers indicate that pallasite olivine was formed in a low-temperature environment. Following its delivery to the magma ocean/core-mantle boundary, Al-P systematics were not substantially modified. Assuming diffusivities for Al and P that are similar to Si (since they reside in the same crystallographic site) and temperatures of 1600-1650 K (from the melting point of the metal and the absence of orthopyroxene in pallasites) an upper limit on the residence time of pallasite olivine of ˜1 Ma can be inferred by the persistence of trace element detail over scales of 100 ?m. Following the olivine-metal mixing event, homogeneous Ni and Co distributions were modified by diffusion; Cr and V were partially modified; Al and P were essentially unchanged.

  14. 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.

  15. Number Line Bars

    NSDL National Science Digital Library

    2000-01-01

    Teachers and students can use this interactive Java applet to model and carry out arithmetic operations on the number line. Users manipulate the size, position, and direction of color bars to represent addition, subtraction, multiplication and division with whole numbers, integers and fractions. Options include the ability to zoom in and out, change the colors of the bars, and adjust the step size of the bars and number line increments.

  16. Annealing of deformed olivine single-crystals under 'dry' conditions

    NASA Astrophysics Data System (ADS)

    Blaha, Stephan; Katsura, Tomoo

    2013-04-01

    Knowledge of rheological properties of Earth's materials is essential to understand geological processes. Open questions are the water content and crystallographic orientation dependences of dislocation creep rate, because the dominant slip system changes with increasing water content, which suggest different dislocations have different water content dependence. This project focuses on olivine, which is the most abundant mineral of the upper mantle. It is also considered to be the weakest phase and hence should control the rheology of the upper mantle. Several slip systems were reported for olivine, which are [100](010), [001](010), [001](100) and [100](001), each of which appear under different water content and stress conditions [1]. For this purpose we started to obtain data for 'dry' conditions, providing basic knowledge to understand the effect of water. Variation in dislocation creep rate according to change in physical conditions can be estimated by dislocation recovery experiments [2]. In this technique, deformed crystals are annealed, in which the dislocation density is expected to decrease due to coalescence of two dislocations. Dislocation densities are measured before and after the annealing. Dislocation mobility, which should be directly proportional to the dislocation creep rate, is estimated based on the change in dislocation density and duration of annealing. This technique has significant advantages partly because informations of strain rate and deviatoric stress, which are difficult to measure, are unnecessary, and partly because dislocation annealing is conducted under quasi-hydrostatic conditions, which allows wide ranges of P and T conditions. The first step of the experiments is to deform a single crystal of olivine. For this purpose, we developed an assembly, which deforms a single crystal in simple-shear geometry and prevent breakage, sub-grain formation and recrystallization of the crystal. Olivine single-crystals were placed in the high-pressure assembly so that a particular slip system is activated. The assemblies were compressed to 3 GPa. The shear deformation was conducted at 1600 K. EBSD measurements indicate that the recovered crystals are single crystals and sub-grain formation did not occur in most cases. The second step is to anneal the samples under the same P-T conditions as those of the deformation experiments. Annealing experiments are also performed at ambient pressures at 1600 K. Dislocation density was measured by means of the oxidation decoration technique [3]. The samples were firstly polished and then oxidized at 1200 K for 50 min. The dislocations are preferably oxidized, so that presence of dislocation can be observed using SEM. First Results indicate that the dislocation density decreased by annealing by 1/4 with an annealing period of 10 h for dislocations with b = [001]. References [1] H. Jung and S. I. Karato. Water-induced fabric transitions in olivine. Science, 293(5534):1460-1463, 2001. [2] S. I. Karato, D. C. Rubie, and H. Yan. Dislocation recovery in olivine under deep upper mantle conditions: Implications for creep and diffusion. Journal of Geophysical Research, 98(B6):9761-9768, 1993. [3] D. L. Kohlstedt, C. Goetze, W. B. Durham, and J. V. Sande. New technique for decorating dislocations in olivine. Science, 191(4231):1045-1046, March 1976.

  17. 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.

  18. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

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

    E-print Network

    Hitoshi Miura; Taishi Nakamoto

    2006-11-09

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

  1. Serpentinization and alteration in an olivine cumulate from the Stillwater Complex, Southwestern Montana

    USGS Publications Warehouse

    Page, N.J.

    1976-01-01

    Some of the olivine cumulates of the Ultramafic zone of the Stillwater Complex, Montana, are progressively altered to serpentine minerals and thompsonite. Lizardite and chrysotile developed in the cumulus olivine and postcumulus pyroxenes; thompsonite developed in postcumulus plagioclase. The detailed mineralogy, petrology, and chemistry indicate that olivine and plagioclase react to form the alteration products, except for H2O, without changes in the bulk composition of the rocks. ?? 1976 Springer-Verlag.

  2. Coronas in olivine gabbros and iron ores from Susimäki and Riuttamaa, Finland

    Microsoft Academic Search

    Hans van Lamoen

    1979-01-01

    Coronas have been studied by petrographie and microprobe techniques in metamorphosed olivine gabbros and associated iron ores\\u000a from Susimäki and Riuttamaa in Southwest Finland. Three types of coronas are distinguished occurring between the following\\u000a primary minerals: (1) olivine-plagioclase, (2) opaque oxides-plagioclase, (3) opaque oxides-clinopy-roxene. Secondary corona\\u000a minerals are, in order of decreasing abundance, hornblende, orthopyroxene, spinel, olivine, ilmenite, and magnetite.

  3. The rate of water loss from olivine-hosted melt inclusions

    Microsoft Academic Search

    Yang Chen; Ariel Provost; Pierre Schiano; Nicolas Cluzel

    2011-01-01

    Diffusive water loss from olivine-hosted melt inclusions has been reported previously. This process must be considered when\\u000a interpreting melt inclusion data. This study measured the rate of water loss from olivine-hosted melt inclusions during heating-stage\\u000a experiments to test a previous diffusive reequilibration model and the hydrogen diffusion mechanism that controls the rate.\\u000a Olivine-hosted melt inclusions were heated to a constant

  4. 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

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

    Microsoft Academic Search

    E. C. Ferre; F. Martin-Hernandez

    2004-01-01

    Olivine [(Fex, Mg1-x)2 SiO4] is an orthosilicate solid solution between fayalite [Fe2 SiO4] and forsterite [Mg2 SiO4]. Olivine is a major constituent of the Earth mantle that is abundant in oceanic and continental peridotites and mantle xenoliths. The magnetic properties of olivines have been previously investigated using gem quality natural crystals known as peridots (Zabargad) or using laboratory grown synthetic

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

    PubMed

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

    2013-09-01

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

  7. Development of orthopyroxene-Fe\\/Mg ferrite symplectites by continuous olivine oxidation

    Microsoft Academic Search

    A. Dana Johnston; James H. Stout

    1984-01-01

    The development of orthopyroxene-Fe\\/Mg ferrite symplectites associated with olivine is discussed with respect to the chemical reactions by which they form. Previously proposed reactions are presented graphically and the differences between them are reviewed. With the exception of exsolution, these are all discontinuous reactions in the sense that olivine is replaced by the two-phase symplectite assemblage. Olivine-hosted symplectites developed in

  8. Cooling rate estimations based on kinetic modelling of Fe-Mg diffusion in olivine

    Microsoft Academic Search

    L. A. Taylor; P. I. K. Onorato; D. R. Uhlmann

    1977-01-01

    A finite one-dimensional kinetic model was developed to estimate the cooling rates of lunar rocks. The model takes into consideration the compositional zonation of olivine and applies Buening and Buseck (1973) data on ion diffusion in olivine. Since the 'as-solidified' profile of a given olivine is not known, a step-function, with infinite gradient, is assumed; the position of this step

  9. 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.

  10. 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

  11. Inherited Pb isotopic records in olivine antecryst-hosted melt inclusions from Hawaiian lavas

    NASA Astrophysics Data System (ADS)

    Sakyi, Patrick Asamoah; Tanaka, Ryoji; Kobayashi, Katsura; Nakamura, Eizo

    2012-10-01

    Dislocation textures of olivine grains and Pb isotopic compositions (207Pb/206Pb and 208Pb/206Pb) of olivine-hosted melt inclusions in basaltic lavas from three Hawaiian volcanoes (Kilauea, Mauna Loa, and Koolau) were examined. More than 70% of the blocky olivine grains in the studied samples have a regular-shaped dislocation texture with their dislocation densities exceeding 106 cm-2, and can be considered as deformed olivine. The size distribution of blocky olivine grains shows that more than 99% of blocky olivines coarser than 1.2 mm are identified as deformed olivine. These deformed olivine grains are identified as antecrysts, which originally crystallized from previous stages of magmatism in the same shield, followed by plastic deformation prior to entrainment in the erupted host magmas. This study revealed that entrainment of mantle-derived crystallization products by younger batches of magma is an important part of the evolution of magnesium-rich Hawaiian magma. Lead isotopic compositions of melt inclusions hosted in the olivine antecrysts provide information of the evolutionary history of Hawaiian volcanoes which could not have been accessed if only whole rock analyses were carried out. Antecryst-hosted melt inclusions in Kilauea and Koolau lavas demonstrate that the source components in the melting region changed during shield formation. In particular, evidence of interaction of plume-derived melts and upper mantle was observed in the earliest stage of Koolau magmatism.

  12. 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/Mg rich mineral Olivine OlivineSerpentine 0 5 10 15 20 O Mg Si Fe Ni Mg2.58Fe0.39Ni0.03Si2O5(OH)4 6 (Mg, Fe)SiO4 + 5 H2O + 1 O2 2 Mg3Si2O5(OH)4 + 3 Fe2O3 + 2 SiO2aq + H2 Olivine Serpentine Hematite DCi

  13. 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.

  14. 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.

  15. Multi Bar Graph

    NSDL National Science Digital Library

    Shodor

    2012-04-02

    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.

  16. 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.

  17. Bar-biting

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  18. 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.

  19. 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).

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  1. Thermodynamic mixing properties of olivine derived from lattice vibrations

    Microsoft Academic Search

    Michel Henricus Gerardus Jacobs; Bernard H. W. S. de Jong

    2009-01-01

    We use a lattice vibrational technique to derive thermophysical and thermochemical properties of fayalite, Fe2SiO4. This semi-empirical technique is based on an extension of Kieffer’s model to incorporate details of the phonon spectrum.\\u000a It includes treatment of intrinsic anharmonicity and electronic effects based on crystal field theory. We extend it to predict\\u000a thermodynamic mixing properties of olivine (Mg,Fe)2SiO4\\u000a solid solutions

  2. Complex Zoning of Olivine from Udachnaya-East Kimberlite (yakutia, Russia): Evidence for Kimberlite Evolution

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Olivine (Fo 86-94) is a dominant mineral in kimberlites, and it is completely altered in absolute majority of them. Udachnaya kimberlites contain a huge block of absolutely unaltered ultrafresh olivine with a lack of serpentine even in thin sections. Two main olivine populations which are represented by rounded or anhedral olivine-I macrocrysts and euhedral olivine-II phenocrysts are clearly distinguished in any kimberlites including Udachnaya (e.g. Kamenetsky et al., 2008, J. Petrol. 49: 823-839; Brett et al., 2009, Lithos, 112S: 201-212). Both of these olivine types are represented by variable proportions of resorbed homogeneous core and complex zoned rim parts. Several grains of zoned olivines with both normal and reverse zoning, and wide variations of "core" and "rim" ratios were selected for this study. The zones of "rims" area vary in width with number of zones sometimes exceeding five or six. Concentrations of Ni, Mn, Co, Ca, Cr, Al, Ti, P, and Zn were measured by EPMA using an innovative method, which has been developed based on earlier publication (Sobolev et al., Science, 2007, 316: 412-417). The method made possible to obtain external precision down to 10 ppm (2SD) and detection limit down to 2 ppm. In addition, high resolution compositional maps of olivine zoning for all mentioned elements are produced. Five and more different zones of variable width and shape were detected for "rims" area of several zoned olivine grains. It has been confirmed both by element maps and EPMA study. As a result several growth events of olivine rims with variations of all measured trace element contents are documented which may provide new approach in understanding the origin of kimberlitic olivine, dynamics of its growth and evolution of kimberlite itself.

  3. Morphology and surface features of olivine in kimberlite: implications for ascent processes

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    Most kimberlite rocks contain large proportions of ellipsoidal-shaped xenocrystic olivine grains that are derived mainly from disaggregation of peridotite. Here, we describe the shapes, sizes and surfaces of olivine grains recovered from kimberlite lavas erupted from the Quaternary Igwisi Hills volcano, Tanzania. The Igwisi Hills kimberlitic olivine grains are compared to phenocrystic olivine, liberated from picritic lavas, and mantle olivine, liberated from a fresh peridotite xenolith. Image analysis, scanning electron microscopy imagery and laser microscopy reveal significant differences in the morphologies and surface features of the three crystal populations. The kimberlitic olivine grains form smooth, rounded to ellipsoidal shapes and have rough flaky micro-surfaces that are populated by impact pits. Mantle olivine grains are characterised by flaked surfaces and indented shapes consistent with growth as a crystal aggregate. Phenocrystic olivine exhibit faceted, smooth-surfaced crystal faces. We suggest that the unique shape and surface properties of the Igwisi Hills kimberlitic olivine grains are products of the transport processes attending kimberlite ascent from mantle source to surface. We infer that the unique shapes and surfaces of kimberlitic olivine grains result from three distinct mechanical processes attending their rapid transport through the thick cratonic mantle lithosphere: (1) penetrative flaking from micro-tensile failure induced by rapid decompression; (2) sustained abrasion and attrition driven by particle-particle collisions between grains within a turbulent, volatile-rich flow regime; and (3) higher-energy particle-particle collisions producing 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.

  4. B-type LPO of olivine in diamond-bearing garnet peridotites from Finsch, South Africa

    NASA Astrophysics Data System (ADS)

    Lee, J.; Jung, H.

    2011-12-01

    Olivine is a major mineral in the upper mantle and plays an important role in deformation processes and seismic anisotropy. It has been known that water and stress influence lattice preferred orientation (LPO) of olivine and seismic anisotropy in the upper mantle. In addition, recent experimental study at high pressure & high temperature showed that LPO of olivine is also affected by pressure. To understand the deformation processes in the deep upper mantle, garnet peridotites from Finsch, South Africa were studied. Lattice-preferred orientation (LPO) of olivine was determined by the electron back-scattered diffraction (EBSD) with CHANNEL 5 software. Water content of olivine was measured using the Nicolet 6700 FTIR with Continuum FTIR Microscope. Thermo Scientific DXR Raman Microscope was used to identify high pressure mineral phases. All samples showed that [001] axes of olivine are aligned subparallel to the lineation and [010] axes are aligned normal to the foliation, which is known as B-type LPO of olivine (Jung and Karato, 2001; Jung et al., 2006). FTIR study revealed that olivines in three samples are dry. It is found that all samples were equilibrated at relatively high pressure (~4 GPa) and low temperature (~1000 °C). Study of Raman spectroscopy of specimens showed that diamonds exist in garnet. We found peaks at the Raman shift wavenumbers of 1320cm-1 and 1331cm-1 which are known to be diamond peaks. These results suggest that the peridotite from Finsch, South Africa, originated from a depth greater than ~120 km, and the LPO of olivine was formed by high pressure. This is the first report of natural samples showing the type-B LPO of olivine induced by high pressure. Seismic anisotropy beneath Finsch, South Africa can be attributed to the type-B LPO of olivine.

  5. 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.

  6. Introduction to Bar Graphs

    NSDL National Science Digital Library

    2011-05-24

    This lesson is designed to introduce students to bar graphs as a way to represent categorical data. Caution should be used not to use bar graph and histogram interchangeably when using this lesson. This lesson provides links to discussions and activities related to bar graphs as well as suggested ways to integrate them into the lesson. Finally, the lesson provides links to follow-up lessons designed for use in succession with the current one. Note, reading level is not indicated because the lesson does not include student reading material.

  7. 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.

  8. Annealing behaviour of ion tracks in olivine, apatite and britholite

    NASA Astrophysics Data System (ADS)

    Afra, B.; Lang, M.; Bierschenk, T.; Rodriguez, M. D.; Weber, W. J.; Trautmann, C.; Ewing, R. C.; Kirby, N.; Kluth, P.

    2014-05-01

    Ion tracks were created in olivine from San Carlos, Arizona (95% Mg2SiO4), apatite (Ca5(PO4)3(F,Cl,O)) from Durango, Mexico, and synthetic silicates with the apatite structure: Nd8Sr2(SiO4)6O2 and Nd8Ca2(SiO4)6O2 using 1.6 and 2.2 GeV Au ions. The morphology and annealing behaviour of the tracks were investigated by means of synchrotron based small angle X-ray scattering in combination with ex situ annealing. Tracks in olivine annealed above ?400 °C undergo a significant change in track radius due to recrystallisation of the damage tracks. At temperatures higher than 620 °C, the scattering images indicate fragmentation of the track cylinders into smaller subsections. Ion tracks were annealed at elevated temperatures up to 400 °C in the Durango and Ca-britholite, and up to 560 °C in Sr-britholite. While there was a significant change in the track radii in the Durango apatite, tracks in the two synthetic samples remained almost unchanged.

  9. 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.

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

    USGS Publications Warehouse

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

    1978-01-01

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

  11. ORIGINAL PAPER Titanium-and water-rich metamorphic olivine in high-pressure

    E-print Network

    Jung, Haemyeong

    ORIGINAL PAPER Titanium- and water-rich metamorphic olivine in high-pressure serpentinites from 2013 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract Titanium- and water-rich metamorphic olivine (Fo into the deeper mantle as well as introduce significant B isotope anomalies. Release of hydrogen from H2O

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

    E-print Network

    Montes-Hernandez, German

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

  13. 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.

  14. Influence of hydrogen on the electronic states of olivine: Implications for electrical conductivity

    E-print Network

    density of state calculations for olivine containing hydrogen-related defects and discuss implicationsInfluence of hydrogen on the electronic states of olivine: Implications for electrical conductivity; accepted 29 February 2012; published 28 March 2012. [1] The influence of hydrogen on the electronic states

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

    E-print Network

    van Keken, Peter

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

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

    Microsoft Academic Search

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

    2010-01-01

    In this study, we carried out experiments investigating the rheological contrast between olivine and garnet, two major components of the mantle, at mantle temperatures and pressures. Experiments were carried out using a deformation-DIA at the National Synchrotron Light Source at Brookhaven National Laboratory. Samples were fabricated from powdered minerals; olivine was from San Carlos and garnet from the Dabie-Sulu orogenic

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

    E-print Network

    Demouchy, Sylvie

    Onset and Progression of Serpentinization and Magnetite Formation in Olivine-richTroctolite from ADVANCE ACCESS PUBLICATION FEBRUARY 19, 2009 Serpentinization of olivine-rich troctolite from core 227 of serpentinization are recognized. The first, dominant in weakly serpentinized samples, is an approxi- mately

  18. MINERALOGY AND PETROLOGY OF AN OLIVINE DIABASE SILL COMPLEX AND ASSOCJATED UNUSUALLY POTASSIC GRANOPHYRES,

    E-print Network

    Sierra Anc Fa; Central Arizona; Douglas Smith

    1969-01-01

    Potassic hornblende granophyre and pyroxene granophyre form these bold cliffs north of Reynolds Creek at the roof of the Sierra Ancha sill complex. Olivine diabase and feldspathic olivine-rich diabase underlie the slopes below the granephyre mass. The sharp upper contact of the granophyre with the

  19. 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

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

    E-print Network

    Montes-Hernandez, German

    alteration High-carbonate alkalinity Magnesite Lizardite Crystal growth Hydrothermal systems The present and carbonation of olivine with relevance in Earth systems (e.g. functioning of hydrothermal fieldsSimultaneous precipitation of magnesite and lizardite from hydrothermal alteration of olivine under

  1. Effect of water on the slip systems in olivine single crystals at high pressure

    Microsoft Academic Search

    J. Girard; J. Chen; P. C. Raterron; C. W. Holyoke

    2009-01-01

    Seismic velocity anisotropies observed in the upper mantle are interpreted by lattice-preferred orientations (LPO) produced experimentally in olivine, which depends on the dominant dislocation slip systems. At low pressure P200 km [2]. According to those studies, the slip systems activities depend on pressure. However previous studies revealed that the water could affect the olivine plastic deformation and induce the transition

  2. melt fraction will be more gradual, reflecting the gradual increase of water solubility in olivine and

    E-print Network

    Calov, Reinhard

    of plate tectonics as we know it--is possible only in a planet with a water-bearing mantle. Referencesmelt fraction will be more gradual, reflecting the gradual increase of water solubility in olivine melting (1, 2, 6). However, even in the absence of melting, the partitioning of water between olivine

  3. Effects of water and iron content on the rheological contrast between garnet and olivine

    NASA Astrophysics Data System (ADS)

    Katayama, Ikuo; Karato, Shun-Ichiro

    2008-01-01

    The effects of water and iron content on the relative creep strengths of garnet and olivine were investigated by shear deformation experiments. Garnet and olivine samples were sandwiched together between alumina pistons in a simple shear geometry and were deformed at P = 1-2 GPa, T = 1473 K and strain rates ranging from 10 -5 to 10 -3 s -1 using a Griggs-type solid-medium apparatus. The stress- and strain-rate relation, as well as the deformation microstructures including lattice-preferred orientation and dynamic recrystallization, indicates that the deformation by dislocation creep. The creep tests show that the Fe-rich garnet (Alm 67Prp 29Grs 3) was slightly weaker than olivine (Fo90), whereas the Mg-rich garnet (Alm 19Prp 68Grs 12) was significantly stronger than olivine under dry conditions. The wet experiments show that the creep rate of the Mg-rich garnet is more sensitive to water than olivine; the water fugacity exponent on strain rate was estimated to be ˜2.4 for garnet and ˜1.2 for olivine, and the Mg-rich garnet becomes weaker than olivine in a water-rich environment. The experimental results show that the rheological contrast between garnet and olivine depends strongly on water content and to a lesser degree on Fe content. Consequently, the geodynamic behavior of geochemical reservoirs can be sensitive to their chemical environments in the upper mantle.

  4. FTIR spectroscopy of OH in olivine: A new tool in kimberlite exploration

    NASA Astrophysics Data System (ADS)

    Matveev, S.; Stachel, T.

    2007-11-01

    Our study of olivines from Canadian kimberlites shows that the application of FTIR spectroscopy significantly improves the reliability of olivine as a kimberlite indicator mineral (KIM). We have developed an algorithm that yields the water concentration and the normalized intensity of the OH IR absorption band at 3572 cm -1 from unpolished olivine grains of unknown thickness. For 80% of kimberlitic olivines these two parameters are significantly higher than those for olivines from non-kimberlitic magmas and consequently, olivines with water concentrations >60 ppm and a strong absorption band at 3572 cm -1 can be reliably classified as being kimberlitic. We have identified two major spectral features in the OH absorption bands of kimberlitic olivines that allow for a more detailed classification: (a) the presence of three types of high-requency OH absorption bands (Group 1A, 1B and 1C) and (b) the proportion of low-frequency OH absorption bands (Group 2) relative to high-frequency bands (Group 1). Comparison of our results with experimental studies suggests that differences within Group 1 OH absorption bands are due to different pressures of crystallization or hydrogenation. The three identified types of Group 1 OH absorption bands approximately correspond to high ( P > 2 GPa, Group 1A), moderate (2-1 GPa, Group 1B), and low (<1 GPa, Group 1C) pressures of hydrogenation. Group 2 OH IR absorption bands in olivines with NiO > 3500 ppm are interpreted to reflect olivine-orthopyroxene equilibria and hence are indicative of xenocrystic olivine derived from lherzolitic or harzburgitic mantle sources. Interaction of xenocrystic olivine with hydrous kimberlitic melts with low silica activity likely will cause a gradual increase in Group 1 absorption bands. Therefore, FTIR spectra of olivine can be used to obtain qualitative estimates of the duration of interaction between mantle material and a kimberlitic melt. In addition to applications in kimberlite and diamond exploration, FTIR spectra of olivine phenocrysts, combined with mineral chemical data, may also provide insights into kimberlite evolution. Our data suggest that in some instances the ascent of kimberlitic magmas could have been interrupted at or near the Moho, followed by olivine crystallization and exsolution of aqueous fluids.

  5. 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.

  6. Histograms and Bar Graphs

    NSDL National Science Digital Library

    2011-01-18

    This lesson is designed to introduce students to histograms and bar graphs as graphical representations of data. The lesson also covers the distinction between histograms and bar graphs and the concepts of class intervals and scale. The lesson provides links to discussions and activities related to these topics as well as worksheets for further practice. Finally, the lesson provides links to follow-up lessons designed for use in succession with this one.

  7. Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites

    NASA Technical Reports Server (NTRS)

    Zolensky, Michael; Barrett, Ruth; Browning, Lauren

    1993-01-01

    The degree of compositional variation of fine-grained minerals displayed by the members within any carbonaceous chondrite group (i.e., CI, CM, CV, CR) is a direct reflection of the range of aqueous alteration assemblages present. Matrix and fine-grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another, but not necessarily similar in bulk elemental composition, even though they have subsequently experienced postaccretional secondary processing (aqueous alteration) under identical conditions. We propose that CO chondrites experienced parent body conditions of low f(O2), low water/rock ratios, and temperatures below 50 C. CR chondrites experienced higher water/rock ratios, potentially higher temperatures (not above 150 C), and a wide range of f(O2). The alteration mineralogy of CV chondrites indicates water/rock ratios at the high end (at least) of the range for CR chondrites, Essebi, and MAC 87300. CM chondrites experienced temperatures below 50 C, low f(O2) and low water/rock ratios, except EET 83334, which probably experienced relatively higher f(O2), and B-7904 and Y-86720, which experienced postalteration temperatures in the range 500-700 C. Most CI chondrites experienced temperatures between 50 and 150 C, relatively high water/rock ratios, and variable f(O2). Y-82162 witnessed postalteration heating, possibly as high as 400 C.

  8. 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.

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

    USGS Publications Warehouse

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

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Sanfilippo, Alessio; Tribuzio, Riccardo; Tiepolo, Massimo

    2014-09-01

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

  11. PartialLy Shock-Transformed Olivine in Shocked Chondrites: Mechanisms of Solid-State Transformation

    NASA Astrophysics Data System (ADS)

    Sharp, T. G.; Xie, Z.

    2007-12-01

    High-pressure minerals, produced by shock meta-morphism, are common in and around melt veins in highly shocked chondrites. These minerals either crys-tallized from silicate melt in the shock-vein or formed by solid- state transformation of host-rock fragments entrained in the melt or along shock-vein margins. Olivine- ringwoodite transformation kinetics can be used to constrain shock duration if one knows P-T conditions and transformation mechanisms. Here we examine the solid-state transformation of olivine to ringwoodite and the formation of ringwoodite lamellae in Tenham. Partially transformed olivines show a variety of ringwoodite textures. Some have granular textures whereas others have straight or curved ringwoodite lamellae, made up of distinct (1 to 2 ?m) crystals. Many of these polycrystalline ringwoodite lamellae occur in pairs. Where these paired lamellae cross the are offset, suggesting that the lamellae are associated with shearing. Electron diffraction reveals that the ringwoodites in the polycrystalline lamellae, occur in roughly the same crystallographic orientation, defining a lattice-preferred orientation. TEM also shows that the remnant olivine is highly deformed, with high densities of complex dislocations. This olivine has a poorly organized sub-grain structure that grades into polycrystalline olivine. The nearby untransformed olivine is also highly de-formed, but less than the partially transformed olivine. TEM images of complex dislocation and sub-grain microstructures suggests that the transformation of olivine to ringwoodite involves extensive deformation. High densities of dislocations provide potential sites for heterogeneous nucleation of ringwoodite and may enhance Fe-Mg inter-diffusion. The differential stress at the initial stage of the shock results in high strains and local heating. The paired ringwoodite lamellae in olivine appear to result from shearing and possibly shear heating, where nucleation occurs on both sides of a shear band.

  12. Flow Mechanisms of San Carlos olivine at high pressure

    NASA Astrophysics Data System (ADS)

    Li, L.; Weidner, D.; Chen, J.; Raterron, P.; Vaughan, M.

    2002-05-01

    Flow mechanisms for San Carlos olivine at pressures up to 8 GPa and temperatures up to 1500K are investigated using synchrotron x-radiographic techniques. TEM observations on recovered samples are used to define the microstructures and illuminate processes. We conclude that dislocation creep assisted by dynamic recrystallization dominates deformation of polycrystalline San Carlos olivine above 1000K with little dependence on grain boundary sliding and no indication of a grain-size dependence of flow. Below this temperature dislocation glide, also assisted by dynamic recrystallization, dominates deformation. Strain rates derived from the digital images of stressed samples have the precision up to 10-6s-1. Two piggy-backed San Carlos olivine specimens have average grain sizes of 0.5 ? m and 5 ? m. Each specimen achieves a total of 6-7% strain after heating process begin. With identical differential stress states, and for a range of temperatures, the strain rates for both specimens are virtually identical indicating the absence of a grain-size sensitive flow process in these experiments. This implies that an activation volume of 5 cc/mole or less for `power-law-creep' is required to define the boundary between grain-size sensitive flow (diffusion creep) and grain-size insensitive flow (dislocation creep). TEM observations reveal that grain sizes of both samples remained different by at least a factor of 2 during the entire experiment. However, indications of dynamic recrystallization and grain-growth are observed in the samples. Often, the grain size of the fine-grain sample increased while that of the coarse-grain sample decreased during the same experiment indicating that the grain size of both samples are controlled by dynamic recrystallization. No evidence of grain boundary sliding is found in our samples. Strain contrasts are widespread at grain boundaries before dynamic recrystallization is fully activated. Well-equilibrated samples are accompanied by triple-junctions rather than the quad-junctions which are typical of active grain boundary sliding. Taken together with the grain-size insensitivity of the flow process, we conclude that there are no`super-plastic' mechanisms active in these experiments.

  13. Calibrations of phase abundance, composition, and particle size distribution for olivine-orthopyroxene mixtures from reflectance spectra

    NASA Technical Reports Server (NTRS)

    Cloutis, Edward A.; Gaffey, Michael J.; Jackowski, Timothy L.; Reed, Kevin L.

    1986-01-01

    An analytical method for quantifying the characteristics (phase abundances, phase composition, and grain size) of an olivine-orthopyroxene mixture from reflectance spectra is described. The spectral parameters related to reflectance, wavelength position, and albedo are investigated; the absorption bands for the olivine-orthopyroxene mixture is also studied. Primary calibrations useful for the determination of the olivine-orthopyroxene mixture characteristics are examined.

  14. A Re-appraisal of Olivine Sorting and Accumulation in Hawaiian Magmas.

    NASA Astrophysics Data System (ADS)

    Rhodes, J. M.

    2002-12-01

    Bowen never used the m-words (magma mixing) in his highly influential book "The Origin of the Igneous Rocks". Yet, in the past 20-30 years, magma mixing has been proposed as an important, almost ubiquitous, process at volcanoes in all tectonic environments ranging from oceanic basalts to large silicic magma bodies, and as the possible trigger of eruptions. Bowen regarded Hawaiian olivine basalts and picrites as the result of olivine accumulation in a lower MgO magma that was crystallizing and fractionating olivine. This, with variants, has been the party line ever since, the only debate being over the MgO content of the proposed parental magmas. Although magma mixing has been recognized as an important process in differentiated, low-MgO (below 7 percent), Hawaiian magmas, the wide range in MgO (7-30 percent) in Hawaiian olivine tholeiites and picrites is invariably attributed to olivine crystallization, fractionation and accumulation. In this paper I will re-evaluate this hypothesis using well-documented examples from Kilauea, Mauna Kea and Mauna Loa that exhibit well-defined, coherent linear trends of major oxides and trace elements with MgO . If olivine control is the only factor responsible for these trends, then the intersection of the regression lines for each trend should intersect olivine compositions at a common forsterite composition, corresponding to the average accumulated olivine in each of the magmas. In some cases (the ongoing Puu Oo eruption) this simple test holds and olivine fractionation and accumulation can clearly be shown to be the dominant process. In other examples from Mauna Kea and Mauna Loa (1852, 1868, 1950 eruptions, and Mauna Loa in general) the test does not hold, and a more complicated process is required. Additionally, for those magmas that fail the test, CaO/Al2O3 invariably decreases with decreasing MgO content. This should not happen if only olivine fractionation and accumulation are involved. The explanation for these linear trends that approach, but fail to intersect, appropriate olivine compositions is a combination of magma mixing accompanied by olivine crystallization and accumulation. One of the mixing components is a is a high-MgO (about13-15 percent) magma laden with olivine phenocrysts and xenocrysts and the other is a consanguineous low-MgO (about 7 percent) quasi "steady-state" magma, with a prior history of clinopyroxene and plagioclase fractionation.

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

    NASA Astrophysics Data System (ADS)

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

    2007-04-01

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

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

    SciTech Connect

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

    2007-01-01

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

  17. 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.

  18. 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.

  19. 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

  20. Phyllosilicate and Olivine around a Fracture in Nili Fossae

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) took this observation of part of the Nili Fossae region at the western margin of the Isidis impact basin at 3:07 (UTC) on December 12, 2006, near 21.9 degrees north latitude, 78.2 degrees east longitude. The image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 18 meters (60 feet) across. The image is about 11 kilometers (7 miles) wide at its narrowest point.

    The Isidis basin resulted from a gigantic impact on the surface of Mars early in the planet's history. The image of the Isidis basin at the top left is the colored elevation data from the Mars Orbiter Laser Altimeter (MOLA) overlain on a digital image mosaic from the Viking mission. Reds represent higher elevations, and blue lower elevations. The western rim of the Isidis basin has numerous, concentric troughs (or 'fossae') which may have formed during faulting associated with the impact event. Since then, the Nili Fossae region has since been heavily eroded, and is one of the most mineralogically diverse spots on Mars.

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

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

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

  1. Olivine friction at the base of oceanic seismogenic zones

    USGS Publications Warehouse

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

    2007-01-01

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

  2. The Fidelity of Olivine-Hosted Melt Inclusions as Recorders of Pre-Eruptive Water Content and Oxygen Fugacity

    NASA Astrophysics Data System (ADS)

    Gaetani, Glenn; O'Leary, Julie; Shimizu, Nobumichi

    2010-05-01

    Olivine-hosted melt inclusions represent an important source of information on both the pre-eruptive H2O contents and oxygen fugacities of basaltic magmas [1]. The principal uncertainty involved with deriving pre-eruptive H2O concentrations from melt inclusions is the potential for diffusive loss or gain of H+ (protons) through the host olivine. Further, it has been proposed that the proton flux associated with H2O loss/gain affects the oxidation state of the inclusion [2,3]. Results from hydration and dehydration experiments carried out on natural inclusion-bearing olivines analyzed by SIMS and XANES confirm that H2O re-equilibratrion occurs rapidly via proton diffusion through the host olivine, and demonstrate that re-equilibration of oxygen fugacity within the inclusion occurs on comparable timescales via diffusion of point defects. Therefore, an olivine-hosted melt inclusion provides a reliable record of both the H2O content and oxygen fugacity of the external melt with which it most recently equilibrated. However, efficient re-equilibration of both H2O and oxygen fugacity limits the utility of olivine-hosted melt inclusions as indicators of mantle processes. Hydration experiments were performed on olivines from Puu Wahi, a scoria cone on the NE rift zone of Mauna Loa volcano. Melt inclusions initially containing 0.36±0.05 wt% H2O were held at 1 GPa and 1250° C in water enriched in 18O (18O/?O = 0.977) and D (2H/?H = 0.998) to map the transport of protons and oxygen during equilibration of melt inclusions with an external fluid. Dehydration experiments were carried out for 1 to 18 hrs at 1 bar and 1250 ° C on inclusion-bearing olivines in scoria erupted from Cerro Negro volcano, Nicaragua, in 1999. The initial concentration of H2O in these melt inclusions was uniformly high (3.6±0.6 wt%). All run products were analyzed for major elements by electron microprobe and for H2O by SIMS on the Cameca 1280 ion microprobe at WHOI. The oxidation state of Fe was determined by XANES at beamline 13-IDC of the Advanced Photon Source at Argonne National Laboratory. The D/H ratios of the melt inclusions from our hydration experiments range from 18.4-25.6, as compared to ~1.448 x 10-4 for mantle-derived basalt, indicating significant addition of deuterium. The 18O/17O ratios of melt inclusions are within uncertainty of natural ratios for mantle-derived materials. The H2O content of individual melt inclusions increased by as much as 3.9 wt %, while the oxidation state of Fe in the hydrated melt inclusions is not significantly different from the starting materials. The concentration of H2O in melt inclusions from the dehydration experiments ranges from 2.8 to 0.05 wt%, and dehydration is nearly complete after 18 hours. The ?D value of the melt inclusions increases significantly as dehydration progresses and is consistent with a calculated diffusive fractionation of hydrogen isotopes. Neither diffusive fractionation of H2O nor equilibrium fractionation via vapor loss is consistent with the isotopic enrichment observed in dehydrated melt inclusions. The oxidation state of Fe ranges from Fe3+/?Fe = 0.58±0.04 (NiNiO+4) for the starting materials to Fe3+/?Fe = 0.21±0.03 (NiNiO+0.6) for melt inclusions that were heated for 18 hours, and re-equilibrates on the same timescale as H2O. References: [1] K.A. Kelley, E. Cottrell, Science 325, 605 (2009); [2] A. V. Sobolev, L. V. Danyushevsky, J Petrol 35, 1183 (1994); [3] L. V. Danyushevsky, A. W. McNeill, A. V. Sobolev, Chem Geol 183, 5 (2002).

  3. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  5. A microstructural investigation of natural lamellar ringwoodite in olivine of the shocked Sixiangkou chondrite

    NASA Astrophysics Data System (ADS)

    Chen, Ming; Chen, Jing; Xie, Xiande; Xu, Jun

    2007-12-01

    Olivine adjacent to the shock-produced veins of Sixiangkou meteorite contains several sets of ringwoodite lamellae nucleated and grown along planar fractures in olivine. These lamellae consist of two generations of crystallite aggregates of ringwoodite, and show features of incoherent nucleation and growth of ringwoodite along fractures of olivine. The lamellae are of zonal Fe-Mg distribution characterized as Fe-rich rim and Mg-rich interior. It indicates that the intracrystalline transformation of olivine to ringwoodite proceeds through Fe-Mg interdiffusion during growth of ringwoodite. The formation of the lamellae favors a fracture-involved phase transformation mechanism. Firstly, a thin layer of crushed or distorted olivine along a gliding plane of a fracture was produced and then transformed into the first generation of crystallite layer of ringwoodite; subsequently, the second generation of relatively coarse-grained ringwoodite grew on both interfaces of the firstly formed thin layer of ringwoodite. This study brings forward a new observation of intracrystalline olivine-ringwoodite transformation, in addition to other mechanisms. Since mechanical deformations resulting in planar fractures are common in olivine of terrestrial mantle rocks, this proposed mechanism could play an important role in the subducting lithospheric slabs.

  6. Deformation microstructures and water content of olivine in peridotite from the Lindås Nappe, Bergen Arc, western Norway

    NASA Astrophysics Data System (ADS)

    Jung, S.; Jung, H.; Austrheim, H.

    2011-12-01

    Two peridotite outcrops in Lindas Nappe anorthosite complex, Bergen Arc, western Norway were studied to understand deformation microstructures of olivine. A mylonite zone was found in the peridotites and deformation fabrics of recrystallized olivine in the area were also studied. Lattice preferred orientation (LPO) of olivine was determined using electron backscattered diffraction (EBSD) in SEM. Water content of olivine in the samples was measured using the Fourier transformation infrared (FTIR) spectroscopy and small inclusions inside olivine and pyroxene grains were identified by using Micro-Raman spectroscopy. We observed various types of LPOs of olivine in wall rock area. A sample (372) showed that [100] axes of olivine are aligned subparallel to the lineation and [001] axes aligned normal to the foliation, which is known as E-type LPO of olivine (Jung et al., 2006). Most of other samples in wall rock showed a combination of two different types of LPOs: both [100] and [001] axes were aligned parallel to the lineation, and [010] axes were aligned normal to foliation plane. This is a combination of A- and B-type LPO of olivine. In the mylonite area, we discovered that there is a change in LPO of olivine from wall rock to mylonite. We observed olivine fabrics of B-, C-type LPO and a combination of B- and C-type LPO of olivine. The wall rock fabric is Grenvillian in age (ca 1000 Ma) while the ultramylonite zone is Caledonian (ca 400 Ma). Spinel is also present in the wall rock while small garnets have been found around the spinel in the mylonite zone. This suggests that the fabric in the wall rock developed in the spinel lherzolite field while the mylonite fabric evolved under garnet lherzolite conditions. FTIR analysis of olivine revealed that olivine in wall rock contains about 300 ppm H/Si of water content, while olivine in mylonite zone contains over 700 ppm H/Si, showing water content of olivine in mylonite area was much higher than that in wall rock area. In addition, we also found amosite and antigorite in mylonite area. These observations indicate that olivine fabric difference between wall rock and mylonite was caused by water. We observed a strong LPO and high dislocation density of olivine in wall rock area, indicating that dominant deformation mechanism of olivine in wall rock was dislocation creep. On the other hand, we found a weak LPO, low dislocation density of olivine and four grain junctions in the mylonite area which are indicative of enhanced grain boundary sliding.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  9. 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.

  10. 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.

  11. 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.

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

    NASA Technical Reports Server (NTRS)

    Rietmeijer, Frans J. M.

    1996-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Brearley, A. J.; Geiger, T.

    1993-07-01

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

  14. 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.

  15. 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.

  16. 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.

  17. 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…

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

    SciTech Connect

    DeHart, J.M.; Lu Jie; Benoit, P.H.; Sears, D.W.G. (Univ. of Arkansas, Fayetteville (United States)); Lofgren, G.E. (NASA Johnson Space Center, Houston, TX (United States))

    1992-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Bulle, F.; Layne, G. D.

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  1. Metastable olivine wedge beneath northeast China and its applications

    NASA Astrophysics Data System (ADS)

    Jiang, G.; Zhao, D.; Zhang, G.

    2013-12-01

    When the Pacific slab subducted into the mantle transition zone, there might exist a metastable olivine wedge (MOW) inside the slab due to the phase transition. Lots of researchers have adopted such various methods to detect the characteristics of this MOW as the forward modeling of travel times, shear wave amplitude patterns, teleseismic P wave coda, receiver function imaging, thermodynamic simulation and so on. Almost all results could be more or less affected by the source, the receiver and/or the velocity model passed through by the seismic rays. In this study, we have used 21 deep earthquakes, greater than 400 km and locating beneath northeast China, to study the velocity within the MOW. For more precisions, we have done further modifications in two ways based on our previous studies. (1) Double-difference location method is used to relocate all events with an error of 1-2 km with the data recorded by stations both at northeast China and at Japan. All relocated events locate in a zone about 30 km away from the upper boundary of Pacific slab. (2) Double residual travel times, generated by an event-pair at a common station at only Japan, are used to constrain the velocity anomaly rather than the residuals themselves. As a result, we have found that an ultra-lower velocity zone (ULVZ), averagely -7% relative to the iasp91 model, exists within the subducted Pacific slab around the deep earthquakes, which might be represented as the metastable olivine wedge. Because of the lower-velocity corresponding to the lower-density, the MOW would provide upward buoyancy forces which might prevent the slab from free subduction into the mantle transition zone. This feed-back mechanism of MOW to the slab is called ';parachute-effect', which is characterized by other researchers. In addition, the existence of the ULVZ or the MOW in the slab may supply a possible mechanism for triggering deep earthquakes, called ';phase transformation faulting', which was already proposed few decades ago but now is proved further by our result. Therefore, our study is not only instructive for realizing the dynamic process of slab subduction, but also helpful for analyzing the mechanism of deep earthquakes.

  2. Relationship between Olivine Normative and Quartz Normative lunar Basalts: an experimental study

    NASA Astrophysics Data System (ADS)

    Nanne, J. A. M.; Tronche, E. J.; van Westrenen, W.

    2011-10-01

    We investigate the genetic relationship between olivine-normative basalts (ONB) and quartznormative basalts (QNB) found on the Moon. We experimentally test the hypothesis that QNB are derived from a primitive ONB through extensive polybaric and polythermal fractional crystallization.

  3. Trace Element Distribution Between Olivine and Kirschsteinite in Angra Dos Reis

    NASA Technical Reports Server (NTRS)

    Fittipaldo, M. M.; Jones, R. H.; Shearer, C. K.

    2003-01-01

    The angrites are a small and enigmatic group of basaltic achondrites that possess unique mineralogical and chemical properties. The dominant mineralogy of the seven angrite members (Angra dos Reis, LEW 86010, LEW 87051, Asuka 881371, Sahara 99555, D Orbigny, and a new Moroccan member) is fassaite, olivine, and plagioclase. Angrites display a wide range of thermal histories, with Angra dos Reis (AdoR) exhibiting a cooling history different from that of the rapidly cooled members and from LEW86010, a more slowly cooled member. AdoR could represent either a cumulate or a porphyritic igneous rock that was later altered by metamorphism. We are re-examining the thermal history of AdoR in light of the more recently described angrite members. Our emphasis is a trace element study of low-Ca olivine, which we refer to as olivine, and high-Ca olivine, which we refer to as kirschsteinite, in AdoR.

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

    E-print Network

    Demouchy, Sylvie

    Serpentine Mineral Replacements of Natural Olivine and their Seismic Implications: Oceanic microscopy and transmission electron microscopy concerning the crystallographic rela- tionships of serpentine-textured lizardite (liz) is developed in a standard 60% serpentinized oceanic harzburgite from the Oman ophiolite

  5. 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 ...

  6. 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

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

    E-print Network

    Meethong, Nonglak

    2009-01-01

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

  8. FeO IN CHONDRITIC OLIVINE: IMPLICATIONS FOR . L. Grossman1,2

    E-print Network

    Grossman, Lawrence

    of fayalite. This occurs at very low temperature in solar gas, where the Fe-Mg interdiffusion coefficient, D, in olivine is so low that diffusion of Fe into the pre- existing forsterite crystals ceases before XFa

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

    E-print Network

    Grossman, Lawrence

    at relatively low temperatures. Fe-Mg interdiffusion rates in olivine are so low that a 1µ grain could only+ to condense at equilibrium, it must diffuse into the interiors of previously condensed forsterite grains

  10. Cooling rate estimations based on kinetic modelling of Fe-Mg diffusion in olivine

    NASA Technical Reports Server (NTRS)

    Taylor, L. A.; Onorato, P. I. K.; Uhlmann, D. R.

    1977-01-01

    A finite one-dimensional kinetic model was developed to estimate the cooling rates of lunar rocks. The model takes into consideration the compositional zonation of olivine and applies Buening and Buseck (1973) data on ion diffusion in olivine. Since the 'as-solidified' profile of a given olivine is not known, a step-function, with infinite gradient, is assumed; the position of this step is based on mass balance considerations of the measured compositional profile. A minimum cooling rate would be associated with the preservation of a given gradient. The linear cooling rates of lunar rocks 12002 and 15555 were estimated by use of the olivine cooling-rate indicator to be 10 C/day and 5 C/day, respectively. These values are lower than those obtained by dynamic crystallization studies (10-20 C/day).

  11. Genesis of Apollo 15 olivine normative mare basalts - Trace element correlations

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    Chemical and petrographic studies of 21 Apollo 15 rake basalts are reported; one pyroxene-phyric basalt, four olivine-phyric basalts, 15 olivine microgabbros, and one brecciated basalt are distinguished. The olivine-normative basalts (i.e., all samples but the pyroxene-phyric basalt) show correlation trends of La/Sm vs. La and Sm/Eu vs. La that are within the observed dispersion ranges of La/Sm and Sm/Eu ratios for a single lava flow. Trace element fractionation trends in the sample could be due to mobilization (perhaps by filter pressing) of fractionated residual liquid during the crystallization of a lava flow. However, it is also possible that the suite of olivine-normative basalts represents several basalt flows produced by partial melting of cumulate layers having interstitial liquids with variable trace-element compositions.

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

    E-print Network

    de Vries, B L; 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; 10.1038/nature11469

    2012-01-01

    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 has been done for the protoplanetary disk HD100546 and for olivine crystals in the warm inner parts of planetary systems. The latter compares well with the iron-rich olivine in asteroids (xcomets. Here we report the detection of the 69-micrometre-wavelength band of olivine crystals in the spectrum of Beta Pictoris. Because the disk is optically thin, we can associate the crystals with an extrasolar proto-Kuiper b...

  13. Fe?Mg interdiffusion in single crystal olivine at very high pressure and controlled oxygen fugacity: technological advances and initial data at 7 GPa

    NASA Astrophysics Data System (ADS)

    Bertran-Alvarez, Yves; Jaoul, Olivier; Liebermann, Robert C.

    1992-02-01

    The interdiffusion of iron and magnesium in natural single crystals of San Carlos olivine (Fo 90) has been determined using a 2000 ton uniaxial split-sphere apparatus (USSA-2000) and Rutherford back-scattering spectrometry (RBS). Advances in the microanalysis technique made it possible to perform high-pressure experiments for short-duration runs at low temperatures in a controlled chemical and mechanical environment. Olivine crystals were coated with a thin film of fayalite, inserted in an Fe capsule and placed inside an 18 mm pyrophyllite octahedral cell assembly. After experiments at 7 GPa and 900°C for 6 h at pO 2 ? 10 -14 bar, the specimens were recovered with very few fractures and chemically unaltered. Analysis of RBS spectra from these crystals yields a value of DFe?Mg = 10 -13.7cm2s-1. Comparison of this value with previous data at atmospheric pressure suggests that the activation volume for Fe?Mg interdiffusion is V Fe?Mg? ? 2.2 ± 0.9 cm 3 mol -1 which, if proven correct, has important implications for electrical conductivity and creep in the upper mantle.

  14. The isotopic composition of magnesium in mantle olivine: Records of depletion and metasomatism

    Microsoft Academic Search

    N. J. Pearson; W. L. Griffin; O. Alard; Suzanne Y. O'Reilly

    2006-01-01

    We have investigated detailed Mg isotopic variations in the lithospheric mantle by analysing olivine in mantle-derived peridotite xenoliths and megacrysts. High-precision in situ analyses of 26Mg\\/24Mg and 25Mg\\/24Mg are made using a laser-ablation microprobe and MC-ICPMS. Measurements are done using a standard-sample bracketing technique with an in-house olivine standard. Replicate analyses of this standard give a precision of 0.20‰ (2sd)

  15. The formation of garnet in olivine-bearing metagabbros from the Adirondacks

    Microsoft Academic Search

    Craig A. Johnson; Eric J. Essene

    1982-01-01

    A regional study of olivine-bearing metagabbros in the Adirondacks has permitted testing of the P(pressure)-T(temperature)-X(composition) dependence of garnet-forming reactions as well as providing additional regional metamorphic pressure data. Six phases, olivine, orthopyroxene, clinopyroxene, garnet, plagioclase and spinel, which can be related by the reactions: orthopyroxene+clinopyroxene+spinel +anorthite=garnet, and forsterite+anorthite=garnet occur together both in coronal and in equant textures indicative of equilibrium.

  16. Ancestor's bones and palimpsests: Olivine in ALH 84001 and orthopyroxene in Chassigny

    NASA Astrophysics Data System (ADS)

    Harvey, R. P.; McSween, H. Y., Jr.

    1994-07-01

    One of the reported characteristics of the orthopyroxenite ALH 84001 (A84) is the absence of olivine distinguishing it from the other martian meteorites, all of which are olivine-bearing. However, olivine is present in A84, as widely dispersed 5-10 micron grains enclosed within orthopyroxene. This olivine is compositionally homogeneous with a distinctly Fe-rich composition (34.5% Fa). Another newly discovered mineral in martian meteorites is cumulate orthopyroxene in Chassigny. Both observations have profound implications for the magmatic and alteration histories of these meteorites. A84 is dominated by nearly homogeneous cumulus orthopyroxene, and minor chromite found within cumulus orthopyroxene grains and interstitial areas. Olivine and orthopyroxene show disequilibrium compositions. Similar assemblages of olivine, chromite and orthopyroxene can be found in other martian meteorites, such as the nearly identical shergottites LEW 88516 and ALH 77005 (L&A) and the lithology A megacryst assemblage of EETA 79001 (EET-A). The relatively consanguine mineralogy and texture of these lithologies suggests that they could have been derived from similar basaltic parental magmas. Although complex scenarios of mixing or assimilation are required to account for the varying observed trace-element and isotopic compositions for these rocks, the possible parental similarities suggest that a generic brand of Al-poor basaltic magma was (or is) globally prevalent on Mars. Although olivine in A84 may have been resorbed during magmatic evolution, another way to reduce its abundance is metamorphic reaction at much lower temperatures. Substantial olivine may have been present before its removal by magmatic resorption and metamorphic alteration.

  17. High-Pressure High-Temperature Raman Spectroscopy of San Carlos Olivine

    Microsoft Academic Search

    P. Beck; A. F. Goncharov; R. J. Hemley

    2006-01-01

    Olivine (Mg2SiO4-Fe2SiO4) is the most abundant silicate phase in the Earth upper mantle. Its vibrationnal properties have been studied only at high-pressure\\/low temperature or room pressure high-temperature. We are currently undergoing an HP-HT Raman spectroscopy study of olivine polymorphs. High-temperature, high-pressure Raman and IR spectra on geologically important materials are scarce in the literature, though they are fundamental in understanding

  18. Electrical Conductivity of Olivine at High Pressure and Under Controlled Oxygen Fugacity

    Microsoft Academic Search

    A. Duba; H. C. Heard; R. N. Schock

    1974-01-01

    It is now generally accepted that the major phase in the earth's upper mantle is olivine with an approximate composi- tion Mgx.sFe0..SiO4 (Fujisawa, 1968). Published values of elec- trical conductivity a of olivine of this composition (either single crystal or polycrystalline) at high temperatures show very poor agreement (Duba and Lilley, 1972). In many in- stances the difference can be

  19. 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.

  20. Viscosity measurements of subliquidus magmas: Alkali olivine basalt from the Higashi-Matsuura district, Southwest Japan

    Microsoft Academic Search

    Hidemi Ishibashi; Hiroaki Sato

    2007-01-01

    We carried out viscosity measurements and sampling of a crystal suspension derived from alkali olivine basalt from the Matsuura district, SW Japan, at subliquidus temperatures from 1230 °C to 1140 °C under 1 atm with NNO oxygen buffered conditions. Viscosity increased from 31 to 1235 Pa s with a decrease in temperature from 1230 to 1140 °C. On cooling, olivine first appeared at 1210 °C, followed

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

    PubMed

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

    2014-03-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Jurewicz, A. J. G.; McKay, G. A.

    1993-03-01

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

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

    USGS Publications Warehouse

    McSween, H.Y.; Wyatt, M.B.; Gellert, R.; 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.

  5. Water in Pyroxene and Olivine from Martian Meteorites

    NASA Technical Reports Server (NTRS)

    Peslier, A. H.

    2012-01-01

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

  6. Hydration effects on molar volume and compressibility of olivine

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    Hydrous olivines have been synthesized at 12 GPa at various conditions of temperature, silica activity, and fayalite content. Samples were characterized by FTIR and Raman spectroscopy and single crystal X-ray diffraction. We observe a maximum water content of 8800 parts per million by weight H2O at 1250°C in both Fo90 and Fo100 compositions, with lower H2O contents at 1100°C and 1400°C. We observe similar amounts of hydration and FTIR spectra in samples coexisting with clinoenstatite and with clinohumite. We observe a systematic expansion of the unit cell volume with hydration so that an addition of 5000 ppmw H2O has the same effect on density as raising the temperature by 240°C. Compression experiments have been carried out in the diamond anvil cell to 8 GPa. We observe a decrease in the isothermal bulk modulus from about 128 GPa to about 120 GPa at 8000 ppmw H2O, which is similar in magnitude to the elastic softening of wadsleyite and ringwoodite with hydration. FTIR spectra and X-ray structure refinements indicate that the principal hydration mechanism is substitution of 2H+ for Mg2+ so that the geochemical compatibility of H appears to dramatically increase with pressure in the upper mantle near the 410 km discontinuity.

  7. Measurements of vertical bar Vcb vertical bar and vertical bar Vub vertical bar at BaBar

    SciTech Connect

    Rotondo, M. [Dipartimento di Fisica Galileo Galilei, Via Marzolo 8, Padova 35131 (Italy)

    2005-10-12

    We report results from the BABAR Collaboration on the semileptonic B decays, highlighting the measurements of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix elements Vub and Vcb. We describe the techniques used to obtain the matrix element |Vcb| using the measurement of the inclusive B {yields} Xclv process and a large sample of exclusive B {yields} D*lv decays. The vertical bar Vub vertical bar matrix elements has been measured studying different kinematic variables of the B {yields} Xulv process, and also with the exclusive reconstruction of B {yields} {pi}({rho})lv decays.

  8. Kolsky Bar Impact Test Facility

    SciTech Connect

    Contreras, P.; Montoya, J.

    1998-12-31

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

  9. 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…

  10. Bar coded retroreflective target

    DOEpatents

    Vann, Charles S. (Fremont, CA)

    2000-01-01

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

  11. 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.

  12. 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.

  13. Kinetics of diffusion-controlled evaporation of Fe-Mg olivine: experimental study and implication for stability of Fe-rich olivine in the solar nebula

    Microsoft Academic Search

    Kazuhito Ozawa; Hiroko Nagahara

    2000-01-01

    Evaporation is a process that caused chemical fractionation in the solar nebula. The evaporation rates of meteorite-forming minerals and silicate melts are key parameters for constraining the timescale of high temperature processes in the early solar nebula and for understanding the mechanisms of cosmochemical fractionation. The kinetics of evaporation of olivine (initial Fo = 92), the most common silicate in

  14. Verification of a Model to Calculate Cooling Rates in Olivine by Consideration of Fe-Mg Diffusion and Olivine Crystal Growth, II

    Microsoft Academic Search

    M. Miyamoto; E. Koizumi; T. Mikouchi

    2006-01-01

    We developed a model to calculate the olivine cooling rate by analyzing zoning on the basis of Fe-Mg diffusion during crystal growth. We verify this model by using zoning profiles produced by dynamic crystallization for Martian and lunar meteorites.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  16. Segregation of olivine grains in volcanic sands in Iceland and implications for Mars

    NASA Astrophysics Data System (ADS)

    Mangold, N.; Baratoux, D.; Arnalds, O.; Bardintzeff, J.-M.; Platevoet, B.; Grégoire, M.; Pinet, P.

    2011-10-01

    Basaltic sands cover several plains in volcanic regions on Earth and dominate the aeolian sediments on Mars but basaltic sands are not as well characterized as felsic sands. The Lambahraun sandy-lava plain in Iceland was chosen as a martian analog to study the physical sorting of basaltic sands. The strong winds affecting the plain and its young age (< 4000 yr) have preserved unaltered sand grains. Sands displayed subtle differences in bulk chemical composition from the basaltic source rocks suggesting that mineral abundances are modified by the aeolian transport. A paired enrichment in Mg and Ni in sands relative to the source rock is observed and results from a higher proportion of olivine grains in sand. This enrichment is variable among sand samples and is correlated with the decrease of the mean grain size of sand; a value related to the degree of aeolian sorting. This enrichment is explained by the presence of well-developed olivine minerals (100 to 500 ?m in length) in the source rocks, olivine hardness and density, and the removal of plagioclases. As olivine has been detected by spectral data in several sand dunes on Mars, these results have important implications for martian studies. It shows that olivine abundances deduced from spectral data on martian sand dunes could overestimate that of the source rocks, whereas the presence of a few percents of olivine in the rocks can cause olivine enrichment by aeolian processes. In general, our results show that mineral segregation in basaltic sands should be considered when mineralogical and chemical data of the Mars surface are interpreted.

  17. 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.

  18. Shear wave attenuation and dispersion in melt-bearing olivine polycrystals: 2. Microstructural interpretation and seismological implications

    Microsoft Academic Search

    Ulrich H. Faul; John D. Fitz Gerald; Ian Jackson

    2004-01-01

    The torsional forced oscillation tests of melt-bearing olivine aggregates reported by Jackson et al. [2004] consistently show a peak in attenuation that is absent from melt-free aggregates tested under similar conditions and grain sizes. Characterization by SEM shows that the melt resides in triple junction tubules and larger pockets as previously described. TEM imaging and EDS analysis reveals that olivine-olivine

  19. Towards consistent chronology in the early Solar System: high resolution 53Mn-53Cr chronometry for chondrules.

    SciTech Connect

    Yin, Q; Jacobsen, B; Moynier, F; Hutcheon, I D

    2007-05-02

    New high-precision {sup 53}Mn-{sup 53}Cr data obtained for chondrules extracted from a primitive ordinary chondrite, Chainpur (LL3.4), define an initial {sup 53}Mn/{sup 55}Mn ratio of (5.1 {+-} 1.6) x 10{sup -6}. As a result of this downward revision from an earlier higher value of (9.4 {+-} 1.7) x 10{sup -6} for the same meteorite (Nyquist et al. 2001), together with an assessment of recent literature, we show that a consistent chronology with other chronometers such as the {sup 26}Al-{sup 26}Mg and {sup 207}Pb-{sup 206}Pb systems emerges in the early Solar System.

  20. Mechanism of the olivine-ringwoodite transformation in the presence of aqueous fluid

    NASA Astrophysics Data System (ADS)

    Ando, Jun-Ichi; Tomioka, Naotaka; Matsubara, Kazunari; Inoue, Toru; Irifune, Tetsuo

    2006-09-01

    The mechanism of the high pressure transformation of olivine in the presence of aqueous fluid was investigated by high pressure experiments conducted nominally at the wadsleyite + ringwoodite stability field at 14.5 GPa and 700 and 800°C. The microstructures of recovered samples were observed using an analytical transmission electron microscope (ATEM) for which foils were prepared using a focused ion beam technique. Glass films approximately 1 ?m in width always occupied the interface between olivine and hydrous ringwoodite. ATEM measurements showed that the chemical compositions of the glass films had approximately the same Mg/Fe ratio as that of olivine, but a higher Si content. Micro-structural and -chemical observations suggest that these glass films formed as quenched glass from the aqueous fluid dissolving olivine and that hydrous ringwoodite was crystallized from the fluid. This indicates that the transformation of olivine to hydrous ringwoodite was prompted by the dissolution-reprecipitation process. The dissolution-reprecipitation process is considered an important mineral replacement mechanism in the Earth’s crust by which one mineral is replaced by a more stable phase or phases. However, this process has not previously been reported for deep mantle conditions.

  1. Shock-induced fine-grained recrystallization of olivine - Evidence against subsolidus reduction of Fe/2+/

    NASA Technical Reports Server (NTRS)

    Ahrens, T. J.; Tsay, F.-D.; Live, D. H.

    1976-01-01

    Electron spin resonance (ESR) studies have been carried out on three single grains of terrestrial olivine (Fo90) shock loaded along the 010 line to peak pressures of 280, 330, and 440 kbar. The results indicate that neither metallic Fe similar to that observed in returned lunar soils nor paramagnetic Fe(3+) caused by oxidation of Fe(2+) has been produced in these shock experiments. Trace amounts of Mn (2+) have been detected in both shocked and unshocked olivine. The ESR signals of Mn(2+) show spectral features which are found to correlate with the degree of shock-induced recrystallization observed petrographically. The increasing mass fraction of recrystallized olivine correlates with increasing shock pressures. This phenomenon is modelled assuming it results from the progressive effect of the shock-induced transformation of the olivine to a yet unknown high-pressure phase and its subsequent reversion to the low-pressure olivine phase. The mass fraction of recrystallized material is predicted to be nearly linear with shock pressure.

  2. Barred disks in dense environments

    NASA Astrophysics Data System (ADS)

    Marinova, I.; Jogee, S.; Heiderman, A.; Barazza, F. D.; Gray, M. E.; Barden, M.; Wolf, C.; Peng, C. Y.; Bacon, D.; Balogh, M.; Bell, E. F.; Böhm, A.; Caldwell, J. A. R.; Häußler, B.; Heymans, C.; Jahnke, K.; van Kampen, E.; Lane, K.; McIntosh, D. H.; Meisenheimer, K.; Sánchez, S. F.; Somerville, R.; Taylor, A.; Wisotzki, L.; Zheng, X.

    We investigate the properties of bright barred and unbarred disks in the Abell 901/902 cluster system at z˜ 0.165 with the STAGES HST ACS survey. We find that the global optical bar fraction in the clusters is ˜ 30% regardless of the method of disk selection. Within a given absolute magnitude bin, the bar fraction increases for galaxies with no significant bulge component. Within each morphological type bin, the bar fraction increases for brighter galaxies. We find no strong trend for the bar fraction with local density within the cluster between the core and virial radius. We discuss the implications of our results for the evolution of bars and disks in dense environments.

  3. Beyond Hopkinson's bar.

    PubMed

    Pierron, F; Zhu, H; Siviour, C

    2014-08-28

    In order to perform experimental identification of high strain rate material models, engineers have only a very limited toolbox based on test procedures developed decades ago. The best example is the so-called split Hopkinson pressure bar based on the bar concept introduced 100 years ago by Bertram Hopkinson to measure blast pulses. The recent advent of full-field deformation measurements using imaging techniques has allowed novel approaches to be developed and exciting new testing procedures to be imagined for the first time. One can use this full-field information in conjunction with efficient numerical inverse identification tools such as the virtual fields method (VFM) to identify material parameters at high rates. The underpinning novelty is to exploit the inertial effects developed in high strain rate loading. This paper presents results from a new inertial impact test to obtain stress-strain curves at high strain rates (here, up to 3000?s(-1)). A quasi-isotropic composite specimen is equipped with a grid and images are recorded with the new HPV-X camera from Shimadzu at 5?Mfps and the SIMX16 camera from Specialised Imaging at 1?Mfps. Deformation, strain and acceleration fields are then input into the VFM to identify the stiffness parameters with unprecedented quality. PMID:25071232

  4. Bar-Code-Scribing Tool

    NASA Technical Reports Server (NTRS)

    Badinger, Michael A.; Drouant, George J.

    1991-01-01

    Proposed hand-held tool applies indelible bar code to small parts. Possible to identify parts for management of inventory without tags or labels. Microprocessor supplies bar-code data to impact-printer-like device. Device drives replaceable scribe, which cuts bar code on surface of part. Used to mark serially controlled parts for military and aerospace equipment. Also adapts for discrete marking of bulk items used in food and pharmaceutical processing.

  5. Number Line Bars--Fractions

    NSDL National Science Digital Library

    2005-01-01

    Students use these virtual fraction bars to model fractional addition, subtraction, multiplication (of fractions by whole numbers), and division on a number line. Students can create bars in positive or negative fractional lengths; align, stack, or remove bars; and change the number line marks in increments between 1/2 and 1/15. Applet instructions and teaching ideas are included in the links at the top of the page.

  6. 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.

  7. Bars in a cosmological context

    NASA Astrophysics Data System (ADS)

    Martig, Marie; Kraljic, Katarina; Bournaud, Frédéric

    2015-03-01

    We study the properties of bars in a series of zoom cosmological simulations (Martig et al. 2012, Kraljic et al. 2012). We find that bars are almost absent from galaxies at z>1, and if they form they tend to be quickly destroyed by mergers and instabilities. On the contrary, at z<1 bars are long-lived, and the fraction of barred galaxies rises steadily. Bars are eventually found in ~ 80% of z=0 spiral galaxies. This redshift evolution is quantitatively consistent with existing data from the COSMOS survey (Sheth et al. 2008), although the detectability of bars is presently limited to z<0.8 because of band-shifting and resolution effects. We predict later bar formation in lower-mass galaxies, also in agreement with existing data (e.g., Sheth et al. 2012). We actually find that the characteristic epoch of bar formation is the epoch of massive thin disk formation, corresponding to the transition between an early violent phase at z > 1 and a later secular phase. Bar formation thus traces the emergence of the disk-dominated morphology of today's spirals.

  8. Ladder supported ring bar circuit

    NASA Technical Reports Server (NTRS)

    Kosmahl, H. G. (inventor)

    1983-01-01

    An improved slow wave circuit especially useful in backward wave oscillators includes a slow wave circuit in a waveguide. The slow wave circuit is comprised of rings disposed between and attached to respective stubs. The stubs are attached to opposing sidewalls of the waveguide. To the end that opposed, interacting magnetic fields will be established to provide a very high coupling impedance for the slow wave structure, axially orientated bars are connected between rings in alternate spaces and adjacent to the attachment points of stubs. Similarly, axial bars are connected between rings in the spaces which do not include bars and at points adjacent to the attachment of bars.

  9. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

  11. 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.

  12. 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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

    De Vries, B.

    2014-09-01

    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 HD100546 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 Beta Pictoris system, an analogue to the young Solar System, olivine crys