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1

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

NASA Technical Reports Server (NTRS)

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

Lumpkin, G. R.

1980-01-01

2

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

NASA Astrophysics Data System (ADS)

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

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

2006-10-01

3

The origin of ferrous zoning in Allende chondrule olivines  

Microsoft Academic Search

Very similar major and minor element compositions are noted in the ferrous olivine occurring in chondrules at olivine grain boundaries, along cracks in olivine grains, interleaved with enstatite, and in the inner portions of exposed olivine grain surface rims; simultaneous formation by a single process is therefore suggested. The ferrous chondrule olivine probably formed by the reaction of chondrules with

J. A. Peck; J. A. Wood

1987-01-01

4

The origin of ferrous zoning in Allende chondrule olivines  

NASA Technical Reports Server (NTRS)

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

Peck, Julia A.; Wood, John A.

1987-01-01

5

Experimental Reproduction of Olivine rich Type-I Chondrules  

NASA Technical Reports Server (NTRS)

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.

Smith, Robert K.

2005-01-01

6

Origin of ferrous zoning in Allende chondrule olivines  

SciTech Connect

Olivine crystals in Allende Type 1 chondrules have ferrous rims (Fa/sub 15-44/), a few microns thick, at grain surfaces and along crosscutting cracks. This ferrous olivine contains as much as 2 atomic pct. Al and Cr, and 0.2 pct. Ti. Along cracks, profiles of Fe, Al, Cr, and Ti are consistent with diffusional emplacement: these elements moved from an external source through the cracks as a vapor or by grain boundary diffusion, then into the olivine by lattice diffusion. The emplacement did not occur during an epoch of planetary metamorphism that partly equilibrated matrix and chondrule olivines, because (e.g.) neither matrix nor primary magnesian chondrule olivine contains even 1/10 this much, Al, Cr, and Ti. The authors argue that the source of these elements was the nebular gas, and emplacement occurred prior to accretion. The ferrous zones at olivine grain boundaries do not display simple diffusion profiles: rather they appear to be a composite of two concentric rims. The inner rims have compositions similar to those of the ferrous zones along cracks, and contain the highest concentrations of Al, Cr, and Ti. The outer rims are of uniformly high Fa content and relatively low Al, Cr, and Ti concentration. These outer rims appear to be additional material that condensed onto the chondrules after the diffusional emplacement event discussed earlier. Matrix olivine grains, which are identical to these rims in composition, condensed simultaneously.

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

1987-06-01

7

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

SciTech Connect

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.

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

2011-06-24

8

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

9

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

NASA Astrophysics Data System (ADS)

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

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

1993-06-01

10

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

E-print Network

Relict olivine grains, chondrule recycling, and implications for the chemical, thermal other incompatible ele- ments in olivine. Terrestrial weathering in a hot desert environment may have repeated thermal, chemical, and mechanical process- ing during a ``recycling" process over an extended time

11

Distribution of FeO and MgO Between Olivine and Melt in Natural and Experimental Chondrules  

Microsoft Academic Search

FeO and MgO partitioning between olivine and melt for UOC chondrules has been investigated in order to understand their crystallization behavior. In addition, cooling rate experiments on synthetic chondrules have helped define the limits of the Fe-Mg exchange coefficient.

S. J. Symes; G. E. Lofgren

1999-01-01

12

A relict-grain-bearing porphyritic olivine compound chondrule from LL3.0 Semarkona that experienced limited remelting  

NASA Astrophysics Data System (ADS)

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

Rubin, Alan E.

13

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

NASA Technical Reports Server (NTRS)

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

Ruzicka, A.; Floss, C.

2004-01-01

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)

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.

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

1993-01-01

15

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

NASA Astrophysics Data System (ADS)

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.

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

1993-03-01

16

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

NASA Astrophysics Data System (ADS)

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

Miura, H.; Yamamoto, T.

2014-03-01

17

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

18

Nonthermal Initiation of Nucleation and Chondrule Texture Development  

NASA Astrophysics Data System (ADS)

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

Delaney, J. S.

1995-09-01

19

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

NASA Astrophysics Data System (ADS)

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

Rubin, A. E.; Keil, K.

1984-09-01

20

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

21

Relict and other anomalous grains in chondrules - Implications for chondrule formation  

NASA Technical Reports Server (NTRS)

Relict olivine and pyroxene grains have been identified in chondrules from ordinary and carbonaceous chondrites that probably did not crystallize in situ. Some of these olivines are clear, but others contain fine-grained Fe, Ni ('dusty olivines') and resemble previously described occurrences in ordinary chondrites. There are also chondrules in which all olivine is dusty. It is concluded that: (1) not all relict olivines are dusty, (2) not all dusty olivines crystallized outside the chondrule in which they occur, and (3) some dusty olivines were produced during chondrule formation by a reduction process that affected the whole chondrule. The occurrence of dusty olivines and relict pyroxenes and olivines in chondrules from carbonaceous as well as ordinary chondrites supports the argument that chondrules from all chondrites had similar origins and histories. It is proposed that chondrules and mineral fragments were transported across f(O2) gradients in the solar nebula while they were hot, or were reheated in an environment different from the one in which they formed. Partially molten chondrules sometimes incorporated mineral grains or chondrules with different redox states, producing compound chondrules and chondrules containing anomalous grains. Dusty olivines may also have formed when hot chondrules were transported to regions of lower oxygen fugacity.

Kracher, A.; Scott, E. R. D.; Keil, K.

1984-01-01

22

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

23

Timing of Formation of a Wassonite-bearing Chondrule  

NASA Technical Reports Server (NTRS)

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.

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

2014-01-01

24

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

25

Congruent Melting Kinetics: Constraints on Chondrule Formation  

NASA Technical Reports Server (NTRS)

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

Greenwood, James P.; Hess, Paul C.

1995-01-01

26

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

27

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

NASA Astrophysics Data System (ADS)

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

Nagahara, H.

1992-07-01

28

Shock Effects in Olivine from Mocs Chondrite  

NASA Astrophysics Data System (ADS)

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

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

1995-09-01

29

Impact jetting as the origin of chondrules  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

30

Impact jetting as the origin of chondrules.  

PubMed

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

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

2015-01-15

31

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

NASA Astrophysics Data System (ADS)

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

Fedkin, Alexei V.; Grossman, Lawrence

2013-07-01

32

Chondrules and other components in C, O, and E chondrites Similarities in their properties and origins  

NASA Astrophysics Data System (ADS)

Three types of chondrules are described that are common to H3, LL3, CM2, CO3, and CV3 chondrites. Low- and high-FeO, porphyritic olivine chondrules contain olivine with Fa0.3-8 and Fa5-50 respectively, and can easily be distinguished petrographically. Poikilitic pyroxene chondrules have 1-20 vol pct olivine (Fa0.2-8) enclosed by low-Ca pyroxene (Fs0.5-7), and also occur in E chondrites. These three types formed in separate nebular regions which had dimensions and spacings such that a few percent of the chondrules that collided to form compound chondrules were of different types. Sorting of chondrule precursor material and mixing of chondrule types probably account for most variations in bulk and mineral chemistry among chondrite groups. Metallic Fe,Ni grains containing 0.1-1 percent Cr, Si, and P are present in low-FeO olivine chondrules from all type 2 and least metamorphosed type 3 chondrites. Metal compositions reflect reduction during chondrule formation in the nebula, not nebular condensation. Opaque matrices in type 3 ordinary and carbonaceous chondrites are somewhat similar in composition and mineralogy, and probably have related origins. It is concluded that chondrules in all known chondrite groups share similar nebular origins.

Scott, E. R. D.; Taylor, G. J.

1983-11-01

33

Coarse-grained chondrule rims in type 3 chondrites  

NASA Astrophysics Data System (ADS)

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.

Rubin, A. E.

1984-09-01

34

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

NASA Astrophysics Data System (ADS)

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×.

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

2015-01-01

35

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

36

Oxygen Isotope Systematics of Chondrules from the Least Equilibrated H Chondrite  

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

37

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

NASA Astrophysics Data System (ADS)

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

Rubin, Alan E.; Wasson, John T.

2005-01-01

38

Compound Chondrules fused Cold  

E-print Network

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...

Hubbard, Alexander

2015-01-01

39

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

40

Young Pb-Isotopic Ages of Chondrules in CB Carbonaceous Chondrites  

NASA Technical Reports Server (NTRS)

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).

Amelin, Yuri; Krot, Alexander N.

2005-01-01

41

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

42

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

NASA Astrophysics Data System (ADS)

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

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

1982-06-01

43

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

SciTech Connect

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

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

1991-02-01

44

Modeling Chondrule Formation  

NASA Astrophysics Data System (ADS)

Over the last several decades considerable data on chondrule sizes, compositions, and textures has been collected [1]; experimental studies have greatly improved our understanding of the conditions required to produce chondrule compositions and textures [2]; and models of energetic nebular processes have provided insight into mechanisms by which chondrules may have formed [3]. While much work remains in each of these areas, the information presently available is sufficient to allow the construction of simple numerical models of chondrule formation. We have constructed a computer algorithm to investigate the consequences of forming chondrules under a variety of conditions. Variables that are considered include: 1) the mechanism of heating (e.g., EM radiation, aerodynamic drag, collisions with energetic particles), 2) peak chondrule temperature, 3) heat-source geometry, 4) pre-chondrule dust aggregate size distributions, 5) dust aggregate compositional distributions, 6) chondrule solidus and liquidus temperatures, 7) kinetic barriers to melting, and 8) the duration of heating. Output includes the size distributions and relative abundances of PO, PP, POP, BO, and NP chondrules. Given the uncertainties in the input variables, the primary purpose of the code is not to construct a single (and necessarily somewhat arbitrary) model of chondrule formation, but rather to elucidate the differences in chondrule properties associated with various sets of formation conditions. Results from a number of simulations using a variety of input parameters illustrate the importance of both composition and peak temperature on the proportion of porphyritic to non-porphyritic chondrules produced. Also apparent is the influence of the mechanism of heating on the relative size distributions of chondrule textural types. Results indicate that specific heating mechanisms require unique sets of associated conditions to account for the observed properties of chondrules. These unique sets of conditions not only limit the range of plausible scenarios for chondrule formation, but provide a means of predicting as yet unmeasured chondrule properties. References: [1] Grossman J. N. et al. (1988) in Meteorites and the Early Solar System (J. F. Kerridge and M. S. Mathews, eds.), pp. 619-659, Univ. of Arizona, Tucson. [2] Hewins R. H. (1988) in Meteorites and the Early Solar System (J. F. Kerridge and M. S. Mathews, eds.), pp. 660-679, Univ. of Arizona, Tucson. [3] Hood L. L. and Kring D. A. (1995) in Chondrules and the Protoplanetary Disk (R. Hewins et al., eds.), Cambridge Univ., New York, in press.

Eisenhour, D. D.; Buseck, P. R.

1995-09-01

45

Three Unusual Chondrules in the Bovedy (L3) Chondrite  

NASA Astrophysics Data System (ADS)

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

Hill, H. G. M.

1993-07-01

46

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)

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.

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

2015-02-01

47

A RELICT Spinel Grain in an Allende Ferromagnesian Chondrule  

NASA Astrophysics Data System (ADS)

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

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

1993-07-01

48

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

49

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

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

50

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

SciTech Connect

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

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

1990-06-01

51

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

NASA Technical Reports Server (NTRS)

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

Ruzicka, Alex

1990-01-01

52

Chondrule trace element geochemistry at the mineral scale  

E-print Network

We report trace element analyses from mineral phases in chondrules from carbonaceous chondrites (Vigarano, Renazzo and Acfer 187), carried out by laser ablation inductively coupled plasma mass spectrometry. Results are similar in all three meteorites. Mesostasis has Rare Earth Element (REE) concentrations of 10-20 x CI. Low-Ca pyroxene has light REE (LREE) concentrations near 0.1 x CI and heavy REE (HREE) near 1 x CI respectively. Olivine has HREE concentrations at 0.1-1 x CI and LREE around 10-2 x CI. The coarsest olivine crystals tend to have the most fractionated REE patterns, indicative of equilibrium partitioning. Low-Ca pyroxene in the most pyroxene-rich chondrules tends to have the lowest REE concentrations. Type I chondrules seem to have undergone a significant degree of batch crystallization (as opposed to fractional crystallization), which requires cooling rates slower than 1-100 K/h. This would fill the gap between igneous CAIs and type II chondrules. The anticorrelation between REE abundances and ...

Jacquet, Emmanuel; Gounelle, Matthieu

2015-01-01

53

Preferred chondrule orientations in meteorites  

NASA Astrophysics Data System (ADS)

The orientation of chondrule long-axes has been examined in relatively friable (Allegan, Bjurbole, Chainpur) and more compacted (Allende, Kediri, Knyahinya, Parnallee) meteorites. Preferential chondrule orientations were detected in the more compacted specimens but were found to be much less well developed in the friable meteorites. It is concluded that the chondrule petrofabric was imposed during compaction in the meteorite parent bodies.

Martin, P. M.; Mills, A. A.

1980-11-01

54

Evidence for primitive nebular components in chondrules from the Chainpur chondrite  

NASA Astrophysics Data System (ADS)

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

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

1982-06-01

55

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

56

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

57

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

58

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

USGS Publications Warehouse

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.

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

1991-01-01

59

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

60

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

NASA Technical Reports Server (NTRS)

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

Wasson, John T.; Rubin, Alan E.

2006-01-01

61

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

62

Semarkona: Lessons for chondrule and chondrite formation  

NASA Astrophysics Data System (ADS)

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.

Hubbard, Alexander; Ebel, Denton S.

2015-01-01

63

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

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

64

Strain Measurements of Chondrules and Refraction Inclusion in Allende  

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

65

Chondrule Size Distributions: What Does It Mean?  

Microsoft Academic Search

The restricted range of chondrule size within each chondrite group has been interpreted as indicating a sorting mechanism. We suggest, however, that chondrule size distribution may be primary and reflect formation processes.

P. H. Benoit; S. J. K. Symes; D. W. G. Sears

1999-01-01

66

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

67

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

SciTech Connect

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

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

2013-10-10

68

CONDENSATION OF CHONDRULES: CONDITIONS FOR "FIERY RAIN".  

E-print Network

CONDENSATION OF CHONDRULES: CONDITIONS FOR "FIERY RAIN". L. Grossman1,2 and A. V. Fedkin1 . 1 Dept little Na condenses above the solidus, and Na2O contents of most chondrules plot above Na2O was condensed at near-liquidus temperatures. In the context of melting chondrule precursors, we showed that Na

Grossman, Lawrence

69

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)

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.

Ruzicka, Alex; Floss, Christine; Hutson, Melinda

2012-02-01

70

Magnesium isotopes constraints on the origin of Mg-rich olivines from the Allende chondrite: Nebular versus planetary?  

NASA Astrophysics Data System (ADS)

High precision Mg isotope measurements by multi-collector ion microprobe show that refractory olivines from the Allende chondrite, either olivines isolated in the matrix (2 samples studied) or olivines in type I chondrules (6 samples studied), have variable ?26Mg* enrichments and deficits (calculated in permil as the 26Mg deviation from the instrumental mass fractionation line) relative to the Earth. Most average ?26Mg* (noted ?26Mg*av) values (between 10 and 20 analyses per chondrule) are negative but the total range is from -0.029 (± 0.010) ‰ (2 sigma errors) to + 0.011 (± 0.011) ‰ with an exception of one olivine at + 0.043 (± 0.023) ‰. These variations in ?26Mg*av reflect the formation of the olivines from reservoirs enriched in various amounts of 26Mg by the decay of short-lived 26Al (T1/2 = 0.73 Ma). Similarly, 30 analyses of olivines from the Eagle Station pallasite show a ?26Mg*av value of -0.033 ± 0.008‰, as negative as some olivines from Allende chondrules and the Solar system initial ?26Mg* value of -0.038 ± 0.004‰ (defined at the time of formation of type B Ca-Al-rich inclusions - CAIs - when 26Al/27Al = 5.23 × 10-5, Jacobsen et al., 2008). Because olivines are Al-poor and because their Mg isotopic compositions are not reset during the chondrule forming events, their ?26Mg*av can be used to calculate model crystallization ages relative to various theoretical Mg isotope growth curves. The two end-member scenarios considered are (i) a “nebular” growth in which the Al/Mg ratio remains chondritic and (ii) a “planetary” growth in which a significant increase of the Al/Mg ratio can be due to, for instance, olivine magmatic fractionation. The low ?26Mg*av value of olivines from the Eagle Station pallasite demonstrate that metal-silicate differentiation occurred as early as ~ 0. 15- 0. 23+ 0. 29 Ma after CAIs in either of the growth scenarios. Similarly the variable ?26Mg*av values of refractory olivines can be understood if they were formed in planetesimals which started to differentiate as early as the Eagle Station parent body. Accretion of these planetesimals must have been coeval to the formation of CAIs and their disruption could explain why their fragments (Mg-rich olivines) were distributed in the chondrule forming regions of the disk.

Villeneuve, Johan; Chaussidon, Marc; Libourel, Guy

2011-01-01

71

Olivines and olivine coronas in mesosiderites  

NASA Technical Reports Server (NTRS)

The paper presents a study of olivines and their surrounding coronas in mesosiderites texturally and compositionally using optical and microprobe methods. Olivine composition ranges from Fo(58-92) and shows no consistent pattern of distribution within and between mesosiderites; olivine occurs as large single crystals or as partially recrystallized mineral clasts, except for two lithic clasts. These are Emery and Vaca Muerta, and both are shock-modified olivine orthopyroxenites. Fine-grained coronas surround olivine, except for those in impact-melt group mesosiderites and those without tridymite in their matrices. Coronas consist largely of orthopyroxene, plagioclase, clinopyroxene, chromite, merillite, and ilmenite, and are similar to the matrix, but lack metal and tridymite. Texturally the innermost parts of the corona can be divided into three stages of development: (1) radiating acicular, (2) intermediate, and (3) granular.

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

1980-01-01

72

Magnetite-Pentlandite Chondrules in CK Chondrites  

NASA Astrophysics Data System (ADS)

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

Rubin, A. E.

1992-07-01

73

Chondrule Destruction in Nebular Shocks  

NASA Astrophysics Data System (ADS)

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.

Jacquet, Emmanuel; Thompson, Christopher

2014-12-01

74

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

E-print Network

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

Technische Universiteit Delft

75

Stardust to Planetesimals: A Chondrule Connection?  

NASA Technical Reports Server (NTRS)

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.

Paque, Julie; Bunch, Ted

1997-01-01

76

The formation conditions of chondrules and chondrites.  

PubMed

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

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

2008-06-20

77

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

78

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

79

Tungsten diffusion in olivine  

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

80

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

81

Titanium diffusion in olivine  

NASA Astrophysics Data System (ADS)

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:

Cherniak, Daniele J.; Liang, Yan

2014-12-01

82

Genetic Relationships Between Chondrules, Rims and Matrix  

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

83

Trace elements in rims and interiors of Chainpur chondrules  

NASA Astrophysics Data System (ADS)

Trace elements were measured in the rims and interiors of nine chondrules separated from the Chainpur LL-3 chondrite. Whole rock samples of Chainpur and samples of separated rims were also measured. Chondrule rims are moderately enriched in siderophile and volatile elements relative to the chondrule interiors. The enriched volatile elements include the lithophilic volatile element Zn. The moderate enrichment of volatiles in chondrule rims and the lack of severe depletion in chondrules can account for the complete volatile inventory in Chainpur. These results support a three-component model of chondrite formation in which metal plus sulfide, chondrules plus rims and matrix silicates are mixed to form chondrites.

Wilkening, L. L.; Boynton, W. V.; Hill, D. H.

1984-05-01

84

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

NASA Astrophysics Data System (ADS)

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.

Béjina, Frédéric; Sautter, Violaine; Jaoul, Olivier

2009-01-01

85

Artificial meteor ablation studies: Olivine  

NASA Technical Reports Server (NTRS)

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.

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

1973-01-01

86

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

87

The Origin of Chondrules and Refractory Inclusions in Chondritic Meteorites  

Microsoft Academic Search

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

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

2001-01-01

88

Microbial Weathering of Olivine  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

89

Exogenous Olivine on Vesta  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

90

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

Microsoft Academic Search

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

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

1993-01-01

91

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

NASA Astrophysics Data System (ADS)

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

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

1993-07-01

92

Formation of chondrules by electrical discharge heating  

NASA Technical Reports Server (NTRS)

A possible mechanism for making chondrules in the solar nebula is electrical discharge ('lightning') heating, which can create high-temperature (greater than 1600 K), short-duration (approximately 10 s) thermal events as indicated by the chondritic record. Lightning occurs in many diverse terrestrial and planetary settings, and may have occurred in the solar nebula; it is thus worthwhile to investigate its implications for chondrule formation. Nebular discharges do not appear a viable source of heat for melting chondrule precursors, regardless of the uncertainty in the details of the mode. Nonetheless, we believe nebular lightning worthy of further investigation than what is presented here. Experiments analogous to those currently underway to investigate terrestrial thunderstorm lightning could be fruitful in refining nebular lightning models, and would be double interesting in application to nonthunderstorm and planetary lightnings.

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

1994-01-01

93

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)

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.

Gaetani, Glenn A.; Grove, Timothy L.

1997-01-01

94

Experimental Reproduction of Type 1B Chondrules  

NASA Technical Reports Server (NTRS)

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.

Lofgren, G. E.; Le, L.

2002-01-01

95

Revisiting Jovian-resonance Induced Chondrule Formation  

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

96

Alkali elemental and potassium isotopic compositions of Semarkona chondrules  

USGS Publications Warehouse

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.

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

2005-01-01

97

Evaluating planetesimal bow shocks as sites for chondrule formation  

NASA Astrophysics Data System (ADS)

We investigate the possible formation of chondrules by planetesimal bow shocks. The formation of such shocks is modeled using a piecewise parabolic method (PPM) code under a variety of conditions. The results of this modeling are used as a guide to study chondrule formation in a one-dimensional, finite shock wave. This model considers a mixture of chondrule-sized particles and micron-sized dust and models the kinetic vaporization of the solids. We found that only planetesimals with a radius of ˜1000 km and moving at least ˜8 km/s with respect to the nebular gas can generate shocks that would allow chondrule-sized particles to have peak temperatures and cooling rates that are generally consistent with what has been inferred for chondrules. Planetesimals with smaller radii tend to produce lower peak temperatures and cooling rates that are too high. However, the peak temperatures of chondrules are only matched for low values of chondrule wavelength-averaged emissivity. Very slow cooling (<˜100s of K/hr) can only be achieved if the nebular opacity is low, which may result after a significant amount of material has been accreted into objects that are chondrule-sized or larger, or if chondrules formed in regions of the nebula with small dust concentrations. Large shock waves of approximately the same scale as those formed by gravitational instabilities or tidal interactions between the nebula and a young Jupiter do not require this to match the inferred thermal histories of chondrules.

Ciesla, Fred J.; Hood, Lon L.; Weidenschilling, Stuart J.

2004-11-01

98

Helium Diffusion in Olivine  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

99

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

NASA Astrophysics Data System (ADS)

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

Ruzicka, A.; Boynton, W. V.

1992-07-01

100

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

E-print Network

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

Grossman, Lawrence

101

Cosmochemistry Carbonaceous chondrites, chondrules, pre-solar  

E-print Network

of olivine and pyroxene, commonly without crystal faces or as small grains of olivine included in a single of the diamonds formed somewhere else. #12;SiC Presolar SiC is probably the best-studied of any of the known here are scanning electron micrographs of a SiC grain from the Murchison meteorite; these grains

Mojzsis, Stephen J.

102

Relict Forsterite in Chondrules: Implications for Cooling Rates  

NASA Technical Reports Server (NTRS)

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

Greeney, S.; Ruzicka, A.

2004-01-01

103

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

NASA Technical Reports Server (NTRS)

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

Tomeoka, K.; Buseck, P. R.

1982-01-01

104

Noble Gas Partitioning Between Olivine and Melt to 2 GPa  

NASA Astrophysics Data System (ADS)

We have extended our experimental measurements of noble gas partition coefficients to 2 GPa in the piston-cylinder device. The experimental set-up involves surrounding wafers of gem quality San Carlos olivine (250-1000 microns thick, 3-4 mm diameter) with diamond powder or vitreous carbon spheres. A layer of melt is placed at the bottom of the capsule which infiltrates the porous media and touches the olivine. This allows the original surface of the crystal to be identified and large coherent pieces of olivine to be recovered intact. The inner capsule is graphite and the outer capsule is Pt. Up to 60 bars of HeNeAr were preloaded into the Pt capsule before it was welded shut. This method combines a number of desireable qualities: 1) it avoids producing melt inclusions in the olivine, 2) it yields large areas of olivine to analyze by laser-ablation and 3) it has both melt and crystals present and in contact. The experimental glasses and olivine wafers were analyzed by laser-ablation noble gas mass spectrometry at the Open University, UK. Both depth profiles and cross-sections were analyzed on the olivine wafers. Equilibrium (flat) concentration profiles were only obtained for He in our experiments (up to 20 hr run durations). These yield olivine-melt partition coefficients (D) between 0.0007 and 0.002 at 1-2 GPa and at 1450. These values are within the range of measurements at low pressures (100 MPa or less), suggesting a minimal pressure effect on noble gas partitioning in the upper mantle. Henry’s Law behavior is maintained over 4 orders of magnitude variation in He concentration in the olivine (0.0001 to 1 ppm He). High near-surface concentrations of He (21ppm), Ne (36ppm) and Ar (4,360ppm) were observed in the olivine. The thickness of the enriched layer (5 microns) was the same for all three noble gases. We do not know the origin of the high near-surface concentrations, but if they were due to lattice diffusion of the noble gases, the thickness of the high concentration layer should decrease with the diffusivity of the noble gas from He to Ne to Ar. Thus we speculate that the high near-surface concentrations are due to a change in the material properties of the olivine.

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

2009-12-01

105

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)

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.

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

2014-08-01

106

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

Microsoft Academic Search

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

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

2000-01-01

107

Fe/Mn in olivine of carbonaceous meteorites  

NASA Technical Reports Server (NTRS)

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.

Steele, Ian M.

1993-01-01

108

Kimberlite Ascent: Insights from Olivine  

NASA Astrophysics Data System (ADS)

Olivine is ubiquitous in both extrusive and intrusive kimberlite deposits worldwide. Within kimberlite, it is mainly present as xenocrysts derived from the disaggregation of mantle-derived peridotitic xenoliths. Many textural and chemical features within the mantle-derived olivine xenocrysts result from post entrainment processes. On that basis, these features record physical and chemical changes attending kimberlite ascent and can be used to elucidate the transport and eruption of kimberlite magma. Our textural study of kimberlitic olivine is based on intrusive and pyroclastic kimberlite from the Diavik kimberlite cluster and from the Igwisi Hills kimberlitic lava flows. Based on these observations and the physical and chemical properties of olivine we derive a relative sequence of textural events. Textural features include: sealed cracks, healed cracks, phases trapping in cracks, rounded grains, overgrowths and phase trapping in overgrowths. These features record processes that operate in kimberlite during ascent, and from these features we create a summary model for kimberlite ascent: -- Olivine is incorporated into kimberlitic melts in peridotitic mantle xenoliths continuously during ascent. Xenolith incorporation is focused at the crack tip where the stress regime is highest. -- Shortly after the incorporation of these xenocrysts the tensile strength of the xenoliths is reached at a maximum of 2 km from its source. Disaggregation of mantle xenoliths (producing xenocrysts) is facilitated by expansion of the minerals within the xenoliths causing intra-crystal slip (i.e. along grain boundaries). -- Continued decompression causes olivine to also break in tension approximately 20 km from source. The void space produced by the failure of the crystals (inter-crystal cracks) is filled with melt and crystals consisting of primary carbonate (high-Sr), chromite and spinel crystals. The carbonate later crystallizes to produce sealed fractures. -- Mechanical rounding of the xenocrysts occurs during pressure release (ascent) events characterized by phase separated (fluid at top: liquid at bottom) flow. Turbulent and fluidized flow heads the propagation whereas kimberlite melt state follows. -- Settling of olivine crystals into the melt state occurs when crack propagation halts. At these points, cracks that are not totally sealed begin to heal, and are ultimately present as healed fractures in olivine in the end deposit. -- Saturation of olivine produces rounded overgrowths on large xenocrysts, euhedral overgrowths on smaller xenocrysts, and a volumetrically minor population of olivine phenocrysts. Olivine growth traps fluid, solid and melt inclusions. Calculations based on these relationships suggest that the melt saturates with olivine at a maximum depth of 20 km and a minimum depth of 7 km.

Brett, C.; Russell, K.

2009-05-01

109

Chondrule Formation in Bow Shocks around Eccentric Planetary Embryos  

E-print Network

Recent isotopic studies of Martian meteorites by Dauphas & Pourmond (2011) have established that large (~ 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 rate...

Morris, Melissa A; Desch, Steven J; Athanassiadou, Themis

2012-01-01

110

CHONDRULE FORMATION IN BOW SHOCKS AROUND ECCENTRIC PLANETARY EMBRYOS  

SciTech Connect

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.

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

111

Chondrules in the CB\\/CH-like carbonaceous chondrite Isheyevo: Evidence for various chondrule-forming mechanisms and multiple chondrule generations  

Microsoft Academic Search

The recently discovered metal-rich carbonaceous chondrite Isheyevo consists of Fe, Ni-metal grains, chondrules, heavily hydrated matrix lumps and rare refractory inclusions. It contains several lithologies with mineralogical characteristics intermediate between the CH and CB carbonaceous chondrites; the contacts between the lithologies are often gradual. Here we report the mineralogy and petrography of chondrules in the metal-rich (?70vol%) and metal-poor (?20vol%)

Alexander N. Krot; Marina A. Ivanova; Alexander A. Ulyanov

2007-01-01

112

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

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

113

Origin of olivine at Copernicus  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

114

Producing Ni-rich olivine phenocrysts by mixing partial melts of eclogite and peridotite: an alternative to an olivine-free source for Hawaiian shield basalts  

NASA Astrophysics Data System (ADS)

It has been posited that presence of unusually Ni-rich (2500-4000 ppm) magnesian olivine phenocrysts in SiO2-enriched Hawaiian shield-building basalts, most notably the Koolau lavas, is inconsistent with a deep, olivine-bearing source rock. Instead, Sobolev et al. (2005) proposed that these lavas are generated by a multi- stage process in which partial melts of eclogite react with peridotite within the plume to form an olivine-free source rock with high Ni concentration. As the plume continues to ascend, partial melts of this "hybrid" pyroxenite mix with peridotite melts to produce SiO2- enriched Hawaiian shield-building lavas that crystallize high-Ni olivine. This model has also been used to argue for significant amounts of "hybrid" pyroxenite in the source regions of lavas from other ocean islands, continental basalts, and even MORB, implying that the upper mantle is highly heterogeneous (Sobolev et al., 2007). New experimental results demonstrate that Ni-rich magnesian olivine crystallizes from mixtures of peridotite partial melt and Ni-poor eclogite partial melt that have equilibrated with mantle olivine. This occurs because the concentration of Ni decreases linearly as eclogite partial melt is added to peridotite partial melt, whereas changing major element composition of the mixed melts causes DNi to increase hyperbolically. Experiments were conducted in which either (1) siliceous partial melt of eclogite or (2) primitive basalt was equilibrated with San Carlos olivines at 1 bar and 1201-1350°C. Experimental results demonstrate that eclogite partial melts in equilibrium with mantle olivine retain their high SiO2, low FeO and MgO characteristics. Theoretical modeling calibrated from these experimental results suggest that reaction of siliceous eclogite melt with mantle olivine at low pressure produces a melt containing ~300 ppm Ni. Despite its low Ni content, mixing of this melt with peridotite partial melt produces a high SiO2 melt that crystallizes Ni-rich, magnesian olivine. The dependence of olivine-melt partition coefficients on melt composition also explains the enrichment or depletion of other minor element in Koolau olivines (e.g., Ca and Mn). Our results obviate the need for a multi-step melt generation process in which reaction with large amounts of siliceous eclogite partial melt exhausts olivine from portions of mantle peridotite within the Hawaiian plume. As a result, the amount of eclogite required to explain the composition of the Koolau lavas is greatly reduced. Reference Sobolev, A.V. et al., (2005), Nature, 434, 590-597 Sobolev, A.V. et al., (2007), Science, 316, 412-417

Wang, Z.; Gaetani, G.

2007-12-01

115

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

PubMed

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

Connolly Jr HC; Love

1998-04-01

116

Irradiation Histories of CAIs and LL3/CB Chondrules  

NASA Astrophysics Data System (ADS)

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

Wielandt, D.; Bizzarro, M.

2014-09-01

117

Petrogenesis of Depleted Olivine-Phyric Shergottites  

NASA Astrophysics Data System (ADS)

Model crystallization and phase diagram calculations are used to understand petrogenesis of depleted olivine-phyric shergottites, Tissint and Y 980459, and compare them with an enriched olivine-phyric shergottite, LAR 06319.

Basu Sarbadhikari, A.

2014-09-01

118

A critical analysis of shock models for chondrule formation  

NASA Astrophysics Data System (ADS)

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.

Stammler, Sebastian M.; Dullemond, Cornelis P.

2014-11-01

119

1, 3750, 2006 Olivine in kimberlites  

E-print Network

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

Paris-Sud XI, Université de

120

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

Microsoft Academic Search

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

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

2000-01-01

121

Supernova olivine from cometary dust  

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

122

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)

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].

Burger, Paul V.; Brearley, Adrian J.

2004-01-01

123

Amoeboid olivine aggregates from CH carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

124

Implications of a phase-transition thermostat for chondrule melting  

NASA Technical Reports Server (NTRS)

It is widely accepted that chondrules were formed in brief, localized nebular heating episodes. Given the apparent (at least local) high efficiency of chondrule formation, these thermal events seem to have occurred at a large number of different times and/or azimuthal locations in the solar nebula. It is reasonable to expect that the chondrule-forming events, whatever their underlying cause, were not all identical, but instead occurred with some spread of heating intensities. If this was so, it is puzzling that compositional and textural evidence points to peak temperatures certainly within 1400 - 1750 C, and in most cases within 1500 - 1550 C. This problem is addressed in this article and a possible explanation for this restricted range of peak temperatures is discussed.

Love, S. G.

1994-01-01

125

A chondrule-forming scenario compatible with chondrite metamorphism  

NASA Astrophysics Data System (ADS)

Chondrules evidently formed by the flash melting of precursor solids in the dusty midplane of the solar nebula. Since chondrule production probably overlapped in time with accretion of the earliest planetesimals, possible genetic links between chondrules and accretion have been explored. Primitive bodies that accreted less than 1 m.y. after the solar system began were rapidly heated to melting by the decay of short-lived radioactive isotopes. Subsequent collisions yielded copious volumes of incandescent spray that stuck to, irradiated, sintered, and even melted dust and coarser fragments in the local toroidal 'nebula' already orbiting each planetesimal. In this way various kinds of additional chondrules were produced. Because impact velocity was low, much of the collisional debris fell back to the growing planetesimal surface. The planetesimal interior was still molten, so a steep thermal gradient quickly developed through the insulating blanket of chondritic debris, and metamorphism ensued. This scenario seems reconcilable with most, possibly all, petrographic, chemical, and isotopic constraints imposed by observations in chondrites. The collision scenario is consistent with three important constraints. It yields chondrules with high efficiency, in sufficient quantities to retard radiative heat loss, and with a restricted range of subliquidus temperatures. Total disruption of the smaller molten body would tend to re-mix segregated metal and silicate and restore primitive chemistry on a small scale. The metal core of the larger body would tend not to re-mix. An attractive feature of the model is that a single heat source, namely radiogenic heat stored as thermal energy inside planetesimals, accounts both for chondrule formation and for later metamorphism. The model simplifies the metamorphic regime; it circumvents the narrow time window during which in-situ radioactive decay would be effective, and it can accommodate either hot or cold accretion.

Sanders, I. S.

1994-07-01

126

Papers presented to the Conference on Chondrules and the Protoplanetary Disk  

NASA Technical Reports Server (NTRS)

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.

1994-01-01

127

Olivine-hosted Melt Inclusions in Olivine-Phyric Shergottite LAR 06319  

NASA Astrophysics Data System (ADS)

A newly-found, Antarctic, olivine-phyric shergottite, LAR 06319 which contains an enriched REE signature are studied. The results on olivine-hosted MI and their implications on the evolution of the LAR 06319 parental melt are reported.

Basu Sarbadhikari, A.; Liu, Y.; Day, J. M. D.; Taylor, L. A.

2009-03-01

128

26Al homogeneity of the early solar system demonstrated by high precision Mg isotopic analyses of meteoritic chondrules with an ion microprobe (Invited)  

NASA Astrophysics Data System (ADS)

Short-lived 26Al (T1/2 = 0.73 Myr) is potentially the most precise chronometer of events which took place during the first few Myr of the solar system. However, the resolution of the chronological information which could be obtained from variations of the 26Al/27Al ratios in the different components of chondrites (e.g. refractory inclusions -CAIs- or chondrules) has remained questionable because the level of homogeneity of 26Al in the accretion disk has never been assessed precisely from data on meteorites. Astrophysical hydrodynamic models of mixing in the solar nebula showed that 26Al injected onto the surface of the solar nebula can be spatially homogenized at a level of ±10% in a very short time of a few thousand years [1]. The level of homogeneity which could be reached for 26Al, if a significant fraction of it was produced close to the early Sun by high energy irradiation processes, has not been investigated in details. One way to quantify the level of homogeneity of 26Al in the accretion disk is to compare the composition (Mg and Al isotope compositions) of various components of meteorites (e.g. chondrules) with a theoretical growth curve of Mg isotopes for the solar nebula calculated under the assumption of homogeneous initial Mg and Al isotopic compositions. This has however never been possible because it implies that the slopes (26Al/27Al ratio at the time of crystallization) and the initial (26Mg/24Mg ratio at the time of crystallization) of mineral 26Al isochrons in chondrules are both measured with high precision. We developed high precision Mg isotopic measurements with the CRPG-CNRS (Nancy) Cameca ims 1270 multicollector ion microprobe. The measurements were made at a mass resolution of 2500 and using four Faraday cups to measure simultaneously the ion intensities of 24Mg+, 25Mg+, 26Mg+ and 27Al+. Special attention was paid to (i) the contribution of 24MgH+ on 25Mg, (ii) to the flatness of the Mg peaks and to (iii) the stability of the backgrounds of the Faraday cups. A two sigma of ±0.04‰ (and a two sigma error of ±0.005‰) was obtained for the measurement of ?26Mg (i.e. the deviation of 26Mg/24Mg ratio from the terrestrial mass fractionation line) on our terrestrial olivine, pyroxene and silicate glass standards [2]. We determined mineral 26Al isochrons in 14 type II Fe-Mg chondrules and one Al-rich chondrule from the LL3.0 chondrite Semarkona. The chondrules Mg and Al isotope compositions plot within errors on the solar growth curve calculated with the solar (chondritic) Al/Mg ratio assuming initial 26Al/27Al and 26Mg/24Mg ratios taken to be that of bulk CAIs as determined by [3]. The fact that chondrules of various ages (various 26Al/27Al), bulk CAIs and the Earth plot on the same solar system growth curve of Mg isotopes implies that the solar system was homogeneous at better than ± 10% relative for 26Al/27Al and 26Mg/24Mg at the time of formation of CAIs [2]. The variable 26Al/27Al of chondrules imply that most of them crystallized between ? 1.5 Myr and ? 3 Myr after CAIs but that some of them formed as early as ? 0.9 Myr after CAIs [2]. [1] Boss A. P. (2007) Ap. J. 660, 1707-1714. [2] Villeneuve J., Chaussidon M. and Libourel G. (2009) Science 325, 985-988. [3] Jacobsen B. et al. (2008) Earth Planet Sci. Lett. 272, 353-364

Chaussidon, M.; Villeneuve, J.; Libourel, G.

2009-12-01

129

Forming chondrules in impact splashes. I. Radiative cooling model  

E-print Network

The formation of chondrules is one of the oldest unsolved mysteries in meteoritics and planet formation. Recently an old idea has been revived: the idea that chondrules form as a result of collisions between planetesimals in which the ejected molten material forms small droplets which solidify to become chondrules. Pre-melting of the planetesimals by radioactive decay of 26Al would help producing sprays of melt even at relatively low impact velocity. In this paper we study the radiative cooling of a ballistically expanding spherical cloud of chondrule droplets ejected from the impact site. We present results from a numerical radiative transfer models as well as analytic approximate solutions. We find that the temperature after the start of the expansion of the cloud remains constant for a time t_cool and then drops with time t approximately as T ~ T_0[(3/5)t/t_cool+ 2/5]^(-5/3) for t>t_cool. The time at which this temperature drop starts t_cool depends via an analytical formula on the mass of the cloud, the e...

Dullemond, Cornelis Petrus; Johansen, Anders

2015-01-01

130

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

E-print Network

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

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

2014-01-01

131

Contemporaneous Formation of Chondrules in the Al-26-MG-26 System for Ordinary and CO Chondrites  

NASA Technical Reports Server (NTRS)

Chronometer using the short-lived extinct-nuclide (26)Al has been applied to chondrules in order to obtain of their formation ages. Previous studies were mostly performed on Al-rich chondrules, which constitute only 1% of all chondrules, because of their high Al/Mg ratios. Recently, (26)Al ages of major ferromagnesian chondrules in least equilibrated ordinary chondrites (OC) have been obtained. However, (26)Al ages of ferromagnesian chondrules in least equilibrated carbonaceous chondrites (CC) are very limited. Particularly, age data of FeO-poor (Type I) chondrules in CC have been scarcely obtained, because of their fine textures and lack of phases with high Al/Mg (>100) ratios. In order to clarify the origin and formation processes of chondrules, we started systematic investigations on Type I chondrules in the most pristine CC (CO3.0 Yamato-81020), by examining textures, bulk chemical compositions, (26)Al ages and oxygen isotopic compositions. We find Type I chondrules in CC formed contemporaneously with ferromagnesian chondrules in OC.

Kurahashi, E.; Kita, N. T.; Nagahara, H.; Morishita, Y.

2004-01-01

132

Noble gases in individual chondrules of the Allende CV3 chondrite  

NASA Astrophysics Data System (ADS)

We analyzed noble gases in nine individual chondrules, an assemblage of small chondrules, and four whole-rock samples of the Allende CV3 chondrite. Major elements were also determined for five chondrules. The cosmic ray exposure ages are calculated from cosmogenic 3He to be 5.17 ± 0.38 and 5.15 ± 0.25 Myr for the averages of the chondrules and whole rocks, respectively, showing no significant pre-exposure evidence for the studied chondrules. Large amounts of 36Ar, 80,82Kr, and 128Xe produced by neutron capture are observed in most samples; the abundances of these nuclides are correlated among the samples. The epithermal neutron flux and neutron slowing down density are calculated based on [80Kr]n, from which a sample depth of about 30 cm can be calculated. The measured chondrules contain variable amounts of radiogenic 129Xe. The abundance ratios of radiogenic 129Xe to neutron capture-produced 128Xe are rather constant among the studied chondrules; four chondrules give more precise ratios at the high-temperature fractions, ranging from 1920 ± 80 to 2280 ± 140, which corresponds to a time difference of 3.9 ± 2.4 Myr. It is noticeable that most chondrules also contain 244Pu-derived fission Xe. The average 244Pu/238U ratio for nine chondrules is 0.0069 ± 0.0018, which agrees well with the preferred ratio reported for chondrites.

Miura, Yayoi N.; Nagao, Keisuke; Kimura, Makoto

2014-06-01

133

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

NASA Astrophysics Data System (ADS)

An amoeboid olivine inclusion in CK3 NWA 1559 (0.54 × 1.3 mm) consists of a diopside-rich interior (approximately 35 vol%) and an olivine-rich rim (approximately 65 vol%). It is the first AOI to be described in CK chondrites; the apparent paucity of these inclusions is due to extensive parent-body recrystallization. The AOI interior contains irregular 3-15 ?m-sized Al-bearing diopside grains (approximately 70 vol%), 2-20 ?m-sized pores (approximately 30 vol%), and traces of approximately 2 ?m plagioclase grains. The 75-160 ?m-thick rim contains 20-130 ?m-sized ferroan olivine grains, some with 120º triple junctions. A few coarse (25-50 ?m-sized) patches of plagioclase with 2-18 ?m-thick diopside rinds occur in several places just beneath the rim. The occurrence of olivine rims around AOI-1 and around many AOIs in CV3 Allende suggests that CK and CV AOIs formed by the acquisition of porous forsteritic rims around fine-grained, rimless CAIs that consisted of diopside, anorthite, melilite, and spinel. Individual AOIs in carbonaceous chondrites may have formed after transient heating events melted their olivine rims as well as portions of the underlying interiors. In AOI-1, coarse plagioclase grains with diopside rinds crystallized immediately below the olivine rim. Secondary parent-body alteration transformed forsterite in the rims of CV and CK AOIs into more-ferroan olivine. Some of the abundant pores in the interior of AOI-1 may have formed during aqueous alteration after fine-grained melilite and anorthite were leached out. Chondrite groups with large chondrules tend to have large AOIs. AOIs that formed in dust-rich nebular regions (where CV and CK chondrites later accreted) tend to be larger than AOIs from less-dusty regions.

Rubin, Alan E.

2013-03-01

134

Crystallization kinetics of olivine-phyric shergottites  

NASA Astrophysics Data System (ADS)

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.

Ennis, Megan E.; McSween, Harry Y.

2014-08-01

135

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

NASA Astrophysics Data System (ADS)

Olivine is abundant in Earth’s upper mantle and ubiquitous in basaltic lavas, but rarely occurs in eclogite. Partial melts of eclogite are, therefore, not in equilibrium with olivine, and will react with peridotite as they migrate through the upper mantle. If such melts erupt at Earth’s surface, their compositions will be highly modified and they may be olivine-saturated. We investigated experimentally the reaction between olivine and siliceous eclogite partial melt, and determined element partitioning between olivine and the melt produced by this reaction. Our results demonstrate that mixing of reacted eclogite partial melt with primitive basalt is capable of producing the positive correlation between melt SiO2 content and olivine Ni content observed in some Hawaiian lavas. Experiments were carried out by equilibrating eclogite partial melt or basalt with San Carlos olivine at 1 bar and 1,201 1,350°C. Our results show that eclogite partial melts equilibrated with mantle olivine retain their high SiO2, low FeO and MgO characteristics. Further, olivine-melt partition coefficients for Ni measured in these experiments are significantly larger than for basalt. Mixing of these melts with primitive Hawaiian tholeiitic lavas results in crystallization of high-Ni olivines similar to those in Makapuu-stage Koolau lavas, even though the mixed magmas have only moderate Ni contents. This results from a hyperbolic increase of the Ni partition coefficient with increasing polymerization of the mixed melt. Note that while eclogite partial melt in contact with peridotite will equilibrate with pyroxene as well as olivine, this will have the effect of buffering the activity of SiO2 in the reacted melt at a higher level. Therefore, an eclogite partial melt equilibrated with harzburgite will have higher SiO2 than one equilibrated with dunite, enhancing the effects observed in our experiments. Our results demonstrate that an olivine-free “hybrid” pyroxenite source is not required to explain the presence of high-Ni olivines in Hawaiian lavas and, therefore, indicate that the proportion of eclogite in the Hawaiian plume is less than has been estimated in recent studies.

Wang, Zhengrong; Gaetani, Glenn A.

2008-05-01

136

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

E-print Network

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 ...

Carrera, Daniel; Davies, Melvyn B

2015-01-01

137

Turbulent Concentration of Chondrules: Size Distribution and Multifractal Scaling  

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

138

Electrical discharge heating of chondrules in the solar nebula  

NASA Technical Reports Server (NTRS)

We present a rudimentary theoretical assessment of electrical discharge heating as a candidate mechanism for the formation of chondrules in the solar nebula. The discharge model combines estimates of the properties of the nebula, a mechanism for terrestrial thunderstorm electrification, and some fundamental electrical properties of gases. Large uncertainties in the model inputs limit these calculations to order-or-magnitude accuracy. Despite the uncertainty, it is possible to estimate an upper limit to the efficiency of nebular discharges at melting millimeter-sized stony objects. We find that electrical arcs analogous to terrestrial lightning could have occurred in the nebula, but that under most conditions these discharges probably could not have melted chondrules. Despite our difficulties, we believe the topic worthy of further investigation and suggest some experiments which could improve our understanding of nebular discharges.

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

1995-01-01

139

Unambiguous voids in Allende chondrules and refractory inclusions  

SciTech Connect

Void space can be caused by thin section preparation. 3-dimensional tomographic analysis, prior to sectioning, shows that several very different types of voids are abundant in Allende meteorite inclusions. Formation models are proposed for each type. Void spaces in the components of chondritic meteorites have received little attention, perhaps due to ambiguities attendant upon their very existence, and also their origin. Computer-aided microtomography allows the 3-dimensional imaging and analysis of void spaces within solid objects. Several striking examples of void spaces, apparently enclosed by solid material, resulted from our observations of large chondrules and CAIs from the Allende (CV3) meteorite. These voids are 'unambiguous' because their existence cannot be ascribed to plucking during sample preparation, as would be the case in traditional 2-dimensional thin section petrography. Although we focus on large objects in Allende, preliminary observations indicate that void spaces are prevalent in chondrules and refractory inclusions in many meteorites. Voids remain ambiguous, however, because their structure and appearance vary between chondrules and CAIs, suggesting there may be different causes of void formation in particular objects. Some voids appear to have formed as a result of dilation during cooling. Others are evidence of hydrothermal leaching on the parent body followed by partial chemical replacement. Alternatively, vapor-mediated leaching and replacement may have occurred in the nebula. Yet another possibility is internal brecciation caused by impact, while the object was still free floating in the nebula, and perhaps still partially molten.

Murray, J.; Boesenberg, J.S.; Ebel, D.S. (AMNH)

2003-03-26

140

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

Microsoft Academic Search

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.

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

1994-01-01

141

Incompatible Trace Element Abundances in Hawaiian Olivines  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

142

Transient Heating and Chondrule Formation: Evidence From Sodium Loss in Flash Heating Simulation Experiments  

Microsoft Academic Search

Flash heating simulation experiments have been performed to determine the effects of heating time, cooling rate, ambient gas fO2, and the sample bulk composition on the extent of Na loss of silicate melts and the implications for chondrule formation. The samples studied include type IA, IAB, and IIAB chondrule analog compositions as well as other synthetic silicate materials. The following

Yang Yu; Roger H. Hewins

1998-01-01

143

Gas dynamic heating of chondrule precursor grains in the solar nebula  

Microsoft Academic Search

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

L. L. Hood; M. Horanyi

1991-01-01

144

Growth of dust rims around chondrules in MHD-turbulent protoplanetary disks  

Microsoft Academic Search

The accretion of dust onto chondrule-sized particles is modeled through magnetohydrodynamic (MHD) simulations of a protoplanetary disk. The observed dust rims around chondrules in meteorites, such as CM carbonaceous chondrites, have been suggested to form on the parent body by a combination of compaction and aqueous alteration of a generic enveloping matrix. However, a nebular origin of these rims seems

A. Carballido

2009-01-01

145

Oxygen Isotope Heterogeneity in the Mesostasis of a Semarkona Group A1 Chondrule  

Microsoft Academic Search

Oxygen isotopes in a large group A1 chondrule with compositionally zoned mesostasis show a large spread along a slope one fractionation line with a radial trend of light oxygen increasing toward the edge. The chondrule formation process appears to have produced this trend.

D. W. G. Sears; I. C. Lyon; J. M. Saxton; S. Symes; G. Turner

1999-01-01

146

Chondrule Precursors: The Nature of the S- and Ni-bearing Phases(s)  

NASA Astrophysics Data System (ADS)

Lauretta and Fegley showed that troilite made by S condensation on kamacite should include a significant amount of Ni, but they reported being unsuccessful in their search for Ni-bearing troilite in chondrites. We show the various opaque associations (OAs) found in veneers around chondrules in primitive and less primitive chondrites to be the result of parent body decomposition under different conditions of an initial Ni-bearing monosulfide solid solution (Ni-MSS). OAs in the less melted (finest grained) Semarkona chondrules are similar to the ones in veneers and differ from those in coarser grained chondrules. As fine-grained chondrules must have kept a better memory of their precursor minerals, this indicates that the dominant opaque phase in chondrule precursors was Ni-MSS, the logical end member of S condensation on kamacite in the solar nebula.

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

1996-03-01

147

The origin of chondrules and chondrites: Debris from low-velocity impacts between molten planetesimals?  

NASA Astrophysics Data System (ADS)

We investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin-shelled, largely molten planetesimals collided at low speed during accretion. This scenario, here dubbed "splashing," stems from evidence that such planetesimals, intensely heated by 26Al, were abundant in the protoplanetary disk when chondrules were being formed approximately 2 Myr after calcium-aluminum-rich inclusions (CAIs), and that chondrites, far from sampling the earliest planetesimals, are made from material that accreted later, when 26Al could no longer induce melting. We show how "splashing" is reconcilable with many features of chondrules, including their ages, chemistry, peak temperatures, abundances, sizes, cooling rates, indented shapes, "relict" grains, igneous rims, and metal blebs, and is also reconcilable with features that challenge the conventional view that chondrules are flash-melted dust-clumps, particularly the high concentrations of Na and FeO in chondrules, but also including chondrule diversity, large phenocrysts, macrochondrules, scarcity of dust-clumps, and heating. We speculate that type I (FeO-poor) chondrules come from planetesimals that accreted early in the reduced, partially condensed, hot inner nebula, and that type II (FeO-rich) chondrules come from planetesimals that accreted in a later, or more distal, cool nebular setting where incorporation of water-ice with high ?17O aided oxidation during heating. We propose that multiple collisions and repeated re-accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties, and led to so-called "complementarity" and metal depletion in chondrites. We suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation.

Sanders, Ian S.; Scott, Edward R. D.

2012-12-01

148

Diffusion of highly charged cations in olivine  

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

149

Experimental constraints on the partitioning of rhenium and some platinum-group elements between olivine and silicate melt  

NASA Astrophysics Data System (ADS)

We have performed partitioning experiments to assess the role of olivine in controlling the behavior of rhenium and the platinum group elements (PGEs) during basalt petrogenesis. Olivines were crystallized from an iron-bearing basalt at 1 bar (10 5 Pa) and log fO 2 of -2.6, -4.9 and -7.4 (FMQ +4.3, +2 and -0.5, respectively). In situ analyses of olivine and glass by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) reveal a homogeneous distribution of Ru, Rh, Pd, Re, and Pt, but significant Os heterogeneity at the ?m scale. This latter behavior arises from the presence of undissolved Os micronuggets suspended in the melt, and included in olivine crystals. Olivine-melt partition coefficients ( Ds) for Re and the PGEs follow the order: DRh> DRu? DPd˜ DRe˜ DPt. With decreasing fO 2, Rh and Ru become more compatible, with maximum partition coefficients of ˜2.6 and ˜2, respectively, at log fO 2 of -4.9. In contrast, D values for Pd become smaller with decreasing fO 2, to a value of ˜0.006 at log fO 2 of -7.4. Olivine-melt partitioning of Rh, Ru, Pd, Re and Pt derived from our experiments is confirmed by the behavior of these elements in lavas that have evolved by olivine fractionation. An elastic strain model predicts the olivine-melt partitioning of these elements, excepting our measured value of DPt, which is much lower. The fO 2 dependence on partitioning implies that at higher fO 2 some portion of PGEs exist in higher valence states than predicted from their solubility.

Brenan, J. M.; McDonough, W. F.; Dalpé, C.

2003-07-01

150

Shock-produced olivine glass - First observation  

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

151

A search for olivine activation volume  

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

152

Effect of a Si-rich layer on olivine carbonation under in-situ conditions  

NASA Astrophysics Data System (ADS)

Mineral carbonation, a geochemical reaction between Mg-, Fe-, and Ca-silicate minerals and dissolved carbon dioxide (CO2), results in the long-term, stable storage of CO2 as carbonate minerals. Although the reaction is thermodynamically favored and occurs naturally, the kinetics are typically slow at temperatures < 100°C and thus limit industrial applications of the process. This study presents the results of a series of batch reactions designed to further understand the kinetics and mechanism of olivine carbonation in a three-phase system (water, solid, and supercritical CO2) at conditions relevant to in-situ¬ carbonation (60°C, 100 bar CO2 pressure, water:solid of 20:1 to 50:1, pH 3-6 ). Twin Sisters (OR) olivine ((Mg0.85 Fe0.15)2SiO4) was chosen as the reactive silicate mineral because olivines are abundant and undergo carbonation in nature. The carbonation of olivine in the presence of water and supercritical CO2 proceeds via dissolution of the starting mineral and CO2, followed by precipitation of secondary phases. Two secondary phases are relevant to this study. The first is Mg-carbonate (magnesite, MgCO3), the desired reaction product because it sequesters CO2 for geologic time scales. The second is amorphous silica (SiO2), a side-product that increases the total volume of solids in the system but does not interact with CO2. Because the solubility of silica is much less than that of Mg-carbonate at <100°C, silica reaches thermodynamic saturation first. The present study shows that the rate of olivine dissolution depends on the saturation state of amorphous silica and decreases by up to two orders of magnitude (from 10-11 to 10-13 mol cm-2 s-1) as saturation is approached. This observed effect is likely due to formation of a Si-rich layer on olivine grain surfaces after exposure to acidic solution, observed by x-ray photoelectron spectroscopy. The initial olivine dissolution is incongruent over the timeframe of several hours as shown by solution compositions determined by ICP-AES, but becomes congruent over longer periods. This behavior has been noted by others. We hypothesize that when in contact with an aqueous solution at saturation with respect to silica, the Si-rich layer will significantly lower Mg diffusion as well as the dissolution rate of olivine. The net effect is thus an apparent olivine dissolution rate of near zero for time periods ranging from 1 to 20 days. After this period the measured olivine dissolution rate increases, indicating that the Si-rich layer is no longer plays a role in passivating the surface. We hypothesize that as the surface area of secondary silica increases, there is an increasing movement of SiO2 from the olivine surface layer to physically separate secondary silica particles. We conclude that the rate of olivine carbonation under the conditions of our experiments depends strongly on SiO2 saturation and that this effect must be mitigated for a commercially viable Mg-silicate carbonation process.

Johnson, N. C.; Thomas, B.; Rosenbauer, R. J.; Maher, K.; Brown, G. E.

2011-12-01

153

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

E-print Network

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

Tommasi, Andrea

154

Planetary Embryo Bow Shocks as a Mechanism for Chondrule Formation  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

155

Chondrule-like objects and brown glasses in howardites  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

156

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

PubMed

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

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

2014-05-20

157

Bar Graph  

NSDL National Science Digital Library

This bar graph application allows the learner to interpret one of three sets of pre-existing data or to input their own data and create their own bar graph. The display can be altered to increase or descrease the interval on the y-axis or to increase or descrease the width of the bars on the x-axis.

2012-01-01

158

Different radiation and metamorphic history of the Kainsaz CO 3.2 chondrules  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

159

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

NASA Astrophysics Data System (ADS)

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

Kornacki, A. S.; Fegley, B.

1984-02-01

160

Contrasting Size Distributions of Chondrules and Inclusions in Allende CV3  

NASA Technical Reports Server (NTRS)

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

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

2014-01-01

161

Toward a unified hydrous olivine electrical conductivity law  

NASA Astrophysics Data System (ADS)

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.

Gardés, Emmanuel; Gaillard, Fabrice; Tarits, Pascal

2014-12-01

162

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

NASA Astrophysics Data System (ADS)

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.

Rubin, A. E.

1993-03-01

163

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

Microsoft Academic Search

Lattice diffusion coefficients have been determined for 19 elements (Li, Be, Na, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y,\\u000a Zr, Eu, Gd, Lu and Hf) in a single crystal of San Carlos olivine as a function of crystallographic orientation, at 1,300°C,\\u000a 1 bar and fO2 = 10?8.3 bars, by equilibration with a synthetic silicate melt. Results for Li, Na, V,

Carl Spandler; Hugh St. C. O’Neill

2010-01-01

164

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

E-print Network

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.

Hitoshi Miura; Taishi Nakamoto

2006-07-03

165

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

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

166

Dissolution of Olivine Promoted by Ion Irradiation  

NASA Astrophysics Data System (ADS)

Recent laboratory simulations of ion irradiation effects on planetary minerals show changes in the surface composition of surfaces that are different depending on whether the analysis is done in-situ (without removing the sample from vacuum) or ex-situ using an electron microscope. We found that olivine samples that have been irradiated by keV ions show preferential loss of magnesium when exposed to water. Irradiations were done with 4 keV argon ions to fluences between 1015 and 1018 ions/cm2. Soak times in high purity water ranged from minutes to days, and exhibit the same degree of Mg depletion, independent of soak time. The concentration of magnesium on the surface of irradiated natural olivine decreases by 40% upon contact with water, as measured with x-ray photoelectron spectroscopy. This finding is important for laboratory simulations of regolith processes and for establishing procedures for the handling of irradiated samples, including those from sample return missions.

Cantando, E. D.; Dukes, C. A.; Baragiola, R. A.

2006-12-01

167

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

168

Shock-Produced Olivine Glass: First Observation  

Microsoft Academic Search

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

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

1977-01-01

169

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

E-print Network

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

Grossman, Lawrence

170

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

NASA Astrophysics Data System (ADS)

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).

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

2009-12-01

171

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

USGS Publications Warehouse

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.

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

2000-01-01

172

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

173

Water and Carbon Dioxide Adsorption at Olivine Surfaces  

SciTech Connect

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.

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

2013-11-14

174

Tubular symplectic inclusions in olivine from the Fukang pallasite  

Microsoft Academic Search

Olivine from the Fukang meteorite, like that from many other pallasites, contains distinctive arrays of parallel, straight, tubular inclusions. They differ in their extension and linearity from those in terrestrial olivines. They comprise approximately 1% of the total volume. Most have lens-shaped cross-sections, but some are rounded. The major axis of the lens-shaped inclusions is rigorously oriented along olivine [001],

Michael R. Stevens; David R. Bell; Peter R. Buseck

2010-01-01

175

Search for Olivine Spectral Signatures on the Surface of Vesta  

NASA Technical Reports Server (NTRS)

The occurrence of olivines on Vesta were first postulated from traditional petrogenetic models which suggest the formation of olivine as lower crustal cumulates. An indirect confirmation is given by their presence as a minor component in some samples of diogenite meteorites, the harzburgitic diogenites and the dunitic diogenites, and as olivine mineral clasts in howardites. Another indication for this mineral was given by interpretations of groundbased and Hubble Space Telescope observations that suggested the presence of local olivine-bearing units on the surface of Vesta. The VIR instrument onboard the DAWN mission has been mapping Vesta since July 2011. VIR acquired hyperspectral images of Vesta s surface in the wavelength range from 0.25 to 5.1 m during Approach, Survey and High Altitude Mapping (HAMO) orbits that allowed a 2/3 of the entire asteroid surface to be mapped. The VIR operative spectral interval, resolution and coverage is suitable for the detection and mapping of any olivine rich regions that may occur on the Vesta surface. The abundance of olivine in diogenites is typically lower than 10% but some samples richer in olivine are known. However, we do not expect to have extensive exposures of olivine-rich material on Vesta. Moreover, the partial overlap of olivine and pyroxene spectral signatures will make olivine difficult to detect. Different spectral parameters have been used to map olivine on extraterrestrial bodies, and here we discuss the different approaches used, and develop new ones specifically for Vesta. Our new methods are based on combinations of the spectral parameters relative to the 1 and 2 micron bands (the most prominent spectral features of Vesta surface in the visible and the infrared), such as band center locations, band depths, band areas, band area ratios. Before the direct application to the VIR data, the efficiency of each approach is evaluated by means of analysis of laboratory spectra of HED meteorites, pyroxenes, olivines and their mixtures.

Palomba, E.; De Sanctis, M. C.; Ammannito, E.; Capaccioni, F.; Capria, M. T.; Farina, M.; Frigeri, A.; Longobardo, A.; Tosi, F.; Zambon, F.; McSween, H. Y.; Mittlefehldt, D. W.; Russell, C. T.; Raymond, C. A.; Sunshine, J.; McCord, T. B.

2012-01-01

176

A scanning electron microscope study of olivine crystal surfaces  

NASA Technical Reports Server (NTRS)

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

Olsen, E. J.; Grossman, L.

1974-01-01

177

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

E-print Network

VAPOR PRESSURES AND EVAPORATION COEFFICIENTS OF FE, NA AND K OVER CHONDRULE COMPOSITION MELTS. A. V and isotopic evidence of significant evaporative losses from chondrules is rare. The free evaporation flux and evaporation coefficient of species x, resp., R is the gas constant and T is the temperature. Thus, computation

Grossman, Lawrence

178

Effect of Water on Olivine Metastability in Subducting Lithosphere  

NASA Astrophysics Data System (ADS)

The roles of metastably persisting olivine in subducting lithosphere has been investigated in light of mineralogical and thermal structures, plate velocities, and deep seismogenesis. Many different variables have been used in these examinations: latent heat feedback, kinetic models, and thermal conductivity models, to name a few. In all these models, however, the olivine has been anhydrous, though the presence of H2O in the (Mg,Fe)2SiO4 system is well-known to enhance the rates of phase transformation. Diedrich et al. [2005] recently determined growth rates for olivine with low (300 wt ppm) water content and found that, compared with dry samples, hydrous olivine has growth rates 1.7 orders faster at 1100°C. Using these kinetic data, we modeled 25 subducting slabs with thermal parameters (?) ranging from 3400-17000 km to see the effect of water on olivine metastability. Except within the coldest, fastest slabs, (? > 10000 km) all olivine had transformed to wadsleyite or ringwoodite within 1-2 km of the equilibrium phase boundary, resulting in regions of metastability only 5-10% in size as compared with slabs with dry olivine. Wedges of metastable olivine did form in slabs moving at velocities ?14 cm/yr, yet these were only 4-5% in size with respect to their anhydrous counterparts. Metastable olivine only reached maximum depths of ~360 km, compared with 500-550 km for dry slabs, 5-15 km down-dip of the equilibrium phase boundary. These results suggest that, given small amounts of water, subducting slabs will exhibit near-equilibrium mineralogical structures. Therefore, in consequence, explanations of deep seismogenesis that rely on the persistence of metastable olivine would seem unlikely for hydrous lithosphere. In addition, any decrease in subduction velocity due to the existence of a low-density wedge of metastable olivine (the parachute effect) in dry slabs would not be evident in hydrous ones.

Marton, F. C.; Diedrich, T.; Sharp, T. G.

2006-12-01

179

Olivine in an unexpected location on Vesta's surface  

NASA Astrophysics Data System (ADS)

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.

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

180

Did Ordinary Chondrite Impactors Deliver Olivine to Vesta?  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

181

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

USGS Publications Warehouse

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.

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

2006-01-01

182

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

PubMed

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

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

1993-01-01

183

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

NASA Technical Reports Server (NTRS)

We characterize ten chromatic chondrules, two spinelian chondrules andd one spinel-bearing chondrule and summarize data for 120 chromitic inclusions discovered in an extensive survey of ordinary chondrites. Compositional and petrographic evidence suggests that chromitic chondrules and inclusions are closely related. The Cr/(Cr + Al) ratios in the spinal of these objects range from 0.5 to 0.9 and bulk Al2O3 contents are uniformly high (greater than 10 wt%, except for one with 8 wt%). No other elements having comparable solar abundances are so stongly enriched, and alkali feldspar and merrillite are more common than in normal chondrules. The Cr/Mg ratios in chromitic chondrules are 180-750 times the ratios in the bulk chondrite. With the possible exception of magnetic clumping of chromite in the presolar cloud, mechanical processes cannot account for this enrichment. Examination of nebular equilibrium processes shows that 50%-condensation temperatures of Cr at pH2/pH2O of 1500 are several tens of degrees below those of Mg as Mg2SiO4; the condensation of Cr is primarily as MgCr2O4 dissolved in MgAl2O4 at nebular pressures of 10(exp -4) atm or below. At pH2 = 10(exp -3) atm condesation as Cr in Fe-Ni is favored. Making the nebula much more oxidizing reduces the difference in condensation temperatures but Mg remains more refractory. We conclude that nebular equilibrium processes are not responsible for the enhanced Cr/Mg ratios. We propose that both Cr and Al became enriched in residues formed by incomplete evaporation of presolar lumps. We suggest that spinals remained as solid phases when the bulk of the silicates were incorporated into the evaporating melt; vaporization of Al and Cr were inhibited by the slow kinetics of diffusion. Subsequent melting and crystallization of these residues fractionated Cr from Al. The resulting materials constituted major components in the precursors of chromitic chondrules. Our model implies that chromitic chondrules and inclusions preserve the Cr isotopic record of presolar sources.

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

1993-01-01

184

Development of crystal preferred orientation of olivine during diffusion creep: a matter of olivine crystal shape  

NASA Astrophysics Data System (ADS)

Crystalloagraphic preferred orientation (CPO) of olivine produced during dislocation creep is considered the primary cause of elastic anisotropy in the upper mantle of Earth and is used by seismologists to determine the direction of flow. Here we show that synthetic Fe-free olivine aggregates with either diopside or melt develop strong to weak CPO during grain boundary sliding (GBS) accommodated by diffusion. GBS on boundaries that correspond to specific crystallographic planes produces CPO. By combining the CPO patterns developed during tension and compression experiments, we predict formation in the mantle of three different CPO patterns depending on temperature and the presence of melt. Strong radial anisotropy is anticipated for GBS accommodated by diffusion during simple shear deformation at temperatures from 0.92*Ts to Ts (Ts: solidus temperature). These conditions correspond to depths where melting initiates to 50-100 km deeper and where strongly anisotropic and low seismic velocities are detected.

Miyazaki, T.; Sueyoshi, K.; Hiraga, T.

2013-12-01

185

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

E-print Network

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 ...

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

2015-01-01

186

INCORPORATION OF A LATE-FORMING CHONDRULE INTO COMET WILD 2  

SciTech Connect

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.

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

187

MODEL EVAPORATION OF CHONDRULE PRECURSORS IN NEBULAR SHOCKS. A. V. Fedkin1 Grossman1,2  

E-print Network

MODEL EVAPORATION OF CHONDRULE PRECURSORS IN NEBULAR SHOCKS. A. V. Fedkin1 , L. Grossman1,2 and M, Seattle, WA 98115. Introduction: It is widely accepted that evaporation of such elements as S, Na, K, Fe evaporation [2]; re-introduction of nearly completely volatilized elements either by back- reaction

Grossman, Lawrence

188

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

189

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

NASA Astrophysics Data System (ADS)

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.

Mishra, Ritesh Kumar; Chaussidon, Marc

2014-07-01

190

Olivine Deposits Associated with Impact Basins and Craters on Mars  

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

191

Olivine Weathering: Abiotic Versus Biotic Processes as Possible Biosignatures  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

192

Systematics of Vanadium in Olivine from Planetary Basalts  

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

193

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

USGS Publications Warehouse

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.

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

1985-01-01

194

Dislocation creep of fine-grained olivine  

NASA Astrophysics Data System (ADS)

Deformation experiments conducted in a gas medium apparatus at temperatures from 1200 to 1350°C with a fine-grained, solution-gelation derived Fe-bearing olivine show a stress dependence of the strain rate at stresses above ˜150 MPa, which is much stronger than previously reported for polycrystalline samples. The data can be fit by a power law with ???n with n ˜ 7-8, or equally well by a Peierls creep law with exponential stress dependence. Due to the observed strong stress dependence the samples deform at significantly higher strain rates at a given stress than single crystals or coarse-grained polycrystals with n ˜ 3.5. TEM observations indicate the presence of dislocations with at least two different Burgers vectors, with free dislocations predominantly of screw character. Subgrain walls are present but are only weakly developed and have small misorientation angles. Both the rheology and dislocation structures are consistent with creep rate-limited by dislocation glide or cross slip for aggregates with grain sizes smaller than or approaching the recrystallized grain size. Deformation mechanism maps extrapolated to lithospheric temperatures using the melt-free diffusion creep rheology of Faul and Jackson (2007), the dislocation creep rheology of Hirth and Kohlstedt (2003), and the results described here indicate that deformation conditions of ultramylonitic shear zones fall near the triple point of Peierls, dislocation, and diffusion creep.

Faul, U. H.; Fitz Gerald, J. D.; Farla, R. J. M.; Ahlefeldt, R.; Jackson, I.

2011-01-01

195

Thermal properties of fully delithiated olivines  

NASA Astrophysics Data System (ADS)

Carbon-coated LiMnxFe1-xPO4 (x = 0, 0.5 and 1) is fully delithiated using NO2BF4 oxidant to investigate thermal behavior as a function of temperature as high as 700 °C in an Ar atmosphere. Reitveld refinement of X-ray diffraction (XRD) studies indicates readiness of chemical delithiation, except for Li0MnPO4, hydrated to amorphous MnPO4·2H2O. Thermal studies coupled with thermogravimetric analysis and in situ high temperature XRD demonstrate that the phase stability is affected by substituted Mn at an elevated temperature. The Li0FePO4 is stable up to 500 °C, maintaining the original olivine structure with a small amount of oxygen release. At higher temperatures, the phase was transformed to Fe3(PO4)2 and Fe2P2O7. In contrast, the phase transformation temperature is apparently reduced to as low as 200 °C by the addition of Mn into the crystal structure, which is related to the phase transformation to (Mn0.5Fe0.5)3(PO4)2 associated with fast oxygen loss from the original structure. As a result, the better thermal stability of Li0FePO4 is attributed to less oxygen loss, which delays the phase transformation, resulting in less exothermic heat in the temperature range.

Park, Jae-Sang; Oh, Seung-Min; Sun, Yang-Kook; Myung, Seung-Taek

2014-06-01

196

Thermal Emission Spectroscopy of 1 Ceres: Evidence for Olivine  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

197

Application Bar  

Microsoft Academic Search

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

Henry Lee; Eugene Chuvyrov

198

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

PubMed

CO2 sequestration via carbonation of widely available low-cost minerals, such as olivine, can permanently dispose of CO2 in an environmentally benign and a geologically stable form. We report the results of studies of the mechanisms that limit aqueous olivine carbonation reactivity under the optimum sequestration reaction conditions observed to date: 1 M NaCl + 0.64 M NaHCO3 at Te 185 degrees C and P(CO2) approximately equal to 135 bar. A reaction limiting silica-rich passivating layer (PL) forms on the feedstock grains, slowing carbonate formation and raising process cost. The morphology and composition of the passivating layers are investigated using scanning and transmission electron microscopy and atomic level modeling. Postreaction analysis of feedstock particles, recovered from stirred autoclave experiments at 1500 rpm, provides unequivocal evidence of local mechanical removal (chipping) of PL material, suggesting particle abrasion. This is corroborated by our observation that carbonation increases dramatically with solid particle concentration in stirred experiments. Multiphase hydrodynamic calculations are combined with experimentto better understand the associated slurry-flow effects. Large-scale atomic-level simulations of the reaction zone suggest that the PL possesses a "glassy" but highly defective SiO2 structure that can permit diffusion of key reactants. Mitigating passivating layer effectiveness is critical to enhancing carbonation and lowering sequestration process cost. PMID:16913142

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

2006-08-01

199

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.

2010-12-02

200

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)

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.

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

2014-08-01

201

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

E-print Network

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

Geist, Dennis

202

Formation of a metastable olivine wedge in a descending slab  

SciTech Connect

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

Devaux, J.P. [Department of Earth and Space Sciences, University of California, Los Angeles, California (United States)] [Department of Earth and Space Sciences, University of California, Los Angeles, California (United States); Schubert, G. [Department of Earth and Space Sciences, University of California, Los Angeles, California (United States)] [Department of Earth and Space Sciences, University of California, Los Angeles, California (United States); [Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California (United States); Anderson, C. [Engineering Sciences and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico (United States)] [Engineering Sciences and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico (United States)

1997-11-01

203

Extraction of in situ cosmogenic 14C from olivine  

USGS Publications Warehouse

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.

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

2010-01-01

204

Tracing Oxygen Fugacity in Asteroids and Meteorites Through Olivine Composition  

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

205

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

NASA Technical Reports Server (NTRS)

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

Wood, J. A.

1984-01-01

206

Chondrules in Apollo 14 samples and size analyses of Apollo 14 and 15 fines.  

NASA Technical Reports Server (NTRS)

Chondrules have been observed in several breccia samples and one fines sample returned by the Apollo 14 mission. The chondrules are formed by at least three different processes that appear to be related to large impacts: (1) crystallization of shock-melted spherules and droplets; (2) rounding of rock clasts and mineral grains by abrasion in the base surge; and (3) diffusion and recrystallization around clasts in hot base surge and fall-back deposits. In the case of the Apollo 14 samples, the large impact almost certainly is the Imbrian event. Grain size analyses of undisturbed fines samples from the Apollo 14 site and from the Apollo 15 Apennine Front are almost identical, indicating that the two localities have similar meteoroid bombardment exposure ages, approximately 3.7 x 10 to the 9th yr. This observation is consistent with the interpretation that both the Fra Mauro formation and the Apennine Front material originated as ejecta from the Imbrian event.

King, E. A., Jr.; Butler, J. C.; Carman, M. F.

1972-01-01

207

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

NASA Astrophysics Data System (ADS)

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

Wood, J. A.

1984-09-01

208

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

Microsoft Academic Search

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

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

2000-01-01

209

Exotic Olivine in Antarctic Angrites LEW 87051 and Asuka 881371  

NASA Astrophysics Data System (ADS)

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.

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

1995-09-01

210

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

NASA Technical Reports Server (NTRS)

Size-selective concentration of particles in a weakly turbulent protoplanetary nebula may be responsible for the initial collection of chondrules and other constituents into primitive bodY precursors. This paper presents the main elements of this process of turbulent concentration. In the terrestrial planet region. both the characteristic size and size distribution of chondrules are explained. "Fluffier" particles would be concentrated in nebula regions which were at a lower density and/or more intensely turbulent. The spatial distribution of concentrated particle density obeys multifractal scaling, suggesting a close tie to the turbulent cascade process. This scaling behavior allows predictions of the probability distributions for concentration in the protoplanetary nebula to be made. Large concentration factors (less than 10(exp 5)) are readily obtained, implying that numerous zones of particle density significantly exceeding the gas density could exist. If most of the available solids were actually in chondrule sized particles, the ensuing particle mass density would become so large that the feedback effects on gas turbulence due to mass loading could no longer be neglected. This paper describes the process, presenting its basic elements and some implications, without including the effects of mass loading.

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

2000-01-01

211

An olivine-free mantle source of Hawaiian shield basalts.  

PubMed

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

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

2005-03-31

212

The identification of crystalline olivine in cometary silicates  

NASA Astrophysics Data System (ADS)

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

Campins, H.; Ryan, E. V.

1989-06-01

213

Thermal Emission Spectroscopy of 1 Ceres: Evidence for Olivine  

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

214

Water Retention and Rheology of Ti-doped, Synthetic Olivine  

NASA Astrophysics Data System (ADS)

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).

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

2012-12-01

215

A Survey of Olivine Alteration Products Using Raman Spectroscopy  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

216

Grinding methods to enhance the reactivity of olivine  

SciTech Connect

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.

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

2004-01-01

217

Influence of aluminum on the hydrothermal alteration rate of olivine  

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

218

Chemical zonation in olivine-hosted melt inclusions  

NASA Astrophysics Data System (ADS)

Significant zonation in major, minor, trace, and volatile elements has been documented in naturally glassy olivine-hosted melt inclusions from the Siqueiros Fracture Zone and the Galapagos Islands. Components with a higher concentration in the host olivine than in the melt (e.g., MgO, FeO, Cr2O3, and MnO) are depleted at the edges of the zoned melt inclusions relative to their centers, whereas except for CaO, H2O, and F, components with a lower concentration in the host olivine than in the melt (e.g., Al2O3, SiO2, Na2O, K2O, TiO2, S, and Cl) are enriched near the melt inclusion edges. This zonation is due to formation of an olivine-depleted boundary layer in the adjacent melt in response to cooling and crystallization of olivine on the walls of the melt inclusions, concurrent with diffusive propagation of the boundary layer toward the inclusion center. Concentration profiles of some components in the melt inclusions exhibit multicomponent diffusion effects such as uphill diffusion (CaO, FeO) or slowing of the diffusion of typically rapidly diffusing components (Na2O, K2O) by coupling to slow diffusing components such as SiO2 and Al2O3. Concentrations of H2O and F decrease toward the edges of some of the Siqueiros melt inclusions, suggesting either that these components have been lost from the inclusions into the host olivine late in their cooling histories and/or that these components are exhibiting multicomponent diffusion effects. A model has been developed of the time-dependent evolution of MgO concentration profiles in melt inclusions due to simultaneous depletion of MgO at the inclusion walls due to olivine growth and diffusion of MgO in the melt inclusions in response to this depletion. Observed concentration profiles were fit to this model to constrain their thermal histories. Cooling rates determined by a single-stage linear cooling model are 150-13,000 °C h-1 from the liquidus down to ~1,000 °C, consistent with previously determined cooling rates for basaltic glasses; compositional trends with melt inclusion size observed in the Siqueiros melt inclusions are described well by this simple single-stage linear cooling model. Despite the overall success of the modeling of MgO concentration profiles using a single-stage cooling history, MgO concentration profiles in some melt inclusions are better fit by a two-stage cooling history with a slower-cooling first stage followed by a faster-cooling second stage; the inferred total duration of cooling from the liquidus down to ~1,000 °C ranges from 40 s to just over 1 h. Based on our observations and models, compositions of zoned melt inclusions (even if measured at the centers of the inclusions) will typically have been diffusively fractionated relative to the initially trapped melt; for such inclusions, the initial composition cannot be simply reconstructed based on olivine-addition calculations, so caution should be exercised in application of such reconstructions to correct for post-entrapment crystallization of olivine on inclusion walls. Off-center analyses of a melt inclusion can also give results significantly fractionated relative to simple olivine crystallization. All melt inclusions from the Siqueiros and Galapagos sample suites exhibit zoning profiles, and this feature may be nearly universal in glassy, olivine-hosted inclusions. If so, zoning profiles in melt inclusions could be widely useful to constrain late-stage syneruptive processes and as natural diffusion experiments.

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

2014-07-01

219

Chondrules of the Very First Generation in Bencubbin/CH-like Meteorites QUE94411 and Hammadah Al Hamra 237: Condensation Origin at High Ambient Nebular Temperatures  

NASA Technical Reports Server (NTRS)

Chondrules in QUE94411 and HH 237 formed at high ambient T prior to condensation of Fe,Ni-metal following a large scale thermal event that resulted in complete vaporization of a solar nebula region. These chondrules escaped subsequent remelting.

Krot, Alexander N.; Meibom, Anders; Russell, Sara S.; Young, Edward; Alexander, Conel M.; McKeegan, Kevin D.; Lofgren, Gary; Cuzzi, Jeff; Zipfel, Jutta; Keil, Klaus

2000-01-01

220

Properties of chondrules in EL3 chondrites, comparison with EH3 chondrites, and the implications for the formation of enstatite chondrites  

Microsoft Academic Search

The study of chondrules provides information about processes occurring in the early solar system. In order to ascertain to what extent these processes played a role in determining the properties of the enstatite chondrites, the physical and chemical properties of chondrules from three EL3 chondrites and three EH3 chondrites have been examined by optical, cathodoluminescence (CL), and electron microprobe techniques.

D. M. Schneider; S. J. K. Symes; P. H. Benoit; D. W. G. Sears

2002-01-01

221

^6^0Fe-^6^0Ni Systematics of Chainpur Chondrules and the Plutonic Angrites Northwest Africa 4590 and 4801  

NASA Astrophysics Data System (ADS)

We present ^6^0Fe-^6^0Ni isotope systematics for bulk Chainpur chondrules and plutonic angrites. The Chainpur chondrule data are used to estimate an upper limit on the initial solar system ^6^0Fe/^5^6Fe < ~1 × 10^-^7.

Spivak-Birndorf, L. J.; Wadhwa, M.; Janney, P. E.

2012-03-01

222

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

E-print Network

ORIGINAL PAPER Titanium- and water-rich metamorphic olivine in high-pressure serpentinites from 2013 Ã? Springer-Verlag Berlin Heidelberg 2014 Abstract Titanium- and water-rich metamorphic olivine (Fo

Jung, Haemyeong

223

Olivine-Phyric Shergottite LAR 06319: Its Relation to the Enriched Components in Martian Basalts  

NASA Astrophysics Data System (ADS)

Detailed petrology of Larkman Nunatak (LAR) 06319 are discussed for its olivine megacryst population in olivine-phyric shergottites, as well as the nature of the incompatible-element enriched component in martian basaltic magmas.

Basu Sarbadhikari, A.; Day, J. M. D.; Liu, Y.; Taylor, L. A.

2009-03-01

224

Metal-olivine associations and Ni-Co contents in two Apollo 12 mare basalts  

NASA Technical Reports Server (NTRS)

Olivine crystals in mare basalts 12004,8 and 12022,12 are normally zoned with Cr-poor rims. The Ni content of rare 2- to 10-micron metal inclusions in olivine decreases markedly as Fe/Mg in their immediate olivine hosts increases. Each metal grain appears to have been enclosed by late olivine almost immediately after it crystallized. The fractionation trend for the olivine and metal contrasts with the subsolidus equilibration trend for pallasites. For the basalts, not even local equilibrium of Fe, Ni and Co at metal/olivine interfaces can be detected by microprobe. Ni and Co concentrations range from about 300 ppm in olivine cores to about 70 ppm in rims. The limits of detection, at 95% confidence, are 36 ppm (Ni) and 25 ppm (Co). The distribution of Ni and Co in olivine, like that of Mg and Cr, records the depletion of these elements in the melt.

Hewins, R. H.; Goldstein, J. I.

1974-01-01

225

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

NASA Astrophysics Data System (ADS)

We have examined the relationships between T112 particle and amoeboid olivine aggregates. Slight enrichment of Fe in olivine rim and associated chromites suggest that T112 may have experienced a minor degree of metamorphism.

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

2012-03-01

226

\\'Free Collisions in a Microgravity Many-Particle Experiment. II. The Collision Dynamics of Dust-Coated Chondrules  

E-print Network

The formation of planetesimals in the early solar system is hardly understood, and in particular the growth of millimeter-sized particles has recently turned out to be a difficult task in our understanding [Zsom et al. 2010, A&A, 513, A57]. Laboratory experiments have shown that dust aggregates of these sizes are hardly sticking and if at all only at very low velocities. However, in the protoplanetary disk, millimeter sized particles are known to have been ubiquitous in the form of solid chondrules as a main constituent of their parent bodies, the chondrites. Most of these chondrules were found to feature a fine grained rim, which is hypothesized to have formed from accreting dust grains in the solar nebula. To study the influence of these dust-coated chondrules on the formation of chondrites and possibly planetesimals, we conducted collision experiments between millimeter-sized, dust-coated chondrule analogs at velocities of a few cm/s. For 2 and 3 mm diameter chondrule analogs covered by dusty rims of 8...

Beitz, Eike; Weidling, René; Blum, Jürgen

2011-01-01

227

Spinel-olivine geothermometry in peridotites from ultramafic complexes  

Microsoft Academic Search

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

Jacques Fabriès

1979-01-01

228

A reevaluation of the flow data for olivine  

NASA Astrophysics Data System (ADS)

The solid medium deformation experiments on polycrystalline olivine at pressures of 500-1500 MPa show steadily increasing creep strength with decreasing water content. Thus water content can significantly influence the strength of olivine. Room pressure experiments on olivine single crystals have been conducted under conditions of low pH2O and therefore should be compared with solid medium experiments on dried samples deformed under anhydrous conditions. The single crystals flow more rapidly by 2-3 decades in strain rate for a given stress. Three hypotheses regarding the origin of this strength discrepancy are: (1) solid medium sample strengths are higher due to the finite strength of the confining medium; (2) temperature gradients in the solid medium samples render them stronger; (3) the application of high confining pressure has significantly increased strength. These hypotheses have been analyzed and none of them appears to alter strain rates by more than a decade. Another hypothesis, that dislocations are pinned by iron oxide precipitates in the "dry" solid medium experiments, also does not appear likely. Unless some unknown effect in the solid medium apparatus results in anomalously high strength for olivine, the discrepancy must be attributed to fundamentally different behavior of the single crystal and the aggregate.

Vaughan, Peter J.

229

Scanning electron microscope observation of dislocations in olivine  

Microsoft Academic Search

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

S. Karato

1987-01-01

230

A Study of Olivine Alteration to Iddingsite Using Raman Spectroscopy  

NASA Technical Reports Server (NTRS)

A crucial task of Mars surface science is to determine past environmental conditions, especially aqueous environments and their nature. Identification of mineral alteration by water is one way to do this. Recent work interprets TES spectra as indicating altered basalt on Mars. Olivine, a primary basaltic mineral, is easily altered by aqueous solutions. Alteration assemblages of olivine may be specific to deuteric, hydrothermal, surface water, or metamorphic environments. Raman spectra are produced by molecular vibrations and provide direct means for studying and identifying alteration products. Here, we present a combined study of changes in the chemical composition and Raman spectra of an olivine as it alters to iddingsite. Iddingsite is found in some SNC meteorites and is presumably present on Mars. The term 'iddingsite' has been used as a catch-all term to describe reddish alteration products of olivine, although some authors ascribe a narrower definition: an angstrom-scale intergrowth of goethite and smectite (presumably saponite) formed in an oxidizing and fluid-rich environment. Alteration conserves Fe (albeit oxidized) but requires addition of Al and H2O and removal of Mg and Si. The smectite that forms may be removed by continued alteration. Dehydration of the goethite forms hematite. Our purpose is to study the mineral assemblage, determine the structural and chemical variability of the components with respect to the degree of alteration, and to find spectral indicators of alteration that will be useful during in-situ analyses on Mars.

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

2003-01-01

231

Influence of the olivine additive fineness on the oxidation of magnetite pellets  

Microsoft Academic Search

Olivine is used as an additive in Luossavaara–Kiirunavaara AB (LKAB) blast furnace pellets. The LKAB iron ore is magnetite which oxidizes to hematite during the sintering process. Olivine retards the oxidation of magnetite pellets if the threshold temperature of magnesioferrite formation is exceeded.In this study, we have developed a thermogravimetric measuring method to study the relationship between the olivine reactivity

S. P. E. Forsmo; A. Hägglund

2003-01-01

232

Olivine in kimberlites: metasomatism of the deep lithospheric mantle  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

233

The effect of mineral paragenesis on Al diffusion in olivine  

NASA Astrophysics Data System (ADS)

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.

Zhukova, Irina; O'Neill, Hugh; Capbell, Ian

2014-05-01

234

Geoengineering potential of artificially enhanced silicate weathering of olivine.  

PubMed

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

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

2010-11-23

235

The geoengineering potential of artificially enhanced silicate weathering of olivine  

NASA Astrophysics Data System (ADS)

Geoengineering is a proposed action to manipulate Earth's climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate in more detail the potential of a specific geoengineering technique, the carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. We here show the consequences of this technique for the chemistry of the surface ocean at rates necessary for geoengineering. We calculate that olivine dissolution has the potential to sequestrate up to one Pg C yr-1 directly, if olivine is distributed as fine powder over land areas of the humid tropics. The carbon sequestration potential is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg C yr-1. Open water dissolution of fine grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1 to 5 Pg C yr-1 for the 21st century by this technique. At maximum this technique would reduce global warming by 1 K and counteract ocean acidification by a rise in surface ocean pH by 0.1 in the year 2100.

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

2010-05-01

236

Geoengineering potential of artificially enhanced silicate weathering of olivine  

PubMed Central

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

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

2010-01-01

237

An experimental study of Fe-Mg partitioning between olivine and orthopyroxene at 1173, 1273 and 1423 K and 1.6 GPa  

NASA Astrophysics Data System (ADS)

The partitioning of Mg and Fe2+ between coexisting olivines and orthopyroxenes in the system MgO-FeO-SiO2 has been investigated experimentally at 1173, 1273, 1423 K and 1.6 GPa over the whole range of Mg/Fe ratios. The use of barium borosilicate as a flux to promote grain growth, and the identification by back-scattered electron imaging of resulting growth rims suitable for analysis by electron microprobe, results in coexisting olivine and orthopyroxenene compositions determined to a precision of±0.003 to 0.004 in molar Fe/(Mg+Fe). Quasi-reversal experiments were performed starting with Mg-rich olivine and Fe-rich orthopyroxene (low KD) and vice versa (high KD), which produced indistinguishable results. The distribution coefficient, KD, depends on composition and on temperature, but near Fe/(Mg+Fe)=0.1 (i.e. mantle compositions) these effects cancel out, and KD is insensitive to temperature. The results agree well with previous experimental investigations, and constrain the thermodynamic mixing properties of Mg-Fe olivine solid solutions to show small near-symmetric deviations from ideality, with W_{G_{Mg - Fe}^{ol} } between 2000 and 8000 J/mol. Multiple non-linear least squares regression of all data gave a best fit with W_{G_{Mg - Fe}^{ol} } = 5625 ± 574 J/mol (implying 5450 J/mol at 1 bar) and W_{G_{Mg - Fe}^{opx} } = 2145 ± 614 J/mol, but the two W G parameters are so highly correlated with each other that our data are almost equally well fit with W_{G_{Mg - Fe}^{ol} } = 3700 ± 800 J/mol, as obtained by Wiser and Wood. This value implies W_{G_{Mg - Fe}^{opx} } = 280 ± 900 J/mol, apparently independent of temperature. Our experimental results are not compatible with the assessment of olivine-orthopyroxene equilibria of Sack and Ghiorso.

von Seckendorff, Volker; O'Neill, Hugh St. C.

1993-02-01

238

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

NASA Astrophysics Data System (ADS)

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.

Kohout, T.; Pesonen, L. J.

2005-12-01

239

Gas-grain energy transfer in solar nebula shock waves: Implications for the origin of chondrules  

NASA Technical Reports Server (NTRS)

Meteoritic chondrules provide evidence for the occurrence of rapid transient heating events in the protoplanetary nebula. Astronomical evidence suggests that gas dynamic shock waves are likely to be excited in protostellar accretion disks by processes such as protosolar mass ejections, nonaxisymmetric structures in an evolving disk, and impact on the nebula surface of infalling 'clumps' of circumstellar gas. Previous detailed calculations of gas-grain energy and momentum transfer have supported the possibility that such shock waves could have melted pre-existing chondrule-sized grains. The main requirement for grains to reach melting temperatures in shock waves with plausibly low Mach numbers is that grains existed in dust-rich zones (optical depth greater than 1) where radiative cooling of a given grain can be nearly balanced by radiation from surrounding grains. Localized dust-rich zones also provide a means of explaining the apparent small spatial scale of heating events. For example, the scale size of at least some optically thick dust-rich zones must have been relatively small (less than 10 kilometers) to be consistent with petrologic evidence for accretion of hot material onto cold chondrules. The implied number density of mm-sized grains for these zones would be greater than 30 m(exp -3). In this paper, we make several improvements of our earlier calculations to include radiation self-consistently in the shock jump conditions, and we include heating of grains due to radiation from the shocked gas. In addition, we estimate the importance of momentum feedback of dust concentrations onto the shocked gas which would tend to reduce the efficiency of gas dynamic heating of grains in the center of the dust cloud.

Hood, L. L.; Horanyi, M.

1993-01-01

240

Reading Bar Graphs  

NSDL National Science Digital Library

Bar graphs are simple ways to display data. Taking numbers and creating a bar graph makes it easier to read and draw conclusions. From bar graphs, you can easily compare data from more than one source. In this lesson, students will read two temperature bar graphs of data from Africa using authentic NASA data. They will identify major parts of bar graphs and make a generalization statement based on graphed data.

241

High-temperature elasticity of iron-bearing olivines  

NASA Astrophysics Data System (ADS)

The first high-temperature data on the nine adiabatic elastic moduli for iron-bearing olivine are reported. These measurements are on two single-crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 K. The two specimens contain 8 and 9 modal percent fayalite, which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability. The rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of CO and CO2 gas. A small increase (˜1-2 GPa) in the adiabatic bulk modulus of each specimen, over that of end-member forsterite, was found. The data are high quality to extreme temperatures, with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens. Neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli, which is in contrast to published forsterite data. The temperature derivatives of the isotropic bulk modulus KS are (-1.69, -1.80) × 10-2 GPa K-1 for the two olivine specimens, and the shear modulus G derivatives are (-1.38, -1.36) × 10-2 GPa K-1. These derivatives are only slightly larger in magnitude than |(?KS/?T)P| = 1.56 × 10-2 and |(?G/?T)P| = 1.30 × 10-2 GPa K-1 found previously for iron-bearing olivine over a very small temperature range. There are also no significant differences between the temperature derivatives found here and the average derivatives of end-member forsterite from data retrieved over a slightly larger temperature range. Several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high-pressure phases in Earth's transition zone. One result from these systematics related to the seismic velocities in the Earth, and especially the shear wave velocities, is that an olivine content of less than 50% is implied at the 400-km discontinuity if Earth's upper mantle is isochemical. Furthermore, the substitution of almost 10% iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature.

Isaak, Donald G.

1992-02-01

242

Olivine separates from Murchison and Cold Bokkeveld - Particle tracks and noble gases  

NASA Technical Reports Server (NTRS)

Olivine separates from Murchison and Cold Bokkeveld were analyzed for particle tracks and noble gases. The matrix remaining after olivine separation was also analyzed for noble gases. The olivines from both meteorites have comparable fractions of solar-flare-irradiated grains, but the highest track densities in Murchison are an order of magnitude greater than those in Cold Bokkeveld. Solar Ne content in Murchison olivines follows this trend, being at least an order of magnitude higher than that in Cold Bokkeveld. Track gradients in Cold Bokkeveld olivines are flatter than those in Murchison or recently exposed lunar crystals. Relative to the matrix, olivine separates in both meteorites have small enrichments at the heavy and light Xe isotopes and smaller Ar-36/Ar-38 ratios. These noble-gas effects may be related to a chromite impurity in the olivine separates.

Macdougall, J. D.; Phinney, D.

1977-01-01

243

Grinding methods to enhance the reactivity of olivine  

SciTech Connect

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.

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

2005-08-01

244

The solubility of olivine in basaltic liquids - An ionic model  

NASA Technical Reports Server (NTRS)

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.

Herzberg, C. T.

1979-01-01

245

First-principles studies of native defects in olivine phosphates  

NASA Astrophysics Data System (ADS)

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.

Hoang, Khang; Johannes, Michelle

2011-03-01

246

Carbonation Reaction Layer Study of San Carlos Olivine  

Microsoft Academic Search

Increasing CO2 levels in the earth's atmosphere due to combustion processes are leading researchers to develop several methods to store sequestered CO_2. Oceans, subsurface reservoirs such as depleted oil fields, and terrestrial carbon pools have all been suggested. Our research focuses on mineral sequestration of CO_2. Olivine (e.g., forsterite, Mg_2SiO_4), a widely available mineral, reacts with CO2 to form magnesite

Ryan Nunez; Ray Carpenter; Kim Youngchul; Michael McKelvy; Andrew Chizmeshya; Dierdra Gormley

2004-01-01

247

Diffusion creep of dry, melt-free olivine  

Microsoft Academic Search

Deformation experiments were conducted on fine-grained (3–6 ?m), fully synthetic Fo90 olivine aggregates in a gas-medium apparatus at 300 MPa confining pressure and temperatures of 1150–1360°C. The strain rates of the solution-gelation-derived and therefore genuinely melt-free, dry samples are about two orders of magnitude lower than the strain rates for nominally melt-free aggregates at the same pressure and temperature conditions

Ulrich H. Faul; Ian Jackson

2007-01-01

248

Chemical frost weathering of olivine: Experimental study and implications  

NASA Technical Reports Server (NTRS)

New experimental results are reported on the frost weathering of olivine. After first weathering, a decrease in Fe sup 2(+)M(2) absorption bands were noted. This decrease is related to the protonation of O(+) in the mineral. It is contented that this reaction may result in the regolith storage of 100 to 1000 m of H(sub 2) over the history of Mars.

Harris, S. L.; Huguenin, R. L.

1987-01-01

249

A re-evaluation of the olivine-spinel geothermometer  

Microsoft Academic Search

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

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

1979-01-01

250

Polaron formation and transport in olivine cathode materials  

NASA Astrophysics Data System (ADS)

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.

Johannes, Michelle; Hoang, Khang

2011-03-01

251

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)

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.

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

2013-10-01

252

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)

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).

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

2013-12-01

253

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)

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.

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

2013-01-01

254

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

NASA Astrophysics Data System (ADS)

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.

Blaha, Stephan; Katsura, Tomoo

2013-04-01

255

Solubility of Helium in Olivine at 1 Atmosphere  

NASA Astrophysics Data System (ADS)

We have measured the solubility of He in olivine at 1 atm. Previous measurements of noble gas solubility in mantle minerals have found mineral/melt partition coefficients (D) that are higher [1;2] or close to [3] the D values of U and Th in the mantle. In contrast, geochemical systematics suggest that DHe is lower than DU and DTh. Our experiments were specifically designed to avoid gas trapped in melt pockets or between sintered grains, which may have affected previous studies [1;2]. The starting materials are gem quality San Carlos olivine and synthetic pure forsterite. These materials were examined before and after the experiments for inclusions and bubbles using optical, scanning electron and scanning transmission electron microscopic techniques. No bubbles were found. The primary experiments were performed on cm size grains to avoid trapping of gas in sintered powders. The experiments were run for 17-21 days at 1350° C, in crucibles made from large San Carlos olivine crystals, in an atmosphere of 50% He and 50% a mix of CO2 and H2 (to control fO2 at NNO and QFM). At no time was the olivine in contact with a melt phase. To examine the effects of powder sintering, experiments that span a range of smaller grain sizes (100-1000 microns) were also performed. He concentrations in the olivines were measured by noble gas mass spectrometry using sequential in vacuo crushing followed by melting of the powders. The experimental results are consistent: 8.3(+/-2.6) e-7 cc STP He/g are released by crushing and 6.2(+/-1.3) e-7 cc He STP/g are released by melting. Over 50% of the total gas is released by crushing. Powdered samples release unusually high amounts of gas on the first crush step (interpreted to be trapped between grains), but subsequently follow the same release pattern as the unpowdered samples and yield the same solubility values (excluding the first step). The consistency of the results over a range of compositions, grain sizes and fO2 conditions, and our careful examination of the experimental materials indicate that the gas released during crushing is not trapped in bubbles or inclusions, but is loosely bound within the crystal lattice. Where it resides in the olivine crystal structure is not clear. Using only the gas released by melting, along with published solubilities of He in basaltic melts [4], the ol/melt DHe is 0.003(+/-0.001) at 1 atm. This is most likely an upper limit because the crushing experiments may not have completely eliminated the loosely bound helium. If the gas from both the crushing and melting steps are combined, the apparent DHe is 0.006(+/-0.001). We caution against extrapolating these preliminary values to mantle melting conditions until the location of He in olivine is identified and the effects of pressure and temperature are quantified. [1] Broadhurst et al. (1990) GCA 54: 299-309 [2] Hiyagon and Ozima (1986) GCA 50: 2045-2057 [3] Brooker et al. (2003) Nature 423: 738-741 [4] Jambon et al. (1986) GCA 50: 401-408

Parman, S. W.; Kurz, M. D.; Hart, S. R.; Grove, T. L.

2004-12-01

256

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

257

Calcio-olivine {gamma}-Ca{sub 2}SiO{sub 4}: I. Rietveld refinement of the crystal structure  

SciTech Connect

The structure of the natural mineral calcio-olivine ({gamma}-Ca{sub 2}SiO{sub 4}) found in skarn xenoliths in the region of the Lakargi Mountain (North Caucasus, Kabardino-Balkaria, Russia) is refined by the Rietveld method [a = 5.07389(7) A, b = 11.21128(14) A, c = 6.75340(9) A, V = 384.170(5) A{sup 3}, Z = 4, {rho}{sub calcd} = 2.98 g/cm{sup 3}, space group Pbnm]. The X-ray diffraction pattern of a powdered sample is recorded on a STOE STADI MP diffractometer [{lambda}CuK{sub {alpha}1}; Ge(111) primary monochromator; 6.00{sup o} < 2{theta} < 100.88{sup o}; step width, 2.5{sup o} in 2{theta}; number of reflections, 224]. All calculations are performed with the WYRIET (version 3.3) software package. The structural model is refined in the anisotropic approximation to R{sub p} = 6.44, R{sub wp} = 8.52, R{sub exp} = 5.85, R{sub B} = 4.98, R{sub F} = 6.90, and s = 1.46. It is shown that the sample under investigation is a mixture of several mineral phases, among which calcio-olivine (the natural analogue of the {gamma}-Ca{sub 2}SiO{sub 4} compound) (83%), hillebrandite (13%), and wadalite (4%) are dominant. Only the scale factors and the unit cell parameters are refined for hillebrandite Ca{sub 2}SiO{sub 3}(OH){sub 2} [a = 3.63472(16) A, b = 16.4140(10) A, c = 11.7914(8) A, space group Cmc2{sub 1}, Z = 6] and wadalite Ca{sub 6}Al{sub 5}Si{sub 2}O{sub 16}Cl{sub 3} (a = 12.0088 A, space group, I 4 bar 3d, Z = 4). The results of the structure refinement of the main component of the sample confirm that the mineral calcio-olivine is isostructural to the synthetic compound {gamma}-Ca{sub 2}SiO{sub 4}. The structure of this compound is formed by the heteropolyhedral framework composed of Ca octahedra joined together into olivine-like ribbons and isolated Si tetrahedra.

Gobechiya, E. R., E-mail: elgob@mail.ru; Yamnova, N. A. [Lomonosov Moscow State University (Russian Federation); Zadov, A. E. [Scientific and Production Enterprise OOO 'NPP Teplokhim,' (Russian Federation); Gazeev, V. M. [Russian Academy of Sciences, Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM) (Russian Federation)

2008-05-15

258

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

259

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

Microsoft Academic Search

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.

Hans van Lamoen

1979-01-01

260

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

PubMed

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

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

2013-09-01

261

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

Microsoft Academic Search

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

E. C. Ferre; F. Martin-Hernandez

2004-01-01

262

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

NASA Astrophysics Data System (ADS)

Bulk chondritic meteorites and terrestrial planets show a monotonic depletion in moderately volatile and volatile elements relative to the Sun's photosphere and CI carbonaceous chondrites. Although volatile depletion was the most fundamental chemical process affecting the inner solar nebula, debate continues as to its cause. Carbonaceous chondrites are the most primitive rocks available to us, and fine-grained, volatile-rich matrix is the most primitive component in these rocks. Several volatile depletion models posit a pristine matrix, with uniform CI-like chemistry across the different chondrite groups. To understand the nature of volatile fractionation, we studied minor and trace element abundances in fine-grained matrices of a variety of carbonaceous chondrites. We find that matrix trace element abundances are characteristic for a given chondrite group; they are depleted relative to CI chondrites, but are enriched relative to bulk compositions of their parent meteorites, particularly in volatile siderophile and chalcophile elements. This enrichment produces a highly nonmonotonic trace element pattern that requires a complementary depletion in chondrule compositions to achieve a monotonic bulk. We infer that carbonaceous chondrite matrices are not pristine: they formed from a material reservoir that was already depleted in volatile and moderately volatile elements. Additional thermal processing occurred during chondrule formation, with exchange of volatile siderophile and chalcophile elements between chondrules and matrix. This chemical complementarity shows that these chondritic components formed in the same nebula region. Author contributions: P.A.B. designed research; P.A.B., O.A., G.K.B., A.T.K., O.N.M., L.E.W., and N.W.R. performed research; P.A.B., O.A., G.K.B., and A.T.K. analyzed data; and P.A.B. wrote the paper.This paper was submitted directly (Track II) to the PNAS office.Freely available online through the PNAS open access option.Abbreviations: CAI, Ca-Al-rich refractory inclusion; LA, laser ablation; ICP, inductively coupled plasma.

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

2005-09-01

263

Extreme Ni Concentrations in High Forsterite Olivine from a Cascade Forearc Basalt  

NASA Astrophysics Data System (ADS)

We have evaluated olivine phenocrysts and host glass from a basalt lava flow and associated scoria cone in the Quartzville mining district located on the western forearc margin of the Oregon Cascades. Both lavas and scoria are contemporaneous determined through detailed field mapping, and they share similar petrological and geochemical characteristics. Ar-Ar dating indicates a lava eruption age of 82.3±3.1 ka. Minor clinopyroxene is also present as a phenocryst phase while the groundmass contains apatite, magnetite and plagioclase. Abundant Cr-spinel and lesser magnetite occur as mineral inclusions within olivine phenocrysts and olivine-hosted melt inclusions. Olivine compositions vary from Fo88 to Fo94, and are accompanied by Ni concentrations that range from 0.06 to 0.63 wt%, but average ~0.4 wt%. Ni abundances are positively correlated with olivine composition from Fo88-92. In this compositional range, olivines from the lavas tend to have higher Fo contents and consequently higher Ni concentrations, which is consistent with the idea that the scoria is slightly more evolved than the basaltic melt. At forsterite values above Fo92, however, Ni concentrations decrease to concentrations comparable to Fo88-92 olivines. Fo92-94 olivine compositions are predominantly located at the rims of the olivine phenocrysts. Olivine-hosted melt inclusion compositions were also determined to provide important constraints on volatiles and oxygen fugacity of the magma at time of entrapment. Oxygen fugacity was determined in melt inclusions through sulfur speciation measurements and ranged from ?FMQ + 1.9 log units. This high fO2 is corroborated by oxygen fugacity calculations from spinel-olivine pairs. Additionally, oxygen isotope measurement on an olivine separate records a typical mantle value of ?18O = 5.6‰. Prior studies have identified high Ni olivine in calc-alkaline and highly potassic lavas and have proposed that these magmas are not derived from a peridotite source but rather a pyroxenite source. Additionally, the high Fo and Ni concentrations may be a function of the high oxygen fugacities as recorded by olivine-hosted melt inclusions and spinel-olivine pairs. In the present study we apply detailed petrography and geochemistry of mineral phases and glass to better constrain the source composition and magma evolution for this magmatic system. Our plan is to test our observations against the current hypothesis that high-Ni olivines can be produced from a progressively hybridized peridotite or pyroxenite source (Straub et al., 2008).

Tepley, F. J.; Rowe, M. C.

2009-12-01

264

Thermochemical stability of low-iron, manganese-enriched olivine in astrophysical environments  

NASA Astrophysics Data System (ADS)

Low-iron, manganese-enriched (LIME) olivine grains are found in cometary samples returned by the Stardust mission from comet 81P/Wild 2. Similar grains are found in primitive meteoritic clasts and unequilibrated meteorite matrix. LIME olivine is thermodynamically stable in a vapor of solar composition at high temperature at total pressures of a millibar to a microbar, but enrichment of solar composition vapor in a dust of chondritic composition causes the FeO/MnO ratio of olivine to increase. The compositions of LIME olivines in primitive materials indicate oxygen fugacities close to those of a very reducing vapor of solar composition. The compositional zoning of LIME olivines in amoeboid olivine aggregates is consistent with equilibration with nebular vapor in the stability field of olivine, without re-equilibration at lower temperatures. A similar history is likely for LIME olivines found in comet samples and in interplanetary dust particles. LIME olivine is not likely to persist in nebular conditions in which silicate liquids are stable.

Ebel, Denton S.; Weisberg, Michael K.; Beckett, John R.

2012-04-01

265

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

266

Experimental constraints of the olivine crystals compaction in cumulus layer  

NASA Astrophysics Data System (ADS)

The layered intrusions are the result of magma crystallization and differentiation in a form of lateral structures, which are often observed in magmatic chambers. They are markers of processes occurring during a prolonged cooling stage (several tens of thousands years for bodies 1 km in size). There is no unique explication for the mechanism of layering during the intrusion formation. The most plausible mechanism proposed to explain the observed layering includes the coupled crystal settling and residual liquid advection. In the layers containing a large crystal fraction (> 66 vol%) and a small percentage of the residual liquid, the compaction mechanism and the decrease of cumulate layer porosity due to the diffusion adjustment of grain boundaries could effectively occur. In this study, the compaction mechanisms of crystals settling in magma chambers have been modelled with the use of a high temperature centrifuge. The suspensions of olivine crystals and a basaltic melt (33 vol% and 67 vol%, respectively) were centrifuged at the melting temperature of basalt (temperature range of 1270-1280°C). The experiments were conducted at 200-1500 g under a pressure between 0.8-1.1 GPa. During centrifugation run olivine grains are compacted because of the x-time enhanced centrifugation force which is equivalent to x-time larger volume of crystals compacting from above. After crystals have reached a maximum compaction concentration due to this accelerated piling from above, their locations and porosity in cumulates change under the influence of the solution - recrystallisation process. The concentration of crystals in a cumulate layer increases much slower than during their sedimentation. The solution-precipitation and recrystallisation process is a diffusion type mechanism of compaction and has not been addressed experimentally before. Evidences of the precipitation - recrystallisation process of olivine grains in centrifuged samples with TEM analyses are revealed. In fact, knowing that Ca is characteristic only for MORB-melt, the first feature is the presence of Ca at the interface of two adjacent Ol-grains even when the melt phase is escaped. Another evidence of the diffusion compaction is the presence of some small melt inclusions at the growing Ol-boundaries of compacting Ol-grains. Finally, the precipitation - recrystallisation process of olivine grains during the cumulus compaction stems from the observation that the new boundary between two Ol-grains is distinct and not fully crystallized as the interior of grains. This indicates some MORB melt elements (for example, enrichment in Ca) prevent to recrystallize Ol in a fully crystalline structure.

Forien, M.; Bagdassarov, N.; Schmidt, M. W.

2009-12-01

267

Thermal processing of chondrule and CAI precursors in planetesimal bow shocks  

NASA Astrophysics Data System (ADS)

We test the hypothesis that chondrules (and Type B and C CAI's) originated during passage of precursors through bow shocks upstream of planetesimals moving supersonically relative to nebula gas. A two-dimensional piecewise parabolic method (PPM) hydrocode, supplemented by a one-dimensional adiabatic shock model, is employed to simulate the post-shock gas density, temperature, and velocity fields for given planetesimal sizes, velocities, and ambient nebula densities and temperatures. Thermal histories of incident silicate particles are calculated in the free molecular flow approximation by integration of the one-dimensional equations of gas-grain energy and momentum transfer. For gas number densities $>$ 10$14$ cm$^{-3}$, Mach numbers in the range of 4 to 5 are sufficient to melt isolated spherical particles with radii in the range 0.05 to 0.5 mm during passage of shocked gas thicknesses of 25--35 km. Minimum gas-planetesimal relative velocities are in the range 5.5--7 km/s, implying orbital eccentricities $>$ 0.2 and/or inclinations $>$ 15$^\\circ$. Melting of cm-sized CAI precursors requires either higher Mach numbers (6--7) or ambient gas densities $>$ 10$15$ cm$^{-3}$. For a constant radial distribution of planetesimal orbital eccentricities and inclinations, the model predicts more efficient melting of precursor particles at decreasing radial distances from the sun where planetesimal velocities are largest. In order to process a significant fraction of solids in the nebula, planetesimals near $\\sim$ 2.5 AU during the chondrule formation epoch must have had a range of eccentricities and inclinations comparable to those presently observed in the residual asteroid belt. The most likely energy source for maintaining the necessary gas-planetesimal relative velocities is external gravitational perturbations associated with the forming outer planets, primarily Jupiter. .

Hood, Lon L.

1998-01-01

268

Olivine-rich exposures in the South Pole-Aitken Basin  

NASA Astrophysics Data System (ADS)

The distribution and the geological context of the olivine-rich exposures in the South Pole-Aitken (SPA) Basin on the Moon were investigated based on the spectral data obtained from the Spectral Profiler (SP) and Multiband Imager (MI) onboard the Japanese lunar explorer Kaguya/SELENE. The olivine-rich exposures are found only in the peak rings or central peaks of the Schrödinger basin and Zeeman crater, which are located in the outer region of the SPA Basin and not in the center region. On a localized scale, the olivine-rich materials are exposed on landslide features on the crater walls or sloped wall of the central peaks or the peak rings. Another observational finding is the co-existence of olivine-rich and plagioclase-rich materials on a kilometer scale spanning most of the olivine-rich sites in the Schrödinger basin. Pyroxene-rich materials are found in fresh craters outside the peak rings or the central peaks with olivine-rich materials. Based on these results, the following scenario are proposed: (1) the impact to form the SPA Basin melted a large amount of the lunar upper mantle and crust, and distributed the melted materials to the outer region; (2) local differentiation of melted materials hid the olivine-rich materials in the center region of the SPA Basin; (3) later impacts that formed the Schrödinger and Zeeman craters excavated and exposed the olivine-rich materials to the surface again; and (4) space weathering and regolith gardening obscured the olivine-rich spectra at the exposure sites, but recent, small scale impacts or landslides on the sloped wall exposed fresh olivine-rich materials, allowing the identification of the olivine-rich exposures by spectral remote-sensing. This suggests that several, different scale events play an important role in forming the surface distributions of originally deep-seated materials on the Moon, as well as on other planetary bodies.

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

2012-03-01

269

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

270

Temperature-dependent Infrared Optical Constants of Olivine and Enstatite  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

271

Annealing behaviour of ion tracks in olivine, apatite and britholite  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

272

Number Line Bars  

NSDL National Science Digital Library

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.

2000-01-01

273

Experimental modeling of the cooling history of Apollo 12 olivine basalts  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

274

Cooling rates in the lower crust of the Oman ophiolite: Ca in olivine, revisited  

E-print Network

Cooling rates in the lower crust of the Oman ophiolite: Ca in olivine, revisited Jill A. Van crust of the Khafifah section in the Wadi Tayin massif of the Oman ophiolite. Additionally, very high B.V. All rights reserved. Keywords: calcium; olivine; oman; hydrothermal; cooling; crust 1

VanTongeren, Jill A.

275

SPINELS AND OXYGEN FUGACITY IN OLIVINE-PHYRIC AND LHERZOLITIC SHERGOTTITES. C.A. Goodrich, 2  

E-print Network

SPINELS AND OXYGEN FUGACITY IN OLIVINE-PHYRIC AND LHERZOLITIC SHERGOTTITES. 1 C.A. Goodrich, 2 C (possibly paired with NWA 1068 [9,10]), and to lherzolitic shergottite ALHA77005. Spinels in Olivine-Phyric Shergottites: Spinels in SaU 005 and EET-A are described by [11,12]. Spinels in Dhofar 019 (see also [8

Taylor, Lawrence A.

276

Viscoplasticity of polycrystalline olivine experimentally deformed at high pressure and 900 C  

E-print Network

crystals are rare, because of technical difficulties (i.e., high stresses, close to the brittle failureViscoplasticity of polycrystalline olivine experimentally deformed at high pressure and 900 °C mantle Lithosphere TEM EBSD We have performed tri-axial compression experiments on olivine aggregates

Tommasi, Andrea

277

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

Microsoft Academic Search

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

Herbert Palme; Bruce Fegley Jr.

1990-01-01

278

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

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

279

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

NASA Astrophysics Data System (ADS)

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.

Katayama, Ikuo; Karato, Shun-Ichiro

2008-01-01

280

Interactive WSN-Bar  

NASA Astrophysics Data System (ADS)

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

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

281

Bar Code Labels  

NASA Technical Reports Server (NTRS)

American Bar Codes, Inc. developed special bar code labels for inventory control of space shuttle parts and other space system components. ABC labels are made in a company-developed anodizing aluminum process and consecutively marketed with bar code symbology and human readable numbers. They offer extreme abrasion resistance and indefinite resistance to ultraviolet radiation, capable of withstanding 700 degree temperatures without deterioration and up to 1400 degrees with special designs. They offer high resistance to salt spray, cleaning fluids and mild acids. ABC is now producing these bar code labels commercially or industrial customers who also need labels to resist harsh environments.

1988-01-01

282

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

Microsoft Academic Search

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.

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

2011-01-01

283

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

E-print Network

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.

Hitoshi Miura; Taishi Nakamoto

2006-11-09

284

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

285

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

NASA Astrophysics Data System (ADS)

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.

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

1993-03-01

286

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

SciTech Connect

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

Mishra, R. K.; Goswami, J. N.; Rudraswami, N. G. [Physical Research Laboratory, Ahmedabad-380009 (India); Tachibana, S. [Department of Earth and Planetary Sciences, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033 (Japan); Huss, G. R., E-mail: goswami@prl.res.i [Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)

2010-05-10

287

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

NASA Technical Reports Server (NTRS)

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

Hood, Lon L.; Ciesla, Fred J.

2005-01-01

288

Termination and hydration of forsteritic olivine (0 1 0) surface  

NASA Astrophysics Data System (ADS)

Termination and hydration of the forsteritic (Fo90Fa10) olivine (0 1 0) surface have been investigated with high-resolution specular X-ray reflectivity and Atomic Force Microscopy. The surface was prepared by polishing a naturally grown {0 1 0} face, from which we found the polished surface in acidic (pH 3.5) alumina suspension exhibits regular steps while the basic (pH 9.5) silica polished surface is irregularly roughened, indicating there are two distinguishable mechanochemical processes for the surface dissolution. The quantitative interpretation of the regular steps from the alumina-polished surface suggests that the observed step heights correspond to multiples of crystallographic unit cell. Only this atomically terraced surface is investigated with the high-resolution X-ray reflectivity (HRXR) to determine the surface termination and hydration. The basic silica paste polished surface turned out too rough to measure with X-ray reflectivity. HRXR reveals that the alumina polished olivine (0 1 0) surface in pure water is terminated at a plane including half-occupied metal ion sites (M1), an oxygen vacancy site, and a silicate tetrahedral unit with one of its apices pointing outward with respect to the surface. An ideal termination with the oxygen vacancy would fulfill the stoichiometry of the formula unit; however, in the observation, the vacancy site is filled by an adsorbed water species and about a quarter of the remaining metal ions are further depleted. The terminating plane generates two distinct atomic layers in the laterally averaged electron density profile, on which two highly ordered adsorbed water layers are formed. The first layer formation is likely through the direct interaction with the M1 plane and the second layer is likely through the hydrogen bonding interaction with the first water layer. With this multilayered adsorbed water structure, the surface metal ion is partially hydrated by the vacancy-filling water species and adsorbed water molecules. The bulk water links to these distinct adsorbed water layers, with weak density oscillations that almost completely damp out after the first bulk water layer. The total thickness of the layered water structure including the two distinct adsorbed layers and the first layer of bulk water is slightly less than 1 nm, which corresponds to roughly three molecular layers of water. These results describe the steric constraints of the surface metal ion hydration and the iron redox environment during water-olivine interactions in this particular crystallographic orientation.

Yan, Hongping; Park, Changyong; Ahn, Gun; Hong, Seungbum; Keane, Denis T.; Kenney-Benson, Curtis; Chow, Paul; Xiao, Yuming; Shen, Guoyin

2014-11-01

289

Effect of Water on Fe-Mg Interdiffusion in Olivine  

NASA Astrophysics Data System (ADS)

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 perpendicular to the [001] crystallographic axis. These (001) surfaces were mechanically polished to a 0.1 ? m finish on diamond lapping film and then mechanically polished and chemically etched with colloidal silica with an average grain size 0.04 ? m to remove the work-hardened surface layer. Each diffusion couple was formed from a Fo83 and a Fo91 crystal by placing their (001) planes in contact. Annealing experiments under both dry and water-saturated conditions were carried out at 1373 K and 300 MPa with oxygen fugacity buffered near the Ni-NiO phase boundary and a water fugacity about 300 MPa. Diffusion-bonded bi-crystals were successfully prepared following this procedure. In our hydrothermal experiments, hydrogen diffusion out of the sample capsule limits the annealing time to a few hours. Fourier transform infrared analyses demonstrate that the samples are water-saturated after the hydrothermal anneal. After each diffusion anneal, the Fe-Mg concentration profile was determined using energy dispersive x-ray spectroscopy in an analytical transmission electron microscope and/or Rutherford backscattering spectroscopy. The interdiffusion coefficient was calculated using the Boltzmann-Matano method. Under the imposed hydrous conditions, the interdiffusion coefficient is about 10-16 m2/s, a value approximately one order of magnitude larger than that determined under anhydrous conditions. The enhancement in Fe-Mg interdiffusion coefficient in the presence of water is a combined effect of the increase in the concentrations of water-derived point defects and the associated increase in the concentrations of intrinsic point defects in olivine as governed by the electroneutrality condition. The present result provides a basis for a quantitative understanding of the influence of water on the homogenization of geochemical anomalies through interdiffusion in the upper mantle.

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

2001-12-01

290

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

NASA Astrophysics Data System (ADS)

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

Burgess, Katherine D.; Cooper, Reid F.

2013-10-01

291

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

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

292

Bar v4.0  

NSDL National Science Digital Library

Bar provided the script author with a simple two-color bar graph with an optional numeric output field located below the bar. It is usually used as a data listener in conjunction with other Physlets. Its series in the data connection is ignored since Bar supports only a single bar.

Christian, Wolfgang; Belloni, Mario

2008-02-01

293

Multi Bar Graph  

NSDL National Science Digital Library

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.

2010-01-01

294

Bar Graph Sorter  

NSDL National Science Digital Library

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.

2010-01-01

295

Fe 2+-Mg partitioning between olivine and basaltic melts: Applications to genesis of olivine-phyric shergottites and conditions of melting in the Martian interior  

NASA Astrophysics Data System (ADS)

Fe 2+-Mg partitioning between olivine and basaltic melt, expressed by the exchange coefficient, K Dol - melt Fe - Mg [=( XmeltMg/ XolivineMg)/( XmeltFe 2 + / XolivineFe 2 + )] is widely used to check if a rock composition may represent a mantle-derived magma, to demonstrate equilibrium between coexisting olivine and groundmass in mafic-ultramafic systems, both in experiments and in natural assemblages, and to constrain liquid lines of descent where olivine is the dominant fractionating phase. However, K Dol - melt Fe - Mg of 0.30, which is appropriate for understanding most terrestrial basalts petrogenesis may not apply for Martian basalts as K Dol - melt Fe - Mg is known to depend strongly on the melt compositions and Martian systems produce basalts that are distinctly richer in iron than terrestrial basalts. Here we compiled experimental data on olivine-melt equilibria of Martian and terrestrial basalt compositions to parameterize the effect of magma composition on K Dol - melt Fe - Mg and derive the K Dol - melt Fe - Mg applicable for Martian magmatic systems. We find that the equilibrium relationship between olivine and basaltic melt in Martian systems is described by K Dol - melt Fe - Mg of 0.35 ± 0.01. Applying the newly parameterized values of K Dol - melt Fe - Mg to olivine-phyric shergottites suggest that the only known Martian meteorites where the olivine cores and the bulk composition are in equilibrium and therefore could represent magma compositions are: Yamato 980459, NWA 5789, and NWA 2990. LAR 06319, which has been suggested to represent a near magma composition, actually contains ~ 11 wt.% excess olivine. All other ol-phyric shergottites contain significant excess olivine (20-52 wt.%). Further, assuming that the basalts analyzed by the Mars Exploration Rovers at Gusev crater and the Bounce Rock in Meridiani Planum lie on olivine control lines, we have used our newly parameterized K Dol - melt Fe - Mg to estimate primary magmas in equilibrium with the model Martian mantle. Application of geothermobarometers to new primitive magma compositions suggest that basalt generation in the Martian mantle occurs at greater depths and higher temperatures than previously thought.

Filiberto, Justin; Dasgupta, Rajdeep

2011-04-01

296

Serpentinization of Sintered Olivine during Seawater Percolation Experiments  

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

297

Collisional Processing of Comet Surfaces: Impact Experiments into Olivine  

NASA Technical Reports Server (NTRS)

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.

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

298

Olivines in angrite LEW 87051: Phenos or xenos  

NASA Technical Reports Server (NTRS)

Nyquist et al. recently reported the presence of live Mn-53 in angrite LEW 86010 when it crystallized. Hence, melting must have occurred within approx. 10 Ma of the accretion of the angrite parent body, and LEW 86010 is the oldest known differentiated meteorite. This discovery has made it even more desirable to understand teh petrogenesis of angrites, which presumably were all formed at a similar time. As part of the continuing work on angrite petrogenesis, crystallization experiments were conducted on LEW 87051, the other Antarctic angrite, to clarify its petrogenesis. Several aspects of the experimental work is reported. Although the details are not understood, it is clear that the Cr abundance in the experimental olivines must be controlled by spinel crystallization.

Mckay, G.; Le, L.; Wagstaff, J.

1991-01-01

299

The distribution of olivine in the crater Copernicus  

NASA Technical Reports Server (NTRS)

Multispectral imaging in the visible and near-IR at four wavelengths (0.73, 0.96, 1.45, and 1.99 micron) of Copernicus crater has been used to map the distribution of olivine-rich, pyroxene-poor material known previously to occur in the central peak complex. Three additional portions of the crater exhibit spectral characteristics similar to those of the central peaks, strongly suggesting the presence of material similar to that exposed in the central peaks. These areas are a scarp forming a portion of the northern rim of Copernicus, and two slump blocks in the north wall which may have been derived from the same portion of the ejecta now exposed in the rim scarp. These occurrences decrease the minimum allowable depth for this unusual material in the Copernicus target site though still represent some of the deepest material exposed by Copernicus.

Lucey, Paul G.; Hawke, B. R.; Horton, Keith

1991-01-01

300

Olivine friction at the base of oceanic seismogenic zones  

USGS Publications Warehouse

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.

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

2007-01-01

301

Stereochemically constrained complex organic molecules extracted from olivine crystal matrix  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

302

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

NASA Astrophysics Data System (ADS)

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.

Rhodes, J. M.

2002-12-01

303

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

SciTech Connect

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.

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

2007-01-01

304

Phase equilibria controls on the chemistry of vent fluids from hydrothermal systems on slow spreading ridges: Reactivity of plagioclase and olivine solid solutions and the pH-silica connection  

NASA Astrophysics Data System (ADS)

Theoretical reaction path models were combined with experimental data to determine fluid-mineral equilibria controls on the chemistry of vent fluids issuing from ultramafic-hosted hydrothermal systems (e.g., Rainbow and Logatchev I) on the slow spreading Mid-Atlantic Ridge. The model involves the incremental reaction of Ca-bearing (evolved seawater) with a calcic-plagioclase and olivine-bearing mineral assemblage, and simulates aspects of an open geochemical system. Incipient reaction predicts Ca removal in exchange for Na, low silica, and high pH. With reaction progress, however, the Na for Ca exchange reaction reverses, while dissolved silica and pH increase and decrease, respectively. The combination of significant dissolved silica (8-9 mmol kg-1), together with elevated dissolved Ca concentrations (60-70 mmol kg-1) coexisting with secondary calc-silicate (tremolite) and Mg-chlorite mineralization, constitutes an important pH buffer. The inherently reducing nature (high H2) of the model system enhances Fe solubility, while low dissolved H2S contributes to elevated dissolved Cu, in keeping with compositional effects reported for Rainbow and Logatchev vent fluids. Data indicate that H2S is controlled at values more than 10 times lower than H2 owing to bornite-chalcocite-magnetite-fluid equilibria. Olivine is not unreactive in the silica-bearing fluid at 400-425°C (500 bars) and is predicted to participate in the formation of calc-silicate, talc, and chlorite alteration phases. Model predictions, however, also indicate metastability of Fe-rich olivine. Experimental studies performed to examine olivine recrystallization reactions in silica bearing fluid indicate preferential dissolution of the forsterite component and precipitation of a more Fe-rich phase along with talc on the surface of the precursor olivine. Additional experimental data are required, however, to better determine the implications of this for the redox and pH evolution of vent fluids at slow spreading mid-ocean ridges.

Seyfried, W. E., Jr.; Pester, Nicholas; Fu, Qi

305

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

NASA Astrophysics Data System (ADS)

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).

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

2010-05-01

306

Timescales for Reequilibration of Major Elements in Olivine-Hosted Melt Inclusions  

NASA Astrophysics Data System (ADS)

Geochemical evidence demonstrates that near-fractional partial melts form over a range of upper mantle conditions from peridotites with variable bulk compositions. The importance of determining the initial compositions of melt inclusions lies in the ability of the major elements to record information about the conditions at which melt generation takes place, and the involvement of exotic lithologies in the melt generation process. However, before the major-element compositions of melt inclusions can be interpreted reliably, the effects of post-entrapment processes must be quantitatively understood. Diffusive reequilibration of olivine-hosted melt inclusions during cooling, magma mixing, or decompression can produce irreversible compositional changes in response to changes to the melt outside of the host olivine. Factors that influence the timescales for reequilibration of major elements in olivine-hosted melt inclusions are the sizes of the inclusion and the host olivine, which control the diffusion lengthscale, and the olivine-melt partition coefficient and diffusivity, which control the flux through the olivine grain. Among the major elements, Fe, Mg and Ca have the greatest potentials for undergoing diffusive reequilibration. The concentration of H2O in olivine-hosted melt inclusions must also be evaluated with care. Based on experimentally determined diffusivities and partition coefficients, reequilibration of Fe and Mg occurs on a timescale of years, while Ca reequilibrates over a few decades. Diffusion of H in olivine is rapid enough to allow reequilibration in a matter of hours. Important questions the must be answered in order to fully assess the reliability of the melt inclusion compositions are whether the history of Fe/Mg transport through the olivine can be uniquely determined, whether there are factors that rate limit transport of H, and whether gradients in slower diffusing elements can be used to constrain re-equilibration timescales.

Gaetani, G. A.; Hauri, E. H.

2008-12-01

307

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

NASA Astrophysics Data System (ADS)

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.

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

2004-12-01

308

Introduction to Bar Graphs  

NSDL National Science Digital Library

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.

2011-05-24

309

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

NASA Technical Reports Server (NTRS)

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.

Rietmeijer, Frans J. M.

1996-01-01

310

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)

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.

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

1994-01-01

311

Experimentally reproduced relict enstatite in porphyritic chondrules of enstatite chondrite composition  

NASA Technical Reports Server (NTRS)

Experiments are presented that test a model for the origin of porphyritic pyroxene (PP) chondrules in enstatite chondrites that contain phenocrysts of enstatite with blue cathodoluminescence (CL) set in a matrix of radial, dendritic enstatite with red CL. Established one-atmosphere, gas-mixing techniques were used. Relict enstatite phenocrysts with blue CL in a matrix of coarsely radial to dendritic enstatite with red CL were successfully produced. The relict crystals are preserved in runs with a melt time of 36 minutes or less at 1537 C. The relicts remain angular with smooth crystal/melt interfaces, and thus melting has occurred uniformly. Partial melting does occur along fractures produced when the blue CL enstatite was initially grown and cooled through the proto/ortho enstatite transition with the attendent volume change. There is either reaction with the melt and diffusion of Mn and Cr into the blue CL En, or there is an overgrowth of red CL En along the fractures. The bulk of the relicts remain blue. The melt enclosing the relicts crystalized to a coarsely radial to dendritic to micro porphyritic texture comprised of enstatite that has a bright red CL with decreasing melt time. The blue CL En has Mn and Cr contents at or below detection limits of the electron probe as described in earlier studies and in natural blue CL En. In the red CL En in this study, the Mn, Al2O3, and Cr are at previously observed levels and the levels change rapidly.

Lofgren, Gary E.; Dehart, John M.; Dickinson, Tammy L.

1993-01-01

312

Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites  

NASA Technical Reports Server (NTRS)

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.

Zolensky, Michael; Barrett, Ruth; Browning, Lauren

1993-01-01

313

An Olivine-Rich Crater in Tyrrhena Terra  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

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

2008-01-01

314

Bar Graph Investigations  

NSDL National Science Digital Library

In this lesson plan students conduct a survey of ten students, collect data in a tally chart, and then display and analyze the results in a bar graph. In the analysis students must compare numbers, add, and subtract using the data in the bar graph to generate questions as well as answer them. The lesson plan includes a graph template, a link to an interactive graphing tool, extension questions, and a fact family sheet to show the related facts from their graph analysis.

Burton, Grace M.

2008-01-01

315

Histograms and Bar Graphs  

NSDL National Science Digital Library

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.

2010-01-01

316

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

E-print Network

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 ...

Malik, Rahul

2013-01-01

317

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

E-print Network

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 ...

Meethong, Nonglak

2009-01-01

318

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

319

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

E-print Network

to form fayalite, is con- sumed by reaction with H2S to form troilite, FeS. Be- cause all three dust,5], making diffusion slower; as well as recognition of non-ideality in olivine solid solutions, lowering

Grossman, Lawrence

320

FULL PAPER Open Access Characterization of olivine fabrics and mylonite in  

E-print Network

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

Jung, Haemyeong

321

Trace Element Distribution Between Olivine and Kirschsteinite in Angra Dos Reis  

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

322

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

323

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

Microsoft Academic Search

COâ sequestration via carbonation of widely available low-cost minerals, such as olivine, can permanently dispose of COâ in an environmentally benign and a geologically stable form. The paper reports the results of studies of the mechanisms that limit aqueous olivine carbonation reactivity under the optimum sequestration reaction conditions observed to date: 1 M NaCl + 0.64 M NaHCOâ at T

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

2006-01-01

324

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

Microsoft Academic Search

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 (M3) 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

Peter J. Isaacson; Carle M. Pieters; Sebastien Besse; Roger N. Clark; James W. Head; Rachel L. Klima; John F. Mustard; Noah E. Petro; Matthew I. Staid; Jessica M. Sunshine; Lawrence A. Taylor; Kevin G. Thaisen; Stefanie Tompkins

2011-01-01

325

Demonstration of the Electrical Conductivity Jump Produced by the Olivine-Spinel Transition  

Microsoft Academic Search

The electrical conductivity of both the olivine and spinel polymorphs of Fe2SiO, has been determined at 300 to 1200øK and at 31 to 62 kb by means of a tetrahedral anvil-type high-pressure apparatus. It is established that the olivine-spinel transition is responsible for the discontinuous change in the electrical conductivity of Fe2SiO, the conductivity jump at the time of the

Syun-Iti Akimoto; Hideyuki Fujisawa

1965-01-01

326

Eutectoid phase transformation of olivine and spinel into perovskite and rock salt structures  

Microsoft Academic Search

Microstructural observations of the products of the transformation of (Mg, Fe)2SiO4 olivine and spinel and Ca2GeO4 olivine into magnesiowuesite, a transformation postulated to occur in the mantle. The transformation was achieved using a diamond anvil cell with a center pressure of about 400 kbar. The specimens were also heated with a YAG laser up to 2000 C to study the

J. P. Poirier; J. Peyronneau; M. Madon; F. Guyot; A. Revcolevschi

1986-01-01

327

Water diffusion as a natural process in olivine crystals from garnet-perodotite xenoliths in basalts  

Microsoft Academic Search

Experimental work on the kinetics of hydration\\/dehydration of olivine indicates that the water content in natural olivine is representative only of the last hydration\\/dehydration event in its geologic history. This dissolved water would be lost in just a few hours on ascent from depths at which temperatures are over 800oC. However, to date, water diffusion profiles in natural nominally anhydrous

S. Demouchy; F. Gaillard; C. R. Stern; S. Mackwell

2003-01-01

328

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

329

Excitation and relaxation of olivine after swift heavy ion impact  

NASA Astrophysics Data System (ADS)

A multiscale model was developed to describe excitation and initial relaxation of an insulator after an impact of a swift heavy ion (SHI) decelerated in the electronic stopping regime. This model consists of a combination of three methods: (a) Monte Carlo simulations of the nonequilibrium kinetics of the electron subsystem of a solid at the femtosecond scale after the projectile passage. The complex dielectric function (CDF) is used to construct the cross sections for the MC model taking into account a collective response of the electron ensemble to excitation. (b) A molecular-kinetic approach describing further spatial spreading of electrons after finishing of ionization cascades up to hundred femtoseconds. And (c) molecular dynamics simulations of a reaction of the lattice on the excess energy transferred from the relaxing electron subsystem at the picosecond time scale. The dynamic structure factor (DSF) formalism is used to calculate the electron-lattice energy exchange in a general way which is valid for sub-picosecond timescales, beyond the phononic approximation of the lattice dynamics. The calculations were performed for 2 GeV Au ion in olivine, demonstrating a heating of the lattice up to 700 K in the nanometric scale picoseconds after the projectile passage.

Gorbunov, S. A.; Medvedev, N. A.; Rymzhanov, R. A.; Terekhin, P. N.; Volkov, A. E.

2014-05-01

330

Water in Pyroxene and Olivine from Martian Meteorites  

NASA Technical Reports Server (NTRS)

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

Peslier, A. H.

2012-01-01

331

The effect of manganese on olivine-quartz-orthopyroxene stability  

NASA Astrophysics Data System (ADS)

The effect of manganese on the stability of ferrosilite relative to fayalite + quartz has been experimentally determined to assess its importance to orthopyroxene barometry. Reaction reversals in a piston-cylinder apparatus were obtained to within 0.1-kbar intervals indicating instability of Fs 95Rh 5 below 10.3, 10.9, 11.4, 12.2, 12.9, 13.7 kbar and Fs 90Rh 10 below 9.8, 10.4, 10.9, 11.6, 12.4 and 13.2 kbar at 750, 800, 850, 900, 950 and 1000°C, respectively. Each mole % MnSiO 3 extends the pyroxene stability by approximately 0.12 kbar relative to FeSiO 3. Electron microprobe analyses of run products indicate a small preference of Mn for pyroxene over olivine with KDMn-Fe opx-oliv = 1.2-1.5, similar to values observed for natural pairs. Mössbauer spectra are consistent with a random distribution of Mn between the M1 and M2 sites in the orthopyroxene. These experimental data allow downward revision of pressure estimates based on the orthopyroxene barometer in areas where Mn is a significant component in orthopyroxene.

Bohlen, Steven R.; Boettcher, Arthur L.; Dollase, Wayne A.; Essene, Eric J.

1980-03-01

332

Deformation induced slip-system transition in olivine at high pressures  

NASA Astrophysics Data System (ADS)

Deformation-induced olivine fabrics provide vital information for understanding seismic anisotropy in the upper mantle since olivine is the primary mineral in this region. Our recent analysis of the fabric of deformed olivine aggregates has documented the influence of deformation conditions (e.g., temperature and stress) on the fabric evolution of olivine at high pressures. Experiments were carried out using a deformation-DIA on an X-ray beamline at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory. Samples of polycrystalline olivine were deformed at a constant displacement rate of ~ 3.0 × 10- 5 s-1 over true axial strains of ~ 30% at temperatures of 673 to 1573 K and pressures of 5 to 9 GPa. Electron backscattered diffraction (EBSD) analyses of the fabrics of the deformed samples reveal a transition in slip system. For low temperatures (T < 1173 K) and high stresses (? > 2 GPa), the normals to the (100) lattice planes are parallel to the maximum principal stress; while at high temperatures (T > 1473 K) and lower stresses (? < 1 GPa), the normals to the (010) lattice planes switch to be parallel to the maximum principal stress. This transition in fabric occurs even if pressure is fixed, indicating that pressure is not a primarily factor causing the transition in dominant slip system. Our observations indicate that deformation of olivine is dominated by the (100) [001] slip system at low temperatures and high stresses and by the (010) [100] slip system at high temperatures and low stresses.

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

2008-12-01

333

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

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

334

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

PubMed

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

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

2014-03-01

335

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

336

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

NASA Astrophysics Data System (ADS)

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.

Yang, Xiaozhi; Liu, Dingding; Xia, Qunke

2014-10-01

337

Diffusive Fractionation of Lithium Isotopes in Olivine Grain Boundaries  

NASA Astrophysics Data System (ADS)

Diffusive fractionation of isotopes has been documented in silicate melts, aqueous fluids, and single crystals. In polycrystalline rocks, the meeting place of two grains, or grain boundaries, may also be a site of diffusive fractionation of isotopes. We have undertaken an experimental and modeling approach to investigate diffusive fractionation of lithium (Li) isotopes by grain boundary diffusion. The experimental procedure consists of packing a Ni metal capsule with predominantly ground San Carlos olivine and subjecting the capsule to 1100C and 1GPa for two days in a piston cylinder apparatus to create a nominally dry, 'dunite rock'. After this synthesis step, the capsule is sectioned and polished. One of the polished faces of the 'dunite rock' is then juxtaposed to a source material of spodumene and this diffusion couple is subject to the same experimental conditions as the synthesis step. Li abundances and isotopic profiles (ratios of count rates) were analyzed using LA-ICP-MS. Li concentrations linearly decrease away from the source from 550ppm to the average concentration of the starting olivine (2.5ppm). As a function of distance from the source, the 7Li/6Li ratio decreases to a minimum before increasing to the background ratio of the 'dunite rock'. The 7Li/6Li ratio minimum coincides with the lowest Li concentrations above average 'dunite rock' abundances. The initial decrease in the 7Li/6Li ratio is similar to that seen in other studies of diffusive fractionation of isotopes and is thought to be caused by the higher diffusivity (D) of the lighter isotope relative to the heavier isotope. The relationship between D and mass (m) is given by (D1/D2) =(m2/m1)^?, where ? is an empirical fractionation factor; 1 and 2 denote the lighter and heavier isotope, respectively. A fit to the Li isotopic data reveals an effective DLi of ~1.2x10^-12 m/s^2 and a ? of 0.1. Numerical modelling was utilized to elucidate the relationship between diffusive fractionation produced in the grain boundaries versus the lattices of the individual grains of the 'dunite rock'. The model assumes a linear grain boundary juxtaposed to the long side of a rectangular crystal lattice. During a simulation, the diffusant may directly enter the lattice or the grain boundary. Once in the grain boundary, the diffusant may then continue to diffuse away from the source until the end of the simulation or, alternatively, it may be incorporated into the lattice at some point during its travels down the grain boundary. The model system is similar to that considered by Whipple-LeClaire (1963) and our model results agree well with their analytical solution. Preliminary modeling results show that the distinctive minimum in the isotopic ratio is only produced when diffusive fractionation occurs in the grain boundary and not when the fractionation occurs only in the lattice. This suggests that the isotopic profile observed in the experiments may be a product of diffusive fractionation in grain boundaries. Implications of these results extend to the longevity of Li isotopic heterogeneities in the mantle, and suggest that the isotopes of other elements, which have a large relative mass difference, may also be diffusively fractionated by grain boundary diffusion.

Homolova, V.; Watson, E. B.

2012-12-01

338

Abiotic Versus Biotic Weathering Of Olivine As Possible Biosignatures  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

339

Experimental petrology, crystallization history, and parental magma characteristics of olivine-phyric shergottite NWA 1068: Implications for the petrogenesis of ``enriched'' olivine-phyric shergottites  

NASA Astrophysics Data System (ADS)

Northwest Africa (NWA) 1068 is one of the few olivine-phyric shergottites (e.g., NWA 1068, Larkman Nunatak [LAR] 06319, and Roberts Massif [RBT] 04262) that is not depleted in light rare earth elements (LREE). Its REE pattern is similar to that of the basaltic shergottite Shergotty, suggesting a possible connection between the olivine-phyric and the basaltic shergottites. To test this possible link, we have investigated the high-pressure near-liquidus phase equilibria for the NWA 1068 meteorite bulk composition. Our results show that the NWA 1068 bulk composition does not represent an unmodified mantle-derived melt; the olivine and pyroxene in our near-liquidus experiments are more magnesian than in the rock itself, which suggests that NWA 1068 contains cumulate minerals (extra olivine). We have then used these experimental results combined with the pyroxene compositions in NWA 1068 to constrain the possible high-pressure crystallization history of the parental magma. These results suggest that NWA 1068 had a complex polybaric history. Finally, we have calculated a model parental magma composition for the NWA 1068 meteorite. The calculated parental magma is an evolved basaltic composition which is too ferroan to be a primitive melt directly derived from the mantle. We suggest that it ponded and crystallized at approximately the base of the crust. This provided an opportunity for the magma to become contaminated by an ``enriched'' crustal component prior to crystallization. The results and modeling from these experiments are applicable not only to the NWA 1068 meteorite, but also to LAR 06319 and possibly any other enriched olivine-phyric shergottite.

Filiberto, Justin; Musselwhite, Donald S.; Gross, Juliane; Burgess, Katherine; Le, Loan; Treiman, Allan H.

2010-08-01

340

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

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.

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

341

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

E-print Network

density of hot, post-shock gas in- creases with increasing P tot and water abundance, re- quiring moreSHOCK WAVE MODELS: DEPENDENCE OF THERMAL HISTORY AND TYPE II CHONDRULE COMPOSITION ON WATER for evaporation and recondensation of chondritic matter, based on metal-silicate, liquid-crystal phase relations

Grossman, Lawrence

342

Nickel, Cobalt and Chromium in early lunar magma ocean olivine: Constraints on the petrogenesis of the Mg-suite  

Microsoft Academic Search

The parental magmas of the lunar highlands Mg-suite cumulates had enigmatic chemical signatures. They co-crystallized Mg-rich olivine and Ca-rich plagioclase and had extremely evolved trace element signatures (KREEP). Most models of Mg-suite petrogenesis call upon early, Mg-rich, olivine dominated LMO cumulates as a source to explain the high Mg* of the parental magmas. The olivine in the Mg-suite, however, contains

S. M. Elardo; C. Shearer Jr.; D. S. Draper

2010-01-01

343

Diffusion kinetics of Cr in olivine and 53Mn– 53Cr thermochronology of early solar system objects  

Microsoft Academic Search

We have determined the diffusion coefficient of Cr in olivine as function of temperature, oxygen fugacity (fO2), and crystallographic orientation and used these data to develop a quantitative understanding of the resetting of the short-lived 53Mn–53Cr decay system in olivine during cooling within meteorite parent body. The diffusion of Cr in olivine was found to be anisotropic, and effectively independent

Motoo Ito; Jibamitra Ganguly

2006-01-01

344

Bahasa Indonesia Kfir Bar  

E-print Network

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

Dershowitz, Nachum

345

Permanent Bar Magnets  

NSDL National Science Digital Library

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.

346

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

347

Temperature-dependent distribution of Cr between olivine and pyroxenes in lherzolite xenoliths  

NASA Astrophysics Data System (ADS)

The temperature effect on the exchange reaction Cr2O3(ol)=Cr2O3(px) was studied for coexisting olivine and both clino and ortho pyroxenes. The distribution of Cr between olivine and clinopyroxene in 31 coarse garnet lherzolites and 10 porphyroclastic garnet lherzolites from kinberlites, and in 17 coarse spinel lherzolites from basalts, obeys a van't Hoff relation (c.f. Stosch 1981) with the Wells two-pyroxene temperature: T(Kelvin)=8,787 (In D Cr+ 2.87) where D Cr(opx/ol)=wt.% Cr(clinopyroxene)/Cr(olivine). An analogous exchange for olivine and orthopyroxene with 0.7 1.6 wt.% Al2O3 in 41 garnet lherzolites from kimberlites shows considerable scatter about the following relation: T(Kelvin)=5,540/(ln D cr+1.86) where D cr(opx/ol)= wt.% Cr(orthopyroxene)/Cr(olivine). Spinel lherzolites and a garnet lherzolite from the Malaita alnöite do not obey the second relation. For orthopyroxene with 2.5 5.1 wt.% Al2O3, D cr(opx/ol) is 1.7 to 3 times higher, and for 0.1 wt.% Al2O3 is 2 times lower than for the garnet lherzolites. Experimental calibration is needed, especially to check the possible effect of Al on D cr(opx/ol).

Hervig, R. L.; Smith, J. V.

1982-12-01

348

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

SciTech Connect

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.

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

2005-10-12

349

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

350

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

NASA Astrophysics Data System (ADS)

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

Ozawa, K.; Nagahara, H.

2009-04-01

351

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

352

Experimental Constraints on Lithium Exchange Between Clinopyroxene, Olivine and Aqueous Fluids at Elevated P and T  

NASA Astrophysics Data System (ADS)

Lithium partitioning has been experimentally determined between clinopyroxene, olivine and hydrous fluid at 800-1100°C and 1 GPa. Experiments were done by equilibrating natural mineral powders with Li-doped fluids in sealed noble metal capsules for durations of 48 to 142 hours. Lithium concentrations were determined in run-product solids using LA-ICPMS, and partition coefficients determined by mass balance. Lithium was found to be more compatible in olivine than clinopyroxene, and both sets of D-values decrease with temperature following the relationships: ln DLicpx/fluid = -7.38(±0.55) + 7.04(±0.66) × 1000/T and ln DLiol/fluid = -5.93(±1.60) + 6.46(±2.09) × 1000/T. Similar slopes indicate that lithium partitioning between olivine and clinopyroxene is independent of temperature, which has been confirmed in experiments containing both these phases. Preliminary experiments examining the effect of REE content and fO2 suggest that DLiol/cpx may be a function of crystal chemistry. Lithium isotope partitioning between clinopyroxene + fluid and olivine + clinopyroxene has also been determined in experiments in which fluids of known isotopic composition were equilibrated with natural cpx and olivine. Run-product solids were analysed by MC-ICPMS and SIMS. The isotopic fractionation between clinopyroxene and fluid at temperatures greater than 900°C is ˜2.5‰ (±2‰) and the measured isotopic exchange between olivine and clinopyroxene is ˜5‰ (±4‰). These results have been supplemented by lithium diffusion measurements done on a natural clinopyroxene at 800-1000°C and in San Carlos olivine at 1000°C. The experiments were conducted in sealed silica tubes with either a LiCl Li-source or NaCl Li- sink and containing solid oxygen buffers. The lithium diffusion coefficient is independent of the diffusion gradient as values are the same if the flux of lithium is into or out of the crystal. Additionally the lithium diffusion coefficient in clinopyroxene appears to be independent of fO2. A single measurement of lithium diffusion in olivine was made and found to be two orders of magnitude slower than for clinopyroxene at similar conditions. Our results indicate that slab-derived fluids migrating by porous flow will rapidly exchange Li with their mantle wall-rock, effectively buffering the fluid composition close to ambient mantle values, and rapidly attenuating the slab Li signature.

Caciagli, N.; Brenan, J.; McDonough, W.; Phinney, D.

2009-05-01

353

Development of olivine Crystal Preferred Orientation in Oshima peridotite body as a remnant of oceanic lithosphere  

NASA Astrophysics Data System (ADS)

To know the mantle flow kinematics, investigation of the seismic anisotropy is common method in upper mantle. Anisotropy is linked to crystal preferred orientations (CPOs) of olivine which is most abundant and weakest mineral in upper mantle. However the quantitative investigation analyses of natural CPO data have not succeeded yet. So, we must understand how olivine CPOs develops with strain in deformation settings. The Oshima peridotite body is the lower part of the Yakuno ophiolite in SW Japan (Ishiwatari, 1985a, b). This body consists dominantly of dunite and harzburgite deformed in upper mantle. This peridotites display various microstructures such as coarse grained granoblastic texture (0.7-1.0mm), elongated porphyroclastic texture (1.0mm-) and fine grained equigranular texture (0.1mm-). We analyzed CPOs of olivine using EBSD method. The results show that CPOs of olivine was formed by (0kl)[100] or (010)[100] slip system. In order to characterize the CPOs, we first determined the fabric strength and orientation distribution density of the principal crystallographic axes (J-index and M-index; Tommasi et al., 2000 and Skemer et al., 2005). According to those studies with increasing monotonously strain, the value of J- and M-index also increases. The Oshima peridotite body shows the various fabric strength from J=2.95 to 16.26 (M=0.040 to 0.384). On this presentation, we propose a new inversion method of mantle deformation by matching the model CPO patterns with natural CPOs in the Alpine type peridotites. Furthermore, we investigated two kind of angles of olivine together with CPOs at the same time to analyze CPOs development during mantle deformation. There are; (1) Angles between slip plane of each olivine grain and sample lineation. (2) Misorientation angles between adjacent olivine grains. The different angles between the slip plane of olivine grains and the rock lineation (1) are controlled by lattice rotation due to dislocation glide (Sevillano et al., 1976). And the misorientation angles between neighboring grains (2) are governed by the local deformation kinetics involving dislocation climb process. From these two parameters (1) and (2) associated with strain, we can construct "gfabric distribution diagrams"h for deformed mantle rocks which can be compared to the J-index of the some samples. The more strain increases (=stronger fabrics), the more "gfabric distribution diagrams"h tends to concentrate. This study enables us to study together dislocation glide and recrystallization, which both contribute to CPO development.

Tasaka, M.; Toriumi, M.; Wataru, N.

2008-12-01

354

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

NASA Astrophysics Data System (ADS)

The largest Mars trojan, 5261 Eureka, is one of two prototype "Sa" asteroids in the Bus-Demeo taxonomy [1]. Analysis of its visible/near-IR spectrum [2] led to the conclusion that it might represent either an angritic analog or an olivine-rich composition such as an R chondrite. Spitzer IRS data (5-30 ?m) have enabled us to resolve this ambiguity. The thermal-IR spectrum exhibits strong olivine reststrahlen features consistent with a composition of ? Fo60-70. Laboratory spectra of R chondrites, brachinites, and chassignites are dominated by similar features.

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

2011-10-01

355

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

PubMed

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

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

2009-08-01

356

Solubility of Hydrogen in Olivine as a Function of Pressure and Oxygen Fugacity  

NASA Astrophysics Data System (ADS)

The incorporation of hydrogen into olivine is influenced by many of thermodynamic variables (pressure, temperature, oxygen fugacity, etc.) [1, 2, 3]. Given the strong influence that water has on the melting and mechanical behavior of mantle peridotite, it is necessary to determine the solubility of hydrogen in olivine over the range of chemical environments found in the upper mantle. We present results from new high temperature water-saturated hydration experiments to determine the effect of pressure and oxygen fugacity on hydrogen solubility in San Carlos olivine at upper mantle conditions. Our results indicate that at 1 to 2 GPa varying the fugacity of oxygen between the Fe-FeO and Ni-NiO buffers produces significantly smaller change in the concentration of hydrogen in the olivine than has been found at in previous experiments carried out at 300 MPa. Experiments were carried out in a piston-cylinder device at 1 to 2 GPa and 1200 °C using natural San Carlos olivine as a starting material. The fugacity of oxygen was controlled at Fe-FeO, FeO-Fe3O4 and Ni-NiO using solid buffers. Water content in experimental products was measured by secondary ionization mass spectrometry. Variable duration experiments indicate that hydrogen is homogeneously distributed in the olivine at 12 hrs. Our experimental results indicate that pressure strongly effects water content, in agreement with previous studies. For example, as pressure increases from 1 to 2 GPa, the water content of olivine increases from 32 ± 3 to 78 ± 7 ppm at the Ni-NiO buffer, and from 29 ± 3 to 69 ± 3 ppm at the FeO- Fe3O4 buffer. At each pressure the water content is only weakly affected by changing oxygen fugacity conditions, a result that disagrees with a recent report of a 5 times increase in water content between Fe-FeO and Ni-NiO at 2 GPa [3]. Differences between studies may result from variable degrees of defect equilibration or from differences in measurement techniques. However, when compared with the relationship between olivine water content and fslash O2 determined by [2], data from both this study and [3] suggest that the effect of oxygen fugacity on total water content is significantly weaker at upper mantle pressures than at 300 MPa. [1] Kohlstedt, Keppler, and Rubie (1996) Contrib Mineral Petrol 123:345-357. [2] Bai and Kohlstedt (1993) Phys Chem Minerals 19:460-471. [3] Grant et al. (2007) EPSL, doi:10.1016/j.epsl.2007.06.024

O'Leary, J. A.; Hauri, E. H.; Gaetani, G. A.

2007-12-01

357

Hydration of mantle olivine under variable water and oxygen fugacity conditions  

NASA Astrophysics Data System (ADS)

The incorporation of H into olivine is influenced by a significant number of thermodynamic variables (pressure, temperature, oxygen fugacity, etc.). Given the strong influence that H has on the solidus temperature and rheological behavior of mantle peridotite, it is necessary to determine its solubility in olivine over the range of conditions found in the upper mantle. This study presents results from hydration experiments carried out to determine the effects of pressure, temperature, and the fugacities of H2O and O2 on H solubility in San Carlos olivine at upper mantle conditions. Experiments were carried out at 1-2 GPa and 1,200 °C using a piston-cylinder device. The fugacity of O2 was controlled at the Fe0-FeO, FeO-Fe3O4, or Ni0-NiO buffer. Variable duration experiments indicate that equilibration is achieved within 6 h. Hydrogen contents of the experimental products were measured by secondary ion mass spectrometry, and relative changes to the point defect populations were investigated using Fourier transform infrared spectroscopy. Results from our experiments demonstrate that H solubility in San Carlos olivine is sensitive to pressure, the activity of SiO2, and the fugacities of H2O and O2. Of these variables, the fugacity of H2O has the strongest influence. The solubility of H in olivine increases with increasing SiO2 activity, indicating incorporation into vacancies on octahedral lattice sites. The forsterite content of the olivine has no discernible effect on H solubility between 88.17 and 91.41, and there is no correlation between the concentrations of Ti and H. Further, in all but one of our experimentally hydrated olivines, the concentration of Ti is too low for H to be incorporated dominantly as a Ti-clinohumite-like defect. Our experimentally hydrated olivines are characterized by strong infrared absorption peaks at wavenumbers of 3,330, 3,356, 3,525, and 3,572 cm-1. The heights of peaks at 3,330 and 3,356 cm-1 correlate positively with O2 fugacity, while those at 3,525 and 3,572 cm-1 correlate with H2O fugacity.

Gaetani, Glenn A.; O'Leary, Julie A.; Koga, Kenneth T.; Hauri, Erik H.; Rose-Koga, Estelle F.; Monteleone, Brian D.

2014-02-01

358

1 Thermal diffusivity of olivine single-crystals and polycrystalline 2 aggregates at ambient conditions--a comparison  

E-print Network

1 Thermal diffusivity of olivine single-crystals and polycrystalline 2 aggregates at ambient mantle materials highlights a large 16 scatter of absolute values of thermal diffusivity. In 17. Here 19 we present new thermal diffusivity measurements on San 20 Carlos olivine single crystals

Tommasi, Andrea

359

Noble-metal mineralization in olivine clinopyroxenite within idgimskiy gabbro-peridotite-pyroxenite complex (West Sayan Mountains)  

NASA Astrophysics Data System (ADS)

The study of noble-metal mineralization in olivine clinopyroxenite within idgimsky gabbro- peridotite-pyroxenite complex was carried out. Palladium minerals were identified: palladium telluride and palladium and platinum telluride with mercury impurity. The discovered noble- metal mineralization in olivine clinopyroxenites suggests the presence of perspective low sulfidation platinemetal mineralization in mafic within Verkhne-Amyl ore field.

Cherkasova, T. Y.; Korotchenko, T. V.

2014-08-01

360

Kinetics of the olivine-spinel transformation in subducting lithosphere: experimental constraints and implications for deep slab processes  

Microsoft Academic Search

The persistence of metastable olivine to depths greater than 400 km in subducting slabs has implications for the generation of deep-focus earthquakes, the magnitude of buoyancy forces driving plate motion, and the state of stress in the slab. The depth to which metastable olivine (alpha) can survive in a subduction zone and the depth interval over which transformation to beta-

David C. Rubie; Charles R. Ross II

1994-01-01

361

Grain-size evolution in subducted oceanic lithosphere associated with the olivine-spinel transformation and its effects on rheology  

Microsoft Academic Search

We investigate the role of grain-size reduction during the olivine-spinel transformation on rheological properties of subducting slabs on the basis of a scaling model for microstructural development during nucleation and growth. In this model, the size of spinel grains nucleating at olivine grain boundaries is controlled by the relative rates of nucleation and growth, taking into account the impingement through

Michael R. Riedel; Shun-Ichiro Karato

1997-01-01

362

Space Weathering of Olivine in Lunar Soils: A Comparison to Itokawa Regolith Samples  

NASA Technical Reports Server (NTRS)

Regolith particles from airless bodies preserve a record of the space weathering processes that occurred during their surface exposure history. These processes have major implications for interpreting remote-sensing data from airless bodies. Solar wind irradiation effects occur in the rims of exposed grains, and impact processes result in the accumulation of vapordeposited elements and other surface-adhering materials. The grains returned from the surface of Itokawa by the Hayabusa mission allow the space weathering "style" of a chondritic, asteroidal "soil" to be compared to the lunar case. Here, we present new studies of space-weathered olivine grains from lunar soils, and compare these results to olivine grains from Itokawa. Samples and Methods: We analyzed microtome thin sections of olivine grains from the 20-45 micron fractions of three lunar soils: 71061, 71501 and 10084 (immature, submature and mature, respectively). Imaging and analytical data were obtained using a JEOL 2500SE 200kV field-emission scanning-transmission electron microscope equipped with a thin-window energy-dispersive x-ray spectrometer. Similar analyses were obtained from three Hayabusa olivine grains. Results and Discussion: We observed lunar grains showing a range of solar flare track densities (from <10(exp 9) to approx.10(exp 12)/sq cm). The lunar olivines all show disordered, highly strained, nanocrystalline rims up to 150-nm thick. The disordered rim thickness is positively correlated with solar flare track density. All of the disordered rims are overlain by a Si-rich amorphous layer, ranging up to 50-nm thick, enriched in elements that are not derived from the host olivine (e.g., Ca, Al, and Ti). The outmost layer represents impact-generated vapor deposits typically observed on other lunar soil grains. The Hayabusa olivine grains show track densities <10(exp 10)/sq cm and display disordered rims 50- to 100-nm thick. The track densities are intermediate to those observed in olivines in immature and submature lunar soils and indicate surface exposures of approx. 10(exp 5) years. The outermost few nanometers of the disordered rims on Hayabusa olivines are more Si-rich and Mg- and Fe-depleted relative to the cores of the grains and likely represent a minor accumulation of impact-generated vapors or sputter deposits. Nanophase Fe metal particles are less abundant in the Hayabusa rims compared to the rims on lunar grains. Conclusions: The Hayabusa and lunar olivine grain rims have widths and microstructures consistent with formation from atomic displacement damage from solar wind ions. The space weathering features in the Hayabusa grains are similar to those observed in olivines from immature to submature lunar soils. A major difference, however, is that the Hayabusa grains appear to lack the hypervelocity impact products (melt spherules, thick vapor deposits, and abundant nanophase Fe metal particles) that are common in lunar soil grains with a similar exposure history.

Keller, L. P.; Berger, E. L.

2014-01-01

363

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

364

Decoupling of H2O, Oxygen Fugacity and Incompatible Elements in Olivine-Hosted Melt Inclusions By Diffusive Re-Equilibration (Invited)  

NASA Astrophysics Data System (ADS)

Mineral-hosted melt inclusions provide information on the pre-eruptive H2O contents of degassed magmas. The strength of the host mineral protects included silicate melts from the decompression experienced by the entraining magma. This allows melt inclusions to retain their pre-eruptive volatiles and, thereby, provides a source of information on the amount of H2O in magmatic systems. Recent studies have used this to investigate (1) relationships between H2O and oxygen fugacity [1] and (2) the influence of H2O on extent of peridotite partial melting beneath back arc spreading centers [2,3]. We combined experiments and numerical models to investigate the potential for decoupling of these variables through diffusive re-equilibration during episodes of degassing or magma mixing. Our results demonstrate that re-equilibration of H2O and oxygen fugacity occur on short timescales and are independent of one another. Therefore, relationships between H2O and oxygen fugacity are likely to be robust, reflecting pre-eruptive condition. For incompatible elements, such as TiO2, slow diffusivity and low concentration in olivine results in inefficient diffusive re-equilibration. Therefore, relationships between H2O and incompatible elements, such as TiO2, can be significantly perturbed by loss or gain of protons through the host olivine. Hydration experiments were performed on olivines from 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. Initial concentrations of H2O in these melt inclusions are uniformly high (3.6±0.6 wt%). All run products were analyzed 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. Results from our experiments confirm that the mechanism for loss or gain of H2O from olivine-hosted melt inclusions is lattice diffusion of protons, and that the concentration of H2O in melt inclusions changes rapidly. Re-equilibration of oxygen fugacity occurs via diffusion of point defects on timescales comparable to proton diffusion. Further, our results demonstrate that these processes are independent of one another, so that correlations between H2O concentration and the oxidation state of Fe in the melt do not result from diffusive re-equilibration. However, melt inclusions that initially had significantly different H2O and TiO2 contents can end up with a range of TiO2 at nearly constant H2O following loss or gain of protons. In this case, use of TiO2 as an indicator of extent of peridotite partial melting results in erroneous conclusions about the influence of H2O on peridotite partial melting. References: [1] Kelley, K. A. & Cottrell, E., Science 325, 605-607 (2009); [2] Kelley, K. A. et al., J Geophys Res 111 (2006); [3] Kelley, K. A. et al., J Petrol 51, 1711-1738 (2010).

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

2010-12-01

365

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

E-print Network

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

Shen, Guoyin

366

Moessbauer spectra of olivine-rich achondrites - Evidence for preterrestrial redox reactions  

NASA Technical Reports Server (NTRS)

Moessbauer spectral measurements at 4.2 K were made on several ureilites and the two shergottites found in Antarctica, as well as two ureilite falls, three SNC meteorite falls, and two finds in order to distinguish products of preterrestrial redox reactions from phases formed during oxidative weathering on the earth. The spectra indicated that several ureilites contain major proportions of metallic iron, much of which resulted from preterrestrial carbon-induced reduction of ferrous iron in the outermost 10-100 microns of olivine grains in contact with carbonaceous material in the ureilites. The cryptocrystalline nature of these Fe inclusions in olivine renders the metal extremely vulnerable to aerial oxidation, even in ureilites collected as falls. It is inferred that the nanophase ferric oxides or oxyhydroxides identified in Brachina and Lafayette were produced by terrestrial weather of olivines before the meteorites were found. The absence of goethite in two olivine-bearing Antarctic shergottites suggests that the 2 percent ferric iron determined in their Moessbauer spectra also originated from oxidation on Mars.

Burns, R. G.; Martinez, S. L.

1991-01-01

367

Numerical models of ionic diffusion in one and three dimensions: application to dehydration of mantle olivine  

NASA Astrophysics Data System (ADS)

The hydrogen content of nominally anhydrous minerals is of great interest, because it can influence many physical and mechanical properties of mantle rocks. Moreover, the hydrogen diffusion profiles can be used to constrain timescales related to magma eruptions. Here, we report models of ionic diffusion for trace elements in anisotropic crystals and apply them to hydrogen diffusing out of mantle-derived olivine. We first compare and discuss the characteristics of 1D and 3D models and show that only 3D anisotropic diffusion models can lead to diffusion profiles exhibiting non-equilibrium plateau at the center of the solid along the slowest axis, as measured in natural samples. In a second part, we discuss the differences between hydration and dehydration of olivine for diffusion that is linked to two different atomic sites involved in hydrogen mobility. Finally, we apply our 3D anisotropic model to previous results on mantle-derived olivine from Pali-aike to better characterize diffusion coefficients and their anisotropy that could be relevant for dehydration of olivine. Our results show that dehydration has to be strongly anisotropic, with a fast [100] axis and a significantly slower [001] axis.

Thoraval, Catherine; Demouchy, Sylvie

2014-10-01

368

Fe-Ni Metal and Magnetite Nano-Particles in ``Brown'' Color Olivines from Martian Meteorites  

NASA Astrophysics Data System (ADS)

Our TEM study revealed that brown olivines in Dhofar 019, LAR 06319 and NWA 1950 contained magnetite nano-particles instead of Fe-Ni metal nano-particles. These results indicate that magnetite nano-particles are widely present in martian meteorites.

Kurihara, T.; Mikouchi, T.; Saruwatari, K.; Kameda, J.; Miyamoto, M.

2009-03-01

369

In situ Ultrasonic Velocity Measurements Across the Olivine-spinel Transformation in Fe2Si04  

SciTech Connect

Compressional (P) and shear (S) wave velocities across the olivine-spinel transformation in Fe{sub 2}SiO{sub 4} were investigated in situ using combined synchrotron X-ray diffraction, X-ray imaging, and ultrasonic interferometry up to 5.5 GPa along the 1173 K isotherm. The onset of the spinel to olivine transformation at 4.5 GPa and olivine to spinel transition for Fe{sub 2}SiO{sub 4} at 4.8 GPa was concurrently observed from X-ray diffraction, the amplitude of the ultrasonic signals, the calculated velocities, and the ratio of P and S wave velocities (v{sub P}/v{sub S}). No velocity softening was observed prior to the fayalite to spinel transition. The velocity contrasts across the Fe{sub 2}SiO{sub 4} spinel to fayalite phase transition are derived directly from the measured velocities, which are 13 and 12% for P and S waves, respectively, together with a density contrast of 9.4%. A comparison with literature data indicates that the changes in compressional-wave velocity and density across the olivine-spinel transformation in Fe{sub 2}SiO{sub 4} are comparable to those with different iron concentrations in the (Mg,Fe){sub 2}SiO{sub 4} solid solution, whereas the shear wave velocity contrast decreases slightly with increasing iron concentration.

Liu, Q.; Liu, W; Whitaker, M; Wang, L; Li, B

2010-01-01

370

Structure of the Olivine-Spinel Phase Boundary in the Descending Lithosphere  

Microsoft Academic Search

Seismic evidence shows that the descending lithosphere penetrates the mean depth at which the olivine-spinel phase change occurs. As a result of the low temperature in the sinking lithosphere, the phase boundary will be elevated about 150 km. An analysis is given for the structure of a univariant phase boundary in the presence of flow. The phase boundary is discontinuous

D. L. Turcotte; G. Schubert

1971-01-01

371

Chlorine/Bromine Ratios in Fracture-filling Aqueous Alteration Products in Nakhla Olivine  

NASA Technical Reports Server (NTRS)

The Cl/Br ratios in fracture-filling materials in veins in Nakhla olivine was determined using x-ray microprobe (Br) and EDX (Cl) techniques. The Cl/Br ratio of 55 (standard deviation: 13) shows that the secondary altered material is pristine, extraterrestrial and akin to the Martian soil. Additional information is contained in the original extended abstract.

Sutton, S. R.; Rao, M. N.; Dreibus, G.; McKay, D. S.; Waenke, H.; Wentworth, S.; Newville, M.; Trainor, T.; Flynn, G. J.

2002-01-01

372

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

373

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

E-print Network

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

Perfect, Ed

374

Measurement of activation volume for creep of dry olivine at upper mantle pressure  

NASA Astrophysics Data System (ADS)

Olivine is the most abundant and weakest phase in the upper mantle, and thus its rheological properties have a critical role in controlling convective flow in this region. A resilient obstacle to understanding the behavior of olivine in the mantle has been the difficulty of determining activation volume (V*), the influence of hydrostatic pressure on flow strength. The bulk of previous studies examining V* were conducted at low pressure (<300 MPa) and small pressure ranges in gas-medium deformation apparatuses, limiting precision and raising questions about application to relevant geological conditions. For this study, we conducted deformation experiments on dry polycrystalline olivine in the D-DIA apparatus. The development of a new hybrid soft-fired pyrophyllite/mullite sample assembly allowed for a broadened pressure range (2-9 GPa), while stress and strain were measured in-situ with synchrotron x rays. Refinement in diffraction technique has allowed stress resolution of ±0.01 GPa. For the pressure range in this study, we have measured an average activation volume of about 17 cm^3/mol for dry polycrystalline San Carlos olivine. This is a substantial pressure effect, representing a pressure-induced viscosity increase of nearly 7 orders of magnitude from the base of the lithosphere to the bottom of the upper mantle.

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

2011-12-01

375

Amoeboid Olivine Aggregates in NWA 1152: Connection to CR Chondrites and the Cometary Particle T112  

NASA Astrophysics Data System (ADS)

We have examined the mineralogy of AOAs in NWA 1152 and compared with an AOA-like STARDUST particle. Based on our study, the coexistence of chromite and olivine suggests that the AOA-like cometary particle may have experienced incipient alteration.

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

2012-09-01

376

doi:10.1016/j.gca.2003.08.012 Northwest Africa 773: Lunar mare breccia with a shallow-formed olivine-cumulate  

E-print Network

volcanic components, including a prominent igneous clast lithology. The clast lithology is an olivine-gabbro compositionally to volcanic components in the meteorite. The olivine-gabbro lithology exhibits cumulus textures, including extremely low Eu concentration, that make it a candidate parent melt for the olivine-gabbro

377

Origin of Aristarchus Olivine Deposits Based on M3, WAC, and Diviner Analyses  

NASA Astrophysics Data System (ADS)

The Aristarchus region contains geologically diverse deposits and the Aristarchus impact crater, located on the SE margin of the plateau near the contact between plateau materials and western Procellarum basalts, has exposed materials with variable compositions. Of particular interest is the origin of olivine-bearing deposits that occur on the SE portion of the crater rim and ejecta in association with impact melt [1]. NW portions of the rim and ejecta expose plateau materials and are spectrally dominated by pyroxene in the VNIR. Spectra of the NW rim and ejecta are consistent with a noritic composition and with the inferred origin of the plateau as uplifted upper crust [2,3,4]. Therefore, it is unlikely that the olivine- bearing materials, which exhibit a strong 1 micron olivine absorption and only minor pyroxene contributions, are derived from plateau materials similar to those exposed in the NW portion of the crater. Potential sources of the olivine-bearing material excavated by the impact include western Procellarum basalts or buried material associated with the Marius Hills volcanic complex. Alternatively, the olivine-bearing deposits could be derived from a shallow pluton that is not represented by other surface exposures or could have formed as re-crystallized impact melt. Both the western Procellarum basalts [5,6] and some units associated with the Marius Hills [7] are olivine-bearing. In order to differentiate between these hypotheses, we are integrating spectral data in the UV/VIS (LRO WAC), VIS/NIR (Chandrayaan-1 M3), and TIR (LRO Diviner) to further characterize the assemblages of minerals that occur in association with the olivine-bearing deposits in Aristarchus crater, western Procellarum, and units within the Marius Hills volcanic complex. [1] Mustard et al., 2011, JGR 116. [2] McEwen et al., 1994, Science 266. [3] Lucey et al., 1986, LPSC 16. [4] Chevrel et al., 2009, Icarus 199. [5] Staid and Pieters 2001, JGR. [6] Staid et al., 2011, JGR 116. [7] Besse et al., 2011, JGR 116.

Wiseman, S. M.; Mustard, J. F.; Donaldson Hanna, K. L.; Isaacson, P.; Jolliff, B. L.; Besse, S.; Staid, M.; Pieters, C. M.

2011-12-01