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At least 199 records · Page 11

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NASA NTRS1981

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

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

Andersen, D. J.↗

NASA NTRS1980

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

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

Delaney, J. S.↗

NASA NTRS1984

Minor elements and cathodoluminescence of Mg-rich olivines from Murchison and Allende carbonaceous meteorites

The morphology and inclusions of individual Mg rich olivine grains from C2 chondrites provide disputed evidence for origin either from a liquid or a vapor. Olivine grains from Murchison (C2) and Allende (C3) meteorites were examined to extend data on Belgica 7904 (C2. Cathodoluminescence revealed the relation of chemical zoning to external shape and inclusions. High precision electron probe analyses of selected spots for Na, Al, P, Ca, Ti, Cr and Mn provided chemical constraints on the source material. From several possible explanations tentative suggestions are for at least two stages: (1) growth of the blue core from a vapor enriched in refractory elements (hence lack of inclusions); and (2) growth of red/dark rim from an unenriched liquid which entrapped the blue core. Mechanical transfer may be involved. The channels and networks are puzzling at this time. Whatever the true explanation, a complex history is needed for a simple mineral, and further study should provide additional restraints on formation of carbonaceous meteorites.

Steele, I. M.↗

NASA NTRS1985

The Olivine Asteroids: Discovery, Mineralogy, and Relationship to Palasites

Telescopic observations have recently revealed the existence of a new class of asteroids whose surfaces show the spectral signature of abundant olivine. The mineralogy of a well-observed example (446 Aeternitas) is discussed and the implications for the origins of the olivine-rich meteorites and the thermal evolution of asteroids outlined.

Bell, J. F.↗

NASA NTRS1984

Phosphoran pyroxene and olivine in silicate inclusions in natural iron-carbon alloy, Disko Island, Greenland

A survey of literature data on the P contents of olivine, pyroxene, and garnet in mantle xenoliths and the bulk P contents of mantle xenoliths shows that available data is ambiguous as to whether mantle P is primarily contained in silicates or in phosphates, even though phosphates are rarely observed in mantle xenoliths. Garnet probably contains more of the mantle's P than olivine or pyroxene. Bulk P contents of mantle xenoliths vary significantly. Estimation of the primitive mantle P content from xenoliths requires interpretation of the partial melting and contamination histories of the xenoliths.

Goodrich, C. A.↗

NASA NTRS1987

Alteration of Al-rich inclusions inside amoeboid olivine aggregates in the Allende meteorite

The primary phases of Al-rich inclusions in amoeboid olivine aggregates have undergone alteration reactions with the solar nebular gas. The simplest interpretation of the present observations is that melilite was the first primary phase to disappear with falling temperature, and was replaced by grossular + anorthite + feldspathoids, followed by fassaite; spinel was the last phase to be altered. Thermodynamic calculations suggest that Na-rich phlogopite could have formed at about 470 K and chlorite at about 328 K at a water fugacity of 0.000001, which is that of a gas of solar composition in this temperature range. The olivine around Al-rich inclusions is not serpentized, indicating the cessation of gas-solid equilibrium above 274 K.

Hashimoto, Akihiko↗

NASA NTRS1988

Capture of an olivine micrometeoroid by spacecraft in low-earth orbit

Particulates associated with an impact feature in the solar maximum satellite MEB thermal control blanket are identified as magnesium-rich, Mg/Mg + Fe(2+) = 0.66 - 0.83, olivine and confirm that the impact feature was caused by an olivine micrometeoroid. At a relative impact velocity of about 7 km/s a considerable portion of the micrometeoroid was lost due to back splattering. Analytical electron microscope analysis of recovered particulates shows several degrees of mineralogical and chemical degradation such as mechanical fragmentation, melting, loss of sulfur and iron, and formation of Fe, Ni grains. The results indicate that recovery of information is sufficient to establish the character of the impacted micrometeoroid.

Rietmeijer, Frans J. M.↗

NASA NTRS1989

Dynamic crystallization of chondrule melts of porphyritic olivine composition - Textures experimental and natural

A full range of textures characteristic for porphyritic olivine chondrules was reproduced in melts of the same composition, crystallized under dynamic crystallization conditions (under controlled cooling), as determined by electron microprobe analyses. The primary differences between the natural and experimentally produced porphyritic olivine textures were the nature and the extent of matrix crystallization, which reflected the subsolidus or low-temperature cooling history. The most confining limits on the chondrule-forming process were found to be the presence of crystalline precursors for the chondrule melts and the upper temperature limit of melting.

Lofgren, Gary↗

NASA NTRS1990

Chemical differences between small subsamples of Apollo 15 olivine-normative basalts

Results are presented on the chemical and petrological characterization of nine samples of an Apollo 15 mare basalt suite. The results show that all nine samples are low-silica olivine normative basalts (ONBs) similar to those described earlier for low-silica ONBs from Apollo 15 site. The samples were found to vary in texture and grain size, from fine-grained intergranular or subophitic basalts to coarse-grained granular 'microgabbros'. Several displayed macroscopic heterogeneity. Variation diagrams show that the overall trend of the data is consistent with the fractionation of olivine (plus minor Cr-spinel) from a high-MgO parent magma.

Shervais, J. W.↗

NASA NTRS1990

An in situ X ray diffraction study of the kinetics of the Ni2SiO4 olivine-spinel transformation

The kinetics of the olivine-spinel transformation in Ni2SiO4 were investigated in an in situ X-ray diffraction experiments in which synchrotron radiation was used as an X-ray source. The starting material was Ni2SO4 olivine which was hot-pressed in situ at 980 C and 2.5 GPa; during the transformation, X-ray diffraction patterns were collected at intervals of 30 or 120 sec. The kinetic data were analyzed using Cahn's (1956) model. The activation energy for growth at 3.6-3.7 GPa was estimated as 438 + or - 199 kJ/mol. It is shown that, in order to make significant extrapolations of the kinetic data to a geological scale, the dependence of the rates of both nucleation and growth on temperature and pressure must be evaluated separately.

Rubie, D. C.↗

NASA NTRS1990

Melt migration in a silicate liquid-olivine system - An experimental test of compaction theory

An experimentally derived melt migration profile is compared with those obtained from compaction theory. A couple is prepared in which a source-for-melt (a disk composed of a silicate glass and olivine) was placed in contact with a sink-for-melt (a disk of polycrystalline olivine) in order to induce melt migration under laboratory conditions. It is noted that melt infiltrates into the sink disk along triple junctions driven by capillary forces. In order to analyze the melt migration profile in terms of compaction theory, the equations developed by McKenzie (1984) to describe porous flow of a liquid in a deformable matrix were modified. The bouyancy force term is replaced with a capillary force term and governing equations are then solved numerically with the initial boundary conditions specified by the experimental design. Also, it is determined that compaction theory provides a good description of the experimental results provided that the permeability of these solid-liquid materials increases linearly with increasing liquid fraction.

Riley, G. N., Jr.↗

NASA NTRS1990

Dynamic crystallization study of barred olivine chondrules

The 'classic' barred olivine (BO) texture was defined by Donaldson (1976) as a single-plate dendrite which shares the entire chondrule with the remaining glass or subsequent crystallization products. This paper describes experiments in which BO textures were produced experimentally from two starting compositions: one modeled after the average BO chondrule composition in L-chondrites determined by Weisberg (1987), and the other after an olivine-rich composition (CH-1) studied by Lofgren (1989). It is shown that most of the textural features observed in natural BO chondrules are replicated in the experimentally produced chondrules. Several new constraints on models for the chondrule-forming process are proposed.

Lofgren, Gary↗

NASA NTRS1990

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

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

Warner, Richard D.↗

NASA NTRS1991

Waveform effects of a metastable olivine tongue in subducting slabs

Velocity models of subducting slabs with a kinetically-depressed olivine to beta- and gamma-spinel transition are constructed, and the effect that such structures would have on teleseismic P waveforms are examined using a full-wave finite-difference method. These 2D calculations yielded waveforms at a range of distances in the downdip direction. The slab models included a wedge-shaped, low-velocity metastable olivine tongue (MOTO) to a depth of 670 km, as well as a plausible thermal anomaly; one model further included a 10-km-thick fast layer on the surface of the slab. The principal effect of MOTO is to produce grazing reflections at wide angles off the phase boundary, generating a secondary arrival 0 to 4 seconds after the initial arrival depending on the take-off angle. The amplitude and timing of this feature vary with the lateral location of the seismic source within the slab cross-section.

Vidale, John E.↗

NASA NTRS1993

On origin of the olivine inclusions from the Kainsaz CO carbonaceous chondrite

Olivine inclusions and chondrules of Kainsaz were formed in a unique process of dust matter melting. The elemental abundances of four fractions of olivine (01) inclusions from Kainsaz were analyzed by INAA. The inclusions of fraction A (160 less than d less than 260 microns) have Fe-Ni grains, the inclusions of fractions B (100 less than d less than 160 microns), C (160 less than d less than 260 microns), and D (260 less than d less than 360 microns) do not. The average elemental enrichment factors relative to CI chondrite for each fraction and chondrules of Kainsaz is shown. The enrichment factors of siderophile Co, Ni, Ir, Au, and non-refractory Na in all fractions are less than 1. The factors of refractory Ca, Sc, La, Sm, and Yb are comparative with the corresponding values of O1 aggregates of Allende CV (average 4.76). For chondrules of Kainsaz these values are lower. Fraction A is enriched in Co, Ir, Au, and relative Ni and CI chondrites: Ir greater than Au greater than Co. The values of (Me/Ni)inc/(Me/Ni)CI are equal to 3.25 for Ir, 2.1 for Au, and 1.2 for Co. The superabundances in Ir and Au relative to Ni witness to formation of Fe-Ni grains of O1 inclusions by agglomeration of grains enriched in refractory metal with grains enriched in non-refractory metal (Au). The enrichments of fraction A in Ca, Sc, La, Sm, and Yb witness about presence of high-temperature phases in O1 inclusions.

Lavrukhina, A. K.↗

NASA NTRS1993

Hydrothermal alteration experiments of olivine with varying Fe contents: An attempt to simulate aqueous alteration of the carbonaceous chondrites

Hydrothermal alteration experiments of olivine powder with several Fe/Mg ratios were carried out under acidic and neutral conditions, and transition electron microscopy (TEM) observations were made on the run products. Well-developed tubular crystals of serpentine (chrysotile) were synthesized from Fo100 under both acidic and neutral conditions, and from Fo92 and Fo80 under acidic condition. Abundance and size of chrysotile apparenlty dependent on the Fe contents of olivine, i.e. with increasing Fe contents, less and smaller chrysotile was formed. Acidity of the solution plays an important role for the formation of chrysotile. Platy and fibrous crystals of phyllosilicate, probably serpentine, were obtained from Fo50 and Fo20 treated under acidic condition, which are most similar to the phyllosilicates in the CI and CM chondrites. Framboidal aggregates of Fe-rich grains (presumably Fe-hydroxide) were formed from Fa100 and Fo20, but no phyllosilicate was formed from Fa100.

Takatori, Koichi↗

NASA NTRS1994

Partition coefficients for Al, Ca, Ti, Cr, and Ni in olivine obtained by melting experiment on an LL6 chondrite

We report the partition coefficients for Ca, Al, Ti, Cr, and Ni in olivine obtained through a series of melting experiments on an LL6 chondrite under varying conditions of temperature and oxygen fugacity. It is necessary to examine the variation of partition coefficients up to extremely reducing conditions in order to study meteoritic olivines. For Ca, Al, and Cr, the partition coefficients tend to decrease as temperature increases, but do not change even under extremely reducing conditions.

Miyamoto, M.↗

NASA NTRS1994

Compositional variations of olivines and pyroxenes in chondritic interplanetary dust particles

We report here analyses of olivines and pyroxenes, and petrofabrics of 27 chondritic interplanetary dust particles (IDPs), comparing those from anhydrous and hydrous types. Approximately 40% of the hydrous particles contain diopside, a probable indicator of parent body thermal metamorphism, while this mineral is rarely present in the anhydrous particles. Based on this evidence, we find that hydrous and anhydrous IDPs are, in general, not directly related, and we conclude that olivine and pyroxene major-element compositions can be used to help discriminate between IDPs that are (1) predominantly nebular condensates, and lately resided in anhydrous or icy (no liquids) primitive parent bodies, and (2) those originating from more geochemically active parent bodies (probably hydrous and anhydrous asteroids).

Zolensky, Michael E.↗