Engineering topics

Rubin, Alan E.

Publications and source records attributed to Rubin, Alan E..

64 records · Page 4

NASA NTRS1989

Chondrules in the Sharps H3 chondrite - Evidence for intergroup compositional differences among ordinary chondrite chondrules

Bulk compositions of 19 chondrules and one matrix-rich sample from H3.4 Sharps were determined by instrumental neutron activation analysis. Samples were characterized petrographically, and mineral compositions were determined by electron microprobe analysis. There is constancy among ordinary chondrite (OC) groups in the compositional interrelationships of different chondrule types; e.g., in H3 as well as L3 and LL3 chondrites, porphyritic chondrules are more refractory than nonporphyritic chondrules. Precursor components of H3 chondrules are closely related to those of LL3 chondrules. The mean Ir/Ni, Ir/Co, and Ir/Au ratios of H3 chondrules differ from the corresponding ratios of LL3 chondrules at the 99, 90, and 79 percent confidence levels, respectively. The ratios in H3 chondrules exceed those in LL3 chondrules by amounts similar to those by which H whole-rocks exceed LL whole-rocks. These data suggest that there are primary systematic differences in bulk composition between H and LL chondrules. These differences support the inference that chondrule formation occurred after major nebular fractionation events had established the observed bulk compositional differences among OC groups.

Rubin, Alan E.↗

NASA NTRS1988

ALH85085 - A unique volatile-poor carbonaceous chondrite with possible implications for nebular fractionation processes

The characteristics and possible origin of the chondrite ALH85085 are discussed. It is found that the metal silicate, and sulfide compositions of ALH85085 are similar to those in CM-CO and Al Rais-Renazzo chondrites. High siderophile abundances and volatile depletion are observed. It is found that ALH85085 agglomerated when temperatures in the nebula were near 1000 K, in the same region where Renazzo, Al Rais, and the CI chondrites formed. It is suggested that ALH85085 was annealed and lightly shocked after agglomeration. C1 and other clasts were subsequently incorporated during late-stage brecciation.

Grossman, Jeffrey N.↗

NASA NTRS1988

Formation of ureilites by impact-melting of cabonaceous chondritic material

Ureilites are modeled as impact-melt products of CV-chondrite-like material. This model is consistent with the brecciated nature and cumulate textures of ureilites, O-isotopic constraints (which indicate ureilite derivation from an isotopically heterogeneous body like the CV-chondrite parent), the high abundance of planetary-type noble gases, and the relatively high concentrations of siderophile and chalcophile elements (indicating incomplete separation of metal-sulfide from silicate). Each ureilite may have been derived from a separate cratering event.

Rubin, Alan E.↗

NASA NTRS1988

Chondrules and matrix in the Ornans CO3 meteorite - Possible precursor components

Bulk compositions of 17 chondrules and one sample of matrix from CO3 Ornans were determined by instrumental neutron activation analysis. Chondrule precursor components deduced from chondrule compositions are characterized by: (1) common and slightly volatile siderophiles, Cr and chalcophiles, (2) refractory lithophiles and Na, (3) Mn, Si and modal pyroxene, and (4) FeO and olivine. Component 4 may be closely related to matrix material. Precursor components have now been inferred for OC, EH, CV, CM and CO chondrules. An MN- and Si-rich component occurs exclusively among carbonaceous chondrite chondrules. Although there are significant intergroup differences, common to chondrules in all chondrite groups are refractory-lithophile-rich, common-siderophile-rich, and (with the exception of EH) common-lithophile-rich components. This indicates that the siderophile/lithophile and refractory lithophile/common lithophile fractionations recorded in chondrite whole-rocks were established prior to chondrule formation at all nebular locations.

Rubin, Alan E.↗

NASA NTRS1988

Oxidation state in chondrites

An evaluation is made of extant data on chondrite oxidation states and intrinsic O fugacities. A variety of oxidation states are exhibited by the chondritic meteorites; petrologic and chemical data may be used to arrange the major chondrite groups in order of oxidation state. The intrinsic O fugacity measurements on chondrite whole-rock samples are noted to display a corresponding ordering of oxidation states. Metamorphosed chondrites and igneous meteorites that were substantially altered by metamorphic reactions, outgassing, and igneous processes may preserve information on the oxidation state and size of their parent bodies.

Rubin, Alan E.↗

NASA NTRS1988

Properties of chondrules

Chondrules contain a record of many essential characteristics of the primordial solar nebula, whose high-temperature chondrule-generating events have spanned nearly 10 million years. As chondrules cooled, they became magnetized by nebular fields; chondrule rims show that dust was present in the vicinity of chondrule formation, and that multiple melting events were possible. The chondrule precursors included many large grains, showed variable degrees of Fe-oxidation, and encompassed many isotopic reservoirs. The properties of these nebular materials systematically changed from the enstatite, to ordinary, and finally to carbonaceous chondrite formation regions.

Grossman, Jeffrey N.↗

NASA NTRS1987

Size-frequency distributions of EH3 chondrules

Size-frequency distributions of chondrules in three EH3 chondrites, namely Qingzhen, Kota-Kota and ALHA77156, are presently determined. Radial pyroxene chondrules are larger than cryptocrystalline chondrules, while nonporphyritic chondrules have a broader size-frequency distribution than the porphyritic, and porphyritic olivine-pyroxene chondrules are larger than porphyritic pyroxene chondrules. This last result is due to a reaction of fine-grained olivine with free silica to form pyroxene during mild thermal metamorphism of the whole-rocks.

Rubin, Alan E.↗

NASA NTRS1987

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

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

Rubin, Alan E.↗

NASA NTRS1987

Diverse eucritic pebbles in the Vaca Muerta mesosiderite

Seven 5-cm basaltic pebbles from the Vaca Muerta mesosiderite were studied by neutron activation and electron microprobe analysis, and three additional pebbles were studied petrographically. The cumulate pebbles had low REE concentrations and high Eu/Sm ratios, indicating the absence of intercumulus liquid. Siderophile interelement ratios were similar to those found in Vaca Muerta metal except for anomalously low Ir concentrations. The presence of 20 percent impact-melt breccias among the pebbles and 35-40 percent melt breccias among the mesosiderite whole-rocks suggests that the mesosiderites were more extensively impact melted than the howardites. Three alternative models to explain this greater proportion of impact-melted material among the mesosiderites are proposed.

Rubin, Alan E.↗

NASA NTRS1987

Original structures, and fragmentation and reassembly histories of asteroids - Evidence from meteorites

The validity of an onion shell model (OSM) for chondrite parent asteroids was assessed using metallographic cooling rates (MCR) derived from the compositions of metallic Fe-Ni grains. The hypothesis evaluated was that the hottest materials in chondrites would have been buried the deepest and cooled the slowest. The survey covered breccia from regolith and 13 different chondrites. The MCRs agreed well with cooling rates predicted by fission-track thermometry and Ar-40/Ar-39 ages. The OSM predicts an inverse correlation between the cooling rate and the petrographic type. Low correlations found between the MCRs and petrographic type indicate that chondrite parent asteroids were not assembled with onion shell structures.

Taylor, G. Jeffrey↗