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At least 1,171 records · Page 65
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NASA NTRS1982

IUE observations of R Aquarii

High- and low-dispersion observations made in 1980 are compared with earlier observations. Certain ultraviolet lines are apparently constant in the face of Mira pulsation and rotation and orbital motion of the hypothetical hot companion. Other line features and the ultraviolet continuum vary significantly but not in phase with the Mira. The Mg II doublet profile continued to show an asymmetry that is attributable to 200 km/s mass ejection. The remarkable levelness of the 1300-3100 A continuum (in ergs/sq cm s A) is confirmed, and the suggestion of a hot companion photosphere under circumstellar olivine-smoke extinction is discussed.

Johnson, H. M.↗
NASA NTRS1982

Evidence for aqueous alteration in a carbonaceous xenolith from the Plainview /H5/ chondrite

The compositions of the mineral components of two inclusions within a CM-like clast in the Plainview (H5) chondrite are determined. The inclusions have the morphologies of an Allende-like, coarse-grained CAI and an amoeboid olivine inclusion, respectively. Major constituents of the altered inclusions are found to be calcite, Mg-Fe-rich phyllosilicates, Fe-Ti oxides, and an Al-rich phyllosilicate, and it is suggested that the alteration process would have required transport of Ne, Cl, H2O, CO2, and FeO. Liquid water appears to be the medium in which the alterations took place, due to the presence of hydrous phases and significant quantities of iron required to produce the mineral assemblages now present from the inferred starting materials.

Nozette, S.↗
NASA NTRS1982

Troctolite 76535 - A study in the preservation of early isotopic records

The lunar rock considered in the present investigation is a coarse-grained troctolite granulite containing about 58(vol)% plagioclase, 37% olivine, 4% pyroxene, and less than 1% accessory phases with a texture which indicates formation as a cumulate at depths between 10 and 30 km followed by an extended period of slow cooling. A description is presented of noble gas studies of separated minerals from 76535. The quantity of fission xenon from the in situ decay of Pu-244 provides further evidence for different, mineral-specific, isotopic closure times. The presented data shows that 76535 loses its surface-correlated xenon component upon disaggregation. No other xenon component is lost. The presence of solar gases in 76535 would seem to argue in favor of the external acquisition of the parentless extinct isotope effects and consequently favor 'thermal diffusion' and 'adsorption' over local redistribution models.

Caffee, M.↗
NASA NTRS1982

The relationship of the lunar regolith less than 10 micrometer fraction and agglutinates. I - A model for agglutinate formation and some indirect supportive evidence

The first part of a study of the 'less than 10 micrometer' soil fraction and agglutinates is concerned with the chemical systematics of the considered fraction of lunar soils, taking into account a model for agglutinate formation based on the fusion of the finest fraction (FFF). Attention is given to some evidence which supports the FFF model. The evidence is based on some indirect approaches to an estimation of the composition of the fused soil component. It is found that the 'less than 10 micrometer' soil fraction from all Apollo sites except Apollo 16 (which can be explained) is more feldspathic and enriched in incompatible elements (e.g., K and Th) than the bulk soil. It is concluded that these systematics result from simple comminution in which feldspar breaks down to finer sizes than pyroxene and olivine and the fine-grained incompatible-element-enriched mesostasis concentrates in the 'less than 10 micrometer' soil fraction.

Papike, J. J.↗
NASA NTRS1982

Petrology of Apollo 15 station 9A surface and drive tube soils

Modal analysis data are presented for six samples from the upper part of the Apollo 15 lunar core 15010/011 in order to further investigate the maturation profile of the core and to estimate the source rock contribution. The core data are compared with those of the adjacent soils 15531 and 15601. The soils analyzed are relatively immature and remarkably homogeneous. Surface soil 15531 is the most immature one, which is attributed to the fact that it was sampled from the rim of a relatively recent 3 m-diameter crater and thus contains an admixture of fresh bedrock material ejected by this cratering event. The major source of rock contribution to the soils is from petrographically identifiable mare basalts (about 89% to the core and to 15601 and about 87% to 15531). Olivine basalts and quartz normative basalts occur in an approximate ratio of 3:1; contributions of KREEP basalts and the Front are relatively minor.

Griffiths, S. A.↗
NASA NTRS1982

A chemical study of individual green glasses and brown glasses from 15426 - Implications for their petrogenesis

Systematic chemical analyses of individual Apollo 15 green glasses were performed in order to: (1) study chemical variations among them; (2) understand their petrogenesis and source region; and (3) study their possible relationships with mare basalts in general. Brown glasses were also analyzed in order to study their chemical variations and their petrogenetic relationships to green glasses and mare basalts. The chemical composition of green and brown glasses is shown and variation diagrams of Sc, Cr2O3, FeO, and Co abundances in green glasses are presented. Igneous fractionation, two component magma mixing, and partial melting of heterogeneous source materials are alternate scenarios to explain strong observed correlations. The composition of green glasses indicates that they were derived by partial melting of the fractionated cumulate source materials formed from a magma ocean which had experienced certain degrees of olivine and plagioclase fractional crystallization.

Ma, M.-S.↗
NASA NTRS1982

SEM, optical, and Moessbauer studies of submicrometer chromite in Allende

New scanning electron and optical microscope results are presented showing that sub-micrometer chromite is abundant along healed cracks and grain boundaries in Allende chondrule olivine. Some wider healed cracks also contain pentlandite and euhedral Ni3Fe grains. Also reported are Moessbauer measurements on Allende HF-HCl residues confirming a high Fe(+++)/Fe(++) ratio.

Housley, R. M.↗
NASA NTRS1982

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

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.↗
NASA NTRS1982

Lunar anorthosite 60025, the petrogenesis of lunar anorthosites, and the composition of the moon

The mineral chemistry of the lunar anorthosite 60025 is investigated, and a model for the differentiation of the moon is proposed based on these findings. Among other results, it is concluded that 60025 is a mixture of pieces from a related sequence of anorthosites, and that this sequence was generated by near-perfect accumulate growth during strong fractional crystallization. The parent liquid of the most primitive anorthosite was saturated with olivine, plagioclase, pigeonite, and chromite, and evolved to one saturated with plagioclase, pigeonite, high-Ca clinopyroxene, and ilmenite. The steep slope of anorthosites on an Mg (mafics) vs. Ab (plagioclase) diagram is a result of the very low alkali content of the magma and of the original magma ocean. The bulk moon had low Al2O3, a sub-chondritic Ca/Al ratio, and REE abundances and patterns which were probably close to chondritic. In addition, mare basalt sources were found to be too magnesian and some contain too much high Ca clinopyroxene to be directly or simply complementary to a floated anorthosite crust.

Ryder, G.↗
NASA NTRS1982

Evidence for primitive nebular components in chondrules from the Chainpur chondrite

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.↗
NASA NTRS1982

Microchondrule-bearing clast in the Piancaldoli LL3 meteorite - A new kind of type 3 chondrite and its relevance to the history of chondrules

Electron microprobe, scanning electron microscope, and petrographic analyses of the microchondritic clast of the Piancaldoli LL3 chondrite are reported and compared with other type three chondrites. The clast, like other type three chondrites, has a fine-grained Fe-rich opaque silicate matrix, sharply defined chondrules, abundant low-Ca clinopyroxene and minor troilite and Si and Cr-bearing metallic Fe, Ni. However, the very high model matrix abundance, unique characteristics of the chondrules, and absence of microscopically observable olivine indicate that the clast is a new type of type three chondrite. It is concluded that the microchondrules were formed by the same process that formed normal-sized chondrules in type three chondrites: melting of preexisting dustballs. It is suggested that dust grains were mineralogically sorted in the nebula before aggregating into dustballs.

Rubin, A. E.↗
NASA NTRS1982

Chemical composition of the Howardite Parent Body deduced from Kapoeta primary 'mafic' magmas

Chemical data are presented for three 'mafic' clasts extracted from the Kapoeta howardite. Bulk compositions and petrologic observations suggest that two of these lithic clasts represent olivine-plagioclase bearing orthopyroxenites. Chondrite-relative refractory large ion lithophile abundances of two of the clasts are inferred to represent primary Mg-rich magmas produced by extensive (greater than about 70%) partial melting of a source composition indistinguishable from the silicate fraction of average CH-CL ordinary chondrites, with the exception of the depletion of the alkalis Na and K by a factor of 13 + or - 1 in the source composition. A metal-free and volatile depleted Kapoeta Parent Body (KPB) is subsequently deduced and is shown to compare very well with other similarly derived Achondrite Parent Body and Howardite Parent Body estimates but not to parent body estimates derived from inferences based on eucrite phase equilibrium studies. Other implications suggest that the KPB is heterogeneous with respect to Fe/Mg ratios.

Smith, M. R.↗
NASA NTRS1982

Primary igneous carbon in ureilites - Petrological implications

The ureilite meteorites are carbonaceous olivine-pyroxene achondrites. They typically contain up to 4 wt.% carbon (carbonaceous matrix) as graphite, diamond, and lonsdaleite. Shock degradation has effectively obliterated primary textures in the carbonaceous matrix of previously described ureilites, a factor that has hampered efforts to explain the origin of this material. In contrast, the Antarctic ureilite ALHA78019 displays perfectly preserved primary textures in the carbonaceous matrix characterized by euhedral graphite blades intergrown with Fe-Ni metal and sulfide (diamonds are absent). This petrographic feature suggests that most graphite in ureilites originated by crystallization from a C-rich metallic phase. Assuming that fO2 is controlled by C-CO-CO2 reactions, the compositions of silicates and metals in ureilites imply a two-stage redox history. The noble gases and rare earths of ureilites are discussed in light of this model.

Berkely, J. L.↗
NASA NTRS1982

The survival of solar flare tracks in interplanetary dust silicates on deceleration in the earth's atmosphere

Pulse heating experiments on magnesium-rich olivine and pyroxene, two silicates often found in micrometeorites collected in the stratosphere, show that iron ion tracks remain detectable in the transmission electron microscope for temperature maxima up to approximately 600 C. Assuming thermal emissivities near unity, this implies that micrometeorites with surface densities above 1 mg/sq cm are likely to have their track record erased, and that tracks in reentrant or low-density micrometeorites smaller than 7 microns in size are likely to survive atmospheric entry.

Fraundorf, P.↗
NASA NTRS1982

Petrography, mineral chemistry and origin of Type I enstatite chondrites

The petrography and mineralogy of four Type I enstatite chondrites were examined by optical and cathololuminescent and electron microprobe means to discern particular chemical and mechanical processes present during solar system condensation. The specimens examined included sections of the Indarch, Abee, Kota-Kota, and Adhi-Kot chondrites. Textural interpretations were performed, as well as chemical analyses of the degree of similarity of the clinoenstatite, olivine, accessory silicates, metal, schreibersite, troilite, oldhamite, and niningerite grains in each sample. Simple models of progressive condensation either at equilibrium or with mechanical removal of early condensates were ruled out due to the occurrence of both blue and red enstatite crystals in metal clasts. A need for sequential processes of mixing, melting, crystallization, condensation, fracturing, and mechanical aggregation are suggested as necessary to model the formation mechanisms of the mineral aggregates.

Leitch, C. A.↗
NASA NTRS1983

Lunar and Planetary Science Conference, 13th, Houston, TX, March 15-19, 1982, Proceedings. Part 2

The second part of the proceedings of the Thirteenth Lunar and Planetary Science Conference considers sedimentary processes and crustal cycling on Venus, a model for the formation of the earth's core, evidence of resurfacing in the lunar nearside highlands, the geology of Tethys, thermal stresses in planetary elastic lithospheres, the petrology and comparative thermal and mechanical histories of clasts in breccia 62236, lunar paleointensity data and its implications for the origin of lunar magnetism, and a model for the accumulation of solar wind radiation damage effects in lunar dust grains. Also discussed are fluid inclusions in stony meteorites, nuclear track and compositional studies of olivines in CI and CM chondrites, the impact of an asteroid or comet in the ocean and the extinction of terrestrial life, cooling rates for glass-containing lunar compositions, and the homogeneity of lava flows.

Boynton, W. V.↗
NASA NTRS1983

Homogeneity of lava flows - Chemical data for historic Mauna Loan eruptions

Chemical analyses of basalts collected from the major historic eruptions of Mauna Loa volcano show that many of the flow fields are remarkably homogeneous in composition. Despite their large size (lengths 9-85 km), large areal extents (13-114 sq km), and various durations of eruption (1-450 days), many of the flow fields have compositional variability that is within, or close to, the analytical error for most elements. The flow fields that are not homogeneous vary mainly in olivine content in an otherwise homogeneous melt. Some are composite flow fields made up of several, apparently homogeneous subunits erupted at different elevations along the active volcanic rifts. Not all volcanoes produce lavas that are homogeneous like those of Mauna Loa. If studies such as this are to be used to evaluate compositional diversity in lavas where there is a lack of sampling control, such as on other planets, it is necessary to understand why some flow units and flow fields are compositionally homogeneous and others are not, and to develop criteria for distinguishing between them.

Rhodes, J. M.↗
NASA NTRS1983

The dark side of Iapetus

Spectrophotometry of the Saturn satellite Iapetus in the 0.3-1.0 micron wavelength range shows the dark hemisphere to be very red, similar to a few asteroids and the earth's moon, but with no spectral features implying olivine or pyroxene. Near-IR spectrophotometry in the 1.4-2.5 and 3.0-3.8 micron ranges shows water ice absorption bands that may be due to the polar caps' intrusion into the dark hemisphere. Three hypotheses for the formation of the dark hemisphere are discussed in light of the observational data, and it is found most likely that debris from Phoebe or other unknown outer satellites of Saturn impacts the dark hemisphere of Iapetus as Poynting-Robertson drag causes the debris to spiral toward Saturn. The high velocity impacts preferentially remove ice from the satellite's surface, yielding the enrichment of included carbonaceous material intrinsic to Iapetus.

Cruikshank, D. P.↗