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At least 253 records · Page 14

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NASA NTRS1972

The Washougal meteorite.

Optical study of the Washougal (Wash.), howardite, and determination of the ranges of composition of plagioclase and pyroxenes from measurements of densities and indices of refraction. Notable among many unique xenoliths are a round object whose morphology is that of an armored chondrule; a stratified fragment; and a centimeter-sized dunite xenolith (olivine Fa sub 12.8). The abundances of 27 elements, including all major elements and 15 trace elements are reported. To a first approximation, the composition of Washougal corresponds to a mixture of 51 wt per cent of eucritic material and 49 per cent of a diogenitic component, but excesses of some elements suggest a minor component of chondritic composition.

Jerome, D. Y.↗

NASA NTRS1974

X-ray electron study of lunar regolith from the Sea of Fertility and the Sea of Tranquillity

X-ray electron spectra were obtained of the 2p-levels of Fe, Ti, Si, Al, and Mg, and of the 1s-level in lunar regolith from the Sea of Fertility and the Sea of Tranquillity. The spectra of the same elements were recorded for approximately 30 rock forming minerals, oceanic gabbro, meteoritic eucrite, and several iron meteorites. Analysis of the results based on line positions showed that all the elements studied have the usual degrees of oxidation, and that oxygen atoms are their nearest neighbors. The predominant coordination number of Al is 4. Analysis and comparison of the Fe2p spectra in regolith, various iron meteorites, and stainless steel leads to these conclusions: Metallic iron in lunar regolith is in a highly dispersed state and is unusually stable with respect to oxidation by the oxygen of the earth's atmosphere.

Vinogradov, A. P.↗

NASA NTRS1975

Infrared spectral observations of asteroid 4 Vesta

An IR spectrum of asteroid Vesta, the first of any asteroid, has been recorded at a spectral resolution of 44/cm with a Fourier spectrometer. An electronic absorption band is observed that is assigned to an iron-rich pyroxene (pigeonite) spectroscopically similar to that found in certain eucrites. Other important rock-forming minerals such as olivine and plagioclase feldspar are not observed. There is no evidence for compositional variation with rotational phase angle. This spectroscopic picture of Vesta suggests considerable evolution including the melting and differentiation of silicates.

Larson, H. P.↗

NASA NTRS1976

Petrography of isotopically-dated clasts in the Kapoeta howardite and petrologic constraints on the evolution of its parent body

Results are presented for petrographic and electron microprobe studies of the isotopically dated A, B, C, and rho basaltic rock fragments separated from the howardite Kapoeta. Other lithic clasts and numerous mineral fragments in thin sections of Kapoeta are investigated in order to outline the range in lithology and chemistry of the source materials from which the Kapoeta meteorite is derived. The data obtained are compared to those from other meteorite and lunar samples, with particular reference to the observational consequences for the evolution of the Kapoeta parent body. A major conclusion is that there is no clearcut evidence for young magmatism on the Kapoeta parent body. The observations preclude the interpretation that the Kapoeta is a simple mixture of eucrites and diogenites. In contrast to the moon, a source of anorthositic rocks does not appear to have been present on the Kapoeta parent body which involved chiefly pyroxene. The FeO-MnO relationships suggest that the source of the materials in the Kapoeta parent planet are fundamentally related.

Dymek, R. F.↗

NASA NTRS1976

Composition of the projectiles that bombarded the lunar highlands

Twenty highland samples from Apollo 14, 15, and 17 and the eucrites Juvinas and Morre County were analyzed by radiochemical neutron activation for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Te, Tl, U, and Zn. The meteoritic components of 82 highland rocks were recalculated with the new corrections for the indigenous contribution and were classified by discriminant and cluster analysis as well as ternary diagrams, using Ir, Re, Au and Ni as diagnostic elements. To characterize these groups more fully, average abundances of meteoritic volatiles (Sb, Ge, Ag, Se, Te, and Bi) were calculated from regressions against Ir.

Gros, J.↗

NASA NTRS1976

Trace element evidence regarding a chondritic component in howardite meteorites

The concentrations of siderophiles Ni, Ge, Ru, Ir, and Au and volatiles Zn, Ga, Cd, and In in howardite meteorites were determined and are discussed along with similar data for eucrites and diogenites. The concentrations of the chondritic component in howardites are remarkably high. The concentrations in four high-siderophile howardites are comparable to those found in mature soils from the lunar highlands. The amounts of excess volatiles are roughly consistent with those expected if the chondritic component resemble CI, CM, or E4 chondrites. Evidence indicates that the howardite parent body had a radius of several hundred kilometers, and the most probable formation location was 1-2 AU from the sun.

Chou, C.-L.↗

NASA NTRS1976

Characterization of crust formation on a parent body of achondrites and the moon by pyroxene crystallography and chemistry

Single crystal X-ray diffraction and electron microprobe techniques were used to study lunar crustal pyroxenes in a cataclastic norite, a pyroxene-rich clast, and anorthosite lunar samples, and also in meteorites including diogenites, eucrites, and the Yamoto (1) howardite. The crystallographic and chemical characteristics of pyroxenes in these materials are compared and are discussed in terms of the lower stability limit of pigeonite. A mechanical mixing model of howardite is proposed.

Takeda, H.↗

NASA NTRS1977

Genesis of the Angra dos Reis and other achondritic meteorites

Major, minor, and trace element abundances were determined in seven Angra dos Reis samples, which included whole rocks, fassaite (clinopyroxene), olivine, and whitlockite separates, via sequential instrumental neutron activation analysis. The rare earth element abundance patterns and the trace element abundance patterns of this achondritic meteorite are discussed. A two-stage crystal-liquid fractionation model with source material containing olivine, orthopyroxene, and clinopyroxine is presented for the genesis of Angra dos Reis. Multilinear regression analysis was used to estimate possible composition and properties of the parent magmas. Angra dos Reis was compared with other achondrites, cumulate eucrites and nakhlites in particular. It is thought that the unique Angra dos Reis could not be related to those achondrites by crystal-liquid fractionation of the same parent body.

Ma, M.-S.↗

NASA NTRS1977

Experimental vaporization of the Holbrook chondrite

The vapor phase composition obtained by heating samples of the Holbrook L6 chondrite to 1300 C was determined quantitatively by Knudsen cell-quadrupole mass spectrometry. Maximum observed vapor pressures, produced at 1200 C, are reported for Na, K, Fe, and Ni, and the implications of the Na/K ratio are considered. The Fe and Ni data are discussed with attention to their migration in individual equilibrated chondrites. S2 (with minor SO2), H2O, and CO2 were also present in the high-temperature gas phase. Vesicles formed by the release of intrinsically derived volatiles are compared with vesicles in the Ibitira eucrite. Chondrite evolution is briefly discussed.

Gooding, J. L.↗

NASA NTRS1977

On the origin of the moon, with emphasis on bulk composition

A new analysis of altimetric, gravimetric, and seismological results, together with petrological and thermal history constraints, obtains an estimated Al2O3 content of 5.0%, 2.1 times chondritic. Hence the moon definitely has a refractory lithophile excess as well as an iron deficiency. In addition, the lunar surface is characterized by refractory siderophile depletions. The combination of these properties appears to require a previous stage of differentiation in a planetary body or bodies. Siderophile and chalcolphile depletions and dispersions in eucrites suggest that these bodies are not necessarily large. Possible mechanisms of lunar formation include impacting of a very large body into the earth; tidal disruption of sizeable differentiated planetesimals by the earth; and selective capture of differentiated planetesimal material by small moonlets. Each mechanism has its difficulties; the major unknown affecting all of them is the size distribution of planetesimals.

Kaula, W. M.↗

NASA NTRS1978

Eleven new meteorites from Antarctica, 1976-1977

Basic petrographic, mineralogic, and chemical descriptions are given for all eleven meteorites recovered by the U.S.-Japan team in Antarctica during the austral summer 1976-1977. The meteorites are: Mt. Baldr a (H6), Mt. Baldr b (H6), Allan Hills 1 (L6), Allan Hills 2 (coarsest octahedrite, chemical group IA), Allan Hills 3 (L6), Allan Hills 4 (LL3), Allan Hills 5 (eucrite), Allan Hills 6 (H6), Allan Hills 7 (L6), Allan Hills 8 (H6), and Allan Hills 9 (L6).

Olsen, E. J.↗

NASA NTRS1978

Aioun el Atrouss - Evidence for thermal recrystallization of a eurite breccia

The Aioun el Atrouss meteorite is a breccia consisting largely of angular fragments of green orthopyroxene and containing scattered clasts of basaltic composition (mostly pigeonite and calcic plagioclase). It appears to be a physical mixture of two meteorite types - diogenite (hypersthene achondrite) and eucrite (basaltic achondrite). The results of a mineral analysis are tabulated, and typical pyroxene compositions in orthopyroxene (diogenite), subophitic and granoblastic portions of the meteorite are presented.

Duke, M. B.↗

NASA NTRS1979

A petrogenetic model of the relationships among achondritic meteorites

Petrological evidence is used to support the hypothesis that although the magma source regions and parent bodies of basaltic achondrite, shergottite, nakhlite, and chassignite meteorites are clearly distinct, they may be simply related. It is proposed that the peridotites which on partial melting generated the parent magmas of the shergottite meteorites differed from those which gave rise to eucritic magmas by being enriched in a component rich in alkalis and other volatiles. Similarly, the source regions of the parent magmas of the nakhlite and chassignite meteorites differed from those on the shergottite parent body by being still richer in this volatile-rich component. These regions could have been related by processes such as mixture of variable amounts of volatile-rich and volatile-poor components in planetary or nebular settings, or alternatively by variable varying degrees of volatile loss from volatile-rich materials.

Stolper, E.↗

NASA NTRS1979

Mesosiderites and howardites - Igneous formation and possible genetic relationships

Neutron activation data are presented for major, minor, and trace elements in whole rock howardites and silicates from mesosiderites. Compositions of howardites and mesosiderites are similar and intermediate between those of eucrites and diogenites. It is indicated that mesosiderites have a higher normative silica component than howardites. It appears that this results partly from a higher content of a highly evolved igneous component and partly from in situ reduction of FeO to Fe followed by magnetic separation of metal prior to analysis. It is shown that light rare earth elements are enriched in some mesosiderites.

Mittlefehldt, D. W.↗

NASA NTRS1979

Pyroxenes in Serra de Mage - Cooling history in comparison with Moama and Moore County

Thin sections and single grains of pyroxenes from the Serra de Mage feldspar cumulate eucrites were studied by X-ray crystallography, electron microprobe and optical techniques. It was concluded that the pyroxene crystallized as pigeonite. On cooling augite was exsolved along (001) and inverted to hypersthene, with exsolution of (100) augite from hypersthene during continued slow cooling. The estimated original bulk composition of the pigeonite pyroxene is Wo10En51Fs39. The compositional data, textural relations, and existence of P2 sub 1 ca hypersthene suggest very low cooling (about 0.0004 deg C/year) below 800 deg. The Serra de Mage augite lamellae were found to be as thick or thicker than those of Moore County and Moama meteorites.

Harlow, G. E.↗

NASA NTRS1979

The distribution of zirconium and hafnium in terrestrial rocks, meteorites and the moon

It is shown that Zr and Hf are not always fractionated in terrestrial igneous differentiation or regional metamorphism. Data do support a Zr-Hf fractionation in the differentiation of the alkali olivine magma at St. Helena Island. A strong Zr-Hf fractionation exists among lunar rocks and minerals. Ilmenite is an excellent concentrator of Zr and Hf and always exhibits high Zr/Hf ratios. Chondritic meteorites exhibit rather uniform Zr abundances and Zr/Hf ratios but a distinct Zr-Hf fractionation is observed among the eucrite and diogenite achondrites.

Ehmann, W. D.↗

NASA NTRS1979

Chemical composition of Mars

The chemical composition of Mars is estimated from the cosmochemical model of Ganapathy and Anders (1974) with additional petrological and geophysical constraints. The model assumes that planets and chondrites underwent the same fractionation processes in the solar nebula, and constraints are imposed by the abundance of the heat-producing elements, U, Th and K, the volatile-rich component and the high density of the mantle. Global abundances of 83 elements are presented, and it is noted that the mantle is an iron-rich garnet wehrlite, nearly identical to the bulk moon composition of Morgan at al. (1978) and that the core is sulfur poor (3.5% S). The comparison of model compositions for the earth, Venus, Mars, the moon and a eucrite parent body suggests that volatile depletion correlates mainly with size rather than with radial distance from the sun.

Morgan, J. W.↗

NASA NTRS1979

Planetary basalts - Chemistry and petrology

Recent literature (1975-1978) on planetary basalts is reviewed. Terrestrial basalts are considered in relation to Nd and Sm isotopic studies, magma mixing, chemical and mineralogical heterogeneities in basalt source regions, and partial melting controls on basalt chemistry. Attention is also given to features of mare basalts, eucrites, and comparisons of basalts for the earth, the moon, and the parent body of basaltic achondrites.

Papike, J. J.↗