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At least 1,063 records · Page 59

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NASA NTRS1977

Electronic absorption spectra of lunar minerals

Techniques for obtaining information on the crystal chemistry of transition-metal ions from measurement of the electronic absorption spectra of lunar minerals are reviewed along with the theory of spectral interpretation. Typical polarized absorption spectra are examined for lunar pyroxenes, pyroxferroite, olivine, and plagioclase feldspars. Oxidation states of Fe, Ti, and Cr in lunar minerals are discussed, and conditions under which they crystallized are considered. It is shown how information on the gross mineralogy and petrology of different regions of the moon's surface may be extracted from remote reflectivity measurements of that surface.

Vaughan, D. J.↗

NASA NTRS1977

Lunar seismicity, structure, and tectonics

Seismic data is used to develop a lunar model consisting of five zones. These include a 50-60 km thick crust characterized by seismic velocities appropriate to plagioclase rich materials, the 250 km thick upper mantle characterized by seismic velocities consistent with an olivine-pyroxene composition, the 500 km thick middle mantle characterized by a high Poisson ratio, the lower mantle characterized by high shear wave attenuation, and a core of radius between 170 and 360 km characterized by a greatly reduced compressional wave velocity.

Lammlein, D. R.↗

NASA NTRS1977

Distribution of the pre-solar component in Allende and other carbonaceous chondrites

Detailed analyses of separated phases of several Allende Ca-Al-rich inclusions are reported which reveal a consistent pattern of large O-16 enrichments in spinel, pyroxene, and sometimes olivine, and small O-16 enrichments in melilite, feldspathoids, and grossular. The heterogeneous distribution of the O-16 excesses, together with their enhancement in minerals believed to be early solar nebular condensates, suggests the existence of pre-solar carriers of the isotopic anomaly, probably grains or molecules with oxygen which was nearly pure O-16. Pre-solar grains of corundum or spinel, and pre-solar molecules of SiO are considered possibilities. Excess O-16, relative to terrestrial abundances, has been found in all samples of C2, C3 (the Allende is this kind), and C4 carbonaceous chondrites which have been analyzed. No direct correlation has yet been observed between the oxygen anomalies and isotope anomalies in neon, magnesium, or xenon.

Clayton, R. N.↗

NASA NTRS1976

Chemical aspects of agglutinate formation - Relationships between agglutinate composition and the composition of the bulk soil

Attention is centered on the nature and intensity of geochemical fractionation accompanying agglutination of several size fractions of the immature Apollo-16 soil sample 67460, from North Ray Crater. The soil features coarse mean grain size about 150 microns, low (20 wt.%) magnetic agglutinate content, and a bimodal grain size distribution. The magnetic fraction included both agglutinates and magnetic non-agglutinates (glass-free microbreccias with 30-60 micron native FeNi grains hosted in a matrix of pyroxene, ilmenite, and olivine). The separation process residue contained nonmagnetic agglutinates with compositions near pure plagioclase. The magnetic agglutinate fraction appears selectively enriched in ferromagnesian elements to the partial exclusion of plagioclase elements. Agglutinate glass chemistry based solely on magnetic separation is deprecated on the basis of the results.

Via, W. N.↗

NASA NTRS1976

Composition and origin of Luna 16 aluminous mare basalts

The mineralogy and petrology of 58 lithic fragments, 52 of which are basaltic, in the Luna 16 samples were studied, with textures, and mineral and bulk compositions determined by petrographic and electron microprobe techniques. These mare basalt fragments differ from other mare basalts in being aluminous (11-20%) which results in plagioclase and (olivine) microphenocrysts; moreover, they have very low-FeO and MgO and high-CaO, FeO/MgO, and normative diopside contents.

Kurat, G.↗

NASA NTRS1976

Variations in chemical composition of Apollo 15 mare basalts

Chemical analyses of 30 different Apollo 15 mare basalts were examined to evaluate the effects of closure on the pearson moment correlation coefficient. It is shown possible to describe the Apollo 15 mare basalts in terms of an opaque, an olivine/pyroxene, an anorthite, and a KREEP component, if significant correlations are identified using the expected correlations as null values. Using Q-mode cluster analysis and nonlinear mapping, it is possible to recognize three groups of the mare basalts, groups 1 and 2 belonging to the olivine normative basalt cluster and group 3 to the quartz normative cluster.

Butler, J. C.↗

NASA NTRS1976

Petrology of 79215 - Brecciation of a lunar cumulate

The paper considers the modal variation and bulk composition, the petrography, and the mineral chemistry of lunar sample 79215, a holocrystalline, nearly monomict breccia that is petrologically and chemically distinct from the majority of lunar highland breccias. The bulk composition of the rock and its REE abundances suggest that the precursor was a plagioclase-olivine cumulate.

Bickel, C. E.↗

NASA NTRS1976

Mineralogy and petrology of complex breccia 14063,14

Breccia 14063,14 is a complex, probably pre-Imbrian, unmetamorphosed breccia dominated almost entirely by mineral clasts. Electron-probe and microscope examination showed at least four distinct lithologies in a centimeter-sized thin-section. Examination of each lithology showed or suggested the following contributing rock types or mineralogies: (1) dunite with minor chromite, very high-Mg ilmenite and bronzite; (2) spinel troctolite with olivine and Mg-Al spinel; (3) high-Ti mare-like basalt with high-Mg ilmenite and coarse pyroxene; (4) low-KREEP noritic breccia; (5) anorthosite; (6) very Ni-rich Fe metal.

Steele, I. M.↗

NASA NTRS1975

Petrographic analysis of Apollo 16 samples 66083,1 and 67943,1

Sample 66083,1 was a 0.5 g sample of 2-4 mm fines from a clod of white impact ejecta. Petrography of 12 fragments of it reveals the following types of fragments: a breccia with a glassy matrix containing about 20-30% of crystal fragments, a fragment of partly devitrified glass, a fine-grained feldspar-rich rock containing plagioclase laths with about 10% of interstitial pyroxene and olivine, a breccia consisting of clasts of plagioclase and plagioclase-rich rock in a fine-grained microcrystalline feldspathic groundmass, a fragment of plagioclase clasts in a fine-grained groundmass of plagioclase and ferromagnesians with some opaques, and a crystalline rock made of subequal amounts of plagioclase and ferromagnesians with some opaque material. For sample 67943,1, all but two fragments could be classed as brecciated anorthosites.

Mason, B.↗

NASA NTRS1977

Vesta - The first pyroxene band from new spectroscopic measurements

Spectral reflectance measurements of asteroid 4 Vesta were obtained using a silicon vidicon spectrometer with a resolution of 2 to 4 thousandths of a micron. A flow chart illustrating the data reduction procedure is given, and the location, absorptivity, and bandwidth of an absorption band detected in the near infrared region are described. The absorption band has been interpreted as due to electronic absorptions in ferrous iron in sixfold coordination in the pyroxene, pigeonite. The heightened spectral resolution obtained from the silicon vidicon imaging system permits determination of the relative calcium content of the pyroxene (10 to 12%). Furthermore, the symmetry of the absorption band implies an absence of olivine, which is commonly associated with pyroxene in terrestrial and meteoritic mineral samples. Support for these conclusions is found in spectral analyses of pyroxene, as well as in spectral reflectance measurements of 4 Vesta obtained by other observers.

Mcfadden, L. A.↗

NASA NTRS1977

Internal structure and properties of Mars

Theoretical physical models of the Martian interior are presented in the light of recent and revised data and constraints. These models include thermal evolution, densities, and seismic-wave velocities. The interior of Mars appears to be earthlike in many respects. Although thermal models indicate that Mars has passed its peak of evolution, it may still have an asthenosphere and may be moderately active tectonically. Mars has an Fe-FeS core with a radius of 1500-2000 km. The mantle is enriched in FeO with an olivine composition of about Fo75. Theoretically determined seismic-wave velocities are relatively well constrained in the mantle, with upper-mantle P-wave velocities ranging from 7.64 to 7.80 km/sec. However, there are wide variations in P-wave velocity in the core, dependent on composition. The shadow zone due to the core is larger than earth's.

Johnston, D. H.↗

NASA NTRS1977

Asteroid surface materials: Mineralogical characterizations from reflectance spectra

Mineral assemblages analogous to most meteorite types, with the exception of ordinary chondritic assemblages, have been found as surface materials of Main Belt asteroids. C1- and C2-like assemblages (unleached, oxidized meteoritic clay minerals plus opaques such as carbon) dominate the population throughout the Belt, especially in the outer Belt. A smaller population of asteroids exhibit surface materials similar to C3 (CO, CV) meteoritic assemblages (olivine plus opaque, probably carbon) and are also distributed throughout the Belt. The majority of remaining studied asteroids (20) of 65 asteroids exhibit spectral reflectance curves dominated by the presence of metallic nickel-iron in their surface materials. The C2-like materials which dominate the main asteroid belt population appear to be relatively rare on earth-approaching asteroids.

Gaffey, M. J.↗

NASA NTRS1977

Lunar igneous rocks and the nature of the lunar interior

Lunar igneous rocks, properly interpreted, can give useful information about mineral assemblages and mineral chemistry as a function of depth in the lunar interior. Though intensely brecciated, terra rocks reveal, in their chemistry, evidence for a magmatic history. Partial melting of feldspathic lunar crustal material occurred in the interval 4.6 to 3.9 Gy. Melting of ilmenite-bearing cumulates at depths near 100 km produced parent magmas for Apollo 11 and 17 titaniferous mare basalts in the interval 3.8 to 3.6 Gy. Melting of ilmenite-free olivine pyroxenites (also cumulates?) at depths greater than 200 km produced low-titanium mare basalts in the interval 3.4 to 3.1 Gy. No younger igneous rocks have yet been recognized among the lunar samples and present-day melting seems to be limited to depths greater than 1000 km.

Hays, J. F.↗

NASA NTRS1977

To the problem about the origin of lunar maria and continents (Moessbauer investigations)

A comparative study of Mossbauer spectra of regolith returned by the Luna 16 and Luna 20 spacecraft is presented. The Mossbauer spectra of the mare regolith differs significantly for all fractions from the spectra for the same fractions of continental regolith. The total quantity of iron is 1.85 times greater in the mare regolith. There is 2.4 times less olivine in the mare region than in the continental region. The pyroxene component of the mare regolith is less homogeneous in composition (contains more augite and glass) and is present in larger quantities. Ilmenite was found only in the mare regolith. In the continental region, the predominant titanium-containing phase is ulvospinel. The mare regolith contains more metallic iron, which is more finely dispersed and contains less nickel. Troilite is found in the maria region. Based on these differences, it is concluded that the formation of continental rocks occurred at an earlier stage of crystallization from the melt and at higher temperatures and higher partial pressures of oxygen. The mare basalts crystallized from a more reduced magma, apparently in a later process.

Malysheva, T. V.↗

NASA NTRS1977

Laboratory simulation of infrared astrophysical features

Intermediate resolution emission spectroscopy was used to study a group of 9 terrestrial silicates, 1 synthetic silicate, 6 meteorites and 2 lunar soils; comparisons were made with the intermediate resolution spectra of Comet Kohoutek in order to determine which materials best simulate the 10um astrophysical feature. Mixtures of silicates which would yield spectra matching the spectrum of the comet in the 10um region include: (1) A hydrous layer lattice silicate in combination with a high temperature condensate; (2) an amorphous magnesium silicate in combination with a high temperature condensate and (3) glassy olivine and glassy anorthite in approximately equal proportions.

Rose, L. A.↗

NASA NTRS1978

Nature and evolution of the meteorite parent bodies: Evidence from petrology and metallurgy

The physical as well as chemical properties of the meteorite parent bodies are reviewed and it is concluded that many differentiated meteorites were likely formed in asteroidal-sized parents. A new model is developed for the formation of pallasites at the interface between an iron core and olivine mantle in differentiated bodies only about 10 km in diameter, which are later incorporated into a second generation of larger (100 km) parent bodies.

Wood, J. A.↗

NASA NTRS1977

Rare earth and trace element geochemistry of a fragment of Jurassic seafloor, Point Sal, California

Rocks from an ophiolite suite once on the seafloor were analyzed for rare earth elements (REE), Sc, Co, Na2O, Cr, Zn and FeO. Strontium isotope exchange noted in some of the lavas is attributed to basalt-seawater interaction; the Ce abundance in smectite- and zeolite-bearing lavas may also be due to prolonged exposure to seawater. The higher grades of metamorphic rock, however, show no variation from the usual flat or slightly light REE depleted profiles. Plutonic igneous rock, all light REE depleted, have total REE abundances varying by a factor of 100 between the dunites and diorites. In order of decreasing REE abundance are hornblende, clinopyroxene, plagioclase, orthopyroxene and olivine. Calculations of REE contents of liquids in equilibrium with early cumulative clinopyroxenes suggest that the parent to the stratiform sequence was more depleted in light REE than the parent to the lava pile.

Menzies, M.↗

NASA NTRS1977

Mineralogy, petrology and chemistry of ANT-suite rocks from the lunar highlands

Anorthositic-noritic-troctolitic (ANT) rocks are the oldest and most abundant rocks of the lunar surface, and comprise about 90% of the suite of the lunar highlands. Consideration is given to the mineralogy, petrology, bulk chemistry, and origin of ANT-suite rocks. Problems associated in classifying and labeling lunar highland rocks because of textural complexities occurring from impact modifications are discussed. The mineralogy of ANT-suite rocks, dominated by plagioclase, olivine and pyrozene, and containing various minor minerals, is outlined. The petrology of ANT-suite rocks is reviewed along with the major element bulk composition of these rocks, noting that they are extremely depleted in K2O and P2O5. Various models describing the origin of ANT-suite rocks are summarized, and it is suggested that this origin involves a parental liquid of high-alumina basalt with low Fe/Fe+Mg.

Prinz, M.↗