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At least 163 records · Page 9

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NASA NTRS1973

The composition and origin of the moon.

Many of the properties of the moon can be explained by early condensation processes in the solar nebula. Thermodynamic calculations show that Ca-, Al- and Ti-rich compounds condense first in a cooling nebula. The inital high-temperature mineralogy is gehlenite, spinel, perovskite, (Ca-Al)-rich pyroxenes and anorthite. Inclusions in type III carbonaceous chondrites such as the Allende meteorite are composed primarily of these minerals and are highly enriched in trace refractories such as REE relative to carbonaceous chondrites. These inclusions can yield basalt and anorthosite in the proportions required to eliminate the europium anomaly, leaving a residual spinel-melilite interior. A high-(Ca-Al) deep interior does not imply an unacceptable mean density of moment of inertia for the moon. The inferred high-U content of the lunar interior, both from the Allende analogy and the high heat flow, indicates a high-temperature interior. The model is consistent with extensive early melting, shallow melting at 3 AE, and with presently high deep internal temperatures.

Anderson, D. L.↗

NASA NTRS1972

Disproportionation of Fe2SiO4 to 2FeO plus SiO2 at pressures up to 250kbar and temperatures up to 3000 C

A sample of Fe2SiO4 (spinel) at approximately 250 kbar in a diamond anvil press was heated to approximately 3000 C for a duration of some ms using a focused light beam from a pulsed ruby laser. After quenching and unloading, X-ray diffraction patterns indicated that the portion of the sample that had been heated contained wustite and stishovite. A sample of Fe2SiO4 (fayalite) at approximately 200 kbar in a diamond anvil press has been heated to 800 C for 20 min in a furnace. After quenching and unloading, the sample was found to have concentric zones with the fayalite phase at the lowest pressure, the spinel phase at the intermediate pressure, and a dark region at the center where the pressure was highest. An X-ray diffraction pattern of the dark central region indicated the presence of wustite. A microprobe analysis of a sample produced by a similar procedure indicated that SiO2 is apparently evolved along with wustite but is not sufficiently crystalline to be detected by X-ray diffraction.

Bassett, W. A.↗

NASA NTRS1974

X-ray spectral microanalysis of composition of individual lunar regolith particles

Determinations were made of the chemical compositions of selected olivine crystals, spherical particles ranging in size from 170 to 350 micrometer, spinels, and magnetic particles. The olivines contain 30 to 50 mole percent fayalite. The spherical particles of various colors are aluminosilicate glasses, significantly enriched in CaO compared with the mean composition of the regolith. The degree of coloration depends on the FeO content and also the admixtures TiO2, MnO, and Cr2O3. Compositionally, the spinel was interpreted to be chromopicotites. Magnetic particles were shown to be complex intergrowths of nickelous iron and aluminosilicates. The composition of the metallic phase of one particle (in percent) was: Fe - 86, Ni - 13.6, and Co - 0.16 in combination with plagioclase and microinclusions of ilmenite in silicate. Kamacite was determined in another intergrowth of Fe, Ni, and Co.

Ilin, N. P.↗

NASA NTRS1974

Formation and composition of the moon

Many of the properties of the moon are discussed including the enrichment in Ca, Al, Ti, U, Th, Ba, Sr and the REE and the depletion in Fe, Rb, K, Na and other volatiles which could be understood if the moon represents a high temperature condensate from the solar nebula. Thermodynamic calculations show that Ca, Al and Ti rich compounds condense first in a cooling nebula. The initial high temperature mineralogy is gehlenite, spinel, perovskite, Ca-Al-rich pyroxenes and anorthite. Inclusions in Type III carbonaceous chondrites such as the Allende meteorite are composed primarily of these minerals and, in addition, are highly enriched in refractories such as REE relative to carbonaceous chondrites. These inclusions can yield basalt and anorthosite in the proportions required to eliminate the europium anomaly, leaving a residual spinel-melilite interior.

Anderson, D. L.↗

NASA NTRS1974

Igneous rocks from Apollo 16 rake samples

Results are reported for a study of seven holocrystalline feldspathic rocks (including a spinel troctolite and six melt rocks) and one mare basalt clast from the Apollo-16 rake samples. The composition and grain structure of each rock is described in detail. Only the spinel troctolite is considered a good candidate for a primary igneous cumulate formed during the original differentiation of the lunar crust. It is shown that the melt rocks probably resulted from shock melting followed by rapid crystallization of heterogeneous highland material and that compositional variations are probably due to mixing of various amounts of heterogeneous cumulates and KREEP components. It is suggested that the mare basalt clast may have been derived from Mare Fecunditatis, although the nearest mare to the Apollo-16 site is Nectaris.

Dowty, E.↗

NASA NTRS1975

Rocks 60618 and 65785 - Evidence for admixture of KREEP in lunar impact melts

We present evidence to support the hypothesis that the fine-grained, basaltic-textured portions of rocks 60618 and 65785 were produced by impact melting of the coarse-grained spinel-olivine anorthosite (60618) and spinel troctolite (65785) portions, coupled with admixture of approximately 33% and 63%, respectively, material of alkalic high-alumina basalt (KREEP) composition. The abundance of impact-modified rocks at the Apollo 16 site with compositional similarities to the impact melts reported here, suggests that the relations observed in these rocks are indicative of widespread impact mixing with KREEP in rocks of the lunar highlands.

Keil, K.↗

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

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 NTRS1977

Formation and composition of the moon

Many of the properties of the Moon, including the enrichment in Ca, Al, Ti, U, Th, Ba, Sr, and the REE and the depletion in Fe, Rb, K, Na, and other volatiles can be understood if the Moon represents a high-temperature condensate from the solar nebula. Thermodynamic calculations show that Ca-, Al-, and Ti-rich compounds condense first in a cooling nebula. The initial high temperature mineralogy is gehlenite, spinel, perovskite, Ca-Al-rich pyroxenes, and anorthite. Inclusions in carbonaceous chondrites such as the Allende meteorite are composed primarily of these minerals and, in addition, are highly enriched in refractories such as REE relative to carbonaceous chondrites. These inclusions can yield basalt and anorthosite in the proportions required to eliminate the europium anomaly, leaving a residual spinel-melilite interior. A deep interior high in Ca-Al does not imply an unacceptable mean density or moment of inertia for the Moon. The inferred high-U content of the lunar interior, both from the Allende analog and the high heat flow, indicates a high-temperature interior. The model is consistent with extensive early melting, with shallow melting at 3 AE, and with presently high deep internal temperatures. It is predicted that the outer 250 km is rich in plagioclase and FeO. The low iron content of the interior in this model raises the interior temperatures estimated from electrical conductivity by some 800 C.

Anderson, D. L.↗

NASA NTRS1977

Petrology of Apollo 15 black-and-white rocks 15445 and 15455 - Fragments of the Imbrium impact melt sheet

The paper describes two macroscopically similar black-and-white rocks, 15445 and 15455, which were collected from the rim of Spur Crater on the Apennine Front. The two Apollo 15 rocks are very similar in chemistry and clast population, but the matrix of 15455 is finer grained than that of 15445. The 15445 sample contains a lithic clast assemblage of plutonic/metamorphic spinel troctolite, troctolite, norite, and anorthosite, and its fine-grained vesicular black coherent matrix consists of a melt-bonded aggregate of small mineral clasts which are mainly olivine, plagioclase, and pink spinel. The two rocks are distinct from any other large samples from the Apollo 15 site. It is suggested that the rocks are samples of an impact melt sheet which forms a bedrock unit of the Apennine Front, and that this melt sheet did not form in a local small-scale event but was produced during the Imbrium impact event.

Ryder, G.↗

NASA NTRS1975

Petrologic evidence for a plutonic igneous origin of anorthositic norite clasts in 67955 and 77017

Clasts of anorthositic norite in 67955 and 77017, and several other samples, are suggested to represent material which crystallized from a silicate magma in a plutonic environment. Although no statement can be made regarding the ultimate origin of the parent melt, its composition was relatively felsic, starting within the primary field of crystallization of either plagioclase or spinel. The sequence of crystallization was: plagioclase (and/or spinel) olivine - low-Ca pyroxene - high-Ca pyroxene.

Ashwal, L. D.↗

NASA NTRS1978

Catalysts for electrochemical generation of oxygen

Single crystal surfaces of platinum and gold and transition metal oxides of the spinel type were studied to find more effective catalysts for the electrolytic evolution of oxygen and to understand the mechanism and kinetics for the electrocatalysis in relation to the surface electronic and lattice properties of the catalyst. The single crystal studies involve the use of low energy electron diffraction (LEED) and Auger electron spectroscopy as complementary tools to the electrochemical measurements. Modifications to the transfer system and to the thin-layer electrochemical cell used to facilitate the transfer between the ultrahigh vacuum environment of the electron surface physics equipment and the electrochemical environment with a minimal possibility of changes in the surface structure, are described. The electrosorption underpotential deposition of Pb onto the Au(111), (100) and (110) single crystal surfaces with the thin-layer cell-LEED-Auger system is discussed as well as the synthesis of spinels for oxygen evolution studies.

Hagans, P.↗

NASA NTRS1978

Clast assemblages of possible deep-seated /77517/ and immiscible-melt /77538/ origins in Apollo 17 breccias

Breccia samples 77517 and 77538 are composed of abundant mineral and lithic clasts set in porous, poorly sintered matrices. Clast assemblages in the two rocks are of contrasting composition and origin. Breccia 77517 has Mg-rich olivine and pyroxene and calcic plagioclase clasts, indicating limited, almost exclusively ANT-suite parentage. A significant feature is the presence of an assemblage (aluminous enstatite, forsterite, anorthite, aluminous spinel) corresponding to spinel cataclasite, a rock type of deep-seated (about 60 km) crustal origin. Breccia 77538 contains Fe-rich pyroxene and rather sodic plagioclase clasts, indicative of predominantly KREEP and/or mare derivation. An important feature is the occurrence of high-K and high-Fe lithic clasts whose compositions resemble those of immiscible-melts produced during late-stage magmatic crystallization, and which probably originated via silicate liquid immiscibility in a KREEP or mare basalt magma. Both rocks contain numerous fine-grained breccia clasts which represent material that has been modified by impact processes at or very near the moon's surface.

Warner, R. D.↗

NASA NTRS1978

Mineralogy, textures and mode of formation of a hibonite-bearing Allende inclusion

The origin of a Type A, hibonite-rich, coarse-grained inclusion is investigated with the electron microprobe and petrographic and scanning electron microscopes. The primary phases are hibonite, rhonite, Ti-Al-pyroxene, spinel, perovskite and melilite. Evidence for the crystallization of the bulk of the primary phases, hibonite and melilite, from a melt is lacking, suggesting that they may have condensed directly from a solar nebular gas instead. Primary phases were intensely altered during a later condensation event which deposited grossular, anorthite, nepheline and wollastonite in veins and cavities. Four or five condensate rims were deposited as successive layers on the outside of the inclusion. From inside to outside, they consist of perovskite + spinel, nepheline + anorthite, Ti-Al-pyroxene + diopside, hedenbergite + or - wollastonite + or - andradite and, finally, prisms of diopside and hedenbergite with wollastonite and andradite. Reverse zoning in melilite; alteration phases and rim phases, which are not stable condensates from a gas of solar composition; and details of the sequence of rim condensates all suggest that the entire condensation history of this inclusion was interrupted by changes in pressure and/or temperature and/or gas phase composition.

Allen, J. M.↗

NASA NTRS1979

The Moho as a magnetic boundary

Magnetism in the crust and the upper mantle and magnetic results indicating that the seismic Moho is a magnetic boundary are considered. Mantle derived rocks - peridotites from St. Pauls rocks, dunite xenoliths from the Kaupulehu flow, and peridotite, dunite, and eclogite xenoliths from Roberts Victor and San Carlos diatremes - are weakly magnetic with saturation magnetization values from 0.013 emu/gm to less than 0.001 emu/gm which is equivalent to 0.01 to 0.001 wt% Fe304. Literature on the minerals in mantle xenoliths shows that metals and primary Fe304 are absent, and that complex Cr, Mg, Al, and Fe spinels are dominant. These spinels are non-magnetic at mantle temperatures, and the crust/mantle boundary can be specified as a magnetic mineralogy discontinuity. The new magnetic results indicate that the seismic Moho is a magnetic boundary, the source of magnetization is in the crust, and the maximum Curie isotherm depends on magnetic mineralogy and is located at depths which vary with the regional geothermal gradient.

Wasilewski, P. J.↗

NASA NTRS1979

The upper mantle transition region - Eclogite

The upper mantle transition region is usually considered to be peridotite which undergoes a series of phase changes involving spinel and post-spinel assemblages. There are difficulties associated with attempts to explain the 220, 400 and 670 km discontinuities in terms of phase changes in a peridotitic mantle. Moreover, in a differentiated earth there should be large quantities of eclogite in the upper mantle. Eclogite is denser than Al2O3-poor mantle to depths of 670 km, but it stays in the garnet stability field to pressures in excess of those required to transform depleted mantle to denser phases such as ilmenite and perovskite. Eclogite, therefore, remains above 670 km. The seismic properties of the transition region are more consistent with eclogite than peridotite. Most of the mantle's inventory of incompatible trace elements may be in this layer, which is a potential source region for some basalt magmas. The radioactivity in this layer is the main source of mantle heat flow, 0.7 microcalorie/sq cm-sec, and drives upper mantle convection.

Anderson, D. L.↗

NASA NTRS1979

One atmosphere melting experiments on ilmenite basalt 12008

An evaluation of a crystal-fractionation model for Apollo 12 ilmenite basalts with melting experiments under controlled oxygen fugacities is reported. The crystallization sequence including olivine, chromium spinel, and pigeonite phases was determined, showing that the changes in melt composition are dominated by olivine crystallization and the decrease in MgO with a corresponding increase in CaO, Al2O3, and TiO2. It is concluded that the bulk composition of the ilmenite basalts was established by crystallization of olivine and minor spinel prior to the onset of pyroxene and plagioclase.

Rhodes, J. M.↗

NASA NTRS1979

Li, Be, and B in minerals of a refractory-rich Allende inclusion

The abundances of Li, Be, and B and the isotopic ratios of Li and B have been measured by ion microprobe in melilite, pyroxene, anorthite, and spinel grains in a coarse-grained inclusion from the Allende meteorite. Based on the measurements, it is estimated that the bulk inclusion contains 200 ppb Li, 310 ppb Be, and 18 ppm B. The B is probably due to contamination. The Li-7/Li-6 ratios in spinels, pyroxene, and melilite are indistinguishable at the + or - 15% level and lie within the uncertainty (+ or - 15%) of the range of values reported for samples of the earth and meteorites. It has been determined that this inclusion contains an excess of Al-correlated Mg-26, implying that Al-26 was once present in it. The Li-Be-B effects for two solar-system proton-irradiation models which propose to account for Al-26 in Allende inclusions have been calculated. It is found that the predicted Li-Be-B abundances and isotopic ratios are grossly different from those observed in any solar-system materials.

Phinney, D.↗