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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Further efforts to limit lunar internal temperatures from electrical conductivity determinations

A representative set of 18 electrical conductivity profiles consistent with lunar transfer function data in the 0.00001 to 0.001 Hz range is generated by means of a Monte Carlo procedure. Laboratory electrical conductivity vs temperature data extrapolated to lower and higher temperatures are used to convert the 18 profiles into temperature profiles for a series of radially homogeneous olivine-pyroxene mixtures ranging from 100% olivine to 100% aluminous orthopyroxene. The former yields selenotherms approaching the Ringwood-Essene solidus at depths near 500 km, while additions of the latter in concentrations greater than 15-30 vol% leads to cooler selenotherms which approach the solidus only at depths greater than about 1000 km. On the basis of independent geophysical constraints, the profile envelopes for compositions containing more than 15-30 vol% aluminous orthopyroxene are considered to be the most probable.

Hood, L. L.↗
NASA NTRS1982

Chemistry and phase relations of VLT volcanic glasses from Apollo 14 and Apollo 17

The VLT (very low titanium) volcanic glasses from Apollo 14 and Apollo 17 have been analyzed for the major elements and trace Ni. These glasses display compositional trends that may not result entirely from olivine fractionation. The phase relations have been determined experimentally. Olivine is the liquidus phase in the pressure interval from 0 to about 18 kbar. Pigeonite is the liquidus phase from about 18 kbar to 22 kbar or more. If these VLT volcanic glasses are samples of primary melts that had been in chemical equilibrium with olivine and low-Ca pyroxene in their source regions, then these liquids were derived from depths of 360-380 km within the moon.

Chen, H.-K.↗
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

Crystallization sequences of Ca-Al-rich inclusions from Allende - An experimental study

The results of equilibrium crystallization experiments at one atmosphere on a sample of the Type B Ca-Al-rich inclusions (CAI) of the Allende meteorite are reported. All the experiments were performed on a synthetic sample approximating the Allende CAI characteristics. The crystallization sequence observed comprised spinel at 1550 C, then melilite at 1400 C, anorthite at 1260 C, and then Ti-Al-rich clinopyroxene, formed at 1230 C. The observation that pyroxenes similar to the titaniferous fassaites found in Type B inclusions can be formed by equilibrium crystallizations of melts with Type B composition indicate that some Type B CAIs were at least partially molten. If the temperatures were not too far above the solidus, the molten condensate compositions would be similar to that occurring in gas-to-solid condensation.

Stolper, E.↗
NASA NTRS1982

Fractionation of mineral species by electrophoresis

The fractionation of fine-grained aggregates into their major components is a problem in many scientific areas including earth and planetary science. Electrophoresis, the transport of electrically charged particles, immersed in a suspension medium, by a direct current field (Bier, 1959), was employed in this study as a means of separating simulated lunar soil into its constituent minerals. In these tests, conducted in a static analytical cylindrical microelectrophoresis apparatus, samples of simulated lunar soil and samples of pure mineral constituents were placed in the chamber; the electrophoretic mobilities of the lunar soil and the individual mineral constituents were measured. In most of the suspension buffers employed separability was indicated, on the basis of differences in mobility, for all the constituent mineral species except ilmenite and pyroxene, which were not efficiently separable in any of the buffers. Although only a few suspension media were employed, the success of this initial study suggests that electrophoresis may be an important mineral fractionation option in fine-grained aggregate processing.

Dunning, J. D.↗
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.↗
NASA NTRS1983

A semiempirical method for analysis of the reflectance spectra of binary mineral mixtures

A simple semiempirical method is presented for determination of the spectral reflectance of a powdered binary mineral mixture. This technique uses a two-stream radiative transfer model (a modified Kubelka-Munk model) on a particulate medium of isotroic scatterers The particles are assumed to be much larger than the wavelength of light under consideration. This same method can be used to determine the relative proportion of components in a mixture for which the spectral reflectance is known. Binary mixtures of olivine, two pyroxenes, and magnetite are used to test this model. The theoretical and empirical results agree approximately within experimental errors.

Johnson, P. E.↗
NASA NTRS1983

Kinetic effects on trace element partitioning

A potential difficulty regarding the application of trace element abundance data to problems in igneous petrogenesis is related to the possibility that partitioning of trace elements among minerals and melt may not be an equilibrium process. It may rather be controlled by kinetic processes, specifically the interplay between crystal growth and diffusion of the trace elements in crystals and melt. The present investigation has the objective to quantify kinetic effects on trace element partitioning. Crystals of olivine, pyroxene, and plagioclase were grown rapidly from synthetic melts resembling naturally-occurring mafic melts and doped with La, Sm, and Lu to quantify the magnitude of the effect of crystal growth rate on concentration of excluded trace elements. Olivine melt partitioning failed to show any appreciable kinetic effects, while diopside/melt distribution coefficients increased by 70 percent when the crystals grew very rapidly.

Lindstrom, D. J.↗
NASA NTRS1983

Solidus and liquidus temperatures and mineralogies for anhydrous garnet-lherzolite to 15 GPa

Strong convergence is noted, in experimental data for systems pertaining to anhydrous fertile garnet-lherzolite in the 6.5-15 GPa range, either to a common temperature or to temperatures differing by only about 100 C. The major element composition of magmas generated by even minor degrees of partial melting may be similar to the composition of the primordial, bulk silicate earth in an upper mantle stratigraphic column more than 160 km deep. Whether or not the solidus and liquidus intersect, the liquidus mineralogy for undepleted garnet-lherzolite compositions is found to change from olivine, at low pressures, to pyroxene, garnet, or a solid solution of both, at pressures greater than 10-15 GPa.

Herzberg, C. T.↗
NASA NTRS1983

Replacement textures in CAI and implications regarding planetary metamorphism

Formation by a secondary metamorphic event, rather than primary crystallization from a melt or a sequential nebular condensation, is indicated by textural and chemical features of five coarse grained, Ca- and Al-rich inclusions (CAI) from the Allende meteorite which contain embayed pyroxene surrounded by melilite. It is suggested that the most probable environment for a metamorphic process (requiring the addition of Ca derived from calcite or from the introduction of a fluid phase) is that of a small planetary body, rather than the solar nebula. These results are compatible with O isotopic heterogeneities within CAI, and offer a mechanism for the production of lower temperature alteration phases, together with the rim phases found in these inclusions.

Meeker, G. P.↗
NASA NTRS1982

Lunar utilization

The resources, techniques, and purposes to which lunar materials could be put are discussed, with attention given to transporting lunar materials to cislunar space for the construction of space manufacturing and habitable facilities. A model molecule, demandite, which represents the mole fraction of all materials used in the U.S. in 1967, is used to assess the lunar resources defined during Apollo missions. It is shown that duplication of the same manufacturing, fuel, and life-support systems in space as those on earth would cost several orders of magnitude more if the materials originated on earth than on the moon. The demandite would be sent into cislunar orbit using linear electric motors. Lunar surface concentrations of pyroxenes, olivine, feldspars, ilmenite, basalts, anorthostatic rocks, and breccias are reviewed, noting that carbon in the regolith is solar-wind derived, while in lunar rocks the carbon is indigenous. Lunar mining techniques are envisioned, especially the capacity to move large masses at 1/6 the effort required on the earth.

Waldron, R. D.↗
NASA NTRS1983

Regolith breccia Allan Hills A81005 - Evidence of lunar origin, and petrography of pristine and nonpristine clasts

It is shown that the ratios of MnO/FeO in pyroxene, texture (abundant brown and swirly glass, which are typical of lunar regolith breccias) and overall composition (approximately 75 percent plagioclase) indicate a lunar origin for the regolith breccia Allan Hills A81005, presumably from an unsampled region of the moon. The rock is found to differ in detail from other regolith samples; for example, it has exceptionally low contents of Na and KREEP. In addition, a pristine clast is found to contain exceptionally coarse augite in comparison with similar Apollo samples. It is found that ALHA81005 is not perceptibly more shocked than typical Apollo regolith breccias. It is concluded that the discovery of this rock on earth strengthens the suggestion that SNC achondrites were derived by impact ejection from Mars.

Warren, P. H.↗
NASA NTRS1983

FUN with PANURGE - High mass resolution ion microprobe measurements of Mg in Allende inclusions

Isotopic ratios have been determined, at a precision level approaching that of counting statistics using beam switching, by employing PANURGE, a modified CAMECA IMS3F ion microprobe at a mass resolving power of 5000. This technique is used to determine the isotopic composition of Mg and Si and the atomic ratio of Al/Mg in minerals from the Allende inclusion WA and the Allende FUN inclusion C1. Results show enrichment in Mg-26 of up to 260 percent. Results of Mg and Al/Mg measurements on cogenetic spinel inclusion and host plagiclase crystals show Mg-Al isochrons in excellent agreement with precise mineral isochrons determined by thermal emission mass spectrometry. The measurements are found to confirm the presence of substantial excess Mg-26 in WA and its near absence in C1. Data is obtained which indicates a metamorphic reequilibrium of Mg in Allende plagioclase at least 0.6 my after WA formation. Ion probe measurements are obtained which confirm that the Mg composition in Allende C1 is highly fractionated and is uniform among pyroxene, melilite, plagioclase, spinel crystals, and spinel included in melilite and plagioclase crystals.

Huneke, J. C.↗
NASA NTRS1984

High-temperature inclusions in the Murchison meteorite

Inclusions found in type 3 carbonaceous chondrites such as the Allende meteorite are described and compared with those in the Murchison type 2 carbonaceous chondrite. Scanning electron microscope studies of the SH-6 (containing abundant hibonite) and the GR-1 (containing abundant hibonite and corundum) are discussed. Because corundum and hibonite are higher temperature condensates than the melilite and pyroxene found in the Allende meteorite, it is concluded that most refractory inclusions in the Murchison meteorite were isolated from the solar nebular gas at a higher temperature than their counterparts in the Allende meteorite. Whether the inclusion crystallized from a liquid or condensed directly from solar nebular gas is discussed.

Grossman, L.↗
NASA NTRS1983

Seventh Foray - Whitlockite-rich lithologies, a diopside-bearing troctolitic anorthosite, ferroan anorthosites, and KREEP

Seventeen nonmare samples, most of them pristine, are characterized, and implications of the new data are discussed. Five pristine samples are from Apollo 14, near the center of the KREEP-rich zone in the moon's western hemisphere. Three of them are alkali anorthosites rich in Ca-phosphate (whitlockite), which apparently crystallized from magmas with REE contents roughly 6 x those of high-K KREEP. The alkali anorthosites probably formed from Mg-rich magmas that assimilated large amounts of urKREEP, but some might have formed by metasomatism of ferroan anorthosite by urKREEP. The gabbronorite/norite classification scheme is not well suited to western hemisphere lithologies, probably due mainly to the overriding effects of longitude-petrochemistry correlations. A diopside-bearing Mg-rich lithology indicates that a low degree of melting was not a prerequisite for producing gabbroic (high-Ca pyroxene-rich) Mg-rich magmas, and suggests that some source regions of Mg-rich magmas were relatively Ca-rich. Several pristine KREEP fragments from Apollo 15 station 2 are texturally and compositionally much like other pristine KREEP, and thus reinforce the evidence that KREEP is highly uniform. The pristine anorthosites, on the other hand, demonstrate further that lunar anorthosites are diverse.

Warren, P. H.↗
NASA NTRS1983

Mineral chemistry of the shergottites, nakhlites, Chassigny, Brachina, pallasites and urelites

The mineral chemistry is compared for selected achondrites. Olivine in the ALHA 77005 and EETA 79001 shergottites, olivine-rich Chassigny and Brachina, and the nakhlites, contains Ni indicative of oxidizing conditions, whereas pallasitic and ureilitic olivines contain much lower Ni due to reducing conditions. The Brachina olivine and pyroxene have distinctively higher Fe/Mn than the shergottites and Chassigny, further indicating that Brachina is unique. The Chassigny and 77005 olivines contain lower Cr2O3 (0.03 wt. pct) than the Brachina and 79001 olivines. Values of Fe/Mn for cumulus augites in nakhlites are higher than for the shergottites, whereas those for ferropigeonites are not. The 77005 shergottite contains troilite FeS in contrast to 79001, Shergotty, Zagami, and Chassigny, which contain pyrrhotite. Further analyses are needed, but the present survey indicates that at least Brachina is not chemically cogenetic with the other 'oxidized achondrites', and that the Fe/Mn ratio of the cumulus augites in nakhlites is a problem for the assignment of the nakhlites, shergottites, and Chassigny to a single genetic group.

Smith, J. V.↗
NASA NTRS1983

I-Xe studies of individual Allende chondrules

Nine Allende chondrules and a sample of oxidized Allende matrix material are subjected to iodine-xenon studies, and the model compositions derived are compared with those of the Bjurbole chondrules. Chondrule 6 yields a well-defined isochron, with an apparent age that is later than Bjurbole whole rock. Elemental abundances suggest that all the chondrules except 6 may be pyroxene- or mesostasis-rich. The oxidized matrix sample gives a well defined isochron with an initial I-129/I-127 ratio higher than any plateaus seen in the chondrules, suggesting that the matrix predates the chondrules.

Swindle, T. D.↗