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At least 271 records · Page 15

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NASA NTRS1976

Mare basalt genesis - A cumulate-remelting model

In the framework of the cumulative-remelting model of lunar evolution, high-Ti basalts can be produced by extensive melting of a late-stage cumulate consisting of ilmenite-plagioclase-clinopyroxene-olivine at shallow depths immediately beneath about 60 km thick plagioclase-rich crust. Low-Ti mare basalts can be derived by small degrees of partial melting of an earlier cumulate containing mainly olivine-clinopyroxene-orthopyroxene with minor plagioclase or spinel at greater depth.

Shih, C.-Y.↗

NASA NTRS1976

Consortium investigation of breccia 67435

The paper presents results of the initial phase of a consortium investigation of lunar rock 67435, a glass coated breccia which contains a unique spinel-troctolite clast. These results include oxygen isotopic data for the host breccia, bulk composition data for the host breccia, glass coating and a large aphanitic clast, and detailed petrographic descriptions of all lithologies encountered.

Warner, R. D.↗

NASA NTRS1976

Sulfidation of 310 stainless steel at sulfur potentials encountered in coal conversion systems

The sulfidation of SAE 310 stainless steel was carried out in gas mixtures of hydrogen and hydrogen sulfide over a range of sulfur potentials anticipated in advanced coal gasification processes. The kinetics, composition, and morphology of sulfide scale formation were studied at a fixed temperature of 1065 K over a range of sulfur potentials from .00015N/sqm to 900N/sqm. At all sulfur potentials investigated, the sulfide scales were found to be multilayered. The relative thickness of the individual layers as well as the composition was found to depend on the sulfur potential. The reaction was found to obey the parabolic rate law after an initial transient period. Considerably longer transient periods were found to be due to unsteady state conditions resulting from compositional variations in the spinel layer.

Rao, D. B.↗

NASA NTRS1977

Chemical composition of crystalline rock fragments from Luna 16 and Luna 20 fines

The chemical composition (bulk, rare earth, and trace elements) of the Luna 16 mare regolith and luna 20 highland regolith is discussed. The rock samples considered are 14 basaltic rock fragments (Luna 16) and 13 rock fragments of the ANT suite (Luna 20). On the basis of bulk composition, two types of basaltic rocks have been differentiated and defined in the Luna 16 regolith: mare basalts (fundamental crystalline rocks of Mare Fecunditatis) and high-alumina basalts. The bulk analyses of rock fragments of the ANT suite also enabled distinction of two rock types: anorthositic norites and troctolites and/or spinal-troctolites (the most abundant crystalline rocks of the highland region, the landing site of luna 20), and anorthosites. The chemical compositions of Luna 16 and Luna 20 regolith samples are compared. Differences in the chemistry of the Luna 16 mare regolith and that of mare basalts are discussed. The chemical affinity between the Luna 20 highland regolith and (a) anorthositic norites and (b) troctolites and/or spinel-troctolites has been ascertained.

Cimbalnikova, A.↗

NASA NTRS1977

Mossbauer spectroscopy of iron in the Luna 20 regolith

Results of the Mossbauer effect measurements on Fe-57 in the average sample of the Luna 20 regolith, and their comparison with similar measurements of the Luna 16 samples are presented. Room temperature measurements of the nonmagnetic as well as magnetic components of the spectra were performed. By careful least-squares analysis, six quadrupole doublets in the inner parts of spectra were resolved. According to their splittings, they were interpreted as four types of iron in silicates (olivine, two inequivalent pyroxene sites, and a glassy fraction) and two types of nonmagnetic iron-titanium oxides (ilmenite and a spinel). Velocity-window measurements, were used to determine the average nickel content of (2.01 plus or minus 0.84) wt. %. These results are discussed in terms of distribution of iron among different phases. In comparison with the Luna 16 sample, the Luna 20 sample contains more olivine and less ilmenite as well as metal with a slightly higher nickel content.

Zemcik, T.↗

NASA NTRS1978

Lunar breccias, petrology, and earth planetary structure

Topics covered include: (1) petrologic studies of poikiloblastic textured rocks; (2) petrology of aluminous mare basalts in breccia 14063; (3) petrology of Apollo 15 breccia 15459; (4) high-alumina mare basalts; (5) some petrological aspects of imbrium stratigraphy; (6) petrology of lunar rocks and implication to lunar evolution; (7) the crystallization trends of spinels in Tertiary basalts from Rhum and Muck and their petrogenetic significance; (8) the geology and evolution of the Cayman Trench; (9) The petrochemistry of igneous rocks from the Cayman Trench and the Captains Bay Pluton, Unalaska Island and their relation to tectonic processes at plate margins; and (10) the oxide and silicate mineral chemistry of a Kimberlite from the Premier Mine with implications for the evolution of kimberlitic magma.

Ridley, W. I.↗

NASA NTRS1977

Trace element distribution in mineral separates of the Allende inclusions and their genetic implications

Concentrations of the rare earth elements (REE), Sc, Co, Fe, Zn, Ir, Na, and Cr were determined for mineral separates of the coarseand fine-grained types (group I and II) of the Allende inclusions. These data in combination with other data suggest that the minerals in the coarse-grained inclusions (group I) crystallized in a closed system with respect to refractory elements although a totally molten stage is precluded. The data also indicate that fine-grained (group II) inclusions were formed by condensation from a super-cooled nebular gas; REE-rich clinopyroxene and spinel were formed earlier than REE-poor sodalite and nepheline. In addition, pre-existing Mg isotope anomalies in the coarse-grained inclusions must have been erased during the heating stage.

Nagasawa, H.↗

NASA NTRS1977

Experimental melting relations of 63545, 76015, and 76055

The experiments discussed were conducted for the purpose of placing additional constraints on the origin of lunar highlands noritic compositions. The sample 63545 represents a fine-grained, crystalline melt rock consisting of pink spinel, plagioclase, divine, interstitial glass, minor oxides, and metal. According to Chao (1973), 76055 is an olivine-bearing micronorite hornfels with abundant xenocrysts and xenoliths. The sample 76015 is a vesicular, poikilitic impact melt with a homogeneous matrix. The obtained experimental melting relations of 63545, 76055, and 76015, are examined, taking into account experimental petrology and trace element chemistry of mare basalts. It is concluded that the studied compositions do not represent magmas derived by partial melting of either cosmic or differentiated source regions at any pressure in the moon. Presently available information would seem to favor an origin by impact-fusion of several highlands components.

Delano, J. W.↗

NASA NTRS1978

The moon - Composition determined by nebular processes

The Ganapathy-Anders seven-component model is used as the basis for an analysis of conditions in the early solar nebula as they pertain to the formation of the moon. Calculations incorporating improved geological data and petrological constraints are presented in terms of a model moon which meets trace element restrictions and conforms to known parameters of heat flow, density, and moment of inertia ratio, ie., 40 ppb U, and a core of 2% by weight. It is noted that a melt of the model composition approximates that of Apollo 15 green glass, together with a residuum of olivine, plus 3-4% spinel.

Morgan, J. W.↗

NASA NTRS1975

Minor elements in lunar olivine as a petrologic indicator

Accurate electron microprobe analyses (approximately 50 ppm) were made for Al, Ca, Ti, Cr, Mn, and Ni in Mg-rich olivines which may derive from early lunar crust or deeper environments. Low-Ca contents consistently occur only in olivines from dunitic and troctolitic breccia: spinel troctolite and other rock types have high-Ca olivines suggesting derivation by near-surface processes. Rock 15445 has olivine with distinctly low CaO (approximately 0.01 wt.%). Chromium ranges to higher values (max.0.2 oxide wt.%) than for terrestrial harzburgites and lherzolites but is similar to the range in terrestrial komatiites. Divalent chromium may be indicated over trivalent Cr because olivines lack sufficient other elements for charge balance of the latter. NiO values in lunar specimens range from 0.00 to 0.07 wt.% and a weak anticorrelation with Cr2O3 suggests an oxidation state effect. Al2O3 values are mostly below 0.04-wt.% and show no obvious correlation with fragment type. TiO2 values lie below 0.13-wt.% and seem to correlate best with crystallization rate and plagioclase content of the host rock. High values of Al2O3 and TiO2 reported by other workers have not been confirmed, and are probably wrong.

Steele, I. M.↗

NASA NTRS1975

Evolution of the lunar highland crust

The evolution of three distinct element associations in the lunar highland crust is discussed in terms of the Taylor-Jakes model which involves melting of most of the moon during accretion. Sources for (1) high Ca, Al, Sr, Eu, (2) high Mg and Cr, and (3) high K, REE, Zr, Hf, Nb are suggested. Bombardment by large projectiles during the differentiation process causes melting and mixing, which produces a wide range of compositions in the crust. The formation of dunite, troctolite, high-, medium-, and low-K Fra Mauro basalts, and rocks close to the olivine-spinel-plagioclase peritectic point is considered.

Taylor, S. R.↗

NASA NTRS1978

Static and dynamic cyclic oxidation of 12 nickel-, cobalt-, and iron-base high-temperature alloys

Twelve typical high-temperature nickel-, cobalt-, and iron-base alloys were tested by 1 hr cyclic exposures at 1038, 1093, and 1149 C and 0.05 hr exposures at 1093 C. The alloys were tested in both a dynamic burner rig at Mach 0.3 gas flow and in static air furnace for times up to 100 hr. The alloys were evaluated in terms of specific weight loss as a function of time, and X-ray diffraction analysis and metallographic examination of the posttest specimens. A method previously developed was used to estimate specific metal weight loss from the specific weight change of the sample. The alloys were then ranked on this basis. The burner-rig test was more severe than a comparable furnace test and resulted in an increased tendency for oxide spalling due to volatility of Cr in the protective scale and the more drastic cooling due to the air-blast quench of the samples. Increased cycle frequency also increased the tendency to spall for a given test exposure. The behavior of the alloys in both types of tests was related to their composition and their tendency to form scales. The alloys with the best overall behavior formed alpha-Al2O3 aluminate spinels.

Barrett, C. A.↗

NASA NTRS1979

The Moho as a magnetic boundary

Magnetic data are presented for mantle derived rocks: peridtites from St. Pauls rocks, dunite xenoliths from the kaupulehu flow in Hawaii, as well as peridolite, dunite and eclogite xenoliths from Roberts Victor, Dutoitspan, Kilbourne Hole, and San Carlos diatremes. The rocks are paramagnetic or very weakly ferromagnetic at room temperature. Saturation magnetization values range from 0.013 emu/gm to less than 0.001 emu/gm. A review of pertinent literature dealing with analysis of the minerals in mantle xenoliths provides evidence that metals and primary Fe3O4 are absent, and that complex CR, Mg, Al, and Fe spinels dominate the oxide mineralogy. All of the available evidence supports the magnetic results, indicating that the seismic MOHO is a magnetic boundary.

Wasilewski, P. J.↗

NASA NTRS1979

Some TEM observations of Al2O3 scales formed on NiCrAl alloys

The microstructural development of Al2O3 scales on NiCrAl alloys has been examined by transmission electron microscopy. Voids were observed within grains in scales formed on a pure NiCrAl alloy. Both voids and oxide grains grew measurably with oxidation time at 1100 C. The size and amount of porosity decreased towards the oxide-metal growth interface. The voids resulted from an excess number of oxygen vacancies near the oxidemetal interface. Short-circuit diffusion paths were discussed in reference to current growth stress models for oxide scales. Transient oxidation of pure, Y-doped, and Zr-doped NiCrAl was also examined. Oriented alpha-(Al, Cr)2O3 and Ni(Al, Cr)2O4 scales often coexisted in layered structures on all three alloys. Close-packed oxygen planes and directions in the corundum and spinel layers were parallel. The close relationship between oxide layers provided a gradual transition from initial transient scales to steady state Al2O3 growth.

Smialek, J.↗

NASA NTRS1979

Refractory-element-rich inclusions in CM meteorites

Refractory-element-rich inclusions of a variety of types occur in CM meteorites. Based on detailed study of Murchison and more limited investigations of Murray, Nogoya, Cold Bokkeveld and Mighei, the most common of these inclusions are small spinel-hibonite bodies rimmed with diopside. Bulk chemical compositions are estimated to be approximately 67% Al2O3, 21% MgO, 5.5% CaO, 5.5% TiO2, and 1% SiO2. Although this chemical composition does not agree closely with current theoretically predicted compositions of early condensate assemblages, the inclusions have many features which suggest that they are indeed early condensates. These include texture, mineralogical composition, sequence of minerals and magnesium isotopic composition of hibonite. The CM refractory inclusions exhibit several differences from those observed in Allende and other CV meteorites. These probably record variations in time, place or physical conditions of origin for the two cases.

Macdougall, J. D.↗

NASA NTRS1978

Melt inclusions in Luna 24 soil fragments

Optical examinations of 28 slides of Luna 24 soil fragments revealed melt inclusions in grains of olivine, plagioclase, spinel, and ilmenite as well as interstitial inclusions. In contrast with Apollo samples, the Luna 24 samples contain sulfide melt inclusions, which indicates that saturation with respect to an iron sulfide melt took place throughout much of the crystallization history, even while olivine was crystallizing. The Luna 24 silicate-melt inclusions have recorded a more extensive differentiation toward higher iron magmas than have the Apollo inclusions, but they have also recorded some inexplicably low aluminum values.

Roedder, W.↗

NASA NTRS1978

Feldspathic granulite 79215 - Limitations on T-fo2 conditions and time of metamorphism

Feldspathic granulite 79215, an annealed polymict breccia which has a bulk composition between anorthositic gabbro and gabbroic anorthosite, contains numerous oxide complexes in the matrix. An Ar-39-Ar-40 stepwise heating experiment gives a well-defined plateau corresponding to an age of 4.03 + or - 0.02 AE. The polmict character of this breccia and the variability of the complexes suggest that they formed as a consequence of reactions between spinel-rich clasts and matrix under the high-T low-P conditions of an ejecta blanket. The duration of annealing is estimated to have been less than 10 million yr; the absence of a KREEP component may indicate an inhomogeneous distribution of this component at the lunar surface at 4.0 AE.

Mcgee, J. J.↗

NASA NTRS1978

Petrology of a sequence of pyroclastic rocks from the valley of Taurus-Littrow /Apollo 17 landing site/

Thirteen samples of core 74001/2, collected at Shorty Crater by Apollo 17, have been analyzed. The samples, taken from the core section below 5.5 cm and representing most of the major stratigraphic units described by Nagle (1978), consist entirely of whole and fragmented orange and black droplets. The grain shape, degree of crystallinity, breakage, vesicularity, predominant olivine shapes, and phenocryst content of about 18,000 droplets were investigated. The crystalline droplets were found to contain olivine and ilmenite as major phases and pyroxene, Cr-spinel and metallic Fe as minor phases. The grain shape, degree of crystallization, olivine shape and olivine composition suggest that a wide range of cooling rates is represented. The upper part of the core section (above 5.5 cm) has undergone in situ reworking by micrometeorites. The 74001/2 samples are believed to be from an ultramafic pyroclastic deposit brought to the surface by the Shorty Crater impact and originally formed by a lava fountain active in the Taurus-Littrow valley 3.5 b.y. ago. The sequence represented in the sample was most likely deposited over a very short period of time.

Heiken, G.↗