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Mckay, D. S.

Publications and source records attributed to Mckay, D. S..

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

A model for eruption behavior of a volcanic vent in eastern Mare Serenitatis

The origin is considered of droplets of ultramafic composition which are present in all soils collected from the mare surface at the Apollo 17 landing site. The droplets consist of homogeneous orange glass or their partially crystallized equivalent, the black droplets. These clastic deposits have a mean grain size of 40 micrometers. The droplet formation ages range from 3.5 to 3.83 b.y. It has been proposed that the droplets formed as a spray of low viscosity melt during lava fountaining. Based upon the thermal history as determined by studying olivine and particle shapes, two models for the formation of the sequence of droplets represented by samples 74001 and 74220 are presented. Both models assume, as proposed by Heiken et al. (1974), that the droplets were formed as a spray from a lava fountain and the compound forms were evidence for 'recycling' of solid, cooler droplets back into the fountain, encountering molten droplets before being deposited.

Heiken, G.↗
NASA NTRS1976

Petrographic and ferromagnetic resonance studies of the Apollo 15 deep drill core

Detailed petrographic grain size, and ferromagnetic resonance studies were performed on a representative suite of samples from the Apollo 15 deep drill core. Petrographic analyses of the 90-150 micron size fraction show a subtle upward increase in the ratio of mare to highland components. The agglutinate content at the FMR intensity normalized to FeO show that the soils in the core are generally immature to submature. The most striking feature shown by the maturity indices is a systematic decrease in maturity from the lunar surface to a depth of about 40 cm. Although other mechanisms are possible, the downward decrease in maturity can be attributed to in situ reworking over a time span of 400 m.y. at a 50% probability.

Heiken, G. H.↗
NASA NTRS1976

Comparative studies of grain size separates of 60009

Five samples from 60009, the lower half of a double drive tube, were analyzed via grain-size methods, with particle types classified and counted in the coarser grain sizes. Studies were undertaken of particle types and distributions by petrographic methods, of magnetic fractions, of the size splits and magnetic splits as analyzed by ferromagnetic resonance (FMR) techniques, of maturity (based on agglutinate content, FMR index Is/FeO, mean size of sub-cm material, magnetic fraction), of possible reworking or mixing in situ, and of depositional history. Maturity indices are in substantial agreement for all of the five samples. Strong positive correlation of percent agglutinates and percent bedrock-derived lithic fragments, combined with negative correlation of those components with percent single crystal plagioclase, argue against in situ reworking of the same soil.

Mckay, D. S.↗
NASA NTRS1976

Lithification of vitric- and clastic-matrix breccias - SEM petrography

A scanning electron microscope was used in a petrographic investigation of the matrix textures of 41 lunar breccias ranging from very friable soil clods through coherent microbreccias and tough vitric breccias to tough, fine-grained crystalline breccias. It was found that as their coherence increases, the matrices display a gradual increase in the content of glass from 1 or 2% as filaments less than 1 micron across through 5-50% as irregularly shaped patches up to 200 microns across to over 50% as continuous networks.

Phinney, W. C.↗
NASA NTRS1975

A lunar soil evolution model

Comminution, agglutination, and replenishment processes in a lunar soil are modeled by a system of time-dependent linear differential equations. In the model, a soil is subdivided into coarse-particle, fine-particle, and agglutinate fractions. The relative mass abundance of each component in a mature soil is found to be proportional to rates for the reworking processes. Evolution of the grain-size distribution from a fresh ejecta blanket to a mature soil is described quantitatively in terms of the changing proportions of the three soil constituents. If size data are available for an immature soil and a mature soil of the same system, rates for the various processes can be calculated under certain simplifying assumptions.

Mendell, W. W.↗
NASA NTRS1975

Scanning electron microscopy of a pink inclusion from the Allende meteorite

A scanning electron microscope study of a fine-grained, pin, Ca-rich inclusion from the Allende meteorite has revealed strong evidence for direct condensation of its constituent minerals from a vapor. This observation extends to the alkali-bearing phases in addition to the Ca-, Al-silicates and suggests that the feldspathoids as well as the refractory silicates are solar nebular condensates.

Grossman, L.↗
NASA NTRS1975

Morphology and composition of chalcopyrite, chromite, Cu, Ni-Fe, pentlandite, and troilite in vugs of 76015 and 76215

Vugs from 76015 and 76215 are lined with euhedral crystals of plagioclase, pyroxene, ilmenite, Ni-Fe, and troilite. Smaller crystals of chromite, pentlandite, and chalcopyrite occur on the surface of the troilite in 76015. Wire Cu and dendritic-metallic Cu occurs with metallic Ni-Fe and troilite in some vugs of 76215. Troilite in both samples may have crystallized from an immiscible sulfide liquid. With falling temperature, chalcopyrite, and pentlandite may have exsolved from the troilite in 76015. By contrast, metallic Cu may have formed in 76215 by thermal breakdown of a bornite, troilite, and Ni-Fe assemblage which originally crystallized from a low-Ni immiscible sulfide liquid.

Carter, J. L.↗
NASA NTRS1975

The source of sublimates on the Apollo 15 green and Apollo 17 orange glass samples

Elemental analyses of the thin film of micromounds which coat the surfaces of Apollo 15 green glass and Apollo 17 orange glass are reported. It is thought that Zn, Ga, Pb, Cu, Tl, S, F, and Cl condensed as a sublimate on the outside surface of these glass particles in lava fountains about 3.4 and 3.6 b.y. ago (Apollos 15 and 17, respectively). The heavy metals enriched in these samples may have been mobilized in a halide- and sulfide-rich vapor, while the source of these elements and of the glass may be a sulfide- and halide-rich pyroxenite inside the moon. The isotopic composition of lead on the surface of individual particles was determined, and the composition is considered with respect to the evolution of the source region. The lead on the surfaces is similar to lead that has been mixed into other soils and breccias at nearby sites.

Meyer, C., Jr.↗
NASA NTRS1974

Lunar deposits of possible pyroclastic origin

Orange glass droplets sampled from the Apollo 17 site were found to be both chemically and texturally homogeneous. None of these droplets, which are of possible pyroclastic origin, contained shock-damaged crystals which are common in glass produced by meteorite impacts. Black droplets are apparently the partially crystallized equivalents of the orange glass. Since chemically and texturally homogeneous glass droplets are known to form in terrestrial lava fountains of basaltic melt, the orange glasses from Apollo 11 and 17 sites and the green glasses from the Apollo 15 site may have formed in lava fountains of low-viscosity lunar basaltic magmas.

Heiken, G. H.↗
NASA NTRS1974

Vapor-phase crystallization of iron in lunar breccias

A vuggy breccia fragment from sample 67482 contains an iron crystal with a previously unreported crystal form, the trigonal trisoctahedron. The dominant habit is the trapezohedron with smaller cube and trisoctahedron faces. The geometric relationship of the iron crystal to the plagioclase-pyroxene substrate indicates that the iron crystal was the last mineral to form in the vug. The open network of plagioclase and pyroxene crystals lining the vug wall and the iron crystals with well-developed crystal faces suggests growth from a vapor phase.-

Clanton, U. S.↗
NASA NTRS1974

Petrography of Apollo 17 soils

An analysis of soils collected on the valley floor at Taurus-Littrow (dark mantle) reveals that these soils are formed by comminution of mare basalt flows and a clastic deposit consisting of black and orange glass spheres. There is no evidence for the pyroclastic origin of the dark mantle. It is found that the North Massif soils contain a large amount of mare-derived fragments being transported horizontally from the basaltic valley floor. A light mantle deposit of uniform composition including comminuted noritic and anorthositic breccia is observed. It is suggested that the light mantle is an avalanche deposit from regolith developed high on the South Massif.

Heiken, G.↗
NASA NTRS1974

Grain size and the evolution of lunar soils

Grain-size data are presented for Apollo-17 soils, and the relationship is considered between grain-size distribution and the processes which pulverize the soil, reconstitute it as agglutinates, and replenish it with fresh material. It is shown that a strong inverse correlation exists between mean grain size and standard deviation and that there is a correlation between grain size and agglutinate content whereby the finest samples have the highest agglutinate content. Two evolutionary sequences are described for the soils in which (1) reworking by micrometeorites predominates over mixing with other soils and (2) mixing predominates over reworking. It is shown that the final result of soil evolution may be a steady-state soil where pulverization by micrometeorites is balanced by agglutination and replenishment of coarser grains. A model is presented for such a soil, and it is argued that its grain-size distribution may depend on regolith thickness.-

Mckay, D. S.↗
NASA NTRS1974

Lunar surface phenomena - Solar flare track gradients, microcraters, and accretionary particles

Data are presented concerning the energy spectra of solar flare particles and the distribution of particles producing submicron diameter craters. Processes which alter the albedo and possibly the chemistry of exposed lunar surfaces are also considered. Measurements are reported of solar flare track gradients in rock 64455 which is sufficiently young to have uneroded surfaces on its sides. Attention is also given to accretionary particles adhering to host surfaces, microcraters on soil particles, and microcraters on the oriented surfaces of sample 76015 from a boulder at Station 6 of the Apollo 17 site.

Blanford, G. E.↗
NASA NTRS1973

The South Ray Crater age paradox

Relative exposure ages based on agglutinate content are calculated for 26 Apollo 16 surface and core samples. These ages increase from the northern part of the traverse to the southern part and are in general agreement with cosmogenic gas ages and particle track ages. An apparent paradox exists in which presumed ray soil from South Ray Crater is much older than the age of South Ray Crater itself as determined by a variety of methods. The most likely explanation for the paradox is that the presumed South Ray Crater soil is not ejecta from South Ray Crater but is pre-existing regolith upon which blocks and fragments from South Ray Crater are scattered.

Mckay, D. S.↗
NASA NTRS1973

Preliminary stratigraphy of the Apollo 15 drill core

The crew of Apollo 15 collected a 242-cm-long core of the regolith developed on the surface of Palus Putredinus (3 deg 39 min 20 sec E, 26 deg 26 min 00 sec N). This core consists of 42 major textural units, which range from a few millimeters to 13 cm thick. The regolith at this site was deposited layer by layer, each layer having been reworked, to some degree, by micrometeorite bombardment. The particle composition of six layers for which samples were obtained varies in a random fashion, thus supporting the heterogeneous, layered model of the regolith. The ratio of lithic fragments derived from the Apennine Front to that derived from the mare surface is about 1:1. This lithic ratio, in a regolith section 3.75 km from the base of the front, is an indication of the efficiency of lateral transport of soil by impact processes and mass wasting.

Heiken, G.↗
NASA NTRS1973

Scanning electron microscope study of Apollo 15 green glass

Apollo 15 green glass droplets and related forms show a variety of low velocity impact features which occurred at the time of formation of the droplets. Composite forms, which consist of a crystallized core on which mounds of glass adhere, indicate a sequence of core formation and crystallization, followed by impact of molten droplets. The complicated and time dependent texture and morphology of the green glass forms are best explained by formation in a volcanic lava fountain rather than by meteorite impact.

Mckay, D. S.↗
NASA NTRS1973

Apollo 16 soils - Grain size analyses and petrography

Soils from South Ray Crater, North Ray Crater, and the interray area of Station 10 have a similar provenance, containing breccia fragments of low to medium metamorphic grade and low light/dark lithic fragment ratios; these appear to be characteristic of the Cayley Formation. The primary difference between soils possibly derived from North Ray and South Ray craters is in the agglutinate content. A soil from Stone Mountain (Station 4) is characterized by breccia fragments of medium to high metamorphic grade and a high light/dark lithic fragment ratio; this soil may be derived from the Descartes Formation. Differences between the selenomorphic units, the Descartes and Cayley formations, may be lithologic as well as structural. The mean grain size varies from 84 to 280 microns, and all of the samples are poorly to very poorly sorted. There appears to be a relation between the sorting, grain size, and agglutinate content, with the finer-grained, better sorted soils containing more than 30% agglutinates. 'Shadowed' soils, collected close to large boulders, are similar in all respects to the 'reference' soils collected at least 5 m from the boulders.

Heiken, G. H.↗