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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Compositional variation in late-stage differentiates in mare lavas, as indicated by silicate melt inclusions

Questions regarding an interpretation of data from silicate melt inclusions are considered, taking into account the fragmental nature of the record, the possible effects of cooling rate on late-stage melt composition, and the crystallization of the trapped melt. New data related to 484 new analyses are provided in a separate table. Textural and mineralogical features and bulk chemical composition for an overall characterization of late-stage differentiates are discussed. A description is presented of a grouping and recognition of rock types on the basis of late-stage inclusion analyses. Attention is given to the bimodality of potassium values and the delineation of differentiation trends. It is found that many of the problems in interpretation and much of the scatter found in the composition of silicate melt inclusions in lunar samples can be attributed to the incomplete nature of the record and to crystallization after trapping.

Roedder, E.↗
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 NTRS1975

Magma genesis by in situ melting within the lunar crust

Blue-gray breccia 73217 represents a brecciated and partially melted assemblage of plutonic rock fragments. The textural and chemical evidence leads to the conclusion that the melt was generated within the lunar crust and that subsequent cooling and crystallization occurred prior to the transportation of this rock to the surface. The melt generated in this fashion, by in situ melting at depth, of moderately Mg-rich rocks, produced a liquid enriched in Fe, Ti, K, and P which could produce sodic ferrogabbro and granitic rocks similar to the light portion of 12013, but not KREEP.

Crawford, M. L.↗
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 NTRS1979

The solubility of carbon monoxide in silicate melts at high pressures and its effect on silicate phase relations

Autoradiographic analysis and gas chromatography were used to measure the solubility in silicate melts of CO-CO2 vapors (30 to 40% CO by thermodynamic calculation) in equilibrium with graphite at temperatures up to 1700 deg C and pressures to 30 kbar. At near-liquidus temperatures CO-CO2 vapors were found to be slightly more soluble than CO2 alone. As a result of the apparently negative temperature dependence of CO solubility, the solubility of CO-CO2 at superliquidus temperatures is less than that of CO2. Melting points of two silicates were depressed more by CO than by CO2. Phase boundary orientations suggest that CO/CO + CO2 is greater in the liquid than in the vapor. The effect of the presence of CO on periodotite phase relations was investigated, and it was found that melts containing both CO and CO2 are nearly as polymerized as those containing only CO2. These results suggest that crystallization processes in planetary interiors can be expected to be about the same, whether the melts contain CO2 alone or CO2 and CO.

Eggler, D. H.↗
NASA NTRS1978

Nucleation and growth of plagioclase and the development of textures in a high-alumina basaltic melt

Detailed experiments on the nucleation and growth of plagioclase from an igneous melt are carried out to characterize the magma prior to cooling. It is shown that the nature of the melt directly preceding cooling has a strong effect on texture development, regardless of the origin of the melt. The number, size, and shape of the crystals present in a melt upon extrusion can have a drastic effect on the final textures present in the resulting rocks. Conditions necessary for the formation of poikilitic, intersertal, and porphyritic textures in basaltic rocks are defined.

Nabelek, P. I.↗
NASA NTRS1978

Dynamic crystallization and kinetic melting of the lunar soil

Dynamic crystallization and kinetic melting tests have been conducted for a lunar soil that resembles the bulk composition of the matrices of melt-rock breccias. The melting tests indicate that plagioclase and olivine can exist for finite times above their equilibrium liquidus temperatures; within 20-30 C below its liquidus temperature the sample is choked with crystals. A range of textures from radiate to porphyritic pyroxene-plagioclase granophyric to subophitic to intergranular to intersertal to very fine-grained poikilitic is found in the dynamic crystallization experiments. The number of nuclei, as deduced from the textures, increases as the melting temperature deceases from above the liquidus to below.

Lofgren, G. E.↗
NASA NTRS1979

Negative pressures and melting point depression in oxide-coated liquid metal droplets

Negative pressures and melting point depression in oxide-coated liquid metal droplets are studied. The calculation presented show the existence of large negative pressures when the oxide coating is thick enough. The change in the melting point caused by these negative pressures should be considered in studies of homogeneous crystal nucleation. Furthermore, since the negative pressure raises the entropy of the melt, it increases the entropy loss at the crystal-melt interface; the resulting increase of the surface tension could have a large effect on the homogeneous nucleation frequency.

Spaepen, F.↗
NASA NTRS1981

The nature of melt process changes in microgravity

The effects on melt impurities of the lack of buoyancy-driven convection in melts and the gas phase are outlined. Probable effects noted are: retardation of convective flow by a thin adsorbed impurity layer because of surface tension gradients (Marangoni flow); changes in the transport of volatile impurities to the melt surface and the consequent reduction of evaporation; and the change in dependence of evaporation rates on pressure due to the absence of convective flow in the gas next to the melt.

Wilcox, W.↗
NASA NTRS1982

Preliminary modeling of high pressure partial melting - Implications for early lunar differentiation

A quantitative model is presented for equilibrium crystallization of lunar magmas at high pressure, which, viewed in reverse, is equivalent to equilibrium partial melting. Data are extrapolated from simple systems, mare basalt systems, and from experiments on terrestrial compositions. Liquidus phase equilibria in a portion of the CaO-MgO-Al2O3-SiO2 system serve as a guide for predicting phase equilibria in the natural system. High pressure partial melting sequences are calculated for several proposed whole moon compositions at nominal pressure of 10 and 20 kb. Results show that compositions with chondritic Ca/Al have quite different melting paths from those with subchondritic Ca/Al, and as a result the types of magmas produced are quite different. If the moon possesses a chondritic Ca/Al ratio, models which rely on small degrees of partial melting to produce the early lunar magnetism are suspect.

Longhi, J.↗
NASA NTRS1981

Apollo 17 impact melts and their relation to the Serenitatis basin

Regional geologic relations are seen as suggesting that the distribution of highland landforms is not consistent with their derivation from a single impact event but is consistent with multiple events involving both distant basins and smaller, local craters. Thus the highland samples collected at the Apollo 17 landing site may not consist solely of Serenitatis basin ejecta but probably include both exotic ejecta and reworked local material. On the basis of these observations, it is suggested that the Apollo 17 highland melt breccias are not all derived from the Serenitatis basin impact; that is, the aphanitic melt rocks may be either other basin or local crater ejecta. It is thought that if the melt rocks collected at Apollo 17 are all derived from the same impact, the significant chemical and petrographic differences between the rocks may require modification of current models for impact melt petrogenesis.

Spudis, P. D.↗
NASA NTRS1983

Measured thermal diffusivity of Hg(1-x)Cd(x)Te solids and melts

The thermal diffusivity of Hg(1-x)Cd(x)Te melts is found to rise rapidly with temperature to values characteristic of metals. Solid and melt diffusivities for values of x from 0 to 0.3 and over a temperature range from 150 to 900 C have been determined by the laser flash method of Parker, Taylor, and Cowan. The diffusivity decreases from a maximum at x = 0 in both the solid and the liquid, with the values observed at x = 0.3 being about 40 percent of those for x = 0. The solid diffusivity for x = 0 is 1.7 sq mm/s at 150 C, decreasing to 0.7 sq mm/s at the melting point. The x = 0 liquid diffusivity increases from 0.7 sq mm/s at the melting point to 3.5 sq mm/s at 900 C.

Holland, L. R.↗
NASA NTRS1983

Some fundamental aspects of solidification in a supercooled melt

A model of dendritic growth in both supercooled pure and alloy melts is presented. In a pure melt, dendrite morphology is determined by the value of the dimensionless parameter sigma = 2 alpha (L)d(o)/sq Rr(t) whereas, in an alloy melt it is determined by the parameter sigma = 2 lambda (c)D(L)/sq Rr(t). The application of the above analysis to cylindrical and spherical growth morphologies obtained in highly supercooled melts has been discussed. An upper and lower bound for the particle or tip radius in this case has been obtained in terms of the growth rate and the initial bath supercooling.

Laxmanan, V.↗
NASA NTRS1984

Alkali gabbronorite, ultra-KREEPy melt rock and the diverse suite of clasts in North Ray crater feldspathic fragmental breccia 67975

Lunar breccia 67975 is a feldspathic fragmental breccia from North Ray crater, Apollo 16. It contains clasts of alkali gabbronorite and ultra-KREEPy mafic fragment-laden melt breccias, which are unique among Apollo 16 samples. Both are alkali- and iron-rich rocks with moderate to high REE concentrations. They more strongly resemble Apollo 14 gabbronorites and alkali anorthosites and KREEP-rich rocks than they do other Apollo 16 samples. The other clasts in 67975 are the ferroan anorthosites, feldspathic melt rocks, and magnesian granulites, which are typical of other feldspathic fragmental breccias. Examination of bulk and mineral compositions of other breccias and melt rocks suggests that alkali gabbronorite may be a minor component in other North Ray crater breccias and feldspathic melt rocks. This implies that alkali gabbronorite was a fairly early (4.0 b.y.) crustal component in the North Ray crater region.

Lindstrom, M. M.↗
NASA NTRS1984

Apollo 16 site geology and impact melts - Implications for the geologic history of the lunar highlands

The geology of the Apollo 16 site is reconsidered on the basis of data from photogeology, geochemical remote sensing, and lunar samples. The site possesses an upper surface of anorthositic gabbro and related rocks. Mafic components were deposited as basin ejecta. The events involved in its geological evolution were the Nectaris impact and the Imbrium impact. The role of large, local craters in the history of the region was to serve as topographic depressions to accumulate basin ejecta. The most abundant melt composition at Apollo 16 is an aluminous variety of LKFM basalt supplied by the Nectaris impact as ejected basin impact melt. The mafic LKFM melt may have been supplied by the Imbrium impact. More aluminous melt groups are probably derived from local, small craters. The remainder of the deposits in the region are composed of anorthositic clastic debris derived from the Nectaris basin, the local crustal substrate, and Imbrium and other basins.

Spudis, P. D.↗
NASA NTRS1984

The case for a melt matrix in plagioclase-POIK mesosiderites

Reasons are given for reclassifying former 'poikiloblastic' mesosiderites as 'poikilitic' in order to better represent their thermal histories. Attention is focused on the plagioclase-POIK mesosiderites Bondoc, Budulan, and Mincy, which all display silicate melt matrices similar to the Palisades sill and Apollo 17 mare basalts. The poikilitic textures, resorbed olivine grains, and the crystallization sequence are sufficient to reclassify the three specimens from 3B to 4B mesosiderites. Because the 4B mesosiderites are clast-laden melt rocks, their origins were probably in impact melts, which would have combined hot melts with cold clasts.

Hewins, R. H.↗
NASA NTRS1984

Mineralogical comparison and cooling history of lunar and chondritic vesicular melt breccias

Lunar sample 77135, an impact melt breccia full of vesicles, has been reinvestigated by electron microprobe and X-ray diffraction techniques and compared with a vesicular melt LL chondrite, Yamato 790964, in an attempt to understand their impact heating processes and subsequent cooling history. Notable similarities between the lunar and chondritic melt breccias include: abundant vesicles, similar pyroxene chemical zoning trends, the presence of variable amounts of clastic material, and similar chemical compositions except for K and Na contents of glass and mesostasis. Some constraints on the cooling history are estimated from Mg-Fe diffusion profiles in olivine and pyroxene. The burial depth of lunar sample 77135 during cooling was 0.2-100 m; the depth for the chondrite was probably smaller. Impact melts were probably produced and a layer of regolith retained on the parent body sufficiently thick to allow the olivines to homogenize during slow cooling.

Miyamoto, M.↗
NASA NTRS1984

Morphological stability in the presence of fluid flow in the melt

Recent experiments have shown that the presence of a vertical buoyancy-driven flow adjacent to an initially cylindrical crystal-melt interface may produce a time-dependent helical deformation of the interface, with a rotation period ranging from several minutes to many hours, depending upon the width of the melt. The temperature distribution is such that the interface is expected to be morphologically stable in the absence of fluid flow. A linear stability analysis reveals that the instability is due to a coupling between a basic hydrodynamic instability in the buoyant flow and the deformable boundary separating the two phases. The crystal-melt interface lowers the critical Grashof number of an analogous rigid-walled system by an order of magnitude for succinonitrile with a Prandtl number P = 22.8; furthermore, the hydrodynamic mode that is actually destabilized by the interface is not the least stable mode in the rigid-walled system for P = 22.8. The results show that the instability may be regarded either as a rather large alteration of a basic hydrodynamic instability by the crystal-melt interface, or as a significant modification of the morphological stability of the interface by the presence of the buoyant flow.

Mcfadden, G. B.↗