Search NASA⌕ Search

SEARCH · Search NASA

Results for “Metamorphism”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A geochemical assessment of possible lunar ore formation

The Moon apparently formed without appreciable water or other relatively volatile materials. Interior concentrations of water or other volatile substances appear to be extremely low. On Earth, water is important to the genesis of nearly all types of ores. Thus, some have reasoned that only abundant elements would occur in ore concentrations. The definition and recognition of ores on the Moon challenge the imaginations and the terrestrial perceptions of ore bodies. Lunar ores included solar-wind soaked soils, which contain abundant but dilute H, C, N, and noble gases (including He-3). Oxygen must be mined; soils contain approximately 45 percent (wt). Mainstream processes of rock formation concentrated Si, Mg, Al, Fe, and Ca, and possibly Ti and Cr. The highland surface contains approximately 70 percent (wt) feldspar (mainly CaAl2Si2O8), which can be separated from some highland soils. Small fragments of dunite were collected; dunite may occur in walls and central peaks of some craters. Theoretical extensions of observations of lunar samples suggest that the Moon may have produced ores of trace elements. Some small fragments have trace-element concentrations 10(exp 4) times higher than the lunar average, indicating that effective geochemical separations occurred; processes included fractional crystallization, silicate immiscibility, vaporization and condensation, and sulfide metamorphism. Operations of these processes acting on indigenous materials and on meteoritic material in the regolith could have produced ores. Infalling carbonaceous meteorites and comets have added water and hydrocarbons that may have been cold-trapped. Vesicles in basalts, pyroclastic beads, and reported transient events suggest gag emission from the lunar interior; such gas might concentrate and transport rare elements. Large impacts may disperse ores or produce them through deposition of heat at depth and by vaporization and subsequent condensation. The main problem in assessing lunar resources is the ignorance about the largely unexplored Moon.

Haskin, Larry A.↗
NASA NTRS1990

Tertiary structure and thermal history of the Harquahala and Buckskin Mountains, west central Arizona - Implications for denudation by a major detachment fault system

A regional geometrical model for the Whipple-Buckskin-Bullard detachment system (referred to as the Whipple detachment system) is developed. Mineral separates from samples collected in the Harquahala and Buckskin mountains, which lie in the footwall of the Whipple detachment system, are analyzed by the Ar-40/Ar-39 age spectrum technique to determine the cooling history of the mountain range and the age of the metamorphism. Based on the cooling history of the mountains and the bedrock geology of the Harquahala Mountains, the initial geometry of the Whipple detachment system is reconstructed. Next, estimates of slip on the detachment fault and extension within the upper plate terrane are used to determine the regional pattern of extension. The data on the cooling history, structural geometry, and extension pattern are combined into a geometrical model which reconciles the geological data, according to which the breakaway zones represented by the Harquahala Mountains were unroofed by movement on the gently to moderately dipping segment of a great normal fault system as it cut through the upper crust.

Richard, Stephen M.↗
NASA NTRS1990

Primary and diagenetic controls of isotopic compositions of iron-formation carbonates

Results are presented on parallel analyses of carbonate and chert microbands in segments from the early Proterozoic Dales Gorge Member of the Brockman Iron Formation (western Australia), including data on isotopic, chemical, and mineralogic variations in microbanded carbonates, cherts, and coexisting minerals in four core segments from Paraburdoo and one from Wittenoom. It is shown that patterns of variation observed in isotopic abundance and mineral composition can be consistently explained in terms of diagenetic replacement of fine-grained primary precipitates by secondary ones, rather than by mineral-dependent fractionations, metamorphism, or the influence of large volumes of water in an open system.

Kaufman, Alan J.↗
NASA NTRS1991

The interstellar connection to solar system bodies

Solar system bodies such as comets and meteorites are examined for interstellar signatures which may ultimately indicate what the protoplanetary nebula conditions were at the time the bodies formed. This involves retracing the sequence starting with a dense interstellar cloud, through the accretion disk phase of the protoplanetary nebula to the various steps in the aggregation process and finally to the physical and chemical metamorphic processes in the final body during the subsequent 4.55 billion years. Models of interstellar dust and comets which aid in such analysis are presented.

Greenberg, J. Mayo↗
NASA NTRS1991

Iodine-xenon studies of petrographically and chemically characterized Chainpur chondrules

INAA, noble gas, and petrographic studies conducted on samples of 18 chondrules and matric material from the Chainpur (LL3) indicate that the I-129/I-127 ratio, R(0), varies by a factor of more than 10 among the chondrules. This corresponds to a greater-than-50 Ma span in apparent I-Xe ages. Models which invoke either gas-dust mixing or nebular heterogeneity cannot satisfactorily explain these data, any more than can hypotheses which attribute the variations to differences in formation age, metamorphic rate, or time of aqueous alteration. It is alternatively suggested that the variations represent periods of low-grade shock events.

Swindle, T. D.↗
NASA NTRS1991

Chromite and olivine in type II chondrules in carbonaceous and ordinary chondrites - Implications for thermal histories and group differences

Unequilibrated chromite and olivine margin compositions in type II chondrules are noted to differ systematically among three of the chondrite groups, suggesting that type II liquids differed in composition among the groups. These differences may be interpreted as indicators of different chemical compositions of the precursor solids which underwent melting, or, perhaps, as differences in the extent to which immiscible metal sulfide droplets were lost during chondrule formation. Because zinc is detectable only in type II chromites which have undergone reequilibration, the high zinc contents reported for chondritic chromites in other studies probably reflect redistribution during thermal metamorphism.

Johnson, Craig A.↗
NASA NTRS1991

In situ extraction and analysis of volatile elements and molecules from carbonaceous chondrites

A laser microprobe mass spectrometer was used to measure volatiles released, on a scale of 30-50 microns, from freshly broken, sawed, and weathered surfaces in fragments of the Allende, Murchison, Coolidge, Felix, and Orgueil carbonaceous chondrites. Samples were heated to about 120 C under a vacuum of 200 ntorr and illuminated with the focused beam of a Q-switched Nd:glass laser of variable energy output (0.1-1.0 J); the gases released were analyzed using a computer-controlled mass-selective detector. The results are presented in tables and graphs and discussed in detail, with particular attention to aqueous alteration; weathering; thermal metamorphism; the distribution of sulfur-bearing phases; and differences in the amounts of volatiles in matrix, inclusions, and chondrules.

Hartmetz, C. P.↗
NASA NTRS1991

Thermoluminescence survey of 12 meteorites collected by the European 1988 Antarctic meteorite expedition to Allan Hills and the importance of acid washing for thermoluminescence sensitivity measurements

Natural and induced thermoluminescence (TL) data are reported for 12 meteorites recovered from the Allan Hills region of Antarctica by the European field party during the 1988/1989 field season. The samples include one with extremely high natural TL, ALH88035, suggestive of exposure to unusually high radiation doses (i.e., low degrees of shielding), and one, ALH88034, whose low natural TL suggests reheating within the last 100,000 years. The remainder have natural TL values suggestive of terrestrial ages similar to those of other meteorites from Allan Hills. ALH88015 (L6) has induced TL data suggestive of intense shock. TL sensitivities of these meteorites are generally lower than observed falls of their petrologic types, as is also observed for Antarctic meteorites in general. Acid-washing experiments indicate that this is solely the result of terrestrial weathering rather than a nonterrestrial Antarctic-non-Antarctic difference. However, other TL parameters, such as natural TL and induced peak temperature-width, are unchanged by acid washing and are sensitive indicators of a meteorite's metamorphic and recent radiation history.

Benoit, P. H.↗
NASA NTRS1991

Oxygen isotope studies of ordinary chondrites

Several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components (chondrules, fragments, clasts, and matrix). The whole-rock isotopic compositions reflect the iron-group of the meteorite (H, L, or LL). Isotopic uniformity of H3 to H6 and L3 to L6 are consistent with closed-system metamorphism within each parent body. LL3 chondrites differ slightly from LL4 to LL6, implying a small degree of open-system aqueous alteration and carbon reduction. On the scale of individual chondrules, the meteorites are isotopically heterogeneous, allowing recognition of the solar-nebular processes of chondrule formation. Chondrules for all classes of ordinary chondrites are derived from a common population, which was separate from the population of chondrules in carbonaceous or enstatite chondrites. Chondrules define an isotopic mixing line dominated by exchange between (O - 16)-rich and (O - 16)-poor reservoirs. The oxygen isotopic compositions of chondrites serve as 'fingerprints' for identification of genetic association with other meteorite types (achondrites and iron) and for recognition of source materials in meteoritic breccias.

Clayton, Robert N.↗
NASA NTRS1991

The Carlisle Lakes-type chondrites - A new grouplet with high Delta(17)O and evidence for nebular oxidation

The petrogenesis of the Carlisle Lakes-type chondrites and their relationship to other chondrites are studied using new petrologic data, especially on mineralogical zoning patterns, and oxygen isotopic analyses of the whole chondrites and some of chondrules. Detailed zoning profiles of mafic silicates are measured in order to determine the environment(s) in which their oxidation states are established. It is concluded that the zoning did not form during crystallization from a melt droplet chondrule but post-dated chondrule formation. Parent-body thermal metamorphism and nebular gas-solid exchange reactions accompanied by condensation of new FeO-rich olivine, utilizing existing olivine surfaces as nucleation sites are considered as hypotheses explaining the zoning. The occurrence of zoned grains in a host that is mainly equilibrated suggests that the equilibration of the Carlisle Lakes-type chondrites occurred prior to final lithification.

Weisberg, Michael K.↗
NASA NTRS1991

Low temperature annealing and cathodoluminescence studies of type 1 chondrule compositions

Preliminary results indicate that the yellow luminescing mesostases in type I chondrules can be altered by the effects of the low level thermal metamorphism. Although heat alone was insufficient to alter the CL, reheating for geologically relevant periods could have the same results as we obtained in a second series of experiments with water present. It is known that both water and solutions of sodium metasilicate greatly accelerate the devitrification of glasses. The results of the experiments that will be repeated should further clarify how the CL changes with increased thermal alteration.

Dehart, John M.↗
NASA NTRS1991

On the microphysical state of the surface of Triton

The microphysical processes involved in the pressureless sintering of particulate materials and the physical conditions likely to prevail on Triton are examined in order to investigate the processes leading to the frost metamorphism on Triton. It is argued that the presence of a well-annealed transparent nitrogen layer offers a natural explanation for most of what is seen on the surface of Triton; results of observations suggest that such a layer can form on Triton at 37 K on a seasonal time scale (about 100 earth years), provided the initial grain diameter is less than 1 micron. Grains up to 10 microns are allowed if grain growth does not hinder densification.

Eluszkiewicz, Janusz↗
NASA NTRS1992

Impact-induced thermal effects in the lunar and Mercurian regoliths

Thermal effects of micrometeoroid impact into the regoliths of the moon and Mercury, and some comparisons between the regoliths of the two bodies are presented. The impact calculations used to estimate the volumes of melt and vapor produced in the regoliths of the two bodies are described. An overview of the process of impact metamorphism in a modeled regolith target is presented, in which the roles played by impact velocity and target temperature in determining the quantities of melt and vapor are evaluated. The model impact process and fluxes are combined to estimate the production rates for impact melt and vapor on the two bodies, and the results are compared with those of previous studies. It is concluded that the rates of impact melting and vaporization on Mercury are much greater than on the moon. In a given period of time, a factor of 14 times more melt and 20 times more vapor are produced on Mercury than on the moon. A 'typical' Mercurian microcratering event produces 2.6 times more melt than its lunar counterpart; the flux calculated for Mercury is 5.5 times higher than it is at the moon.

Cintala, Mark J.↗
NASA NTRS1992

Maralinga, a metamorphosed carbonaceous chondrite found in Australia

The Maralinga meteorite was found near the village of Maralinga, South Australia in 1974, but was not recognized as a meteorite until 1989. One weathered individual was recovered with a total mass of 3.38 kg. The bulk composition and petrography of Maralinga indicate that it is a metamorphosed (petrographic type 4) carbonaceous chondrite with major similarities to the Vigarano-subtype. However, recent trace element data from the literature suggest that Maralinga should be included with the CK (Karoonda-type) carbonaceous chondrites. Maralinga is classified as an anomalous CK4 chondrite because of its abundant chondrules and refractory inclusions relative to other known members of the CK group. Maralinga contains homogeneous silicates, including Ni-bearing olivines (Fa34), high-Ca clinopyroxene, and rare orthopyroxene. Plagioclase is chemically heterogeneous and falls into two distinct compositional groups one of about An20 and an about An80 group. Highly oxidizing conditions during metamorphism of Maralinga are indicated by the abundance of magnetite and the paucity of Fe-Ni metal.

Keller, Lindsay P.↗
NASA NTRS1992

A compositional classification scheme for meteoritic chondrules

A compositionally based classification scheme for chondrules is proposed that will help in systematizing the wealth of data available and disentangling the effects of nebular and subsequent processes. The classification is not by texture or the composition of a single phase, or a mixture of these two, but rather is a comprehensive, systematic approach which uses the composition of the two main chondrule components. This scheme is applicable to over 95 percent of the chondrules and is easily applied using an electron microprobe. It stresses the original diversity of the chondrules and the complex yet facile way in which they respond to parent-body metamorphism. Results using this classification scheme suggest that arguments against an important role of chondrules in determining the compositional trends of the chondrites have been premature.

Sears, Derek W. G.↗
NASA NTRS1992

Mesosiderite clasts with the most extreme positive europium anomalies among solar system rocks

Pigeonite-plagioclase gabbros that occur as clasts in mesosiderites (brecciated stony-iron meteorites) show extreme fractionations of the rare-earth elements (REEs) with larger positive europium anomalies than any previously known for igneous rocks from the earth, moon, or meteorite parent bodies and greater depletions of light REEs relative to heavy REEs than known for comparable cumulate gabbros. The REE pattern for merrillite in one of these clasts is depleted in light REEs and has a large positive europium anomaly as a result of metamorphic equilibration with the silicates. The extreme REE ratios exhibited by the mesosiderite clasts demonstrate that multistage igneous processes must have occurred on some asteroids in the early solar system. Melting of the crust by large-scale impacts or electrical induction from an early T-Tauri-phase sun may be responsible for these processes.

Mittlefehldt, David W.↗
NASA NTRS1992

Carbon and oxygen isotope study of carbonates from highly shocked clasts of the polymict breccia of the Haughton Crater (Canada)

It is known that the release of volatiles on impact is an important controlling factor in cratering processes in carbonate terranes and in the mobility of chemical elements. In order to assess the nature and the role of carbon- and oxygen-bearing volatiles during impact-induced metamorphism of sedimentary rocks, the C-13/C-12 and O-18/O-16 ratios and carbonate contents were determined for 30 shocked clasts from the Haughton Crater polymict breccia as well as for some unshocked carbonates from the sedimentary cover adjacent to the crater. Shock-induced CO2 loss during decarbonation of calcite is known to be a function of peak pressure and ambient partial pressure of the volatile species. In our clast samples, shocked from 20 to 60 GPa, we expect about 20 to 100 percent CO2 loss and preferential depletion in C-13 and O-18 in the residual carbonate. Rayleigh model (progressive loss of CO2) and batch model (single-step loss of CO2) curves for this depletion are shown. The magnitudes of the C-13 and O-18 depletions increase with the increase of the CO2 loss. In addition, the isotopic depletions should be correlated with an enrichment in CaO and MgO in the residual solid.

Agrinier, P.↗
NASA NTRS1992

Research core drilling in the Manson impact structure, Iowa

The Manson impact structure (MIS) has a diameter of 35 km and is the largest confirmed impact structure in the United States. The MIS has yielded a Ar-40/Ar-39 age of 65.7 Ma on microcline from its central peak, an age that is indistinguishable from the age of the Cretaceous-Tertiary boundary. In the summer of 1991 the Iowa Geological Survey Bureau and U.S. Geological Survey initiated a research core drilling project on the MIS. The first core was beneath 55 m of glacial drift. The core penetrated a 6-m layered sequence of shale and siltstone and 42 m of Cretaceous shale-dominated sedimentary clast breccia. Below this breccia, the core encountered two crystalline rock clast breccia units. The upper unit is 53 m thick, with a glassy matrix displaying various degrees of devitrification. The upper half of this unit is dominated by the glassy matrix, with shock-deformed mineral grains (especially quartz) the most common clast. The glassy-matrix unit grades downward into the basal unit in the core, a crystalline rock breccia with a sandy matrix, the matrix dominated by igneous and metamorphic rock fragments or disaggregated grains from those rocks. The unit is about 45 m thick, and grains display abundant shock deformation features. Preliminary interpretations suggest that the crystalline rock breccias are the transient crater floor, lifted up with the central peak. The sedimentary clast breccia probably represents a postimpact debris flow from the crater rim, and the uppermost layered unit probably represents a large block associated with the flow. The second core (M-2) was drilled near the center of the crater moat in an area where an early crater model suggested the presence of postimpact lake sediments. The core encountered 39 m of sedimentary clast breccia, similar to that in the M-1 core. Beneath the breccia, 120 m of poorly consolidated, mildly deformed, and sheared siltstone, shale, and sandstone was encountered. The basal unit in the core was another sequence of sedimentary clast breccia. The two sedimentary clast units, like the lithologically similar unit in the M-1 core, probably formed as debris flows from the crater rim. The middle, nonbrecciated interval is probably a large, intact block of Upper Cretaceous strata transported from the crater rim with the debris flow. Alternatively, the sequence may represent the elusive postimpact lake sequence.

Anderson, R. R.↗