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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Petrology of impactites from Lake St. Martin structure, Manitoba

The 23-km Lake St. Martin crater was produced 200 to 250 million years ago in Archean granitic to amphibolic gneiss, overlain by 400 to 500 m of Ordovician to Devonian limestone and dolomite. In the present paper, a schematic model of the field geology, petrology, and geochemistry is presented. The scenario is built in part on the calculations of Kieffer and Simonds and observations made on the Lake St. Martin structure.

Simonds, C. H.↗
NASA NTRS1981

Europa's petrological thermal history

A path of geophysical development which takes into account the petrological sequence is presented to describe the thermal evolution of Europa. On the basis of considerations of the likely temperature-pressure conditions in the Europa zone of the circumjovian nebula during the condensation of the satellite on the one hand and of the early thermal evolution on the other, it is argued that most of the water of Europa can be in the form of hydrated silicates in a thick convective boundary layer or throughout the body of the satellite. Such silicates would include the minerals chlorite and/or serpentine, and brucite, and could be maintained in hydrated states by solid state convection within the body. The model predicts that the ice layer on the surface of Europa is considerably thinner than the 150 km that had been estimated before the Voyager mission.

Ransford, G. A.↗
NASA NTRS1981

Mineralogy, petrology, and trace element geochemistry of the Johnstown meteorite - A brecciated orthopyroxenite with siderophile and REE-rich components

The compositional and petrologic characteristics of the Johnstown meteorite show it to contain uncontaminated and unbrecciated orthopyroxenite clasts of cumulative origin that (1) must have undergone subsolidus recrystalization, (2) are parental to the brecciated matrix, and (3) show no evidence of a xenolithic, meteoritic contribution to the matrix except for contamination by the projectile which crushed it on impact. The trapped liquid was not introduced in the impact process. The variability of such trace elements as the light rare earth elements, and the presence of plagioclase and olivine in only one of the thin sections studied, demonstrates the heterogeneity of coarse-grained diogenites on a millimeter scale and the difficulty of obtaining representative samples of such meteorites. The data presented indicate that this meteorite is a monominct breccia.

Floran, R. J.↗
NASA NTRS1980

Spinel cataclasites in 15445 and 72435 - Petrology and criteria for equilibrium

The problem of establishing the existence of equilibrium among the coexisting phases in the rock is addressed by presenting petrographic and mineral chemistry data on a new spinel cataclasite from 15445 (clast H) and data more extensive than those previously available on two clasts in 72435. Criteria useful in reconstructing the original petrology of these and other spinel cataclasites are analyzed by considering equilibrium among the different phases, that is, the mono- or polymict nature of these cataclasized samples. Finally, the role of impact processes in disturbing the equilibria is discussed.

Baker, M. B.↗
NASA NTRS1982

Petrology of suevitic lunar breccia 67016

The present investigation is concerned with a petrologic study of one of the largest samples of feldspathic fragmental breccia, 67016. Evidence presented indicates that 67016 (and by implication the entire suite of feldspathic fragmental breccias) was originally deposited in a single impact event, possibly in a setting geologically analogous to terrestrial suevite. 'Feldspathic fragmental breccia' is the term adopted for the friable, light-colored breccias with abundant dark clasts which are the predominant rock type on the rim and walls of North Ray crater. Macroscopically 67016 is a light-gray breccia with approximately 20% dark clasts, approximately 10% white lithic clasts, and scattered single grains of plagioclase, mafic silicates, opaques, metal, and spinel.

Norman, M. D.↗
NASA NTRS1982

The Apollo 15 yellow impact glasses - Chemistry, petrology, and exotic origin

The Apollo 15 yellow impact glasses are characterized by moderate TiO2 (about 4.8%) and high abundances of the large ion lithophile elements (e.g., K, P, Hf, Th, REE). Since the chemistry of these glasses cannot be duplicated by any combination of local components presently known to occur at the Apollo 15 landing site, these yellow glasses seem to be exotic to that area. Chemical and petrologic constraints suggest that these samples were produced by impact melting of an immature mare regolith developed upon an unusual variety of mare basalt. It is speculated that the target basalts were the youngest lava flows known to exist on the moon (i.e., Eratosthenian-age lavas in Oceanus Procellarum and Mare Imbrium). Specific tests are proposed for evaluating this provocative hypothesis.

Delano, J. W.↗
NASA NTRS1982

Lunar regolith - Petrology of the less than 10 micron fraction

Petrographic data for the less than 10 micron fraction from four lunar surface soils are presented in an attempt to characterize the modal mineralogy of this fraction. Individual grains were studied with a scanning/transmission electron microscope with an attached energy dispersive spectrometer. Energy dispersive analytical data are presented, and comparative modal petrology of the soils is shown. Also presented are grain size histograms and diagrammatic representation of comparative modal data for the soils, as well as the feldspathic glass/mafic glass ratio, plagioclase/mafic mineral ratio, and SiO2 modal percent for different size fractions of the four types of soil. The modal results are consistent with chemical data regarding feldspathic and KREEP enrichment in the finest fraction. Grain-size distributions are inconsistent with a fine-grained exotic component derived from distant sources.

Devine, J. M.↗
NASA NTRS1982

The lunar regolith - Chemistry, mineralogy, and petrology

The data base on the lunar regolith is surveyed to form a synthesis of the lunar regolith chemistry, mineralogy, and petrology. The data were derived from samples collected by the Apollo missions 11-17 and the Luna 16, 20, and 24 probes. The missions were sent to sample formations and areas which typified the common observed features of the lunar surface. Drive tubes were used to extract samples from beneath the surface in order to study the relationship between the regolith and the bedrock, as well as to identify the processes that formed the regolith, which is regarded as the prime source of raw materials for early lunar industrial activities. Regolith origins are now understood to be destructive processes of comminution and constructional processes of agglutinate formation. Mixing occurs on the local scale, although lateral transport is inefficient on the moon. The usual contents of the fraction of regolith less than 10 microns in diameter are Al2O3, CaO, Na2O, K2O, light REE, and Th.

Papike, J. J.↗
NASA NTRS1984

Mineralogic and petrologic studies of meteorites and lunar samples

During a 13 year period beginning in 1971, the Extraterrestrial Petrology Group examined lunar soils from all 6 Apollo missions and those returned by the Soviet Luna 16, Luna 20, and Luna 24 missions. In addition, the properties and apparent origin of the carbonaceous chondrites were examined. Chondrules, calcium-aluminum-rich inclusions (CAI) and the fine grained matrix materials that accompany chondrules and CAI's in primitive meteorites were investigated. The effects of planetary hydrothermal alteration of matrix materials in the C1 chondrite was also investigated. Full length papers and extended abstracts published during the grant are listed chronologically.

Wood, J. A.↗
NASA NTRS1983

Oxygen isotopic heterogeneities, their petrological correlations, and implications for melt origins of chondrules in unequilibrated ordinary chondrites

Clayton et al. (1976, 1982) established that equilibrated ordinary chondrites (EOC's) can be divided into the H- and L-groups on the basis of their oxygen isotopic composition. The present investigation is concerned with new oxygen isotopic analyses of petrologically well-characterized individual chondrules from the unequilibrated chondrites Dhajala (H3,4), Hallingeberg (L3), and Semarkona (LL3). A study is conducted regarding the implications of isotopic/petrologial correlations for the origin of chondrules in ordinary chondrites. It is found that the oxygen isotopic heterogeneities among chondrules are reminiscent of the bulk elemental and phase compositional heterogeneities among the same and other chondrules as reported by Gooding et al. (1979, 1980). It is concluded that chondrules formed possibly as a result of the melting of preexisting materials which were both chemically and isotopically heterogeneous.

Gooding, J. L.↗
NASA NTRS1984

Mineralogical-petrological characterization of near-earth asteroids

The mineralogy and petrology of 17 near-earth asteroids are characterized using reflectance spectroscopy with ground-based telescopes. Assuming the surfaces are composed of cosmically abundant materials, the presence of certain mineralogical species can be determined from diagnostic absorption features and spectral characteristics which have been studied under known laboratory conditions and understood in terms of crystal-field theory. With one possible exception, the surface composition of near-earth asteroids consists of common rock-forming minerals such as olivine, pyroxene, and phyllosilicates. Opaque components are present but cannot be mineralogically identified with existing experimental data. The spectrum of 2201 Oljato cannot be interpreted in terms of common rock-forming minerals and is examined for cometary features because its high orbital eccentricity suggests a possible relation to comets, but no common cometary features are identified. The predominance of mafic silicate absorption features in spectra of near-earth asteroids (compared to the majority of main-belt asteroids) may be a primary compositional feature or may be the signature of relatively fresher asteroid material.

Mcfadden, L. A.↗
NASA NTRS1984

Petrology and geochemistry of lunar dimict breccia 61015

The results of a petrological and geochemical study of the dimict breccia 61015 at the Apollo 16 site are presented and discussed. The breccia consists predominantly of granulated anorthosite and impact melt rock of very high aluminum-basalt composition. It probably formed in the floor of an expanding crater cavity when impact melt generated within the cavity was injected into underlying anorthositic bedrock and solidified rapidly, the anorthosite and melt rock being fragmented by deformation in the later stages of the impact. A possible source crater for the breccia is identified. The breccia has been affected by at least one recent small impact, which produced internal shock-induced melting of the breccia and injected and coated the rock with externally derived melts. The TiO2 content of the coating and vein glasses establish that they cannot be melted soils; their composition requires a mafic, low-TiO2 protolith component.

James, O. B.↗
NASA NTRS1984

Petrology of Apollo 11 regolith breccias

Petrographic and mineral chemical data for 16 Apollo 11 regolith breccias show that: (1) the regolith breccias differ from soil 10084 with respect to agglutinate content, glass population, plagioclase compositions, and proportions of high-K mare and low-K mare basalt components; (2) the A-11 breccias and soil have highland components that are similar both in abundance and petrology; and (3) lunar regolith breccias provide a better comparison with howardites than do lunar soils. The data and observations are consistent with formation of the regolith breccias from immature soil. It appears that little or no highland material has been added to the Tranquillitatis regolith since the formation of the breccias.

Simon, S. B.↗
NASA NTRS1984

Petrologic profile of Apollo 16 regolith at Station 4

The Apollo 16 double drive tube core 64001/2 (total depth about 60 cm) consists of four petrologic units based on the modal abundance of lithic, monomineralic, and other particles in the 20-500 micron size range of samples from 12 levels. Variation in the abundance of particles derived directly from bedrocks is low and the core soils probably represent only one set of source rocks. The chemical signature of an excessively high mare basalt component at about 42 cm correlates with an excess of regolith breccias, which may then be the physical carrier. The core soils as a whole show a systematic size-composition relationship that may be attributed to a large-scale macroscopic reworking and the consequent masking of any or all previous surface process related mixing event. However, on a much smaller scale (about 0.5 cm), individual soil layers seem to have evolved more via mixing than via in situ reworking.

Basu, A.↗
NASA NTRS1986

Isotopic, petrologic and biogeochemical investigations of banded iron-formations

It is recognized that the first occurrence of banded iron-formations (BIFs) clearly predates biological oxygenation of the atmosphere-hydrosphere system and that their last occurrences extend beyond plausible dates of pervasive biological oxygenation. For this reason, and because enormous quantities of oxidizing power have been sequestered in them, it is widely thought that these massive, but enigmatic, sediments must encode information about the mechanism and timing of the rise of atmospheric O2. By coupling isotopic analyses of iron-formation carbonates with biogeochemical and petrologic investigations, we are studying (1) the mechanism of initial sedimentation of iron; (2) the role of iron in microbially mediated diagenetic processes in fresh iron-formation sediments; and (3) the logical integration of mechanisms of deposition with observed levels of banding. Thus far, it has been shown that (1) carbonates in BIFs of the Hamersley Group of Western Australia are isotopically inhomogenous; (2) the nature and pattern of isotopic ordering is not consistent with a metamorphic origin for the overall depletion of C-13 observed in the carbonates; (3) if biological, the origin of the C-13 depleted carbonate could be either respiratory or fermentative; (4) iron may have been precipitate d as Fe(3+), then reduced to Fe(2+) within the sediment; and (5) sedimentary biogeochemical systems may have been at least partially closed to mass transport of carbonate species.

Hayes, J. M.↗
NASA NTRS1985

SNC meteorites - Clues to Martian petrologic evolution?

Shergottites, nakhlites and the Chassigny meteorites (SNC group) may have originated on Mars. The shergottites are medium-grained basalts, the nakhlites are pyroxenites and the Chassigny is a dunite. The SNC group is petrologically diverse but differs from all other known achondrites in terms of mineral chemistry, the redox state, the oxygen isotopic composition and the radiometric ages. The SNC stones are mafic and ultramafic cumulate rocks with mineralogies that indicate rapid cooling and crystallization from tholeiitic magmas which contained water and experienced a high degree of oxidation. The characteristics suggest formation from a large parent body, i.e., a planet, but not earth. The estimated ages for the rocks match the estimated ages for several mapped Martian volcanoes in the Tharsis region. Additionally, the elemental and isotopic abundances of atmospheric gases embedded in melts in the SNC stones match Viking Lander data for the Martian atmosphere. However, reasons are cited for discounting the possibility that a large meteorite(s) collided with Mars about 180 myr ago and served as the mechanism for ejecting the SNC stones to earth.

Mcsween, H. Y., Jr.↗
NASA NTRS1985

Petrology of the Apollo 12 highland component

Petrologic study of highland rock fragments handpicked from the Apollo 12 coarse fines confirms the KREEPy nature of the A-12 highland components and the importance of norites and alkali anorthosites. This is in contrast to the calcic, non-KREEPy A-16 and A-11 highland lithologies. The results add to the complexity of the igneous lunar highland rocks, which models for the formation of the lunar crust must take into account. A model involving moonwide differentiation followed by serial magmatism and heavy brecciation seems to be required. Results also show that non-KREEPy highland materials are present at the A-12 site and may represent Copernican and Imbrium ejecta, whereas the KREEPy materials may represent pre-Imbrian terra, as at the A-14 site.

Simon, S. B.↗