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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Mineralogy and origin of Fra Mauro fines and breccias.

Textural features, glassy spherule and glassy aggregate contents, and size-frequency distributions of lithic components of the regolith fines indicate that the Fra Mauro regolith of the smooth terrain is a highly reworked accumulation of debris derived primarily by impact comminution of annealed breccias. Analyses of the glassy spherules suggest that mare-derived debris must amount to less than 5% of the regolith, but exotic materials having the composition of the Fra Mauro breccias (highland-like) cannot be recognized. Breccia samples from the Fra Mauro site include (1) regolith breccias derived by lithification of local regolith material, (2) texturally and compositionally unique white rock breccias that may have been derived from ancient ejecta buried beneath the Fra Mauro formation, and (3) annealed breccias that are excavated samples of the Fra Mauro formation. The latter were deposited as heated impact ejecta, probably by avalanches produced by the Imbrian event and were annealed in situ in a thermal regime perhaps equivalent to that responsible for the pyroxene-hornfels facies of metamorphism in terrestrial rocks.

Quaide, W.↗
NASA NTRS1977

Effects of thermal metamorphism on compositions of lunar spinels

The reported study represents an attempt to evaluate experimentally the compositional and textural changes that are likely to be observed in the Fe-Ti-Cr spinels of lunar igneous rocks by subsequent thermal metamorphism. The Apollo 12 igneous rock, 12018,43, was chosen for this investigation because an earlier study of another fraction of this rock by El Goresy et al. (1971) has reported an almost continuous trend of spinel compositions between Cr-Ulvoespinel and Ti-chromite. The nature of the compositional changes in the heated spinels (and ilmenites) is found to be such that the changes cannot be explained by intragranular adjustments alone. In the heated sample, pyroxene grains adjacent to the high-Ti spinels show a decrease in FeO, and an increase in MgO and Al2O3 at the interface. This may account for the MgO depletion and a part of the FeO enrichment in the high-Ti spinels. It is believed that the heating experiment demonstrates that thermal metamorphism of lunar basalts is likely to modify the compositions of their preexisting spinels (and ilmenites).

Misra, K. C.↗
NASA NTRS1988

Geological indicators for impact: The anomalous case of the Vredefort structure, South Africa

The Vredefort Dome is located within and almost central to the Witwatersrand basin in its presently known extent. It exposes a central Archean granite core which is surrounded by a collar of supracrustal rocks. These collar rocks outline a strong polygonal geometry. The Archean core is comprised of two concentric zones, the Outer Granite Gneiss (OGG), and the core central Inlandsee Leucogranofels (ILG). The rocks of the inner core display granulite facies metamorphism, while the OGG is in amphibolite facies. The inner core is believed from recent drill hole information to be underlain by mafic and ultramafic gneisses, the extent of which cannot be assessed at present. A fairly broad zone of charnockites separates the OGG and ILG domains. This zone is characterized by a high concentration of pseudotachylite and ductile shearing. Whereas a number of other domical structures are located within or surrounding the Witwatersrand basin, the Vredefort structure is anomalous, in that it has: a partly polygonal geometry; extensive alkali intrusives in the northwestern sector; granophyre dykes (ring-dykes peripheral to the contact collar-basement and NW-SE or NE-SW trending dykes within the Archean basement); contact metamorphism of the collar supracrustal rocks; the overturning of collar supracrustals in the northern sectors; deformation phenomena widely regarded as representing shock metamorphism (pseudotachylite, (sub)planar microdeformation features in quartz, shatter cones and occurrences of high-P quartz polymorphs); a positive 30 mgal gravity anomaly; and high amplitude magnetic anomalies. Recent geophysical, structural and petrological evidence pertinent for the identification of the processes that led to the formation of the Vredefort structure are summarized.

Antoine, L. A. G.↗
DOE OSTI2023

The iron oxidation state of Ryugu samples

The Hayabusa2 mission sampled Ryugu, an asteroid that did not suffer extensive thermal metamorphism, and returned rocks to the Earth with no significant air exposure. It therefore offers a unique opportunity to study the redox state of carbonaceous Cb-type asteroids and evaluate the overall redox state of the most primitive rocks of the solar system. An analytical framework was developed to investigate the iron mineralogy and valence state in extraterrestrial material at the micron scale by combining x-ray diffraction, conventional Mössbauer (MS), and nuclear forward scattering (NFS) spectroscopies. An array of standard minerals was analyzed and cross-calibrated between MS and NFS. Then, MS and NFS spectra on three Ryugu grains were collected at the bulk and the micron scales. In Ryugu samples, iron is essentially accommodated in magnetite, clay minerals (serpentine–smectite), and sulfides. Only a single set of Mössbauer parameters was necessary to account for the entire variability observed in MS and NFS spectra, at all spatial scales investigated. These parameters therefore make up a fully consistent iron mineralogical model for the Ryugu samples. As far as MS and NFS spectroscopies are concerned, Ryugu grains are overall similar to each other and share most of their mineralogical features with CI-type chondrites. In detail however, no ferrihydrite is found in Ryugu particles even at the very sensitive scale of Mössbauer spectroscopy. The typical Fe 3+ /Fe tot of clay minerals is much lower than typical redox ratios measured in CI chondrites (Fe 3+ /Fe tot = 85%–90%). Furthermore, magnetite from Ryugu is stoichiometric with no significant maghemite component, whereas up to 12% of maghemite was previously identified in the Orgueil's so-called magnetite. These differences suggest that most CI meteorites suffered terrestrial alteration and that the preterrestrial composition of these carbon-rich samples was less oxidized than previously measured. However, it is not clear yet whether or not the parent bodies of CI chondrites were as reduced as Ryugu. Finally, the high spatial resolution of NFS allows to disentangle the redox state and the crystal chemistry of iron accommodated in serpentine and smectite. The most likely polytype of serpentine is lizardite, containing <35% of Fe 3+ , a fraction of which being tetrahedrally coordinated. Smectite is more oxidized (Fe 3+ /Fe tot > 65%) and mainly contains octahedral ferric iron. In conclusion, this finding implies that these clays formed from highly alkaline fluids and the spatial variability highlighted here may suggest a temporal evolution or a spatial variability of the nature of this fluid.

58 GEOSCIENCES↗
NASA NTRS1974

Petrology of the highlands massifs at Taurus-Littrow - An analysis of the 2-4 mm soil fraction

The petrography, phase chemistry, and Ar-40/Ar-39 ages of 2-4 mm fragments from the soils of both mare and highlands stations sampled by Apollo 17 are studied. It is found that the massifs consist of a complex stratigraphy of interlayered noritic breccias of varying metamorphic grades, melt rocks, and anorthositic rocks. A stratigraphic correlation of the lithologies within the North Massif and the South Massif is carried out. The petrogenesis of rock types with respect to thermal and impact history is discussed. The observed spinel cataclasites may represent relatively deep material sampled by the Serenitatis event.

Bence, A. E.↗
NASA NTRS1980

Shear heating and the state of stress on faults

Evidence for shear heating associated with crustal faulting is described for a number of fault zones in a wide variety of tectonic environments. It is shown that a thermal anomaly associated with the fault has resulted in the metamorphism of adjacent rocks to higher grades than can be accounted for by considering other heat sources. If relative displacements across these faults occurred at plate tectonic rates or slower, then shear stresses of a kilobar or so must have existed on the faults in order to produce the observed shear heating.

Scholz, C. H.↗
NASA NTRS1982

The mineralogy of global magnetic anomalies

Problems with the Curie balance, which severely hindered the acquisition of data, were rectified. Chemical analytical activities are proceeding satisfactorily. The magnetization characteristics of metamorphic suites were analyzed and susceptibility data for a wide range of metamorphic and igneous rocks. These rock magnetic signatures are discussed as well as the relationships between geology, gravity and MAGSAT anomalies of West Africa.

Haggerty, S. E.↗
NASA NTRS1984

Petrologic and geophysical sources of long-wavelength crustal magnetic anomalies

The magnetic mineralogy and magnetic properties of the deep crust are studied as they pertain to the interpretation of long wavelength, or regional, crustal magnetic anomalies in satellite magnetic data and near surface magnetic data. The conclusions have relevance to the understanding of regional magnetic anomalies in magnetic field measuring satellite missions data. There are two separable studies: (1) a synthesis of available information of regional magnetic anomalies and the magnetization of metamorphic and igneous rocks, and (2) a detailed field, analytical, and experimental study of in situ and laboratory specimens from a terrain that offers exposures of high grade granlite facies rocks that have associated regional magnetic and gravity anomalies.

Marsh, B. D.↗
NASA NTRS1984

Structural investigation of the Grenville Province by radar and other imaging and nonimaging sensors

The structural investigation of the Canadian Shield by orbital radar and LANDSAT, is outlined. The area includes parts of the central metasedimentary belt and the Ontario gneiss belt, and major structures as well-expressed topographically. The primary objective is to apply SIR-B data to the mapping of this key part of the Grenville orogen, specifically ductile fold structures and associated features, and igneous, metamorphic, and sedimentary rock (including glacial and recent sediments). Secondary objectives are to support the Canadian RADARSAT project by evaluating the baseline parameters of a Canadian imaging radar satellite planned for late in the decade. The baseline parameters include optimum incidence and azimuth angles. The experiment is to develop techniques for the use of multiple data sets.

Lowman, P. D., Jr.↗
NASA NTRS1986

Age constraints on the evolution of the Quetico belt, Superior Province, Ontario

Much attention has been focused on the nature of Archean tectonic processes and the extent to which they were different from modern rigid-plate tectonics. The Archean Superior Province has linear metavolcanic and metasediment-dominated subprovinces of similar scale to cenozoic island arc-trench systems of the western Pacific, suggesting an origin by accreting arcs. Models of the evolution of metavolcanic belts in parts of the Superior Province suggest an arc setting but the tectonic environment and evolution of the intervening metasedimentary belts are poorly understood. In addition to explaining the setting giving rise to a linear sedimentary basin, models must account for subsequent shortening and high-temperature, low-pressure metamorphism. Correlation of rock units and events in adjacent metavolcanic and metasedimentary belts is a first step toward understanding large-scale crustal interactions. To this end, zircon geochronology has been applied to metavolcanic belts of the western Superior Province; new age data for the Quetico metasedimentary belt is reported, permitting correlation with the adjacent Wabigoon and Wawa metavolcanic subprovinces.

Percival, J. A.↗
NASA NTRS1986

Petrogenesis of calcic plagioclase megacrysts in Archean rocks

Anorthositic complexes with large equidimensional plagioclase grains of highly calcic composition occur in nearly all Archean cratons. Similar plagioclase occur as megacrysts in many Archean sills, dikes, and volcanic flows. In the Canadian Shield these units occur throughout the Archean portions of the entire shield and are particularly common as dikes over an area of a few 100,000 sq km in Ontario and Manitoba during a period of at least 100 m.y. in many different rock types and metamorphic grades. The plagioclase generally occurs in three modes: as inclusions in mafic intrusions at various stages of fractionation, as crystal segregations in anorthosite complexes, or as megacrysts in fractionated sills, dikes, and flows. Most occurrences suggest that the plagioclase was formed elsewhere before being transported to its present location. The evidence seems to be quite clear that occurrences of these types of calcic plagioclase require: (1) ponding of a relatively undifferentiated Archean tholeiitic melt at some depth; (2) isothermal crystallization of large, equidimensional homogeneous plagioclase crystals; (3) separation of the plagioclase crystals from any other crystalline phases; (4) further fractionation of melt; (5)transport of various combinations of individual plagioclase crystals and clusters of crystals by variously fractionated melts; and (6) emplacement as various types of igneous intrusions or flows.

Phinney, W. C.↗
NASA NTRS1986

Comparison of the 1984 and 1985 AIS data over the Singatse Range (Yerington), Nevada

The Singatse Range is composed of a series of 53 types of volcanic, plutonic, metamorphic, and sedimentary rocks. In addition the Jurassic plutonic rocks are also of economic interest for their copper mineralization which is contained in a porphyry dike swarm. The 1984 and 1985 flight results from the Airborne Imaging Spectrometer (AIS) instrument flown in the NASA/JPL C-130 aircraft are contrasted and compared. The 1984 data are less noisy than the 1985, in which many sets of vertical stripings from bad detectors can be seen. Significantly however, enough of the hydrothermal alteration patterns can be seen in each line at the mutual crossing points that one can say that the specific targets were detected in both year's flights. The spectra of both years are corrupted by the second-order effect from the grating, but 0-H bond absorption at essentially correct wavelengths for sericite and/or kaolinite can be seen.

Lyon, R. J. P.↗
NASA NTRS1988

Ocean alkalinity and the Cretaceous/Tertiary boundary

A biogeochemical cycle model resolving ocean carbon and alkalinity content is applied to the Maestrichtian and Danian. The model computes oceanic concentrations and distributions of Ca(2+), Mg(2+), and Sigma-CO2. From these values an atmospheric pCO2 value is calculated, which is used to estimate rates of terrestrial weathering of calcite, dolomite, and calcium and magnesium silicates. Metamorphism of carbonate rocks and the subsequent outgassing of CO2 to the atmosphere are parameterized in terms of carbonate rock reservoir sizes, total land area, and a measure of overall tectonic activity, the sea-floor generation rate. The ocean carbon reservoir computed by the model is used with Deep Sea Drilling Project (DSDP) C-13 data to estimate organic detrital fluxes under a variety of ocean mixing rate assumptions. Using Redfield ratios, the biogenic detrital flux estimate is used to partition the ocean carbon and alkalinity reservoirs between the mixed layer and deep ocean. The calcite flux estimate and carbonate ion concentrations are used to determine the rate of biologically mediated CaCO3 titration. Oceanic productivity was severely limited for approximately 500 kyr following the K/T boundary resulting in significant increases in total ocean alkalinity. As productivity returned to the ocean, excess carbon and alkalinity was removed from the ocean as CaCO3. Model runs indicate that this resulted in a transient imbalance in the other direction. Ocean chemistry returned to near-equilibrium by about 64 mybp.

Caldeira, K. G.↗
NASA NTRS1989

An alternate hypothesis for the origin of Angra dos Reis - Porphyry, not cumulate

The Angra dos Reis achondrite is a unique meteorite of potentially great importance for understanding the origins of the solar system and of the terrestrial planets. It is proposed that the meteorite, which consists of megacrysts of Al-Ti augite (fassaite) in skeletal or cellular shapes, olivine, and possibly whitlockite in a fine-grained groundmass of the same materials plus spinel, is a porphyritic igneous rock modified by metamorphism. In this interpretation, the megacrysts represent cellular-textured phenocrysts, and the fine-grain groundmass represents crystallized or devitrified magma. Phase equilibria suggest that Angra dos Reis-like compositions could grow phenocrysts of fassaite pyroxene, olivine, and whitlockite. These same compositions could crystallize, without crystal sorting or accumulation, to an almost monomineralic fassaite pyroxenite.

Treiman, A. H.↗
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

Emissivity of terrestrial materials in the 8-14 microns atmospheric window

Remotely sensed infrared radiance emitted by a surface is a function both of its kinetic temperature and its spectral emissivity. Consequently, assumptions are usually made about the emissivity of earth surface materials to allow their temperatures to be determined, or vice versa. To increase the accuracy of these assumptions, the directional hemispherical spectral reflectance of a wide range of natural earth surface materials has been measured and is summarized here. These include igneous, metamorphic, and sedimentary rocks, desert varnish, soils, vegetation, water, and ice. Kirchhoff's Law can be used to predict directional spectral emissivity from these data.

Salisbury, John W.↗
NASA NTRS1993

Twenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Z

Papers from the conference are presented, and the topics covered include the following: planetary geology, meteorites, planetary composition, meteoritic composition, planetary craters, lunar craters, meteorite craters, petrology, petrography, volcanology, planetary crusts, geochronology, geomorphism, mineralogy, lithology, planetary atmospheres, impact melts, K-T Boundary Layer, volcanoes, planetary evolution, tectonics, planetary mapping, asteroids, comets, lunar soil, lunar rocks, lunar geology, metamorphism, chemical composition, meteorite craters, planetary mantles, and space exploration.

Source record↗
NASA NTRS1994

The Twenty-Fifth Lunar and Planetary Science Conference. Part 1: A-G

Papers from the conference are presented, and the topics covered include the following: planetary geology, meteorites, planetary composition, meteoritic composition, planetary craters, lunar craters, meteorite craters, petrology, petrography, volcanology, planetary crusts, geochronology, geomorphism, mineralogy, lithology, planetary atmospheres, impact melts, volcanoes, planetary evolution, tectonics, planetary mapping, asteroids, comets, lunar soil, lunar rocks, lunar geology, metamorphism, chemical composition, meteorite craters, and planetary mantles.

Source record↗