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At least 865 records · Page 48
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NASA NTRS1983

Lead isotope systematics of some igneous rocks from the Egyptian Shield

Lead isotope data on whole-rock samples and two feldspar separates for a variety of Pan-African (late Precambrian) igneous rocks for the Egyptian Shield are presented. It is pointed out that the eastern desert of Egypt is a Late Precambrian shield characterized by the widespread occurrence of granitic plutons. The lead isotope ratios may be used to delineate boundaries between Late Precambrian oceanic and continental environments in northeastern Africa. The samples belong to three groups. These groups are related to a younger plutonic sequence of granites and adamellites, a plutonic group consisting of older tonalites to granodiorites, and the Dokhan volcanic suite.

Gillespie, J. G.↗
NASA NTRS1983

Al-Sm-Eu-Sr systematics of eucrites and moon rocks Implications for planetary bulk compositions

Constraints are placed on the bulk compositions of the eucrite parent body (EPB) and the moon through analysis of the Eu and Sr 'anomalies' of eucrites and lunar rooks. It is noted that the elements Al, REE, and Sr are incompatible with the major minerals of these small, low-f(O2) bodies,except for plagioclase. Predictions can be derived about the concentrations of Al, REE, and Sr in samples affected by plagioclase fractionation, based on the hypothesis that these elements in the EPB and moon are all in proportions close to those in the bulk solar system. It is determined that the predictions are almost idealy fulfilled by eucrites and lunar samples. For the EPB, the ratios REE/Al, Sr/Al, and Sr/REE are found to be constrained probably within 10 percent of the chondritic ratios. For the moon, the constraints are found to be less precise: REE/Al is very probably within 25 percent of chondritic; Sr/Al and Sr/REE are probably within 35 percent of chondritic; Sr/Al and Sr/REE are probably within 35 percent of chondritic. It is concluded that there is a very strong similarity between the bulk compositions of the planets and the compositions of chondritic meteorites.

Warren, P. H.↗
NASA NTRS1983

Sm-Nd isotopic systematics of the ancient Gneiss complex, southern Africa

In order to shed some new light on the question of the absolute and relative ages of the Ancient Gneiss Complex and Onverwacht Group, a Sm-Nd whole-rock and mineral isochron study of the AGC was begun. At this point, the whole-rock study of samples from the Bimodal Suite selected from those studied for their geochemical characteristics by Hunter et al., is completed. These results and their implications for the chronologic evolution of the Kaapvaal craton and the sources of these ancient rocks are discussed.

Carlson, R. W.↗
NASA NTRS1984

Applicability of La-Ce systematics to planetary samples

Cesium isotopic compositions in several terrestrial and extraterrestrial materials were determined in order to investigate the applicability of using Ce as an isotropic tracer to geological processes. A tenuous anticorrelation was observed between (epsilon)Ce and (epsilon)Nd for terrestrial basalts and granites, indicating that with some improvement in analytical techniques the Ce isotopic composition may prove useful as tracer for geological processes. A very low (epsilon)Ce predicted from the Ce anomaly in the REE pattern of the Kholar L3 chondrite was not observed, indicating that the anomaly may be caused by terrestrial contamination or alteration.

Nakamura, N.↗
NASA NTRS1984

Systematic data interpretation of remote sensing in the reception of hydrocarbons, volume 1

The utilization of MSS-LANDSAT and RADAR imagery in the definition of morphostructural anomalies, which are indicative of hydrocarbon entrapment sites in the limit of the Middle and Lower Amazons basins was systemized. The identification and classification of the morphostructural anomalies were accomplished by means of the drainage network interpretation, based on the criteria previously proposed. Thirty anomalies were recognized, being subdivided into twenty domes, two fault controlled domes, six structural depressions, one fault controlled structural depression and one structure developed on a tilted fault block. Many anomalies are not randomly located. Rather, they seem to be aligned according to directions ENE and NNW, suggesting the presence of morphstructural trends in this part of the Amazons Basin. Significant orientations of lineaments were determined through statistical analysis, which defined many regional trends. The directions coincide with morphostructural trends orientations and with the directions of important structures in the Precambrian basement.

Demiranda, F. P.↗
NASA NTRS1984

Nickel-cobalt systematics and their bearing on lunar origin

The earliest metal phases to crystallize from the least-fabricated low Ti mare basalts contain about 30% Ni and 2 to 7% of Co. Experimental investigations of partitioning of Ni and Co between primitive lunar basaltic magmas and metal phases are currently in progress. Preliminary results show that the metal phase crystallizing near the liquidus of Green Glass (185 ppm Ni, 70 ppm Co) would contain about 40% Ni and 2.3% Co. It seems, therefore, that if a lunar core does exist, as suggested by the results of (2), it is relatively rich in Ni (30-40%) and Co (2-7%). This composition presents a remarkable contrast to that of the Earth's core which is estimated to contain about 6% Ni and 0.3% Co. Explanations for the differing densities of Earth and Moon are imvestigated.

Ringwood, A. E.↗
NASA NTRS1985

A systematic plan for the continued study of dimensional stability of metallic alloys considered for the fabrication of cryogenic wind tunnel models

Interrelated research and development activities, phased development of stepped specimen program are documented and a sequence for a specific program of machining, validation and heat treatment cycles for one material are described. Proposed work for the next phase of dimensional stability research is presented and further technology development activities are proposed.

Wigley, D. A.↗
NASA NTRS1984

The many faces of Capella - A search for rotational modulations and a study of systematic velocities of emission lines in the ultraviolet

The UV spectra of Capella were monitored for fluctuations using IUE instrumentation, and radial velocities of the emission lines were determined. The possible fluctuations were studied from March through April 1981, and radial velocity data were taken over six days in 1982. The Capella surface activity emissions proved to be steady, while redshifts from high excitation were found in the photospheric plasma. Downflows of 100,000 K plasma in the stellar transition zone could produce the redshifts. The FWHMs of the emission lines exceeded the redshift by an order of magnitude, suggesting that the observed excitations could be only averaged values of the dynamics of the outer atmosphere of Capella.

Ayres, T. R.↗
NASA NTRS1985

The age and emplacement of obducted oceanic crust in the Urals from Sm-Nd and Rb-Sr systematics

The Sm-Nd and Rb-Sr isotopic characteristics of two mafic-ultramafic bodies, the Kemperai Massif in the South Ural Mountains and the Voykar-syninsky Massif in the Polar Ural mountains are examined. The data are found to be consistent with the hypothesis that these bodies represent fragments of old oceanic crust. Whole rock samples of pillow basalt, troctolite, gabbros, diabase, and a metasediment give Sm-Nd values which lie on this isochron indicating that the rock units are genetically related and formed 397 My ago. Basic and ultrabasic rocks from Kempersai and Voykar-Syninsky have an initial isotopic composition at time T, epsilon Nd(397 My), of +8.4, indicating derivation for an ancient depleted mantle source. The Sr isotopic data and the correlation with epsilon Nd indicate extensive alteration by seawater which is particularly strong on ultrabasic rocks. The results show that the segments of oceanic crust formed at least 80 My before the collision that produced the Urals.

Edwards, R. L.↗
NASA NTRS1985

Some morphologic systematics of complex impact structures

Current measurements of the horizontal dimensions of complex meteorite structures are summarized. The measurements were used in a least squares analysis of correlations among the dimensions of the crater rings and central peaks of compact meteorites. Some geometric similarities between terrestrial complex impact structures and the large multiring basin of the planets are demonstrated, and the possible physical constraints on ring formation are discussed.

Pike, R. J.↗
NASA NTRS1985

Evidence for systematic flows in the transition region around prominences

The solar transition region in the neighborhood of prominences has been studied from observations with the Ultraviolet Spectrometer and Polarimeter of NASA's Solar Maximum Mission satellite. Dopplergrams from observations of the transition-region lines C IV 1548 A and Si IV 1393 A, which are formed at about 100,000 K, give velocity amplitudes typically in the range + or - 15 km/s. Prominences are found to be located very close to dividing lines between areas of up- and down-drafts in the transition-region. The observed pattern suggests that the 100,000 K gas flows take place within arcades of magnetic loops, which most likely are part of the supporting magnetic structure for the prominence matter. An additional band of blue-ward Doppler shifts is frequently seen close to quiescent prominences. This may be the source of outward flowing matter along the helmet streamers above filament channels.

Engvold, O.↗
NASA NTRS1985

Sm-Nd and Rb-Sr isotope systematics of an Archean anorthosite and related rocks from the Superior Province of the Canadian Shield

Sm-Nd and Rb-Sr isotopic data for the Bad Vermilion Lake anorthosite in the Rainy Lake area of the Superior Province of northwesten Ontario show that direct ages of Archean anorthosites can be obtained with these isotopic systems despite the effects of low-grade metamorphism. There is sufficient spread in Sm/Nd between plagioclase megacrysts and coexisting mafic groundmass to allow the determination of reasonably precise internal Sm-Nd isochrons. Initial isotopic ratios of Nd and Sr add to the growing body of data indicating the Superior Province is underlain by depleted mantle.

Ashwal, L. D.↗
NASA NTRS1985

A systematic study of magnetic braking in low-mass binaries

A short summary is given of Rappaport et al. (1983) which described results of extending a simplified stellar evolution code covering the evolution of low-mass compact binaries. Magnetic braking is probably an important process in the evolution of such binaries (such as cataclysmic variables and low-mass X-ray sources). The initial simplified code describes the mass-losing star as an n = 3/2 polytrope and was developed to study the evolution of binaries with a secondary of low mass (between 0.01 and 0.4 solar mass) when the angular momentum losses are due to gravitational radiation. In the extended code, a composite polytrope model is used for the secondary, wherein the structure of the radiative core is described by an n = 3 polytrope and the convective envelope by an n = 3/2 polytrope.

Verbunt, F.↗
NASA NTRS1986

Zircon Lu-Hf systematics: Evidence for the episodic development of Archaean greenstone belts

A combined U-Th-Pb and Lu-Hf isotopic study of zircons was undertaken in order to determine the provenance and age of an Archean granite-greenstone terrain and to test the detailed application of the Lu-Hf system in various Archean zircons. The eastern Wawa subprovince of the Superior province consists of the low grade Michipicoten and Gamitagama greenstone belts and the granitic terrain. The Hf isotopic data indicate that the typical lithological features of a greenstone belt cycle could be accommodated in a crustal growth model that involved decreasing depth of melting in three isotopically distinct reservoirs: mantle, lower crust and upper crust. The model age of the sources given by the intersection of the lower crustal curve with the bulk earth evolution curve is about 2900 My, in good agreement with the zircon U-Pb basement age. This linear array also has a similar intersection age to that of Proterozoic carbonatite complexes. The general convergence of the other reservoir vectors around this age suggests that mantle depletion, crustal extraction and intracrustal differentiation were all part of the same episodic event. It is also apparent that recycling of older basement was important in the formation of many of the later greenstone belt rocks.

Smith, P. E.↗