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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.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Accretionary history of the Archean Barberton Greenstone Belt (3.55-3.22 Ga), southern Africa

The 3.55-3.22 Ga Barberton Greenstone Belt, South Africa and Swaziland, and surrounding coeval plutons can be divided into four tectono-stratigraphic blocks that become younger toward the northwest. Each block formed through early mafic to ultramafic volcanism (Onverwacht Group), probably in oceanic extensional, island, or plateau settings. Volcanism was followed by magmatic quiescence and deposition of fine-grained sediments, possibly in an intraplate setting. Late evolution involved underplating of the mafic crust by tonalitic intrusions along a subduction-related magmatic arc, yielding a thickened, buoyant protocontinental block. The growth of larger continental domains occurred both through magmatic accretion, as new protocontinental blocks developed along the margins of older blocks, and when previously separate blocks were amalgamated through tectonic accretion. Evolution of the Barberton Belt may reflect an Early Archean plate tectonic cycle that characterized a world with few or no large, stabilized blocks of sialic crust.

NASA Discipline Exobiology↗
NASA NTRS1988

Impact, and its implications for geology

The publication of seminal texts on geology and on meteoritics in the 1790s, laid the groundwork for the emergence of each discipline as a modern branch of science. Within the past three decades, impact cratering has become universally accepted as a process that sculptures the surfaces of planets and satellites throughout the solar system. Nevertheless, one finds in-depth discussions of impact processes mainly in books on the Moon or in surveys of the Solar System. The historical source of the separation between meteoritics and geology is easy to identify. It began with Hutton. Meteorite impact is an extraordinary event acting instantaneously from outside the Earth. It violates Hutton's principles, which were enlarged upon and firmly established as fundamental to the geological sciences by Lyell. The split between meteoritics and geology surely would have healed as early as 1892 if the investigations conducted by Gilbert (1843-1918) at the crater in northern Arizona had yielded convincing evidence of meteorite impact. The 1950s and 1960s saw a burgeoning of interest in impact processes. The same period witnessed the so-called revolution in the Earth Sciences, when geologists yielded up the idea of fixed continents and began to view the Earth's lithosphere as a dynamic array of horizontally moving plates. Plate tectonics, however, is fully consistent with the geological concepts inherited from Hutton: the plates slowly split, slide, and suture, driven by forces intrinsic to the globe.

Marvin, Ursula B.↗
NASA NTRS2002

NEPTUNE: an under-sea plate scale observatory

The NEPTUNE project will establish a linked array of undersea observatories on the Juan de Fuca tectonic plate. This observatory will provide a new kind of research platform for real-time, long-term, plate-scale studies in the ocean and Earth sciences.

shore station backbone↗
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 NTRS1973

Plate motion and the secular shift of the mean pole

The global plate motion indicates that changes in the products of inertia of the earth due to tectonic plate movement may provide a secular shift of the mean pole. A mathematical procedure for calculating this shift based on the plate theory is presented. Explicit expressions were obtained for the dependence of the secular polar shift on the dimensions and locations of the plate boundaries. Numerical results show that the secular motion of the mean pole is 0.0002 sec/year in the direction of 67 W. Hence, it is deduced that the influence of the plate motion on the secular polar shift may account for 10% of the observed value.

Liu, H.↗
NASA NTRS1993

The tectonic and volcanic evolution of Venus: Catastrophic or gradual?

Radar imaging and altimetry data from the Magellan mission have yielded important new constraints on the tectonic and volcanic history of Venus and on its internal dynamics. The planet lacks global plate tectonics, but a number of chasm systems and corona moat structures have arcuate planforms, asymmetric topogrpahic profiles, and relief analogous to deep-sea trenches on Earth and may be products of limited lithospheric underthrusting or subduction. Several lines of evidence point to a crust and upper mantle stronger than would be predicted by simple extrapolation from Earth and the 450 K greater surface temperature; these include the unrelaxed depths of impact craters, apparently large values of elastic lithosphere thickness, and large ratios of gravity to topography. The density of impact craters indicates an averate crater retention age of about 500 My, but not more than 5% of the recognized craters have been volcanically embayed. This last observation has led to the proposal that Venus has been subjected to one or more global resurfacing events, the latest about 500 My ago, and that the volcanic flux during intervals between such events has been low. That more recent tectonic activity has been widespread, however, is indicated by the high relief and slopes of mountains, chasm walls, and plateau margins; the significant fraction (0.3) of impact craters deformed by younger faults; and the postformational vertical deformation of long channels. Interior dynamical scenarios advanced to account for episodic volcanic resurfacing include catastrophic overturn of a global lithosphere thickened by cooling or compositional buoyancy and strongly time-dependent mantle convective heat flux. Outgassing considerations and analogy with Earth and other terrestrial planets, however, suggests that such catastrophic models are unlikely. If the mantle of Venus cooled more efficiently than that of Earth because of, say, different boundary conditions, a different flow law, or a different degree of layering, then the planet may in the last 500 My have attained lesser mantle temperatures, lower mantle heat flux, and a significantly lesser rate of magma production than Earth yet still display evidence for ongoing convection and active tectonics. Such a 'cold Venus' scenario would be broadly consistent with observations yet be characterized by a gradual volcanic and tectonic evolution.

Solomon, Sean C.↗
NASA NTRS1990

Pacific-North America plate motions - New results from very long baseline interferometry

The state of Pacific-North America plate interaction is updated using newest VLBI measurements and newly developed rigid plate tectonic models. Particular attention is given to examining the extent of relative motion between the Pacific plate and the North America plate as measured from their stable interiors, the evidence of Pacific plate deformation off the central California coast, and the distribution of path integrated deformaton east of the San Andreas fault. The information obtained on these questions is discussed in the framework of implications for lithospheric rheology and earthquake hazard.

Ward, Steven N.↗
NASA NTRS1980

Stress accumulated mechanisms on strike-slip faults

The tectonic framework causing seismicity on the San Andreas and North Anatolian faults can be understood in terms of plate tectonics. However, the mechanisms responsible for the distribution of seismicity in space and time on these faults are poorly understood. The upper part of the crust apparently behaves elastically in storing energy that is released during an earthquake. The relatively small distances from the fault in which stress is stored argue in favor of a plate with a thickness of 5-10 km. The interaction of this plate with a lower crust that is behaving as a fluid damps the seismic cycling in distances of the order of 10 km from the fault. Low measured heat flow also argues in favor of a thin plate with a low stress level on the fault. Future measurements of stress, strain, and heat flow should help to provide a better understanding of the basic mechanisms governing the behavior of strike-slip faults.

Turcotte, D. L.↗
NASA NTRS1982

Tectonics of the Himalayan thrust belt in northern Pakistan

It is pointed out that the Himalayan ranges of southern Asia represent a dilemma in modern plate tectonic theory. Alvarez (1982) has tried to resolve some of the problems, but inconsistencies remain. The present investigation considers some of the problems which are now encountered in light of present knowledge. The investigation is concerned mainly with the evolution of the Himalaya south of the Main Mantle Thrust (MMT) and the Indus-Tsangpo suture zone, taking into account the neotectonic setting of northern Pakistan. Attention is given to subdivisions of the central Indian Himalaya, the transition from central Himalaya to northern Pakistan, subdivisions of the Himalaya of northern Pakistan, and aspects of neotectonics. Problems for future work are also discussed.

Yeats, R. S.↗
NASA NTRSDate not supplied

Exploring the Geochemistry of Tholeiitic Basalts and Hyaloclastites Formed in Submarine Volcanoes for Comparison With Venus Lavas

Underwater basaltic lavas exhibit distinct rock textures, mineralogy and morphological differences compared to those formed on land, primarily due to rapid cooling caused by contact with cold seawater instead of air and to high pressures – similar to Venus. The geomorphological similarities between terrestrial submarine volcanoes and some morphological classes of Venusian volcanoes have been investigated, but a comprehensive comparison in geochemical terms has yet to be conducted. Only three missions to Venus (Venera-13, Venera-14, and Vega-2) were able to report bulk composition of Venusian rocks, while other four missions (Venera-8, Venera-9, Venera-10, and Vega-1) provided limited geochemical information. Using X-Ray fluorescent (XRF) analysis, we saw that rocks analyzed on the surface of Venus are tholeiitic and alkalic basalts. This study, as part of the “Analogs for VENus's GEologically Recent Surfaces” (AVENGERS) initiative, aims to examine the possibility of seamounts/submarine volcanoes lavas serving as analogues to Venus lava geochemistry and morphology/formational processes. By sampling and analyzing submarine lavas from three distinct tectonic settings on Earth - hot-spot, convergent margins, and divergent margins - we will assess in which tectonic context the analogy with Venus is most comparable. Fieldwork will be conducted in further detail for submarine volcanoes located in Sicily, Hawaiʻi, and the Southern Pacific (Fiji, Vanuatu, Tonga, Samoa); we will use previously collected samples where these submarine areas are not accessible. Sampling efforts will target areas likely to yield submarine tholeiitic lavas and/or hyaloclastites. Samples collected during fieldwork will undergo detailed whole-rock geochemical analysis, including XRF, X-Ray diffraction (XRD) and Inductively Coupled Plasma Mass Spectrometry (ICPMS). Thin sections will be used to constrain differences in morphology/textures. The obtained geochemical data will then be compared with existing data on Venusian lava geochemistry, allowing for a comprehensive evaluation of potential analogies between submarine lavas from Earth and volcanic rocks on Venus. By elucidating these similarities and pinpointing specific tectonic contexts, our study has the potential to enhance our understanding of Venusian geology and the possibility of ephemeral plate tectonics on the planet.

N Mari↗
NASA NTRS1992

Venus tectonic styles and crustal differentiation

Two of the most important constraints are known from Pioneer Venus data: the lack of a system of spreading rises, indicating distributed deformation rather than plate tectonics; and the high gravity/topography ratio, indicating the absence of an asthenosphere. In addition, the high depth/diameter ratios of craters on Venus indicate that Venus probably has no more crust than Earth. The problems of the character of tectonics and crustal formation and recycling are closely coupled. Venus appears to lack a recycling mechanism as effective as subduction, but may also have a low rate of crustal differentiation because of a mantle convection pattern that is more distributed, less concentrated, than Earth's. Distributed convection, coupled with the nonlinear dependence of volcanism on heat flow, would lead to much less magmatism, despite only moderately less heat flow, compared to Earth. The plausible reason for this difference in convective style is the absence of water in the upper mantle of Venus. We have applied finite element modeling to problems of the interaction of mantle convection and crust on Venus. The main emphasis has been on the tectonic evolution of Ishtar Terra, as the consequence of convergent mantle flow. The early stage evolution is primarily mechanical, with crust being piled up on the down-stream side. Then the downflow migrates away from the center. In the later stages, after more than 100 m.y., thermal effects develop due to the insulating influence of the thickened crust. An important feature of this modeling is the entrainment of some crustal material in downflows. An important general theme in both convergent and divergent flows is that of mixing vs. stratification. Models of multicomponent solid-state flow obtain that lower-density crustal material can be entrained and recycled, provided that the ration of low-density to high-density material is small enough (as in subducted slabs on Earth). The same considerations should apply in upflows; a small percent of partial melt may be carried along with its matrix and never escape to the surface. Models that assume melt automatically rising to the crust and no entrainment or other mechanism of recycling lower-density material obtain oscillatory behavior, because it takes a long time for heat to build up enough to overcome a Mg-rich low-density residuum. However, these models develop much thicker crust than consistent with estimates from crater depth/diameter ratios.

Kaula, W. M.↗
NASA NTRS2002

Origin of Magnetic Lineations on Mars

The magnetic lineations discovered by MGS (Mars Global Surveyor) have been considered to be evidence of early plate tectonics on Mars. However, the lineations approximately follow lines of latitude, i.e., small circles. This presents significant geometrical problems for plate-like spreading, particularly at high latitudes. However, the sublatitudinal orientation of the lineations is consistent with meridianal extension and perhaps limited crustal spreading due to a stress event centered near the geographic pole. We hypothesize that this event was the early formation of the crustal dichotomy through mantle-convective processes. This could have taken the form of a southern megaplume that formed the thick highlands crust or as subduction or downwelling in the north. Both would result in tensional stresses in the south that would form extensional fractures perpendicular to the CM-CF (center-of-mass/center-of-gravity) offset. The observed magnitude and distribution of magnetization indicates that crustal intrusion associated with this major mantle-convective event resulted in approximately 1000 km of extension in the Southern highlands. Subsequent spin-axis reorientation due to loss of crust in the north or gain of crust in the south brought the CM-CF offset into its present N-S alignment. A portion of the ancient valley networks observed in the southern highlands are spatially associated with crustal magnetism and are quantitatively shown to be consistent with hydrothermal discharge over crustal intrusions.

Grimm, Robert E.↗
NASA NTRS1993

Kinematics of the New Zealand plate boundary: Relative motion by GPS across networks of 1000 km and 50 km spacing

The NASA/DOSE 'Kinematics of the New Zealand Plate Boundary' experiment is a four-year cooperative Global Positioning System (GPS) experiment involving 6 universities and institutions in New Zealand and the United States. The investigation covers two scales, the first on the scale of plates (approximately 1000 km) and the second is on the scale of the plate boundary zone (approximately 50 km). In the first portion of the experiment, phase A, the objective is to make direct measurements of tectonic plate motion between the Australian and Pacific plates using GPS in order to determine the Euler vector of this plate pair. The phase A portion of this experiment was initiated in December 1992 with the first-epoch baseline measurements on the large scale network. The network will be resurveyed two years later to obtain velocities. The stations which were observed for phase A are shown and listed. Additional regional stations which will be used for this study are listed and are part of either CIGNET or other global tracking networks. The phase A portion of the experiment is primarily the responsibility of the UNAVCO investigators. Therefore, this report concentrates on phase A. The first year of NASA funding for phase A included only support for the field work. Processing and analysis will take place with the second year of funding. The second part of the experiemnt measured relative motion between the Australian and Pacific plates across the pate boundary zone between Hokitika and Christchurch on the South Island of New Zealand. The extent and rate of deformation will be determined by comparisons with historical, conventional surveys and by repeated GPS measurements to be made in two years. This activity was the emphasis of the LDGO portion of the study. An ancillary experiment, phase C, concentrated on plate boundary deformation in the vicinity of Wellington and was done as part of training during the early portion of the field campaign. Details of the objectives of the field investigations are given in the appendix. An overview of the 1992 GPS field program is also given in the appendix.

Meertens, Charles M.↗
NASA NTRS1973

The Origin of Intermediate and Deep Focus Earthquakes

An elastic plate model is used to describe the origin of intermediate and deep earthquakes. It is shown that the earth is covered by about eight tectonic plates that have relative motions; along plate boundary lines, one plate thrusting under the other, causes deflection and buckling of the elastic plate structure in regions of maximum curvature that may trigger earthquakes.

Han-Shou Liu↗
NASA NTRS1979

Application of space technology to crustal dynamics and earthquake research

In cooperation with other Federal government agencies, and the governments of other countries, NASA is undertaking a program of research in geodynamics. The present program activities and plans for extension of these activities in the time period 1979-1985 are described. The program includes operation of observatories for laser ranging to the Moon and to artificial satellites, and radio observatories for very long baseline microwave interferometry (VLBI). These observatories are used to measure polar motion, earth rotation, and tectonic plate movement, and serve as base stations for mobile facilities. The mobile laser ranging and VLBI facilities are used to measure crustal deformation in tectonically active areas.

Source record↗
NASA NTRS1993

The three ages of Venus: A hypothesis based on the cratering record

The elevation range of 6051.9 - 6053.9 km on Venus is deficient in craters but has a high proportion of embayed and tectonically deformed craters. On the basis of this data and previous work, I propose that Venus has experienced three distinct geologic ages: pseudo-plate tectonics until 1 - 2 Ga, volcanic flooding of low-lying areas, and currently hot spot tectonics.

Herrick, R. R.↗
NASA NTRS1975

Absolute plate motions by boundary velocity minimizations

The main interaction of the earth's interior with the lithosphere is as a material source and sink. An absolute reference frame defined by minimizing the translational motion of tectonic plate boundaries differs by 0.6 cm/year from a frame defined by hot spot traces and by 0.4 cm/year from the frame defined by the most plausible model of drag forces on the plates. The rms absolute translational velocities are about 2 cm/year for ocean-ocean plate boundaries and 1.5 cm/year for ocean-continent plate boundaries. The close agreement between the source and sink and the drag-dependent definitions suggests that the lithosphere, as a stress guide, to some extent controls the locations of its sources and sinks.

Kaula, W. M.↗