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At least 163 records · Page 9
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NASA NTRS2014

Geologic Mapping of Ejecta Deposits in Oppia Quadrangle, Asteroid (4) Vesta

Oppia Quadrangle Av-10 (288-360 deg E, +/- 22 deg) is a junction of key geologic features that preserve a rough history of Asteroid (4) Vesta and serves as a case study of using geologic mapping to define a relative geologic timescale. Clear filter images, stereo-derived topography, slope maps, and multispectral color-ratio images from the Framing Camera on NASA's Dawn spacecraft served as basemaps to create a geologic map and investigate the spatial and temporal relationships of the local stratigraphy. Geologic mapping reveals the oldest map unit within Av-10 is the cratered highlands terrain which possibly represents original crustal material on Vesta that was then excavated by one or more impacts to form the basin Feralia Planitia. Saturnalia Fossae and Divalia Fossae ridge and trough terrains intersect the wall of Feralia Planitia indicating that this impact basin is older than both the Veneneia and Rheasilvia impact structures, representing Pre-Veneneian crustal material. Two of the youngest geologic features in Av-10 are Lepida (approximately 45 km diameter) and Oppia (approximately 40 km diameter) impact craters that formed on the northern and southern wall of Feralia Planitia and each cross-cuts a trough terrain. The ejecta blanket of Oppia is mapped as 'dark mantle' material because it appears dark orange in the Framing Camera 'Clementine-type' colorratio image and has a diffuse, gradational contact distributed to the south across the rim of Rheasilvia. Mapping of surface material that appears light orange in color in the Framing Camera 'Clementine-type' color-ratio image as 'light mantle material' supports previous interpretations of an impact ejecta origin. Some light mantle deposits are easily traced to nearby source craters, but other deposits may represent distal ejecta deposits (emplaced greater than 5 crater radii away) in a microgravity environment.

Asteroids↗
NASA NTRS1985

GRM crustal magnetic anomalies: Separating the Lord Howe Rise and Norfolk Ridge submarine structures

Multiple source bodies often lie within the resolution element of the MAGSAT and POGO data. Small weak sources lying near larger stronger sources will tend to be missed, although they do contribute to the total observed anomaly. Lower elevation magnetic anomaly surveys such as GRM alleviate this problem through the combined effects of significantly greater resolution and stronger signal amplitude. This permits the detection of smaller source bodies, and analysis of their structure and nature. The improvement a GRM will provide is demonstrated in the Lord Howe Rise/Norfolk Ridge area east of Australia, between the Tasman Sea and south Fiji Basin. The submarine features origin have important plate tectonic implications. The Lord Howe Rise (LHR) is a continental fragment broken off from Australia by the opening of the Tasman Sea. It is a wide, shallow structure lying between 160 and 165 deg longitude at 23 to 37 deg S latitude. Seismic refraction data show the LHR crust extending to depths in excess of 20 km.

Frey, H.↗
NASA NTRS2016

Design of Superconducting Gravity Gradiometer Cryogenic System for Mars Mission

Measurement of a planets gravity field provides fundamental information about the planets mass properties. The static gravity field reveals information about the internal structure of the planet, including crustal density variations that provide information on the planets geological history and evolution. The time variations of gravity result from the movement of mass inside the planet, on the surface, and in the atmosphere. NASA is interested in a Superconducting Gravity Gradiometer (SGG) with which to measure the gravity field of a planet from orbit. An SGG instrument is under development with the NASA PICASSO program, which will be able to resolve the Mars static gravity field to degree 200 in spherical harmonics, and the time-varying field on a monthly basis to degree 20 from a 255 x 320 km orbit. The SGG has a precision two orders of magnitude better than the electrostatic gravity gradiometer that was used on the ESAs GOCE mission. The SGG operates at the superconducting temperature lower than 6 K. This study developed a cryogenic thermal system to maintain the SGG at the design temperature in Mars orbit. The system includes fixed radiation shields, a low thermal conductivity support structure and a two-stage cryocooler. The fixed radiation shields use double aluminized polyimide to emit heat from the warm spacecraft into the deep space. The support structure uses carbon fiber reinforced plastic, which has low thermal conductivity at cryogenic temperature and very high stress. The low vibration cryocooler has two stages, of which the high temperature stage operates at 65 K and the low temperature stage works at 6 K, and the heat rejection radiator works at 300 K. The study also designed a second option with a 4-K adiabatic demagnetization refrigerator (ADR) and two-stage 10-K turbo-Brayton cooler.

Li, X.↗
NASA NTRS2016

Design of Superconducting Gravity Gradiometer Cryogenic System for Mars Mission

Measurement of a planet's gravity field provides fundamental information about the planet's mass properties. The static gravity field reveals information about the internal structure of the planet, including crustal density variations that provide information on the planet's geological history and evolution. The time variations of gravity result from the movement of mass inside the planet, on the surface, and in the atmosphere. NASA is interested in a Superconducting Gravity Gradiometer (SGG) with which to measure the gravity field of a planet from orbit. An SGG instrument is under development with the NASA PICASSO program, which will be able to resolve the Mars static gravity field to degree 200 in spherical harmonics, and the time-varying field on a monthly basis to degree 20 from a 255 x 320 km orbit. The SGG has a precision two orders of magnitude better than the electrostatic gravity gradiometer that was used on the ESA's GOCE mission. The SGG operates at the superconducting temperature lower than 6 K. This study developed a cryogenic thermal system to maintain the SGG at the design temperature in Mars orbit. The system includes fixed radiation shields, a low thermal conductivity support structure and a two-stage cryocooler. The fixed radiation shields use double aluminized polyimide to emit heat from the warm spacecraft into the deep space. The support structure uses carbon fiber reinforced plastic, which has low thermal conductivity at cryogenic temperature and very high stress. The low vibration cryocooler has two stages, of which the high temperature stage operates at 65 K and the low temperature stage works at 6 K, and the heat rejection radiator works at 300 K. The study also designed a second option with a 4-K adiabatic demagnetization refrigerator (ADR) and two-stage 10-K turbo-Brayton cooler.

Gradiometer↗
NASA NTRS1992

SAR in support of geological investigations of the Sudbury structure

Imaging radar is an important contributing source of information for a range of geological problems and environments. Airborne SAR and ERS-1 data integrated with other geoscience datasets are being used in an attempt to characterize the crustal fracturing associated with the Sudbury structure. This presentation highlights examples of integrated and composite images aimed at facilitating the interpretation of the Sudbury structure. This work is the result of an ongoing cooperative multidisciplinary SAR study of the basin carried out by the Canada Center for Remote Sensing, Ontario's provincial Remote Sensing Office, the Ontario Geological Survey, and the Geological Survey of Canada.

Singhroy, V.↗
NASA NTRS1992

Structural review of the Vredefort dome

The structure of the older-than-3.2-Ga Archean basement and Archean-to-Precambrian sedimentary/volcanic rocks (3.07 to ca. 2.2 Ga) in the center of the Witwatersrand Basin to the southwest of Johannesburg (South Africa) is dominated by the ca. 2.0-Ga megascopic Vredefort 'Dome' structure. The effect of the 'Vredefort event' is demonstrably large and is evident within a northerly arc of about 100 km radius around the granitic core of the structure. Northerly asymmetric overturning of the strata is observed within the first 17 km (strata is horizontal in the south), followed by a 40-km-wide rim synclinorium. Fold and fault structures (normal, reverse, and strike-slip) are locally as well as regionally concentrically arranged with respect to the northern and western sides of the structure. The unusual category of brittle deformation, the so-called 'shock deformation', observed in the collar strata has attracted worldwide attention over the past two decades. These deformation phenomena include the presence of coesite and stishovite, mylonites, and pseudotachylites, cataclasis at a microscopic scale, and the ubiquitous development of multiply striated joint surfaces (which include shatter cones, orthogonal, curviplanar, and conjugate fractures). The macroscopic to microscopic deformation features have led to the formulation of various hypotheses to account for the origin of the Vredefort structure: (1) tectonic hypotheses--deep crustal shear model, doming and N-directed thrust fault model, fold interference model, and diapir model; (2) the exogenous bolide impact hypothesis; and (3) the endogenous cryptoexplosion model.

Colliston, W. P.↗
NASA NTRS1978

An assessment of crustal thickness variations on the lunar near side - Models, uncertainties, and implications for crustal differentiation

The paper presents a series of models for the structure of lunar nearside crust which are consistent with the observed gravity and topography. Each crustal model is derived subject to a specific set of constraints and assumptions. The assumptions/constraints considered include strict isostatic equilibrium, pure Airy compensation mechanism, pure Pratt compensation mechanism, assignment of assumed fixed values for mare basalt thickness, and attribution of all superisostatic mass in the maria to basalt fill. The resulting models are used to assess the degree and mechanism of isostasy, and to investigate the thickness of the mare basalt. Details of the lateral variations in crustal thickness or density and in the degree of isostatic compensation bear strongly on the mode of early crustal differentiation and on the subsequent thermal history of the moon.

Thurber, C. H.↗
NASA NTRS1983

Reports on crustal movements and deformations

This Catalog of Reports on Crustal Movements and Deformation is a structured bibliography of scientific papers on the movements of the Earth crust. The catalog summarizes by various subjects papers containing data on the movement of the Earth's surface due to tectonic processes. In preparing the catalog we have included studies of tectonic plate motions, spreading and convergence, microplate rotation, regional crustal deformation strain accumulation and deformations associated with the earthquake cycle, and fault motion. We have also included several papers dealing with models of tectonic plate motion and with crustal stress. Papers which discuss tectonic and geologic history but which do not present rates of movements or deformations and papers which are primarily theoretical analyses have been excluded from the catalog. An index of authors cross-referenced to their publications also appears in the catalog. The catalog covers articles appearing in reviewed technical journals during the years 1970-1981. Although there are citations from about twenty journals most of the items come from the following publications: Journal of Geophysical Research, Tectonophysics, Geological Society of America Bulletin of the Seismological Society of America, Nature, Science, Geophysical Journal of the Royal Astronomical Society, Earth and Planetary Science Letters, and Geology.

Cohen, S. C.↗
NASA NTRS1992

Geological correlations with the interior density structure of Venus

The paper develops a geophysical model for Venus that allows separation of topography supported by shallow density anomalies, e.g., crustal thickening, from that interpreted to be caused by mantle convection, and produces estimates of the planforms of lithospheric density anomalies and the mantle convection pattern. The topography caused by these two planforms is compared to several global data sets compiled from analysis of Magellan data. The mantle convection pattern agrees qualitatively with numerical simulations by Bercovici et al. (1989) and shows isolated upwellings amidst a network of downwellings. Crustal thickening does not exhibit a similar pattern. Impact crater density is nearly uniform and does not correlate with either crustal thickening or the mantle convection patterns. Large volcanic structures exhibit a good but imperfect correlation with mantle upwellings. Coronae locations are anticorrelated with large upwellings and large downwellings. A scenario is proposed for global tectonics on Venus and its relationship to mantle convection.

Herrick, Robert R.↗
NASA NTRS1981

The application of space technology to geodynamics - An overview

The application of various space technologies to the study of the earth is discussed. The main problems that this technology can study are crustal movement and deformation, and earth structure and rotational dynamics. Laser and VLBI systems are used as fixed observatories and as mobile stations which can move between locations separated by 200 to 500 km. Requirements for more frequency and more densely spaced measurements can be met by the use of geodetic receivers which process signals from the Global Positioning System, and an airborne laser which ranges simultaneously to an array of passive cube corner retroreflectors. A Gravity Field Satellite is expected to survey the earth's field to a resolution of 1000 km and accuracies of one milligal. Data from the Magnetic Field Satellite are being used to develop models of the main field for the 1980 Epoch and maps of crustal anomalies.

Fischetti, T. L.↗
NASA NTRS1978

Local precision nets for monitoring movements of faults and large engineering structures

Along Bocono Fault were installed local high precision geodetic nets to observe the possible horizontal crustal deformations and movements. In the fault area there are few big structures which are also included in the mentioned investigation. In the near future, measurements shall be extended to other sites of Bocono Fault and also to the El Pilar Fault. In the same way and by similar methods high precision geodetic nets are applied in Venezuela to observe the behavior of big structures, as bridges and large dams and of earth surface deformations due to industrial activities.

Henneberg, H. G.↗
NASA NTRS1985

Radial rift and block tectonics around the Tharsis bulge: Introductional postulation

Although the Vallis Marineris canyon and radial fossae grabens have been extensively studied, their origin and formation mechanism is still the subject of numerous questions. Possible rift formation is only one point of view and does not explain the rifting mechanism and the radial pattern of these structures around the Tharsis bulge. Both active and passive rifting must be taken into account. According to the active mechanism the building of a colcanic complex like the Tharsis bulge is caused by the rising of a huge mantle plume and adjoining extrusions which tap the generated magma. The surrounding fossae and valley structures are caused by more passive crustal rifting due to tensional failure of the surface layers. The main rising mantle plume activated and regenerated failure patterns radial to the centre of activity. These radial zones of weakness are then most easily utilized by the rising mantle plume. Deep zones of weakness regulate the penetration and distribution of hot mantle rock into upper levels while, contrarily, the effective impingement of the hot mantle plume into the lithosphere opens up new weakness zones.

Raitala, J.↗
NASA NTRS2004

Geologic Evolution of the Martian Dichotomy in the Ismenius Area of Mars and Implications for Plains Magnetization

The origin of the Martian dichotomy, which divides highlands from lowlands, is unknown. We examine a section of the dichotomy ( 50 - 90E) defined by steep scarps and normal faults. Stratigraphy and age relationships preclude the formation of the 2.5 km high boundary via erosion. The abrupt disappearance of topographic knobs similar to 300 - 500 km to the northeast is interpreted as a buried fault. Alignment of the buried fault with grabens, stratigraphy, and age determinations using crater counts indicate that the lowland bench is down faulted highlands crust. The estimated local strain (3.5%) and fault pattern are broadly consistent with gravitational relaxation of a plateau boundary. Magnetic and gravity anomalies occur on either side of the buried fault. Admittance analysis indicates isostatic compensation. Although nonunique, a model with a 10 km thick intracrustal block under the lowland bench, a 20 km thick block under the plains, and an excess density of 200 kg/m(3) provides a good fit to the isostatic anomaly. A good fit to a profile of the magnetic field perpendicular to the dichotomy is produced using uniformly polarized intracrustal blocks 10 - 20 km thick, an intensity of 6 Am/m, a field inclination of -30 degrees, and gaps aligned with the isostatic anomalies. One interpretation is that high-density intrusions demagnetized the crust after dynamo cessation and that low-lying magnetized areas could be down faulted highlands crust. Another model (inclination of 30 degrees) has magnetized crust beneath the isostatic anomalies, separated by gaps. The gaps could result from hydrothermal alteration of the crust along fault zones.

faulting↗
NASA NTRS1987

Characteristic structures of the highland boundary on Mars: Evidence against a single mega-impact event?

It has been suggested that an early mega-impact event might explain the fumdamental crustal dichotomy on Mars. Detailed morphological mapping of the structures which characterize the boundary between the cratered highlands and northern plains does not support this idea: the distribution of these features along and especially away from the boundary is more consistent with a larger number of smaller but overlapping impacts. A data base was assembled for the study of the highland boundary through quantitative mapping (including crater counts) based on the 1:2 M controlled photomosaics. Whole and partial craters larger than 10 km in diameter, knobby terrain, detached plateaus and intervening plains-forming units have been identified wherever they occur on Mars between +65 and -45 deg latitude. There is evidence for occurrences of possible old cratered terrain (or its remanents) at high latitudes well north of the current or likely former location of the proposed Borealis Basin rim which are difficult to reconcile with an impact structure of the proposed size and location.

Semeniuk, Ann Marie↗
NASA NTRS1973

Mapping of the major structures of the African rift system using ERTS-1

The author has identified the following significant results. The structural margin of western Afar with the Ethiopian plateau is marked by a rather wide zone of crustal deformation. ERTS-1 imagery has now permitted a more precise mapping of the structures of this marginal zone, and in particular of the discontinuous marginal graben. The tectonic style of the graben is different in the north from the south, and in the latter region the graben is discordant with the regional tectonic trend. The structural margin of the southern Afar with the Somalian plateau is formed, in the western sector, by a remarkable series of fault-zone splays. Afar-plateau boundary fault-zones successively curve northeast and then NNE to become Afar floor fault-zones, with a distance of about 25 km separating successive turnoffs. The transition from Ethiopian rift to Gulf of Aden tread faulting along this margin is fascinatingly complex. A simplistic crustal thinning model is not adequate to explain all observed structural features of the Afar margins.

Mohr, P. A.↗
NASA NTRS1988

Lava thicknesses: Implications for rheological and crustal development

The morphology of a lava flow is strongly influenced by its rheological structure. The rheological structure is, in turn, dependent on numerous factors including: (1) bulk composition, (2) crystallingity, (3) vesicularity, and (4) crustal development. Identifying which of the latter factors are most significant, and hence most readily investigated by remote-sensing techniques, is necessary to clarify short-term objectives and expectations from the study of Martian lava flows. Insights into the rheological controls on flow morphology are provided by variations in thickness of undrained lava streams on Etna and Vesuvius, Southern Italy. Both pahoehoe and aa lavas were studied.

Kilburn, C. R. J.↗
NASA NTRS2004

Contribution to the Study of Regional Magnetization of Satellite Magnetic Measurement: Magsat, Orsted, and Champ (with Gravity Field)

A discussion of and introduction to satellite-altitude geopotential field studies and their interpretation with emphasis on results from metalliferous regions will be given. The magnetic and gravimetric measurements from satellite altitudes show heterogeneity in deeper parts of the lithosphere. These patterns of magnetic anomalies do not only reveal the largest iron ore deposits such as Kiruna, Sweden, Kursk, Russia, and Banugi, Central African Republic but also linear features indicating structural discontinuities. Changes of magnetic amplitude of these patterns are caused by intersecting transverse fractures localizing magmatism and concentration of metals. In addition satellite altitude data are related to variations in crustal thickness and heat flow. Deep-rooted structural discontinuities, defined by combination of geological and geophysical criteria, with spacing of several hundred kilometers, reveal a quite uniform pattern in the deeper parts of the lithosphere. As these structures provide favorable pathways for the ascent of heat, magmas and ore-forming fluids, their recognition is of crucial importance and can be used in the compilation of a new type of mineral prognosis map. An example from Europe includes a pattern of east west trending structural discontinuities or belts and their junction with the NW-trending Tornqvist-Teisseyre Line. The Upper Silesian-Cracovian Zn-Pb district occurs along one of the latitudinal belts. Leslaw Teper of the University of Silesia has been invited to show the fractures in crystalline basement beneath the sediments hosting the Zn-Pb ores.

Taylor, Patrick T.↗
NASA NTRS1982

NASA geodynamics program

The goals of the NASA geodynamics program comprise the study of the interior structure and composition of the earth, its crustal motions and deformations, the rotational dynamics, and the terrestrial potential fields. Laser ranging an VLBI techniques are being applied in cooperation with 16 other countries. Reflectors on the moon are illumined with laser beams from earth, which are also bounced off the Lageos and French Starlette satellites, permitting monitoring of polar motion, earth rotation, and distance to the moon within 5 cm. Mobile laser systems are being deployed for developing a gravity field model and examining crustal deformation regionally. The VLBI installations use quasars as reference objects and the GPS satellites will give position accuracy within 1-2 cm. Satellite-to-satellite tracking, Magsat, and Shuttle timing experiment data are providing geopotential field data and timing synchronization.

Fischetti, T. L.↗