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Scott, D. H.

Publications and source records attributed to Scott, D. H..

33 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Ignimbrites of Amazonis Planitia region of Mars

The terms ignimbrite and ash flow tuff are used to describe relatively thin but extensive sheets of material interpreted to be of pyroclastic origin and to consist of volcanic ash or pumice fragments. Criteria for distinguishing ignimbrites from other geologic materials are considered, and characteristics observed for rock units interpreted as ignimbrites in Amazonis Planitia are discussed. A series of rock units which are thought to represent ignimbrites have been mapped along an east-west border zone between the highland plateau and lowland plains of Amazonis Planitia. The area is roughly bounded by a triangle whose apices are the volcanoes Apollinaris Patera, Biblis Patera, and Olympus Mons. Attention is given to aspects of general geology, morphology and stratigraphy, and thickness and volume estimates. Correlations with other data are considered and some theoretical aspects of Martian ignimbrite emplacement are discussed.

Scott, D. H.↗
NASA NTRS1982

Mars - A large highland volcanic province revealed by Viking images

Many of the mountains in the rugged highland terrain of the Phaethontis and Thaumasia quadrangles are believed to be of volcanic origin. Those provisionally mapped as volcanoes have diagnostic characteristics such as lobate flow fronts around their bases, depressed central areas, or have massive, bulbous accumulations of material of no determinable origin other than volcanic. Most of the volcanoes are younger than materials forming the highlands but are older than early lava flows from Arsia Mons. Many are aligned along older fault and ridge systems that are transverse to the more recent and prominent faults transecting the region. The older faults are generally buried by plains lava flows but their traces are visible in several places in the highlands. These faults are relatively short in length.

Scott, D. H.↗
NASA NTRS1981

Mars - Paleostratigraphic restoration of buried surfaces in Tharsis montes

Volcanism in the Tharsis province of Mars occurred in several different areas and was generally continuous without large time intervals between eruptive episodes. Major lava flow units are numerous and extensive, but relatively thin. In many places, impact craters on buried surfaces project above younger flows that overlie them. A new application of crater dating methods has been developed to aid in the identification of these buried surfaces and to determine their lateral extent. The technique is especially adaptable to the Tharsis region where the stratigraphic succession of major flow units has been established by detailed geologic mapping. Knowledge of the overall stratigraphy allows correlations to be made between known and unknown surfaces by comparing their crater frequencies at diameters large enough to insure their recognition on the buried unit. The method has been applied to aid in the restoration of buried rock units and to construct a series of paleostratigraphic maps showing the sequence of major eruptive events in the Tharsis region.

Scott, D. H.↗
NASA NTRS1980

Mars Tharsis region - Volcanotectonic events in the stratigraphic record

It is pointed out that the most recent volcanism and much of the oldest tectonic activity on Mars have apparently occurred within the Tharsis region. Detailed geologic mapping from Viking images has provided new information on the evolutionary history of the region. The eruptive sequence and areal extent of lava flows in the Tharsis region have been defined by stratigraphic studies and crater counts made on individual flow units. Faults and fractures transecting these units provide a record of changing tectonic intensity during the period of high volcanic activity. Volcanism began with the resurfacing of basement rocks early in the history of the region and continued without large interruptions through nine major eruptive episodes. Volcanic centers shifted from place to place but resurgent activity occurred at several volcanoes. Volcanism culminated during the foration of large shield volcanoes along Tharsis Montes and thereafter appears to have gradually declined.

Scott, D. H.↗
NASA NTRS1979

Geologic problems in the northern plains of Mars

Viking pictures have made it possible to subdivide the few broad plains categories recognized on Mariner-9 pictures into smaller more definitive geologic units. Mapping problems arise in places where image resolution is sufficient to reveal the texture characteristics of individual units, but does not disclose the nature of their boundaries nor their stratigraphic relations. The mottled plains remain the most extensive undivided geologic unit in the northern Martian hemisphere; they may represent the northern remnant of the highlands, separated by crustal extension. Further resolution of the mottled plains unit may depend largely on digital enhancement of pictures in selected areas.

Scott, D. H.↗
NASA NTRS1978

Mars, highlands - lowlands: Viking contributions to Mariner relative age studies

Stratigraphic relations between lowland plains and highlands, two major types of Martian geologic-terrain units, were not directly distinguishable on Mariner-9 images. Morphologic characteristics and crater densities suggested that the lava plains beneath their eolian cover were younger than adjacent highland rocks, which form a plateau bounded in many places by highly dissected escarpments. Alternatively, the lowland plains could be the older unit and represent a broad erosional surface exhumed by southward retreat of the highlands along their frontal scarp. Viking photos across five areas of the highland-lowland boundary, however, tend to confirm the younger age of the plains-forming lava flows. A time interval of several hundred million years probably occurred between the retreat of the highland scarp and its latest embayment by lava extrusions in the lowlands.

Scott, D. H.↗
NASA NTRS1978

Regional deformation of mare surfaces

The possible tectonic significance of large topographic irregularities within Mare Serenitatis is discussed, and the characteristics of sinuous rilles are considered as possible indicators of structural deformation. It is shown that most sinuous rilles have been structurally warped and that their slopes lie within the laminar flow range. The sinuous rilles may have been formed in the domain of turbulent flow, if the ratios of meander wavelength to channel width can be taken as indicators. Some surface tectonic deformation occurring before the broad uplift of the basin center is suggested by the surface topography and radar reflectors in the Mare Serenitatis.

Scott, D. H.↗
NASA NTRS1977

Moon-Mercury - Relative preservation states of secondary craters

Geologic studies including mapping of the Kuiper quadrangle of Mercury suggest that secondary craters are much better preserved than those on the moon. Factors which may account for the apparent differences between lunar and Mercurian secondary crater morphology include: (1) the rapid isostatic adjustment of the parent crater, (2) different impact fluxes of the two planets, (3) the greater concentration of Mercurian secondaries around impact areas, and (4) differences in crater ejection velocities. It has been shown that the ejection velocities on Mercury are about 50% greater than those on the moon at equivalent ranges. This may account for morphologically enhanced secondary craters, and may explain their better preservation with time.

Scott, D. H.↗
NASA NTRS1977

Lunar farside tectonics and volcanism

The reported study is primarily concerned with the identification and mapping of structural and volcanic features on the lunar farside. The study represents a continuation and extension of a similar investigation made of the nearside of the moon by Scott et al. (1975). Mapping reveals that tectonic structures on the moon's farside are comparatively scarce and such less prominently developed than those on the nearside. Rilles and mare-type ridges that form major linear and basin concentric systems on the nearside are nearly absent on the farside as are large normal faults like Rupes Recta and Rupes Cauchy. The azimuth orientations of five types of geologic structures were measured, including lineaments, crater chains, terra ridges, faults and linear rilles, and straight segments of crater rims. Mare basalts are concentrated in low regions, especially in a large southern basin which is also the site of relatively numerous volcanic constructs as well as geochemical and magnetic anomalies.

Scott, D. H.↗
NASA NTRS1974

Lunar basin formation and highland stratigraphy

Multiring impact basins, formed after solidification of the lunar crust, account for most or all premare regional deposits and structures expressed in the lunar landscape and for major topographic and gravity variations. A fresh basin has two or more concentric mountain rings, a lineated ejecta blanket, and secondary impact craters. Crackled material on the floor may be impact melt. The ejecta blanket was emplaced at least partly as a ground-hugging flow and was probably hot. A suggested model of basin formation is that the center lifts up and the rings form by inward collapse during evisceration. The resulting basin is shallow and has a central uplift of the mantle. This results in a central gravity high and a ring low. Later flooding by mare basalt has since modified most near side basins. Highland deposits of plains, furrowed and pitted terrain, and various hills, domes, and craters that were interpreted before the Apollo missions as being volcanic can now be interpreted as being basin related.

Howard, K. A.↗
NASA NTRS1974

Multiringed basins - Illustrated by Orientale and associated features

Geologic mapping and photographs of the Orientale multiring basin are studied as to origin, size, and nature and distribution of ejecta. Six facies of ejecta are observed around the Cordillera Mountains: concentric, radial, smooth plains, grooved, secondary impact craters, and fissured. Transport of these ejecta occurred by block gliding, landsliding, debris flow, and possibly by base surge, viscous flow, and ballistic ejection. The ejecta are mainly clastic types, but melts and annealed breccias are expected to be abundant. Mixing of ejecta and substrate materials must have occurred; compositions of the ejecta are probably zoned laterally and vertically.

Moore, H. J.↗
NASA NTRS1973

Small structures of the Taurus-Littrow region

Apollo 17 photographs of small structures expressed as scarps, ledges, flow fronts, and mare type ridges are compared in an effort to determine the origin of such structures. The resulting data revealed that these structures were probably developed as lava extrusions from fractures and fissures along with associated faulting and folding.

Scott, D. H.↗
NASA NTRS1972

Structural aspects of Imbrium sculpture, part G

Apollo 16 metric photographs taken at low to high sun angles provided the first stereographic coverage of the distinctive landforms collectively referred to as Imbrium sculpture. The sculpture consists of a series of nearly linear ridges and troughs extending radially outward for more than 1000 km from the rim of the Imbrium Basin. The origin of the ridges and troughs, whether by deposition and impact scoring by fluidized clouds of ejecta from the Imbrium Basin or by faulting and volcanism during and subsequent to basin formation, is controversial. Evidence indicative of the mode of origin of Imbrium sculpture is summarized as follows. Evidence of volcano-tectonic mode of origin is favored by: (1) wide variation in relative age of parts of the sculpture; (2) furrows without rims; (3) absence of ballistic shielding; (4) asymmetry of sculpture; (5) absence of randomly oriented clusters; and (6) association with other features of structural origin. An origin by ejecta scoring and deposition is favored by the gradational ejecta with a Fra Mauro-type texture. Features that are ambiguous as to mode or origin are furrows made of coalesced crater chains and prominent rims on furrows.

Scott, D. H.↗
NASA NTRS1971

Contributions to Astrogeology: Geology of the lunar crater volcanic field, Nye County, Nevada

The Lunar Crater volcanic field in east-central Nevada includes cinder cones, maars, and basalt flows of probably Quaternary age that individually and as a group resemble some features on the moon. Three episodes of volcanism are separated by intervals of relative dormancy and erosion. Changes in morphology of cinder cones, degree of weathering, and superposition of associated basalt flows provide a basis for determining the relative ages of the cones. A method has been devised whereby cone heights, base radii, and angles of slope are used to determine semiquantitatively the age relationships of some cinder cones. Structural studies show that cone and crater chains and their associated lava flows developed along fissures and normal faults produced by tensional stress. The petrography of the basalts and pyroclastics suggests magmatic differentiation at depth which produced interbedded subalkaline basalts, alkali-olivine basalts, and basanitoids. The youngest flows in the field are basanitoids.

Scott, D. H.↗