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Spudis, P. D.

Publications and source records attributed to Spudis, P. D..

50 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Composition of Orientale basin deposits and implications for the lunar basin-forming process

The geologic, spectral and geochemical characteristics of the lunar Orientale basin are discussed, and a model is defined for the generation of Orientale basin deposits. The data indicate that the basin ejecta is composed mainly of anorthositic deposits and no crustal material. The crater was originally 500-600 km across and 50-60 km deep, the latter being too shallow to reach the projected 100 km crustal depth. A proportional growth model is judged acceptable for the Orientale basin. Finally, it is concluded that neither the Apollo 14 nor 16 missions obtained Orientale ejecta material, which could in any case be unidentifiable until more thorough samplings are made of a large portion of the lunar surface.

Spudis, P. D.↗
NASA NTRS1984

Mercury: New identification of ancient multi-ring basins and implications for geologic evolution

A systematic survey of the entire Mariner 10 coverage of Mercury was performed to determine the number, distribution and dimensions of additional ancient basins on the planet. Ancient multi-ringed basins on Mercury can be recognized by the following criteria: (1) arcs of massif chains and isolated massifs that protrude through younger units, (2) arcuate segments of lobate ridges (rupes) that align with massifs in circular patterns, (3) arcuate scarps that are aligned with ridges and massif, and (4) isolated regions of anomalously high topography within the intercrater regions of heavily cratered terrain. All of the newly identified basins predate the mercurian intercrater plains, previously held to be the oldest geologic unit on the planet. Subsequent structural evolution of various regions was influenced by the presence of these basins. Smooth plains units appear to be more extensive than mapped by Mariner 10 and more than 90 percent of them appear to be basin contained or basin related. The concentration of extensive smooth plains material within and associated with basin structural and depositional environments suggests a volcanic origin for most of this unit, analogous to the lunar maria. Basins appear to provide the basic structural pattern of early terrestrial planetary crusts.

Spudis, P. D.↗
NASA NTRS1984

Ring spacing of Mercurian multi-ring basins and basin ring formation

Recent systematic mapping of Mercury has revealed many ancient and previously unrecognized multiring basins. The population of these basins now stands at 20, possibly is as large as 25, and includes at least 76 measurable rings. From the new data base, we present some systematics of basin ring spacing on Mercury, compare them with similar data for the Moon, and draw some preliminary conclusions on conditions of ring formation for basins on the terrestrial planets.

Pike, R. J.↗
NASA NTRS1984

Spectral reflectance studies on the orientale region of the Moon

The Orientale impact occurred in rugged highlands on the southwestern limb of the Moon and was the last of the major basin-forming events. Valuable insight concerning lateral and vertical changes in the composition of the lunar crust can be provided by studies of material exposed by lunar impact basins. These impacts have excavated material from a variety of depths and deposited this ejecta in a systematic manner. In order to investigate the composition of materials exposed on the interior of Orientale basin, near-infrared reflectance spectra were collected for units within the Cordillera ring.

Hawke, B. R.↗
NASA NTRS1983

Beginning and end of lunar mare volcanism

The distribution and characteristics of the early phases of mare vulcanism on the moon are discussed. Breccias have been observed that indicate the presence of magma flows before 3900 Myr BP. A mafic feature has been identified in more than 100 craters at least 1 km across. The absence of buried mare surfaces on the nearside and western hemispheres is attributed to ejecta deposits, and farside basins with no mare fill are suggested to have experienced early mare flooding. Photographs of the bright-rayed Lichtenberg crater have revealed that mare volcanism occurred within the time frame 1700-2000 Myr BP. It is concluded that the moon featured two periods of igneous activity, the last happening at 1000 Myr BP, and beginning 4300 BP.

Schultz, P. H.↗
NASA NTRS1982

Chemical mixing model studies of lunar orbital geochemical data - Apollo 16 and 17 highlands compositions

Chemical mixing model studies of lunar geochemical data for the central and Taurus-Littrow lunar highlands were performed utilizing pristine highland rock types as end member compositions. The central highlands show considerable diversity in composition; anorthosite is the principal rock type in the Apollo 16/Descartes region, while norite predominates in the highlands west of the landing site. This change in crustal composition is coincident with a major color boundary seen in earth-based multispectral data and probably represents the presence of distinct geochemical provinces within the central highlands. The Taurus-Littrow highlands are dominated by norite; anorthosite is far less abundant than in the central highlands. This suggests that the impact target for the Serenitatis basin was different than that of the Nectaris basin and further strengthens the hypothesis that the lunar highlands are petrologically heterogeneous on a regional basis. It is suggested that the lunar highlands should be viewed in terms of geochemical provinces that have undergone distinct and complex igneous and impact histories.

Spudis, P. D.↗
NASA NTRS1981

Volcanism on Mars

In situ chemical analyses of Martian soil by the Viking lander indicate mafic to ultramafic source rocks, consistent with both remote sensing data indicating the presence of pyroxene and olivine and with petrologic modeling which suggests that Martian lavas are iron-rich and ultramafic. Photogeological analysis of the Martian surface reveals two types of volcanic morphology: (1) central volcanoes, developed by continued and prolonged eruption from a point source vent; and (2) volcanic plains, recognized by mare ridges and flow lobes. When these volcanic morphologies are combined with relative age data, a volcanic history may be derived that is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time which gradually suppresses the volcanism.

Greely, R.↗
NASA NTRS1981

Apollo 17 impact melts and their relation to the Serenitatis basin

Regional geologic relations are seen as suggesting that the distribution of highland landforms is not consistent with their derivation from a single impact event but is consistent with multiple events involving both distant basins and smaller, local craters. Thus the highland samples collected at the Apollo 17 landing site may not consist solely of Serenitatis basin ejecta but probably include both exotic ejecta and reworked local material. On the basis of these observations, it is suggested that the Apollo 17 highland melt breccias are not all derived from the Serenitatis basin impact; that is, the aphanitic melt rocks may be either other basin or local crater ejecta. It is thought that if the melt rocks collected at Apollo 17 are all derived from the same impact, the significant chemical and petrographic differences between the rocks may require modification of current models for impact melt petrogenesis.

Spudis, P. D.↗
NASA NTRS1980

Geochemical anomalies on the eastern limb and farside of the moon

A variety of orbital geochemistry and photogeologic data was used to investigate major geochemical anomalies on the east limb and farside of the moon and to determine the processes responsible for their formation. These anomalies are located in the following regions: (1) near Langemak crater, (2) Mare Marginis, (3) Balmer crater, (4) terrain north of Taruntius crater, and (5) Van de Graaff. It was concluded that these anomalies are related to episodes of extrusive igneous activity which produced deposits with a variety of ages and compositions. Some of the associated volcanic deposits exhibit albedos and surface morphologies similar to those of the nearside maria, while others are now thinly covered by highland debris and are commonly represented by light plains units which exhibit clusters of dark-haloed craters. Little evidence was found for a genuine episode of highland volcanism (e.g., Apollo 15 KREEP basalt, highland basalt, etc.). The existence of intermediate basalts on the eastern limb and farside supports previous suggestions that KREEP-like volcanism was not limited to a small area of the lunar nearside. Eastern limb and farside volcanic activity has been more extensive in both space and time and has produced a greater variety of compositions than has previously been thought. Since thinly covered basaltic units can exert a strong influence on regional surface chemistry as determined from orbit, caution is urged in interpreting the surface compositions of highland terrains which exhibit a high density of dark-haloed impact craters.

Hawke, B. R.↗
NASA NTRS1979

Evidence for ancient mare volcanism

The results of the present study suggest that dark-haloed impact craters are indicative of excavated mafic materials, originally emplaced as volcanic units, but subsequently buried by impact ejecta deposits from large craters and basins. Consequently, mapped light plains units should be viewed as soil units that may not reflect the origin of the underlying rock. Some observations which support these conclusions are examined.

Schultz, P. H.↗
NASA NTRS1978

Volcanism in the cratered terrain hemisphere of Mars

Four kinds of Martian volcanoes and their prevalences in the cratered terrain hemisphere (generally the southern hemisphere) are described. Patera, which are large low-profile volcanic structures, appear to be either older shield volcanoes or a unique type of volcano. 'Plains' volcanics represent low-volume eruptions that formed cones, low shields, and other small-scale structures. Flood volcanics are produced by high-volume eruptions, post-date the older and more degraded plateau plains, and occur mostly as basin-fill materials. Plateau plains, the Martian intercrater plains, contain many wrinkle ridges and floor-fractured craters. It is suggested that volcanic processes as well as erosional processes have been important in obliterating small Martian craters and that volcanic products may constitute a significant fraction (up to 44%) of the surface rocks in the cratered terrain

Greeley, R.↗
NASA NTRS1978

Mare volcanism in the Herigonius region of the moon

The paper considers the area in the vicinity of the crater Herigonius. This area contains numerous sinuous rilles, craters with irregular planimetric form, possible pyroclastic cones, and other features of probable volcanic origin, and appears to be the vent region that supplied lavas both northward to Oceanus Procellarum and southward to the Humorum basin. The approach used involves photogeologic interpretation of surface features and mapping of mare units to derive a regional stratigraphic sequence. The sequence of mare volcanism provides insight into the complex emplacement of lunar lavas and the general volcanic history of the moon.

Greeley, R.↗
NASA NTRS1978

Composition and origin of the Apennine Bench Formation

Integration of stratigraphic relationships, geologic setting, surface morphology and remote sensing data suggest that the Apennine Bench Formation is composed of post-Imbrium basin volcanic KREEP basalt flows. This KREEP volcanism occurred shortly after the time of Imbrium basin formation and may have been triggered by the large basin impact which could have provided the structural 'plumbing' through which magma could reach the surface. There are indications that the Apennine Bench Formation may represent the largest surface exposure of highland (nonmare) volcanism preserved on the lunar surface and, as such, provides valuable insight into early lunar crustal processes.

Spudis, P. D.↗