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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Lakshmi Planum: A distinctive highland volcanic province

Lakshmi Planum, a broad smooth plain located in western Ishtar Terra and containing two large oval depressions (Colette and Sacajawea), has been interpreted as a highland plain of volcanic origin. Lakshmi is situated 3 to 5 km above the mean planetary radius and is surrounded on all sides by bands of mountains interpreted to be of compressional tectonic origin. Four primary characteristics distinguish Lakshmi from other volcanic regions known on the planet, such as Beta Regio: (1) high altitude, (2) plateau-like nature, (3) the presence of very large, low volcanic constructs with distinctive central calderas, and (4) its compressional tectonic surroundings. Building on the previous work of Pronin, the objective is to establish the detailed nature of the volcanic deposits on Lakshmi, interpret eruption styles and conditions, sketch out an eruption history, and determine the relationship between volcanism and the tectonic environment of the region.

Roberts, Kari M.↗
NASA NTRS2017

Young Lunar Volcanism: Irregular Mae Patches as Drained Lava Ponds and Inflated Flows

Irregular mare patches (IMPs) were previously proposed as sites of young lunar volcanism and/or endogenic activity [1-3], raising the possibility that volcanism on the Moon may not have ended approximately 1 Ga as determined from surface ages [4]. The wide-spread occurrence of more than 70 IMPs on the lunar nearside suggests a correlation with Th-rich PKT regions and a basaltic composition [1,2]. IMPs exhibit at least two types of deposit morphologies: (a) dome-like, steep-sided and smooth mounds and (b) low-relief ropy (LRR) to hummocky (LRH) materials (Fig. 1). Morphologic indicators such as steep (>40 deg) margin slopes across distances <10 m and crisp boundaries imply ages less than a few 100 Ma [e.g.,1-3]. The IMPs also have relatively few superposed craters >10 m in diameter, and young absolute model ages, which when combined with their superposition on young crater deposits like the continuous ejecta of Aristarchus crater, imply ages approximately 10 Ma to 100 Ma [1,2]. However, the mounds do not exhibit blocky crater morphologies, nor fracturing typical of young volcanic deposits, and the mound texture resembles that of mature regolith [e.g., 2,5], implying a much older age (approximately 3.5 Ga). These contrasting indicators have led to the proposal of widely varying formation mechanisms that range from ancient volcanism modified by recent tectonism [6] or outgassing [3,7], ancient volcanism of atypical materials [8], to Copernican-era volcanism [1,2].

Stopar, J. D.↗
NASA NTRS1992

Thermobarometric studies on the Levack Gneisses: Footwall rocks to the Sudbury Igneous Complex

Granulite and amphibolite facies gneisses and migmatites of the Levack Gneiss Complex occupy a zone up to 8 km wide around the northern part of the Sudbury Igneous Complex (SIC). Orthopyroxene- and garnet-bearing tonalitic and semipelitic assemblages of granulite facies grade occur within 3 km of the SIC together with lenses of mafic and pyroxenitic rock compositions normally represented by an amphibole +/- cpx-rich assemblage; amphibolite facies assemblages dominate elsewhere in this terrain. These 2.711-Ga gneisses were introduced by (1) the Cartier Granite Batholith during late Archaean to early Proterozoic time and (2) the SIC, at 1.85 Ga, which produced a contact aureole 1-1.5 km wide in which pyroxene hornfelses are common within 200-300 m of the contact. A suite of 12 samples including both the opx-gt and amphibole-rich rock compositions have been studied. Garnets in the semipelitic gneisses are variably replaced by a plg-bio assemblage. Thermobarometric calculations using a variety of barometers and thermometers reported in the literature suggest that the granulite facies assemblages formed at depths in the 21-28 km range (6-8 kbar). Textures and mineral chemistry in the garnet-bearing semipelitic rocks indicate that this terrain underwent a second metamorphic event during uplift to depth in the 5-11 km range (2-3 kbar) and at temperatures as low as 500-550 C. This latter event is distinct from thermal recrystallization caused by the emplacement of the SIC; it probably represents metamorphism attributable to intrusion of the Cartier Granite Batholith. These data allow two interpretations for the crustal uplift of the Levack Gneisses: (1) The gneisses were tectonically uplifted prior to the Sudbury Event (due to intrusion of the Cartier Batholith); or (2) the gneisses were raised to epizonal levels as a result of meteorite impact at 1.85 Ga.

James, R. S.↗
NASA NTRS1977

Remote sensing of geobotanical relations in Georgia

The application of remote sensing to geological investigations, with special attention to geobotanical factors, was evaluated. The general areas of investigation included: (1) recognition of mineral deposits; (2) geological mapping; (3) delineation of geological structure, including areas of complex tectonics; and (4) limestone areas where ground withdrawal had intensified surface collapse.

Arden, D. D., Jr.↗
NASA NTRS1991

Geologic history and channeling episodes of the Chryse Planitia region of Mars

The study of the Chryse Planitia region of Mars is based on geologic mapping on a 1:5,000,000 scale shaded relief map. The map area includes Chryse and southern Acidalia Planitiae; the circum Chryse channels and chaotic terrains; Xanthe, southern Tempe, and western Arabia Terrae; Lunae Planum; and northeastern Valles Marineris. The aim of the study is twofold: (1) to obtain relative ages of the outflow channels by performing and compiling detailed stratigraphic analyses; and (2) to correlate channeling episodes with causative mechanisms (such as volcanism and tectonism) and resulting effects (such as climate change). The geologic history given based on this mapping, includes the documentation of a previously unproposed channeling episode in the region as well as the presently favored hypotheses concerning the nature and origin of the channeling events. It is concluded that the history of the Chryse region suggests that two major periods of tectonic activity resulted in two episodes of channeling in the highlands surrounding Chryse Planitia.

Rotto, Susan L.↗
NASA NTRS1993

Original size of the Vredefort structure, South Africa

The Vredefort structure is located approximately 120 km southwest of Johannesburg, South Africa, and is deeply eroded. Controversies remain on the origin of this structure with the most popular hypotheses being: (1) by impact cratering about 2.0 Ga; (2) as a cryptoexplosion structure about 2.0 Ga; and (3) by purely tectonic processes starting at about 3.0 Ga and ending with the Vredefort event at 2.0 Ga. In view of recent work in which the granophyre dikes are interpreted as the erosional remants of a more extensive impact melt sheet, injected downward into the underlying country rocks, the impact origin hypothesis for Vredefort is adopted. In order to estimate the original dimensions of the Vredefort impact structure, it is assumed that the structure was initially circular, that its predeformation center corresponds to the center of the granitic core, and that the pre-Vredefort geology of the area prior to approximately 2.0 Ga ago is as suggested by Fletcher and Reimold. The spatial relationship between shock metamorphic effects, the shock pressures they record, and the morphological features of the crater were established for a number of large terrestrial craters. The principles of crater formation at large complex impact structures comparable in size to Vredefort were also established, although many details remain unresolved. An important conclusion is that the transient crater, which is formed directly by excavation and displacement by the shock-induced cratering flow-field (i.e., the particle velocity flow field existing in the region of the transient crater but behind the initial outgoing shock front), is highly modified during the late stage processes. The original transient crater diameter lies well within the final rim of the crater, which is established by structural movements during late-stage cavity modification.

Therriault, A. M.↗
NASA NTRS2009

Geologic Map of the Snegurochka Planitia Quadrangle (V-1): Implications for Tectonic and Volcanic History of the North Polar Region of Venus

Geologic mapping of Snegurochka Planitia (V-1) reveals a complex stratigraphy of tectonic and volcanic features that can provide insight into the geologic history of Venus and Archean Earth [1,2], including 1) episodes of both localized crustal uplift and mantle downwelling, 2) shifts from local to regional volcanic activity, and 3) a shift back to local volcanic activity. We present our progress in mapping the spatial and stratigraphic relationships of material units and our initial interpretations of the tectonic and volcanic history of the region surrounding the north pole of Venus

Hurwitz, D. M.↗
NASA NTRS1991

Impact craters on Venus

Compared with volcanism and tectonism, impact cratering on Venus has played an overall minor role in sculpting the present-day landscape. The study of Venus impact craters is vital to help place the chronology of the geologic features on the surface in the context of the planet's geological evolution. The degradation of impact craters also provides information on surface and interior processes, particularly alteration by tectonism and volcanism. Through orbit 1422, Magellan mapped about 450 impact craters, with diameters ranging from 2 to 275 km, within an area of about 226 million sq km, or 49 percent of the planet's surface. These craters and their associated deposits show surprisingly little evidence of degradation at the 75 m/pixel resolution of the Magellan SAR. Remarkably few craters in the Magellan images appear to be in the process of being buried by volcanic deposits or destroyed by tectonic activity.

Schaber, G. G.↗
NASA NTRS2004

Europa's Icy Shell: A Bridge Between Its Surface and Ocean

Europa, a Moon-sized, ice-covered satellite of Jupiter, is second only to Mars in its astrobiological potential. Beneath the icy surface, an ocean up to 150 km deep is thought to exist, providing a potential habitat for life,and a tempting target for future space missions. The Galileo mission to the Jovian system recently ended, but there are already long-range plans to send much more capable spacecraft,such as the proposed Jupiter Icy Moons Orbiter (JIMO), to take a closer look at Europa and her siblings, Ganymede and Callisto, some time in the next two decades. Europak outer icy shell is the only interface between this putative ocean and the surface, but many aspects of this shell are presently poorly understood; in particular, its composition, thickness, deformational history, and mechanical properties. To discuss the ice shell and our current understanding of it, 78 scientists from the terrestrial and planetary science communities in the United States and Europe gathered for a 3-day workshop hosted by the Lunar and Planetary Institute in Houston in February. A key goal was to bring researchers from disparate disciplines together to discuss the importance and limitations of available data on Europa with a post-Galileo perspective. The workshop featured 2 days of reviews and contributed talks on the composition, physical properties, stratigraphy, tectonics, and future exploration of the ice shell and underlying ocean. The final morning included an extended discussion period, moderated by a panel of noted experts, highlighting outstanding questions and areas requiring future research.

Schenk, Paul↗
NASA NTRSDate not supplied

Evidence for Early Extension and Pressure Drop Related to Magma Plumbing in Noctis Labyrinthus (Mars)

Noctis Labyrinthus is a complex district located between the western side of Valles Marineris’ large outflow channel and the Tharsis volcanic plateau. This region is characterized by a system of steep-walled canyons and an inter-connected network of scalloped pits that manifest in various orientations and size. The formation history of this area has been a topic of substantial discussion in the past. Previous studies have proposed a karst landscape with associated caves and water-related processes [1,2,3] a network of lava tubes [4,5], or a volcano-tectonic activity as a driving process for the formation of Noctis Labyrinthus [6,7,8,9]. However, none of these models have been confirmed or entirely accepted; although, the erosional nature of Noctis Labyrinthus is supported by the presence of channelized lava flows still visible on its floor [5]. In this work, we use MOLA and HRSC data to produce a new structural map of the region, we analyse fault systems (chronology and orientation), the relationships between faults and pit chains, and we finally propose a deformational model that can explain the sequences of events responsible about the formation of Noctis Labyrinthus.

M. El Yazidi↗
NASA NTRS1973

Analysis of ERTS-1 imagery of Wyoming and its application to evaluation of Wyoming's natural resources

The author has identified the following significant results. Significant results of the Wyoming investigation during the first six months include: (1) successful segregation of Precambrian metasedimentary/metavolcanic rocks from igneous rocks; (2) discovery of iron formation within the metasedimentary sequence; (3) mapping of previously unreported tectonic elements of major significance; (4) successful mapping of large scale fractures of the Wind River Mountains; (5) sucessful distinction of some metamorphic, igneous, and sedimentary lithologies by color-additive viewing of ERTS images; (6) mapping and interpretation of glacial features in western Wyoming; and (7) development of techniques for mapping small urban areas.

Marrs, R. W.↗
NASA NTRS1973

Analysis of ERTS-1 imagery and its application to evaluation of Wyoming's natural resources

The author has identified the following significant results. Significant results of the Wyoming ERTS-1 investigation during the first six months (July-December 1972) included: (1) successful segregation of Precambrian metasedimentary/metavolcanic rocks from igneous rocks, (2) discovery of iron formation within the metasedimentary sequence, (3) mapping of previously unreported tectonic elements of major significance, (4) successful mapping of large scale fracture systems of the Wind River Mountains, (5) successful distinction of some metamorphic, igneous, and sedimentary lithologies by color additive viewing, (6) mapping of large scale glacial features, and (7) development of techniques for mapping small urban areas.

Houston, R. S.↗
NASA NTRS1985

Satellite laser ranging and its applications

Satellite laser ranging (SLR) provides an important capability for precise orbit determination and for geophysical parameter estimation to support a number of contemporary geodynamic and oceanographic investigations. The precision of the SLR measurement has improved from the early meter-level systems to the current capabilities of a few centimeters for the best systems. The accuracy of the orbits and geophysical parameter recovery have shown an associated improvement. Polar motion with accuracies of 2 mas, station coordinates better than 10 cm, and interstation baseline rates indicative of tectonic motion are determined routinely with the current set of global SLR data. This discussion reviews the SLR measurement, analysis approach, and some of the recent results derived from the current SLR data set.

Tapley, B. D.↗
NASA NTRS1986

High precision U-PB geochronology and implications for the tectonic evolution of the Superior Province

The underlying mechanisms of Archean tectonics and the degree to which modern plate tectonic models are applicable early in Earth's history continue to be a subject of considerable debate. A precise knowledge of the timing of geological events is of the utmost importance in studying this problem. The high precision U-Pb method has been applied in recent years to rock units in many areas of the Superior Province. Most of these data have precisions of about + or - 2-3 Ma. The resulting detailed chronologies of local igneous development and the regional age relationships furnish tight constraints on any Archean tectonic model. Superior province terrains can be classified into 3 types: (1) low grade areas dominated by meta-volcanic rocks (greenstone belts); (2) high grade, largely metaplutonic areas with abundant orthogneiss and foliated to massive I-type granitoid bodies; and (3) high grade areas with abundant metasediments, paragneiss and S-type plutons. Most of the U-Pb age determinations have been done on type 1 terrains with very few having been done in type 3 terrains. A compilation of over 120 ages indicates that the major part of igneous activity took place in the period 2760-2670 Ma, known as the Kenoran event. This event was ubiquitous throughout the Superior Province.

Davis, D. W.↗
NASA NTRS1993

Global organization of tectonic deformation on Venus

The geographic organization of surface deformation on Venus as on Earth is a key to understanding the global tectonic system. To date we have mapped the distribution of three unambiguous tectonic land forms on Venus: (1) linear foldbelts analogous to those at plate margins of the Earth; (2) linear rift zones, analogous to continental rifts on the Earth; and (3) distributed plains deformation in the form of wrinkle ridges and extensional faults and fractures. The linear foldbelts are the dominant structural style in the Northern Hemisphere; ninety percent of the planet's foldbelts lie above the equator. In contrast, compressive deformation in the Southern Hemisphere is dominated by two large, sweeping patterns of wrinkle ridges. The two hemispheres are divided by an equatorial region that is largely covered by rift zones and several large tessera blocks. A tectonic model of generally poleward convergence of the Northern Hemisphere explains the distribution of foldbelts and rift zones. In our model, a northern hemispherical plate (or system of plates) moves poleward and deforms along discrete, predominately longitudinal bands. We recognize four types of foldbelts based on their relationships to other large-scale tectonic features on Venus. There are foldbelts that lie within the low plains, foldbelts associated with coronae, novae and chasmata, foldbelts that lie at the margins of poly-deformed tessera plateaus, and the folded mountain belts around Lakshmi Planum. We see a geometric increase in the area of fold belts when normalized to percent area at a given latitude. This increase is consistent with our model of poleward convergence. Also, the orientations of most foldbelts are either approximately north-south or parallel to lines of latitude in the northern hemisphere. This observation is also consistent with the model in that the longitudinal bands are the result of the decreasing area of the sphere as the plate moves poleward and the latitudinal belts are the direct result of poleward compression. The trends of wrinkle ridges have been mapped over the planet and several large, sweeping patterns evidently reflect long-wavelength topography. Using wrinkle ridges as paleostress indicators, we have developed local and regional stress trajectory maps.

Bilotti, Frank↗
NASA NTRS2005

Geological Evolution of the Ganiki Planitia Quadrangle (V14) on Venus

The Ganiki Planitia quadrangle (25-50degN, 180-210degE) is located north of Atla Regio, south of Vinmara Planitia, and southeast of Atalanta Planitia. The region contains a diverse array of volcanic-, tectonic- and impact-derived features, and the objectives for the ongoing mapping effort are fivefold: 1) explore the formation and evolution of radiating dike swarms within the region, 2) use the diverse array of volcanic deposits to further test the neutral buoyancy hypothesis proposed to explain the origin of reservoir-derived features, 3&4) unravel the volcanic and tectonic evolution in this area, and 5) explore the implications of 1-4 for resurfacing mechanisms. Here we summarize our onging analysis of the material unit stratigraphy in the quadrangle, data central to meeting the aforementioned objectives successfully.

Grosfils, E. B.↗
NASA NTRS1975

Lunakhod-2: Preliminary research results

Results from the Lunakhod 2 experiment on the surface property variations and relief structure of lunar craters are presented. Tectonic fractures, iron composition of lunar rocks, magnetic measurements, lunar sky brightness, and corpuscular radiation of the lunar body were studied.

Vinogradov, A. P.↗
NASA NTRS1990

On the nature and rate of resurfacing of Venus

Crrater production and obliteration are modeled for the plains of Venus, using (1) the observed distribution of Venus-crossing asteroids and comets; (2) viscous relaxation of crater topography; and (3) erosion and burial by atmospheric, volcanic, and tectonic processes. Crater lifetimes are assumed to be proportional to crater depths for both classes of obliterative processes although the individual criteria vary. An average crater retention age between 0.4 to 2.0 Gyr is estimated for plains, under the assumption that craters are produced and not removed. The range is driven by uncertainty in identifying degraded impact as opposed to volcanic craters. On the other hand, crater retention ages greater than about 1.6 Gyr are unlikely if viscous relaxation operates without loading of crater floor by burial. The preferred model has plains subject to crater production and obliteration processes that vary over both space and time.

Arvidson, Raymond E.↗