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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Pyroclastic deposits on the western limb of the moon

A geologic characterization is presented of 17 newly identified localized pyroclastic deposits on the western limb of the moon. The results show that lunar pyroclastic deposits are more pervasive on the western limb of the moon than once thought. The western limb dark-mantle deposits in the proximal zone are probably related to faults and fractures associated with the Cordillera ring of Orientale Basin. All the localized pyroclastic deposits on the western limb for which near-infrared reflectance spectra have been obtained exhibit parameter that allowed them to be assigned to the three spectral groups described elsewhere. Western limb pyroclastic deposits appear to represent various stages in a formational sequence in which an initial explosive phase is followed by varying amounts of mare flooding. In view of their sequential formation, both the pyroclastic and mare materials associated with individual volcanic complexes may be the products of the same parent magmas and have very similar compositions.

Coombs, Cassandra R.↗
NASA NTRS1991

Petrology and provenance of Apollo 15 Station 6 core 15009 and its bearing on site geology

Petrographic and microprobe studies were conducted of six soil samples from six different levels of the 30-cm-deep single-drive tube core 15009 obtained from the regolith of the Apennine Front at Station 6 of the Apollo 15 site. A model for the near-surface stratigraphy of the site is constructed, with due account for the results of previous studies of surface and core soils. Highland rocks were found to account for 9 percent of the mineral and lithic fragments in core 15009. The observed correlation between crystalline breccia fragments and green glass indicate that the primitive regolith on the premare Apennine Front contained abundant crystalline breccia fragments that were mixed with puroclastic green glass added to that regolith early in the mare eruptive sequence. KREEP basalts were found to be the parent rocks for 40 percent of the core fragments. It is inferred that KREEP basalts of the Apennine Bench Formation underlie mare basalts at the site. Olivine-normative mare basalt fragments comprise only 14 percent of the core-15009 source rocks but are much more abundant away from the Front.

Basu, A.↗
NASA NTRS1986

Petrology, chemistry, and origin of Apollo 15 regolith breccias

Variations in modal petrology, mineral compositions, and bulk compositions were determined for ten Apollo 15 regolith breccias for comparison with local soils and assessment of the intrasite petrologic variability of the Apollo 15 regolith. Based on the above criteria the breccias are of local origin and mimic the soils from the corresponding sampling stations, with the exception of station 2 breccia 15205. This sample formed from an anomalous regolith, and although not considered exotic to the site is not representative of the soil at the site. KREEP basalt and green glass components vary from trace amounts to dominant in the breccias, evidence that these materials entered the regolith prior to formation of the breccias. Breccias from the edge of Hadley Rille are modally richer in highland fragments than the soils, whereas at the base of Hadley Delta the reverse is true. This is explained by the loss of material into the Rille to be replaced by basalt-derived material, making the soils more basalt-rich. At the base of Hadley Delta highland material is accumulating and the soils are becoming more highland-rich. Over billions of years these processes have developed differences between the present day, evolving soils, and 'fossil' nonevolving soils represented by the regolith breccias. This shows that there has been little change in the geology and the morphology of the Apollo 15 site, probably since the eruption of mare basalts at the site (about 3.3 b.y.).

Simon, S. B.↗
NASA NTRS2001

The Summer 1997 Eruption at Pillan Patera on Io: Implications for Ultrabasic Lava Flow Emplacement

Galileo data and numerical modeling were used to investigate the summer 1997 eruption at Pillan Patera on Io. This event, now defined as 'Pillanian' eruption style, included a high-temperature (greater than 1600 C), possibly ultrabasic, 140-km-high plume eruption that deposited dark, orthopyroxene-rich pyroclastic material over greater than 125,000 sq km, followed by emplacement of dark flow-like material over greater than 3100 sq km to the north of the caldera. We estimate that the high-temperature, energetic episode of this eruption had a duration of 52- 167 days between May and September 1997, with peak eruption temperatures around June 28, 1997. Galileo 20 m/pixel images of part of the Pillan flow field show a widespread, rough, pitted surface that is unlike any flow surface we have seen before. We suggest that th.s surface may have resulted from (1) a fractured lava crust formed during rapid, low-viscosity lava surging, perhaps including turbulent flow emplacement; (2) disruption of the lava flow by explosive interaction with a volatile-rich substrate: or (3) a combination of 1 and 2 with or without accumulation of pyroclastic materials on the surface. Well-developed flow lobes are observed, suggesting that this is a relatively distal part of the flow field. Shadow measurements at flow margins indicate a thickness of approx. 8-10 m. We have modeled the emplacement of putative ultrabasic flows from the summer 1997 Pillan eruption using constraints from new Galileo data. Results suggest that either laminar sheet flows or turbulent channelized flows could have traveled 50-150 km on a flat. unobstructed surface, which is consistent with the estimated length of the Pillan flow field (approx. 60 km). Our modeling suggests low thermal erosion rates (less than 0.1 m/d), and that the formation of deep (greater than 20 m) erosion channels was unlikely, especially distal to the source. We calculate a volumetric flow rate of approx. 2-7 x l0(exp 3) cu m/s, which is greater than those for typical Mauna Loa/Kilauea flows but comparable to those for the (1783) Laki eruption and the inferred flow rates of the Roza flows in the Columbia River flood basalts. The differences in ultrabasic eruption styles on Earth and Io appear to be controlled by the different eruption environments: Plumes at sites of ultrabasic eruptions on Io suggest strong magma-volatile: interactions on a low-gravity body lacking an atmosphere, whereas the geology at sites of komatiite eruptions on Earth suggest mostly submarine emplacement of thick flows with a pronounced lack of subaerial explosive activity.

Williams, David A.↗
NASA NTRS2001

The Summer 1997 Eruption at Pillan Patera on Io: Implications for Ultrabasic Lava Flow Emplacement

Galileo data and numerical modeling were used to investigate the summer 1977 eruption at Pillan Patera on Io. This event, now defined as "Pillanian" eruption style, included a high-temperature (greater than 1600 C), possible ultrabasic , 140-km-high plume eruption that deposited dark, orthopyroxene-rich pyroclastic material over greater than 125,000 sq km, followed by emplacement of dark flow-like material over greater than 3100 sq km to the north of the caldera. We estimate that the high-temperature, energetic episode of this eruption had a duration of 52 - 167 days between May and September 1997, with peak eruption temperatures around June 28, 1997. Galileo 20 m/pixel images of part of the Pillan flow field show a wide-spread, rough, pitted surface that is unlike any flow surface we have seen before. We suggest that this surface may have resulted from: 1. A fractured lava crust formed during rapid, low-viscosity lava surging, perhaps including turbulent flow emplacement. 2. Disruption of the lava flow by explosive interaction with a volatile-rich substrate. or 3. A combination of 1 and 2 with or without accumulation of pyroclastic material on the surface. Well-developed flow lobes are observed, suggesting that this is a relatively distant part of the flow field.Shadow measurements at flow margins indicate a thickness of-8 - 10 m. We have modeled the emplacement of putative ultrabasic flow from the summer 1997 Pillan eruption using constraints from new Galileo data. Results suggest that either laminar sheet flows or turbulent channelized flows could have traveled 50 - 150 km on a flat, unobstructed surface, which is consistent with the estimated length of the Pillan flow field (approx. 60 km). Our modeling suggests low thermal erosion rates (less than 4.1 m/d), and that the formation of deep (greater than 20 m) erosion channels was unlikely, especially distal to the source. We calculate a volumetric flow rate of approx. 2 - 7 x 10(exp 3)cu m/s, which is greater than those for typical Mauna Loa/Kilaueaq flows but comparable to those for the (1783) Laki eruption and the inferred flow rates of the Roza flows in the Columbia River flood basalts. The differences in ultrabasic eruption styles on Earth and Io appear to be controlled by the different eruption environments; Plumes at sites of ultrabasic eruptions on Io suggest strong magma-volatile interactions on a low-gravity body lacking an atmosphere, whereas the geology at sites of komatiite eruptions on Earth suggest mostly submarine emplacement of thick flows with a pronounced lack of subaerial explosive activity.

Williams, David A.↗
NASA NTRS2015

Revisiting the West Clearwater Lake Impact Structure, Canada

The West and East Clearwater Lake impact structures are two of the most distinctive and recognizable impact structures on Earth. Known regionally as the "Clearwater Lake Complex", these structures are located in northern Quebec, Canada (56 deg 10 N, 74 deg 20 W) approximately 125 km east of Hudson Bay. The currently accepted diameters are 36 km and 26 km for the West and East structures, respectively. Long thought to represent a rare example of a double impact, recent age dating has called this into question with ages of approximately 286 Ma and approximately 460-470 Ma being proposed for the West and East structures, respectively. Relatively little is known about the East Clearwater Lake structure. There is no surface exposure and what information there is comes from geophysics and two drill cores obtained in the 1960s. In contrast, the West Clearwater Lake structure is relatively well preserved with large ring of islands in the approximately 30 km diameter lake. Much of the work done on West Clearwater stems from field investigations carried out in 1977 driven by the Apollo program, with a focus on the impact melt rocks and other impactites, which are well exposed on the ring of islands. To our knowledge, the Clearwater Lake impact structures have not been the focus of detailed impact geology field investigations since the 1977 expedition and the only geological map that exists is from the 1960s and is at the reconnaissance level. Our knowledge of impact cratering processes have increased substantially since this time, as have the analytical techniques available for samples. This provided the motivation for a joint Canadian-US-UK expedition to the West Clearwater Lake impact structure in August and September 2015, under the auspices of the FINESSE (Field Investigations to Enable Solar System Science and Exploration) project, part of NASA's Solar System Exploration Research Virtual Institute (SSERVI). We focus here on the impactites of the West Clearwater Lake impact structure. Other ongoing studies, also presented at this conference, focus on central uplift formation, the impact-generated hydrothermal system, xxxx and using WCIS as an analog test site for crew studies of sampling protocols].

West Clearwater Lake↗
NASA NTRS1982

Identification of a precambrian rift through Missouri by digital image processing of geophysical and geological data

A newly discovered feature in the midcontinent - a gravity low that begins at a break in the midcontinent gravity high in SE Nebraska, extends across Missouri in a NW-SE direction, and intersects the Mississippi Valley graben to form the Pascola arch - is discussed. The anomaly varies from 120 to 160 km in width, extends approximately 700 km, and is best expressed in southern Missouri, where it has a Bouguer amplitude of about -34 mGal. It is noted that the magnitude of the anomaly cannot be explained on the basis of a thickened section of Paleozoic sedimentary rock. The gravity data and the sparse seismic refraction data for the region are found to be consistent with an increased crustal thickness beneath the gravity low. It is thought that the gravity anomaly is probably the present expression of a failed arm of a rifting event, perhaps one associated with the spreading that led to or preceded formation of the granite and rhyolite terrain of southern Missouri.

Guinness, E. A.↗
NASA NTRSDate not supplied

SHERLOC: Results of the first 350 sols of operations

On February 18th 2021, the Perseverance rover landed in Jezero crater, Mars. This site was chosen because orbiter data analysis provides evidence that the crater hosted a stream-fed lake during the Martian Noachian period. The Octavia Butler landing site is located ~1.9 km east of the remnants of a river delta. Deltaic and lacustrine sediments can preserve biosignatures, making Jezero crater a prime target for Mars sample return science. One of the seven instruments on Perseverance’s science payload is SHERLOC –Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals. SHERLOC combines fluorescence and Raman spectroscopy with microscopic imaging to analyze surface material to better understand the history of the aqueous environments recorded in the rocks of Jezero crater and to search for potential biosignatures. SHERLOC imaging obtains high spatial resolution images of geological targets to identify grain-scale structure and texture. SHERLOC spectroscopy enables high-sensitivity detection, characterization, and spatially resolved correlation of trace organic materials. Native fluorescence emissions from aromatic organic species allow for detection and classification of aromatic organic molecules, whereas Raman scattered photons from molecules allow identification of functional groups of organics, chemicals, and minerals. In the first 300 sols, SHERLOC has analyzed 3 natural surfaces, and 5 abraded rock patches created during the Crater Floor Campaign within Jezero crater. SHERLOC has been able to identify phosphates, amorphous/microcrystalline silicate (AMS), olivine, sulfates, and carbonates in abraded patches in the green zone campaign within Jezero Crater Máaz and Séítah formations. Within these detections we have begun to tell the story of what this crater was like when it was full of liquid water over 3 billion years ago. In each of these samples we have identified fluorescence features that are likely aromatic organics native to the rock interiors. We have identified multiple unique fluorescence signatures, within each of the abraded patches. The organic signatures have either been widely distributed over an extended area, which is probably due to planetary wide dust, or have spatially resolved locations that are collocated with different mineral signatures. Note: Additional information available on attachment.

L. W. Beegle↗
NASA NTRS1992

Vendian microfossils in metasedimentary cherts of the Scotia Group, Prins Karls Forland, Svalbard

Sedimentary rocks of the Scotia Group, Prins Karls Forland, Svalbard, have been metamorphosed to lower greenschist facies. Yet Scotia chert nodules contain abundant organic-walled microfossils belonging to at least seventeen taxa. Their black colour indicates that the fossils underwent substantial thermal alteration. However, it is suggested that preservation in a matrix of early diagenetic silica shielded them from the most destructive mechanical and chemical effects of metamorphism. Microbial mats and large acanthomorphic acritarchs suggest a coastal marine depositional environment; the acritarchs further indicate an early Vendian age for the sediments. The Scotia fossils bear a close resemblance to assemblages described from the Doushantuo Formation, China and elsewhere, demonstrating the broad geographical distribution of biostratigraphically important Vendian taxa. Briareus and Echinosphaeridium are described as new genera; Briareus borealis is described as a new species, while Echinosphaeridium maximum is proposed as a new combination.

Non-NASA Center↗
NASA NTRS1973

Concerning the meteoritic origin of the Puchezh-Katunki crater

Criticism of the works of Vardaniants (1961) and Goretskii (1962) regarding the origin of the Puchezh-Katunki crater, and development of a new hypothesis regarding this disturbance. Although Vardaniants defines the Puchezh-Katunki disturbance as a structure of explosive nature and assumes that the explosion originated as a consequence of accumulation of gases in the crystalline basement of the Russian platform, he lacks evidence to qualify this explosion as coming from a depth. Goretskii's tectonic-injection hypothesis attributes the formation of the disturbance to penetration of an intrusion of basic and ultrabasic rocks into the Paleozoic rocks of the platform. It is shown that, even if the intrusion were spread somewhere at depth, it could not account for the extent of the deformation in the disturbance. It is suggested that this disturbance is of meteoritic origin, since the structure and morphology of the region are similar to the sloping conical surface produced by an explosive meteor crater. The energy, mass, and size of the asteroid which could cause such a disturbance are estimated, and it is shown that the probability of the occurrence of an impact of this size is finite over geological time.

Firsov, L.↗
NASA NTRS1993

Transmantle flux tectonics

Venus, Earth, and Mars have surfaces that display topographic domes and depressions with quasi-circular planimetric shapes, relief of 0 to several km, and large spatial scales (10(exp 2) to 10(exp 4) km). Our morphostructural mapping reveals hierarchical arrangements of these features. They are explained by a model of long-acting mantle convection, as a particular case of convection in a stratified and random inhomogeneous medium, which develops the form of a hierarchy of different convective pattern scales, each arising from different levels in the mantle. The hypothesis of transmantle flux tectonics parsimoniously explains a diversity of seemingly unrelated terrestrial planetary phenomena, including Earth megaplumes, global resurfacing epochs on Venus, and cyclic ocean formation and global climate change for Mars. All these phenomenon are hypothesized to be parsimoniously explained by a process of transmantle flux tectonics in which long-acting mantle convection generates stresses in blocks of planetary lithosphere to produce distinctive quasi-circular global-hierarchical morphostructure (QGM) patterns. Transmantle flux tectonics differs from plume tectonics in that individual plumes are not considered in isolation. Rather, a wholly interactive process is envisioned in which various spatial and temporal scales of convection operate contemporaneously and hierarchically within other scales. This process of continual change by hierarchical convective cells affects the surface at varying temporal and spatial scales, and its effects are discernable through their relic geological manifestations, the QGM patterns.

Finn, V. J.↗
NASA NTRS1996

Workshop on evolution of igneous asteroids: Focus on Vesta and the HED meteorites

Recently, the geology of the surface of Vesta has been coming to light. In 1983 Gaffey first began showing maps of the surface geology of Vesta constructed from numerous spectra obtained at different times as the asteroid rotated. By noting the details of spectral variation with rotation, he was able to develop two possible gross-scale geologic maps of Vesta showing the distributions of mafic and ultramafic materials. These maps were published in 1997. Finally, the capabilities of the Hubble Space Telescope were brought to bear on Vesta and images with a resolution of about 50 km were obtained using four different filters by Binzel and co-workers. Maps produced by this team published in 1997 began to reveal the geology of Vesta in sufficient detail that crude interpretations of the geologic history of the asteroid could be attempted. Additionally, in 1993 Binzel and Xu published a study of small asteroids in the region near Vesta in orbital-element space. In this study, they showed that there are a number of asteroids a few kilometers in size with reflectance spectra like that of Vesta that form a trail in orbital-element space from near Vesta to near resonances that can more easily supply material to near-Earth space. Binzel and Xu thus concluded that these small asteroids were spells of Vesta ejected by impact and that some of their brethren had been perturbed to Earth-approaching orbits. They suggested that these latter were the immediate parents of HED meteorites. This seemed to remove a long-standing dynamical objection to Vesta as the HED parent body, as discussed by Wasson and Wetherill in 1979. Within the last few years, NASA has initiated the Discovery program of low-cost, rapid-timescale development, exploration missions. Vesta has been proposed as an object worthy of study by a Discovery mission, although a Vesta mission has not yet been selected. With all the recent activity aimed at studying Vesta and the HED meteorites, and the possibility of a space mission to Vesta, we felt that time was ripe to convene a workshop bringing together astronomers, meteoriticists, and planetary geologists to focus on what could be learned about the geologic evolution of Vesta through integrating astronomical and HED meteorite studies. This, of course, assumes that the HED meteorites are from Vesta, and this issue was specifically addressed (but not resolved) in the workshop. Indeed, it seems likely that this issue can only be resolved by returning samples from Vesta for detailed study on Earth. The workshop was held at the LPI on October 16-18,1996, and was attended by some 70 scientists. Sessions included a set of talks on Earth- and space-based astronomical observations of Vesta plus the evidence pro and con for Vesta being the HED parent body, talks on the petrology and geochemistry of HED meteorites, talks on the formation and dynamics of ejecta from Vesta, talks on the thermal history of asteroids and HED meteorites, volcanic processes and differentiation history, and a short session devoted to possible missions to Vestal By all accounts, the workshop was considered a great success, although this is the opinion of a biased set of observers.

Mittlefehldt, D. W.↗
NASA NTRS1985

Tectonic rotations within the Rio Grande rift - Evidence from paleomagnetic studies

Paleomagnetic studies on Miocene Pliocene volcanic rocks from the Espanola basin of the Rio Grande rift, New Mexico, reveal directions discordant form the expected mean direction for North America. The Paliza Canyon Formation, Tschicoma Formation, and Lobato Basalt, all sampled in the Jemez Mountains west of the Pajarito fault zone, have mean declinations east of the expected mean. The Cerros del Rio volcanics, lying east of the Pajarito fault zone, have a westerly declination. Combined with published data on the Santa Fe Group sediments east of the fault zone, and the Valles Rhyolite, west of the fault zone, distinct rotations of the two areas are evident. The western block has rotated clockwise 12 deg, while the eastern block shows 16 deg of conter-clockwise motion. Differential rotations of 25-30 deg are calculated between the two blocks; 4 deg/m.y. is the minimum differential rotation for the past 5 m.y. Geologic explanations for these rotations include the opening of the Rio Grande rift in response to clockwise rotation of the Colorado Plateau and significant left slip along the Rio Grande rift.

Brown, L. L.↗
NASA NTRS1990

Lakshmi Planum, Venus - Characteristics and models of origin

The distinctive and unique Venusian geological structure, Lakshmi Planum, is an expansive relatively smooth flat plateau containing two large shield volcanos and abundant volcanic plains in the midst of a region of extreme relief. The characteristics which distinguish Lakshmi from other volcanic regions known on the planet, such as Beta Regio, are identified. These include its high altitude and plateaulike nature; the presence of two very large low shield structures with distinctive central paterae and long radiating flows; and its compressional tectonic environment. The detailed nature and significance of the volcanic deposits on Lakshmi are determined; the erruption styles and conditions are interpreted; and the link between the observed volcanism and tectonic environment of the region is discussed. Models for the formation of Lakshmi Planum are presented and evaluated.

Roberts, Kari M.↗
NASA NTRS1979

Serenitatis multi-ringed basin - Regional geology and basin ring interpretation

New topographic data allow a reassessment of the ring structure and distribution of facies of the Serenitatis basin (SB) and correlation with the younger and essentially same-size Orientale basin. Three major rings of the main (southern) SB are mapped: the Linne ring, outlined by mare ridges, average diameter 420 km; the Haemus ring, outlined by basin-facing scarps and massifs with crenulated borders, 610 km; and the Vitruvius ring, outlined by basin-facing linear scarps and massifs, 880 km. The second ring is interpreted as the rim of the transient cavity, while Serenitatis ejecta should be present in significant amounts at the junction of the Serenitatis and Imbrium third rings. The new reconstruction indicates that portions of the SB are better preserved than previously thought, consistent with recent stratigraphic and sample studies that suggest an age (as young as 3.87 plus or minus 0.04 b.y.) for SB which is older than, but close to, the time of formation of the Imbrium basin.

Head, J. W., III↗
NASA NTRS1993

Remote sensing studies of the terrain northwest of Humorum basin

We have used near-infrared reflectance spectra and Earth-based radar data to investigate the composition and origin of the various geologic units northwest of Humorum basin as well as the stratigraphy of the Humorum preimpact target site. The results of our spectral analysis indicate that at least a portion of the inner, mare-bounding ring is composed of pure anorthosite. Other highlands units in the region are dominated by noritic anorthosite. The anorthosites on the inner ring may have been derived from a layer of anorthosite that exists at depth beneath a more pyroxene-rich unit. Both Gassendi G and F craters expose mare material from beneath a highlands-rich surface unit that was emplaced as a result of the Letronne, Gassendi, and other impact events. This ancient basalt unit was emplaced after the formation of Humorum basin but prior to the Orientale impact.

Hawke, B. R.↗
NASA NTRS1986

Block rotations in the Rio Grande Rift, New Mexico

Paleomagnetic data from 13 sites of intrusive and extrusive rocks associated with the Oligocene Espinaso Formation around the Ortiz mountains, New Mexico, indicate mean magnetic directions of I = 42.1 deg and D = 337.8 deg, with a corresponding pole position of 67.9 deg N latitude and 142.3 deg E longitude. From comparison with the expected Oligocene direction, 17.8 + or - 11.3 deg of counterclockwise rotation is found, and the similar rotations for Oligocene and Pliocene age rocks suggests that motion has occurred in the past 5 m.y. Data support the previously suggested diamond-shaped crustal block extending from the San Luis basin southward to the Albuquerque basin bounded by well-defined recently active fault zones. The size of the block, the counterclockwise nature of rotation and the timing of motion are supported by geologic and structural data. The counterclockwise rotation of the block has resulted in uplift at the acute ends of the block and subsidence at the obtuse ends, and the driving mechanism may be left slip along the rift.

Brown, L. L.↗
NASA NTRS1992

Global correlation of volcanic centers on Venus with uplands and with extension: Influence of mantle convection and altitude

The observed distribution of volcanism on Venus and its associations with geologic and tectonic characteristics are examined for significant global-scale tectonic, mantle, and volcanic influences. We find that volcanic centers are correlated geologically with zones of extension, infrequent in lowland regions, and infrequent in regions with evidence for tectonic shortening. In addition, volcanic centers are significantly concentrated in a broad region at least 10,000 km in diameter between Beta, Alta, and Themis Regiones. This area is nearly hemispheric in scale and coincides spatially with the area of greatest concentration of extensional characteristics. Our analysis suggests that the observed distribution patterns of volcanic centers reflect the regional patterns of extension, the origin of the extension and volcanism are closely related, and the hemispheric scale of both patterns implies a deep-seated origin such as large-scale interior mantle dynamic patterns. However, altitude-dependent effects on both the formation and preservation of volcanic centers could also strongly influence the observed distribution pattern.

Crumpler, L. S.↗