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At least 109 records · Page 6

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NASA NTRS1991

Regional tectonic analysis of Venus as part of the Pioneer Venus guest investigator project

Over the past year, much of the tectonic analysis of Venus we have done has centered on global properties of the planet, in order to understand fundamental aspects of the dynamics of the mantle and lithosphere of Venus. We have developed convection models of the Earth and Venus. These models assume whole mantle internally-heated convection. The viscosity is temperature, volatile-content, and stress dependent. An initial temperature and volatile content is assumed, and the thermal evolution is tracked for 4.6 billion years. During this time, heating occurs by decay of radiogenic elements in the mantle, and degassing and regassing of volatiles takes place at the surface. For a model assuming plate tectonics as the primary heat loss mechanism, representing the Earth through most of it's history and perhaps Venus' earlier history, degassing of the mantle was found to occur rapidly (approximately 200 My) over a large range of parameters. Even for parameters chosen to represent extreme cases of an initially cool planet, low radiogenic heating, and large initial volatile complement, the mantle water content was degassed to an equilibrium value in about 2 By. These values may be applicable to the early Venus, if a large, Moon-forming impact on Earth resulted in efficient heating and loss of water, leaving Venus with a comparably greater volatile budget and less vigorous early convection. It may therefore be impossible to retain large amounts of water in the interior of Venus until the planet cools down enough for the 'cold-trap' effect to take place. This effect traps crust forming melts within the mantle due to a cusp in the solidus, causing these melts to refreeze at depth into a dense eclogite phase, which will inhibit ascent of this material to the surface. This effect, however, requires a hydrous mantle, so early loss of water might prevent it from taking place. Since without plate tectonics there is no mechanism for regassing volatiles into the mantle, as occurs on Earth at subduction zones, this means the interior of Venus would at present be almost completely dry. We have also calculated argon degassing, and mantle flow velocities. viscosities, and cooling rates in these models, and these values can provide constraints on present day mantle dynamics.

Williams, David R.↗

NASA NTRS1993

Importance of expansion and contraction in the formation of tectonic features on the Moon

The lack of globally distributed tectonic features on the lunar surface has been used to argue against significant changes in the radius of the Moon since the formation of the presently observed surface, which dates to the end of heavy bombardment about 3.9 Ga. This observation has been used previously to limit the maximum stresses to approximately 100 MPa that could be supported by the lunar lithosphere without the formation of globally distributed tectonic features, which in turn limits the maximum radius changes to plus or minus 1 km for a purely elastic lithosphere. In a previous abstract, limits on the elastic expansion or contraction of the Moon were reexamined with respect to realistic failure stresses necessary to produce actual lunar tectonic features. In addition, limits on the permanent (plastic) strain that could be accommodated by non-mascon grabens and wrinkle ridges were considered with more severe constraints placed on the total reasonable expansion and contraction of the Moon since 3.9 Ga. In this abstract, considerations of the distribution and mechanisms of formation due to a planetary radius change or their accommodating much permanent plastic planetary expansion or contraction.

Golombek, M. P.↗

NASA NTRS1993

Tectonics of Neyterkob corona on Venus

Neyterkob double corona (50 deg N 202 deg) presents an area of corona-related interfering tectonic patterns which are formed in different phases of evolution of the corona and modified by regional stresses. Analyzing the patterns can reveal something about the coronal formation. Tectonic features form distinct units on topographic depressions, slopes, and volcanic flows extending over one radius of the corona. A remarkable amount of compressional features were found near the rim and related to interaction between adjacent coronae. Radial extension was mainly observed on a peculiar NE-SW trending high crossing the corona. Concentric fractures were found to the east partly connected to the lithospheric flexure. Tectonic features indicate movements of volcanic activity and modification of the area by more regional stresses.

Kauhanen, K.↗

NASA NTRS1993

Tectonic resurfacing of Venus

Impact crater distributions and morphologies have traditionally played an important role in unraveling the geologic histories of terrestrial objects, and Venus has proved no exception. The key observations are: mean crater retention age about 500 Ma; apparently random spatial distribution; modest proportion (17 percent) of modified craters; and preferential association of modified craters with areas of low crater density. The simplest interpretation of these data alone is that Venus experienced global resurfacing (assumed to be largely volcanic) prior to 500 Ma, after which time resurfacing rates decreased dramatically. This scenario does not totally exclude present geological activity: some resurfacing and crater obliteration is occurring on part of the planet, but at rates much smaller than on Earth. An alternative endmember model holds that resurfacing is also spatially randomly distributed. Resurfacing of about 1 sq km/yr eliminates craters such that a typical portion of the surface has an age of 500 Ma, but actual ages range from zero to about 1000 Ma. Monte Carlo simulation indicates that the typical resurfacing 'patch' cannot exceed about 500 km in diameter without producing a crater distribution more heterogeneous than observed. Volcanic or tectonic processes within these patches must be locally intense to be able to obliterate craters completely and leave few modified. In this abstract, we describe how global geologic mapping may be used to test resurfacing hypotheses. We present preliminary evidence that the dominant mode of resurfacing on Venus is tectonism, not volcanism, and that this process must be ongoing today. Lastly, we outline a conceptual model in which to understand the relationship between global tectonics and crater distribution and preservation.

Malin, Michael C.↗

NASA NTRS1993

Crater destruction on the Venusian highlands by tectonic processes

It is apparent that few, if any, craters as old, or highly modified as Imbrian craters on the surface of the moon are present on the Venusian highlands, or indeed anywhere on the planet's surface. Degraded craters such as those seen on the Moon, Mercury, or Mars are conspicuously absent. Furthermore, virtually all the impact craters on the Venusian surface show modification only by extensional tectonics, whereas the Venusian highlands show modification by compression, strike-slip movement, and finally by extension. Presumably at an earlier time, the surface of Venus resembled the surfaces of the other inner planets. The relatively recent resurfacing event that produced the plains units may be a mechanism for covering the older craters in the plains, but these vast outpourings of lava cannot be invoked as a mechanism for covering the craters on the Venusian highlands. If the plains units had covered the highlands, the entire Venusian surface would appear to be as smooth as the plains units that are embayed by and, therefore, postdate the highlands. The last major tectonic events to affect the highlands such as those seen on Ovda Regio appear to be thrust faulting with consequent folding, followed by at least three episodes of strike-slip faulting and finally extensional faulting. To test whether such tectonic movements could have destroyed highlands crater, a preliminary experiment was conducted by using a Lunar Orbiter mosaic of the lunar uplands as an analog for the ancient Venusian highlands.

Pohn, Howard A.↗

NASA NTRS1993

Use of SPOT and ERS-1 SAR data to study the tectonic and climatic history of arid regions

In order to separate the effects of the different tectonic and climatic processes on the shapes of desert piedmonts, a modified conic equation was fitted to digital topographic data for individual alluvial fans in Death Valley (California, U.S.). The topographic data were obtained from a SPOT panchromatic stereo pair and from the airborne interferometric SAR (Synthetic Aperture Radar) (TOPSAR). The conic fit allows parameters for the epex position, slope, and radial curvature to be compared with unit age, uplift rate, and climatic conditions. Preliminary results indicate that slope flattens with age and radial curvature is concave up, but decreases with age. Work is continuing on correlation of fit residuals and apex position with fan unit age. This information will help in the determination of tectonic uplift rates and the climatic history of the western U.S. ERS-1 SAR images were used to study an area of western China where a large strike slip fault crosses a series of alluvial fans and stream valleys. Previous analysis of SPOT panchromatic images of the area shows that offsets fans and streams can be recognized. Measurement of the rate of motion of this fault will help in the overall model of deformation of the Asian tectonic plate in response to the collision of the Indian plate.

Farr, Tom G.↗

NASA NTRS1994

Hydro-isostatic deflection and tectonic tilting in the central Andes: Initial results of a GPS survey of Lake Minchin shorelines

Sufficiently large lake loads provide a means of probing rheological stratification of the crust and upper mantle. Lake Minchin was the largest of the late Pleistocene pluvial lakes in the central Andes. Prominent shorelines, which formed during temporary still-stands in the climatically driven lake level history, preserve records of lateral variations in subsequent net vertical motions. At its maximum extent the lake was 140 m deep and spanned 400 km N-S and 200 km E-R. The load of surficial water contained in Lake Minchin was sufficient to depress the crust and underlying mantle by 20-40 m, depending on the subjacent rheology. Any other differential vertical motions will also be recorded as departures from horizontality of the shorelines. We recently conducted a survey of shoreline elevations of Lake Minchin with the express intent of monitoring the hydro-isostatic deflection and tectonic tilting. Using real-time differential Global Positioning System (GPS), we measured topographic profiles across suites of shorelines at 15 widely separated locations throughout the basin. Horizontal and vertical accuracies attained are roughly 30 and 70 cm, respectively. Geomorphic evidence suggests that the highest shoreline was occupied only briefly (probably less than 200 years) and radiocarbon dates on gastropod shells found in association with the shore deposits constrain the age to roughly 17 kyr. The basin-side pattern of elevations of the highest shoreline is composed of two distinct signals: (27 +/- 1) m of hydro-isostatic deflection due to the lake load, and a planar tilt with east and north components of (6.8 +/- 0.4) 10(exp -5) and 9-5.3 +/- 0.3) 10(exp -5). This rate of tilting is too high to be plausibly attributed to steady tectonism, and presumably reflects some unresolved combination of tectonism plus the effects of oceanic and lacustrine loads on a laterally heterogeneous substrate. The history of lake level fluctuations is still inadequately known to allow detailed inferences of crust and mantle rheology. However, it is already clear that the effective elastic plate thickness is closer to 40 km than the 60-70 km crustal thickness in the central Andes and the effective viscosity is less than 5 10(exp 20) Pa s.

Bills, Bruce G.↗

NASA NTRSDate not supplied

Lunar TLP's and the Tectonic Processes of the Earth and the Moon

We study the transient lunar phenomena (TLP) as an indicator of lunar tectonic. Seismic phenomena can be used as a direct indicator of some tectonic activities of the planets The Moon-Earth gravitational interaction has been studied extensively as a triggering mechanism to geodynamics. In this work, we study the reverse interaction Earth-Moon in relation to the TLP activities. The lunar outgassing potentially is the leading cause for TLP activities resulting from the lunar interior's dynamic mechanism. We have studied Earth venting and earthquakes processes and have found that radon was frequently activated before significant seismic events due to Moon-Sun interaction with Earth (Ouzounov et al., 2018). Earthquake lights, an associated phenomenon reported before some major earthquakes, are analog to TLP activities on the moon. In 1972, N. Kozyrev suggested a possible moon response to the significant seismic events on Earth. To understand whether TLP's activities have any possible connection with Earth geodynamics, we perform a statistical check between the significant seismic activities from the NEIC catalog and lunar TLPs for 1907-1977 for four lunar areas :Aristarchus, Plato, Gassendi, and Alphonsus. We use TLP compiled catalog based on Middlehurst et al. (1968), Cameron (2006a,b), and Crotts (2008) catalogs. Our results revealed a causal relationship between significant earthquakes and TLP events. However, this relation varies from the location and depth of the seismic events. Deformation triggers the degassing process, and TLPs are indicators for those underlying activities. Our work can provide new information about the origin of TLP and the existence of a possible relationship between the tectonic processes of Earth and the Moon.

D Ouzonov↗

NASA NTRS1996

Plains Tectonics on Venus

Tectonic deformation in the plains of Venus is pervasive, with virtually every area of the planet showing evidence for faulting or fracturing. This deformation can be classified into three general categories, defined by the intensity and areal extent of the surface deformation: distributed deformation, concentrated deformation, and local fracture patterns.

tectonics tectonic formation tectonic deformation ↗

DOE OSTI2025

Structural Evolution of the Hogback Monocline and Its Tectonic Significance in the San Juan Basin

The San Juan Basin is recognized as a Laramide foreland basin. It is located within the Colorado Plateau, a broad tectonic province characterized by a thick sedimentary sequence that was segmented into smaller sub basins during the Late Cretaceous to Paleogene Laramide orogeny. The Hogback Monocline lies along the northwestern margin of the San Juan Basin and is considered a Laramide-age structure formed in response to compressional stress. In this study, we interpret surface and subsurface datasets to construct a structural geological model and evaluate its tectonic significance. Through seismic data, we identify key fault and fold geometries at depth. The seismic dataset used in this study was reprocessed in depth and constrained with well log velocity data to enhance seismic imaging quality. Additionally, we performed well log correlations to identify formation tops and assess variations in basin infill and thickness geometry. A series of structural cross-sections, constructed using seismic data and a high density of boreholes, are presented to evaluate geometric variations along the structure and its evolution during basin development. Furthermore, kinematic restoration and forward modeling analyses were conducted to validate our structural interpretation. This work suggests that the Hogback Monocline formed through fault-propagation folding and flexural slip affecting the pre-Laramide sedimentary sequence under compressional stresses associated with the Laramide orogeny. This structure is interpreted as a high-angle reverse fault that influenced the geometry of the late basin infill. Additionally, monocline bending along the structure may have been controlled by fault relay systems and, in some cases, influenced by strike-slip faulting.

Reyes, Martin [New Mexico Bureau o fGeology and Mi↗

NASA NTRS1974

Tectonic analysis of Baja California and Parras shear belt in Mexico

The author has identified the following significant results. Geological correlation of terrain across the Gulf of California using ERTS-1 imagery revealed significant similarities between Isla Tiburon, Isla Angel de la Guarda, and the San Carlos Range in mainland Mexico. ERTS-1 imagery was used to check the validity of the existence of major trans-Baja fault zones. ERTS-1 imagery also shows that high albedo sediments similar to known late Tertiary marine sediments are widespread in southern and middle Baja and extend in places to the eastern side of the Peninsula. Major faults in northern Mexico and across the border in the United States were mapped, and ample evidence was found that the Parras and parts of the Texas lineament are belts of major transverse shear faults in areas outside the supposed limit of the Texas and Parras lineaments. A fundamental concept which may help explain many complexities in the tectonic development is beginning to emerge: The southwestern part of North America was torn by massive left-lateral shear of transverse trend (east-west) during the compressive stage of the late Mesozoic and early Cenozoic. This tectonic style has changed into tensional rifting (Basin and Range) and right-lateral shear later in the Cenozoic and Quaternary.

Abdel-Gawad, M.↗

NASA NTRS1974

Identification and interpretation of tectonic features from ERTS-1 imagery

The author has identified the following significant results. The transverse faults observed in the central Coast Ranges of California are believed to represent the remnants of a major system of shear faults older than the San Andreas system. The transverse shear system is believed to have developed in the Mesozoic when the Pacific Plate was advancing under the North American Plate. Shear faults thus developed due to unequal rates of underthrusting. This tectonic model indicates that the intrusive belt of the proto-Sierra Nevada and the belt of eugeosynclinal sedimentary belt (Franciscan group) which lay to the west were both subjected to regional left-handed shear. Later development of the San Andreas system as transform faults of the East Pacific Rise changes the tectonic style to right-lateral tangential. The model explains the peculiar distribution of the Franciscan rocks in the Diablo Range east of the San Andreas fault and in Santa Lucia Range west of Nacimiento fault and the presence of Sierra Nevada type granitic blocks in between the two faults in the Salinia block. This model is also consistent with an analysis of the Texas and Parras shears which indicates that the southwestern part of North America has been subjected to a major left-lateral regional shear before the development of the San Andreas fault system.

Abdel-Gawad, M.↗

NASA NTRS1974

ERTS-1, earthquakes, and tectonic evolution in Alaska

In comparing seismicity patterns in Alaska with ERTS-1 imagery, it is striking to see the frequency with which earthquake epicenters fall on, or near, lineaments visible on the imagery. Often these lineaments prove to be tectonics faults which have been mapped in the field. But equally as often, existing geologic and tectonic maps show no evidence of these features. The remoteness and inaccessibility of most of Alaska is responsible, in large part, for the inadequacy of the mapping. ERTS-1 imagery is filling a vital need in providing much of the missing information, and is pointing out many areas of potential earthquake hazard. Earthquakes in central and south-central Alaska result when the northeastern corner of the north Pacific lithospheric plate underthrusts the continent. North of Mt. McKinley, the seismicity is continental in nature and of shallow origin, with earthquakes occurring on lineaments, and frequently at intersections of lineaments. The shallower events tend to align themselves with lineaments visible on the imagery.

Gedney, L.↗

NASA NTRS1974

Gravity tectonics and seismic gaps in the mantle

The concept of gravity tectonics is applied to reveal the major clue as to the conditions which result in the correspondence of seismic and tectonic gaps in the mantle. An asymptotic theory is developed for the calculation of the thrust and moment when a descending lithospheric plate encounters resistance to its downward motion in the mesosphere. Dynamic analysis falls into two parts: (1) deriving equations for forces in the descending lithosphere, (2) deducing moment distribution which causes the detachment of lithosphere. For the analysis of forces a mathematical theory of shells is given. In order to determine the detachment mechanism, solutions of equations are obtained by asymptotic integration. It is found that a thrust N sub phi coupled with a moment M sub phi due to gravitational forces generated by density contrast may play a key role in the initial detachment of a piece of descending lithosphere. The results are in agreement with the observed seismic gaps beneath South America, Toga-Fiji, New Zealand and New Hebrides regions.

Liu, H. S.↗

NASA NTRS1975

Identification and interpretation of tectonic features from ERTS-1 imagery: Southwestern North America and the Red Sea area

The author has identified the following significant results. The ERTS-1 imagery was utilized to study major fault and tectonic lines and their intersections in southwestern North America. A system of transverse shear faults was recognized in the California Coast Ranges, the Sierra Nevada, the Great Basin, and Mexico. They are interpreted as expressions of a major left-lateral shear which predated the San Andreas system, the opening of the Gulf of California and Basin and Range rift development. Tectonic models for Basin and Range, Coast Ranges, and Texas-Parras shears were developed. Geological structures and Precambrian metamorphic trend lines of schistosity were studied across the Red Sea rift.

Abdel-Gawad, M.↗

NASA NTRS1975

Tectonic analysis of folds in the Colorado plateau of Arizona

Structural mapping and analysis of folds in Phanerozoic rocks in northern Arizona, using LANDSAT-1 imagery, yielded information for a tectonic model useful in identifying regional fracture zones within the Colorado Plateau tectonic province. Since the monoclines within the province developed as a response to differential movements of basement blocks along high-angle faults, the monoclinal fold pattern records the position and trend of many elements of the regional fracture system. The Plateau is divided into a mosaic of complex, polyhedral crustal blocks whose steeply dipping faces correspond to major fracture zones. Zones of convergence and changes in the trend of the monoclinal traces reveal the corners of the blocks. Igneous (and salt) diapirs have been emplaced into many of the designated zones of crustal weakness. As loci of major fracturing, folding, and probably facies changes, the fractures exert control on the entrapment of oil and gas.

Davis, G. H.↗

NASA NTRS1977

The relationship between crustal tectonics and internal evolution in the moon and Mercury

The relationship between crustal tectonics and thermal evolution is discussed in terms of the moon and Mercury. Finite strain theory and depth and temperature-dependent thermal expansion are used to evaluate previous conclusions about early lunar history. Factors bringing about core differentiation in the first 0.6 b.y. of Mercurian evolution are described. The influence of concentrating radioactive heat sources located in Mercury's crust on the predicted contraction is outlined. The predicted planetary volume change is explored with regard to quantitative limits on the extent of Mercurian core solidification. Lunar and Mercurian thermal stresses involved in thermal evolution are reviewed, noting the history of surface volcanism. It is concluded that surface faulting and volcanism are closely associated with the thermal evolution of the whole planetary volume. As the planet cools or is heated, several types of tectonic and volcanic effects may be produced by thermal stress occurring in the lithosphere.

Solomon, S. C.↗

NASA NTRS1978

Mercurian global tectonics - A consequence of tidal despinning

The surface of Mercury exhibits a global tectonic system consisting of an ancient set of NE and NW tending lineaments and a younger set of planimetrically arcuate escarpments interpreted as thrust of high-angle reverse faults. The trends, distribution, and age relations of these tectonic features can be explained by a combination of tidal despinning and global contraction of the planet. In our model, early tidal despinning resulted in conjugate shear fractures trending roughly N60 deg E and N60 deg W which were subsequently modified by a variety of surface processes to produce the presently visible set of lineaments. Continued despinning plus global contraction produced thrust faults with roughly north-south trends. Final contraction may have postdated despinning and produced randomly oriented thrust faults. All of these events predated the formation of Caloris basin, because basin-associated deposits blanket both lineaments and arcuate thrust faults.

Melosh, H. J.↗