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  • 1
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    The spatial distribution of coronae and related features on Venus (1993)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: Coronae are large quasi-circular geologica features that are common on Venus. They appear to be the surface tectonic and volcanic expressions of mantle diapirs that have impinged on the underside of the venusian lithosphere. We have investigated the spatial distribution of 335 coronae and related features identified in Magellan radar data. It is more clustered than a Poisson distribution, with a statistical certainty of more than 99%. It is dominated by a single large cluster centered near the equator at about 245 deg longitude. The features are preferentially found at elevation and geoid values close to the planetary mean, with a paucity at both the highest and lowest levels of topgraphy and geoid. Some coronae appear aligned in quasi-linear chains. We attribute the clustering of coronae and related features to preferential formation of these features above regions of broad-scale mantle upwelling, and suggest that a major mantle upwelling underlies the one large cluster. We suggest that coronae are rare at the lowest elevations because these may be regions of mantle downwelling. The shortage of coronae at the highest elevations may result both from obscuration by other intense tectonism there and from suppression there of their formation by an unusually thick crust. Corona chains may be produced by enhanced passive mantle uplift below failed or incipient rifts.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 20; 24; p. 2965-2968
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  • 2
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    Magellan observations of Alpha Regio - Implications for formation of complex ridged terrains on Venus (1992)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The deformational features that make up the complex ridged terrain (CRT) of Alpha Regio are characterized, and observations of these features and their interpretations are used to evaluate quantitative models for the formation of Alpha Regio. In particular, two models are considered: a hotspot or mantle plume model and a coldspot or mantle downwelling model. Based on an analysis of the observed morphology of structures, their distribution, superposition and crosscutting relationships, and Magellan altimetry, a sequence of deformational events is suggested, and the observed topography, tectonics, and volcanism are compared with the predictions of the hotspot and coldspot models. It is found that a number of observations are more consistent with the downwelling than a hotspot model. This is particularly true of margin-parallel compressional features near the plains-CRT boundary in much of Alpha Regio.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 97; E8, A; 13
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  • 3
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    Geophysical models for the formation and evolution of coronae on Venus (1992)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The proposition that Venusian coronae form over sites of mantle upwelling and are modified by subsequent gravitational relaxation is examined using two geophysical models to determine whether and under what conditions these mechanisms can produce the topography and tectonics exhibited by coronae in the Magellan altimetry data and radar images. It is shown that mantle diapirism can produce the domical topography of novae, which may be coronae in the earliest stage of formation. The model stresses induced at the surface by a mantle diapir imply the formation of radially oriented extensional fracturing as observed in novae. The novae dimensions indicate that the diapirs responsible for them are smaller than about 100 km in radius and that the elastic lithosphere is less than 32 km thick. A flattened diapir at the top of the mantle is modeled and shown to result in plateaulike uplift. The volume of the flattened model diapir is similar to that of the spherical diapirs derived for novae.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 97; E10; p. 16,055-16,067.
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  • 4
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    Morphology and evolution of coronae and ovoids on Venus (1991)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Coronae and ovoids on Venus were first identified in Venera 15/16 data. They are distinctive and apparently unique to the planet, and may be important indicators of processes operating in the Venusian mantle. Magellan images have provided the first high resolution views of coronae and ovoid morphology. Herein, the general geologic character is described of coronae and ovoids, and some inferences are drawn about their geologic evolution. Coronae are circular to elongate features surrounded by an annulus of deformational features, with a relatively raised or indistinct topographic signature and, commonly, a peripheral trough or moat. Ovoids are circular to elongate features other than coronae with either positive or negative topographic signatures, associated with tectonic deformation and volcanism. The relationship of these two geologic features to each other and to Venusian geology is briefly discussed.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 37-38
    Format: application/pdf
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  • 5
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    Coldspots and hotspots - Global tectonics and mantle dynamics of Venus (1992)
    In:  Other Sources
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    Publikationsdatum: 2019-07-12
    Beschreibung: Based on geologic observations provided by Magellan's first cycle of data collection and recent models of mantle convection in spherical shells and crustal deformation, the major topographic and geologic features of Venus are incorporated into a model of global mantle dynamics. Consideration is given to volcanic rises, such as Beta Regio and Atla Regio, plateau-shaped highlands dominated by complex ridged terrain (e.g., Ovda Regio and Alpha Regio), and circular lowland regions, such as Atalanta Planitia. Each of these features is related to either mantle plumes (hotspots) or mantle downwellings (coldspots).
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 97; E8 A; 13
    Format: text
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  • 6
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    Corona structures on Venus - Models of origin (1991)
    In:  Other Sources
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    Publikationsdatum: 2019-07-12
    Beschreibung: The present study assesses the mantle diapir models of corona origin using the basic characteristics of coronas: relatively raised topography, annuli of compressional ridges, volcanism, and peripheral trough. Both rising and and sinking diapirs are modeled quantitatively. Rising mantle diapirs are caused by heating at depth, while sinking mantle diapirs may result from cooling or a phase change causing increased density and negative buoyancy at the base of the lithosphere. The hotspot model is most consistent with the major characteristics of coronas, with gravitational relaxation occurring as a modificational process. The sinking mantle diapir produces dominant central compression that is not observed at coronas. Higher-resolution image and altimetry data from Magellan can be used to distinguish more fully between the two models. Coronas in various states of formation and degradation can be identified in the Venera 15/16 data, suggesting that the process may be continuing today.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 96; 20
    Format: text
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  • 7
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    The morphology and evolution of coronae on Venus (1992)
    In:  Other Sources
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    Publikationsdatum: 2019-08-28
    Beschreibung: The morphology and morphometry of a number of coronae and related features on Venus are discussed with reference to new data from the Magellan spacecraft. The specific features discussed are concentrated in the portion of Venus imaged during about the first three months of Magellan mapping. Sequences of events and basic geophysical processes involved in the formation of these features are inferred.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 97; E8, A; 13
    Format: text
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  • 8
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    Venus tectonics - An overview of Magellan observations (1992)
    In:  Other Sources
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    Publikationsdatum: 2019-08-28
    Beschreibung: Magellan observations of the tectonic characteristics of highland regions on Venus are discussed with reference to competing theories for highland formation and evolution. Complex rigid terrain, or tessera, and the extent to which these elevated blocks of intensely deformed crust may be genetically related to highlands are then considered. Further, the tectonics of plains and lowland regions are examined, including deformation belts and coronae, and possible relations between such features and mantle dynamics. Implications of these observations for the global tectonics of Venus are discussed.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 97; E8 A; 13
    Format: text
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  • 9
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    Global distribution and characteristics of coronae and related features on Venus - Implications for origin and relation to mantle processes (1992)
    In:  Other Sources
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    Publikationsdatum: 2019-08-28
    Beschreibung: The increased coverage and resolution of Magellan images and altimetry data have resulted in significant new identifications of coronae and coronalike features and more detailed information on corona morphology, topography, and distribution. The distribution of coronae and coronalike features in Magellan data are assessed in the light of the proposed hotspot origin of these features. The basic characteristics of coronae are then compared with other possible hotspot features on Venus (e.g., major volcanic shields and domelike highlands) in a first-order assessment of the implications of mantle plume-related features on Venus for interior convective processes.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 97; E8, A; 13
    Format: text
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  • 10
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    Styles of deformation in Ishtar Terra and their implications (1992)
    In:  Other Sources
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    Publikationsdatum: 2019-07-12
    Beschreibung: Styles of deformation in Ishtar Terra are examined on the basis of imaging by the Magellan radar between the start of the mission and the start of the first superior conjunction hiatus. Ishtar Terra appears to have characteristics of both plume uplifts and convergent belts, and exhibits a great variety of tectonic and volcanic activity, with large variations within distances of only a few hundred kilometers. The most prominent terrain types are the volcanic plains of Lakshmi and the mountain belts of Maxwell, Freyja, and Danu. Ishtar demonstrates three general properties of Venus. Erosional degradation is absent, leading to the preservation of patterns resulting from past activity. Many surface features are the responses of a competent layer less than 10 km thick to flows of 100 km or broader scale. These broader scale flows are controlled mainly by heterogeneities in the mantle.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 97; E10; p. 16,085-16,120.
    Format: text
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