Evidence From Gravity and Topography That Actively Forming Coronae in the Beta-Atla- Themis Region of Venus are Underlain by Transient Mantle Plumes
Abstract
We have proposed that coronae, volcano-tectonic features found only on Venus, form over zones of partial melt on the tops of the thermally buoyant, transient mantle plumes that impinge from below onto the base of the thermal lithosphere. These "thermals," if actively impinging, should produce signals that might be observable in the gravity field and surface topography of Venus. That no active coronae have been so identified to date may be because the topographic and gravity anomaly signals are superposed with stronger anomalies at longer wavelengths associated with the active mantle dynamics underlying the Venus highlands and lowlands and at shorter wavelengths with the detailed structure of the coronae themselves. Here we report a search for evidence in the topography, geoid, and Bouguer gravity field of Venus of currently impinging thermals in the Beta-Atla-Themis region. Maps of these quantities have been filtered to include only length scales estimated to be appropriate to impinged thermals (~1000-2500 km), scales longer than those of the coronae. Simple, order- of-magnitude estimates suggest positive dynamic topography of 0.1-1 km, a positive geoid of order 10 m, and a negative Bouguer gravity anomaly of 10-100 mgal. Signals that match the predicted magnitudes are found to be associated with seven coronae: Aruru, Atete, Maram, Shiwanokia, Zisa, and two coronae not formally named (centered at 19.5°N, 265.5°E, and 27.5°S, 262.5°E). All seven coronae have been previously interpreted to be active on the basis of their inferred uncompensated states. In addition, regional geological maps have been published for the areas surrounding two of the seven coronae, Atete and Maram, and in both cases the volcanic flows associated with the coronae are locally some of the youngest features in their region. Of course, gravity modeling is inherently non-unique, and it is conceivable that other phenomena have produced the observed signals. It is nonetheless the correspondence of signals of this length scale and these magnitudes with coronae otherwise inferred to be active that provides the strongest evidence that these actively forming coronae are underlain by thermals impinging on the base of the lithosphere of Venus.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.P51B1200D
- Keywords:
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- 5475 Tectonics (8149);
- 5480 Volcanism (6063;
- 8148;
- 8450);
- 6295 Venus