Radiating fissure swarms in Beta Regio, Venus: Evidence of formation from impact craters
Abstract
Venus hosts numerous long and narrow extensional lineaments, with some showing a radiating pattern. A total of 163 large radial extensional systems were identified [1] with two end member mechanisms of origin for these features summarized: (1) domical uplift caused by an ascending mantle diapir; or, (2) emplacement of shallow laterally propagating dikes out from a central magma reservoir. We consider craters located in the Beta Regio (24-45 N, 264-312 E) to further differentiate between models for the 6 radiating graben-fissure structures there. The number of craters on Venus' surface approaches 1000, nearly randomly distributed. The modification of a crater or its ejecta by disruption or embayment by lava from outside documents local tectonic and/or volcanic activity, and the parabolic deposits associated with some craters gives their approximate age, thus dating activity. Also, dip of the crater floor, which forms initially flat, indicates later reorientation. Thus, impact craters have the potential to provide clues about the timing, extent and nature of tectonic and volcanic processes. For this study, we used Magellan's full-resolution and compressed mosaicked radar images to interpret surficial geology, and altimetry to find the dip for each crater. A total of 23 craters are located within this region, with very few showing tectonic or volcanic modification. Venus' radiating fissure swarms have caused surprisingly little modification of impact craters. Almost all craters near the extensional lineaments remain pristine. A single embayed crater lies within the field of one radiating system, the very system that has been identified as the youngest. Dips for 5 craters near the geoid peak on Beta Regio exhibit a discordant pattern. In addition, we find substantial evidence for tectonic disturbance in the northern Beta region. If shallow and recent magma sources had generated the radiating systems, then we would expect to find many more craters embayed by lava. The other scenario for the formation of radiating swarms requires an uplift caused by an ascending diapir. However, the craters within radiating systems do not dip away from the center. Instead, they dip more randomly, often toward the center of the radiating system, suggesting it has collapsed since the time of impact. Thus, the radiating systems may have formed preceding the impacts. [1] Grosfils E.B. and Head J.W., 1994, GRL 21, 701-704.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.P23A0234M
- Keywords:
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- 5420 Impact phenomena (includes cratering);
- 5475 Tectonics (8149);
- 5480 Volcanism (8450);
- 6295 Venus