Other
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p31c..03k&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P31C-03
Other
5475 Tectonics (8149), 6295 Venus, 8010 Fractures And Faults, 8120 Dynamics Of Lithosphere And Mantle: General
Scientific paper
Devana Chasma is a rift system on Venus that formed due to extensional stresses from the Beta Regio and Phoebe Regio mantle plumes. Devana has often been compared to the East African Rift system on Earth. Here, we focus on the portion of Devana in the lowland plains between Beta and Phoebe, 20 North - 4 South, a distance of 2500 km. Over this region, Devana is typically 150 to 250 km wide. Recent gravity modeling (Kiefer and Peterson, Geophys. Res. Lett., Jan. 2003) demonstrated that most of this segment of the rift is presently underlain by hot, low density mantle material. The rift has a 600 km lateral offset near 8 North latitude, where the gravity results show no evidence for hot mantle. This lead Kiefer and Peterson to propose that Devana is actually two propagating rifts, one propagating southward from Beta Regio and the other propagating northward from Phoebe Regio. As a test of this hypothesis, we have examined the detailed structural geology of this section of the rift using topographic profiles and radar imagery from the Magellan mission. We constructed a series of topographic transects spaced at approximately 50 km intervals along the rift and measured the average flank height and the maximum rift depth. We measured the total vertical offset along faulted surfaces and converted this to horizontal extension assuming a characteristic normal fault dip of 60 degrees. Plots of these quantities as a function of distance along the rift reveals several characteristic zones. Average flank height has maximum values near the edges of Beta Regio (3.5 km) and Phoebe Regio (2.75 km) and decreases rapidly as the rift crosses the intervening plains. This is consistent with the rift forming due to thermal anomalies centered at Beta and Phoebe. The virtual absence of elevated rift flanks in the offset region near 8 North is consistent with the absence of hot mantle in this region, as inferred from the gravity model. The horizontal extension decreases strongly with increasing distance from Beta Regio (20 - 10 N), whereas the horizontal displacement shows little trend with distance from Phoebe Regio (4 S - 7 N). The horizontal extension has a minimum in the offset region (8 N), consistent with the observed decrease in fault density in this region. Both the flank height and horizontal extension results appear to be consistent with the propagating rift model. The maximum depth along the rift is typically between -1 and -3 km, with no strong trend along the rift.
Kiefer Walter Scott
Swafford Laura C.
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