Comparison of flat-topped stellate seamounts on Earthʹs seafloor with stellate domes on Venus using side-scan sonar and Magellan synthetic aperture radar

The diameters of many domes on Venus imaged by the Magellan synthetic aperture radar (SAR) are an order of magnitude larger than terrestrial subaerial domes; however, surveys of the seafloor using sonar imaging systems such as GLORIA (Geological Long Range Inclined Asdic) and SeaBEAM have revealed flat-topped volcanic features with similar diameters, volumes and slope angles. Suggested analogies between domes on Venus and seamounts on the northern East Pacific Rise and off Hawaii have been tested by D.K. Smith [J. Volcanol. Geotherm. Res. 73 (1996) 47–64] using comparisons of size and shape and significant differences identified. GLORIA images of flat-topped seamounts near Hawaii show them to have stellate planforms. Over half of the total population of 375 domes on Venus have been modified and many have stellate planforms. We have focused on the similarities in stellate planforms between flat-topped seamounts and modified domes on Venus. We have used GLORIA sonar and Magellan radar data to constrain the formation and evolution of both flat-topped seamounts on the ocean floor and volcanic domes on Venus to see if the processes that formed them are similar. We propose that flat-topped seamounts on the Hawaiian Ridge are built on sediments overlying the oceanic crust and that available evidence supports three processes that can form stellate margins: (1) radial dike intrusions related to flank rift zones; (2) dike intrusions which cause slope failures; and (3) gravitational slope failures unrelated to intrusions. For Venus, where low erosion rates and the absence of a sediment layer results in lavas being emplaced directly onto the crust, the available evidence supports stellate margins originating by gravitational slope failures unrelated to diking, though intrusions cannot be ruled out with existing data.