Topographic domes on Ganymede: Ice vulcanism or isostatic upwarping |
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| Authors: | Steven W Squyres |
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| Institution: | Department of Geological Sciences and Laboratory for Planetary Studies, Cornell University, Ithaca, New York 14853, USA |
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| Abstract: | Voyager images of Ganymede show two broad, gently sloping dome-shaped features. They lie in grooved terrain and have diameters of roughly 250 km. The one observed at high resolution has a summit elevation 2–2.5 km above the surrounding plains, and appears to be surrounded by a field of secondary craters. Two formation processes are considered: water vulcanism triggered by a major impact, and isostatic upwarping of a crater formed in a thin crust. Numerical simulation of nonadiabatic water vulcanism indicates that the volume of the domes is inconsistent with eruption through a conduit created by complete penetration of the crust by an impact. It is consistent, however, with eruption through fractures created by an impact that excavates partly through a thin crust. Isostatic upwarp rates calculated as a function of effective crustal temperature indicate that upwarping could also create such a dome if the impact excavated to depths where the crust was sufficiently warm and mobile. Both models require that the density of the crust slightly exceed that of a liquid water mantle for a short period of time. Morphologic evidence suggests that both processes may have been important. If either of the proposed models is correct, the situation of the domes in grooved terrain implies that grooved terrain formation occurred prior to the thickening and stiffening of Ganymede's crust. |
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