Flexure of Venusian lithosphere measured from residual topography and gravity
David N. Barnett, Francis Nimmo and Dan McKenzie
The elastic lithosphere thickness, Te, for various locations on Venus is estimated by modelling lithospheric flexure associated with rifts, coronae, chasmata and the moats visible around certain large volcanoes. By modelling flexure using the residual topography, a range of elastic thicknesses was found, from around 10 km to 40 km or greater. A number of these values are not well-determined, and only constrain Te to be greater than 10 km. The shear stresses predicted from the topography, given these values for Te, reach several hundred MPa, with surface faulting visible in the synthetic aperture radar (SAR) images at many locations. The elastic thickness was also estimated at seven volcano-like structures by modelling the gravity predicted from the observed topography. This yielded elastic thickness estimates varying between approximately 20 and 60 km, which were generally more tightly constrained. However, an elastic thickness of 25 km fits almost all the observed profiles within uncertainty, and the results from modelling the gravity yield an average global elastic thickness of 29 ± 6 km. There is no evidence that the elastic thickness falls anywhere outside this range. The lack of large-scale regional variations in Te on Venus, in contrast to the situation observed on the Earth, is consistent with a lack of water and plate tectonics on Venus.
Key words: Venus, elastic thickness, lithosphere, flexure, residual topography, gravity.
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