Modelling plume-related uplift, gravity and melting on Venus

Three roughly circular regions on Venus about 1000 km across are identified as potential Hawaii-scale plume sites on the basis of their gravity (70–90 mgal) and topography (1.6–2.0 km) anomalies, and signs of melt generation and rifting. Axisymmetric isoviscous convection models are used to reproduce gravity profiles across these plumes and the line-of-sight acceleration of the Magellan spacecraft as it passes over them. The best fitting models have a conductive lid thickness of less than 150 km, mantle viscosity of 8.9 × 1019 to 9.6 × 1020 Pa s and a basal heat flux of 15–25 m W m−2. The lid thickness is constrained by requiring a modest amount of melt generation and a potential temperature of about 1300°C. The high mantle viscosity relative to that of Earth is probably a consequence of the absence of water in the mantle, and may help to explain the current absence of plate tectonics on Venus. The low heat flux suggests that the thermal evolution of Venus has differed from that of the Earth.