Observational Constraints on Plume-Induced Subduction on Venus

Venus' lithosphere is hot due to the greenhouse-induced high surface temperature. Thus it may be a good dynamical analog to lithospheric processes that operated on early Earth. In particular, plume-induced subduction appears to be initiating today on Venus, and thus may offer clues to how subduction, and eventual plate tectonics, began on Earth. Plume-induced subduction produces roll-back subduction, so no plate motion is implied. However plate tectonics can develop as subduction zones break the entire lithosphere, allowing boundaries to accumulate and form plates. Sites of possible plume-induced subduction were identified on Venus based on analogy with terrestrial subduction zone characteristics (Sandwell and Schubert, 1992; Schubert and Sandwell, 1995). Laboratory simulations (Davaille et al., 2017) of plume-induced subduction defined more fully the observable characteristics of this process, such as partial trench segment(s) at the edge of the plume head, major interior rifting and/or volcanism, and exterior extension perpendicular to the trench. Davaille et al. (2017) also demonstrated that some of the largest coronae on Venus exhibit the predicted characteristics, as well as a gravity signature consistent with deep compensation near the trenches. We are surveying the 100 largest coronae to investigate which of these features may also be candidates for plume-induced subduction. Most large coronae exhibit evidence of partial arcs of apparently flexed lithosphere. Typical elastic thickness estimates from fitting a model of a flexed elastic plate to topographic profiles outboard of the trench are 10-20 km, with a few in the range of 20-45 km. The objective is to assess lithospheric and plume conditions that will or will not initiate subduction. An additional question is whether or not hot lithosphere prevents plate tectonics from occurring on Venus today due to fault annealing (Bercovici and Ricard, 2012).

Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.