Subduction Initiation in a Stagnant Lid and Episodic Overturn on Venus

Abstract:

Subduction initiation is key in understanding the dynamic evolution of the Earth. Despite the recent progress, the question about how a stiff, mostly stagnant planetary lid can break and become part in the global overturn of the mantle is still unresolved. Many mechanisms, externally or internally driven, are proposed in previous studies. In this abstract, we present results on subduction initiation obtained by dynamically self-consistent, time-dependent numerical modelling of mantle convection.

We show that subduction initiation induced by small-scale convection is favoured by a free surface compared to a free-slip surface in simple models applying a maximum yield strength. In addition, we present global, three-dimensional mantle convection experiments that employ basal heating and narrow mantle plumes, which facilitate subduction initiation. Finally, we present results from our model that self-consistently reproduces an episodic lid with a fast global overturn due to the hotter mantle developed below a former stagnant lid.

The models are calculated by the finite-volume code Stag-YY (e.g., Tackley 2008) using a multi-grid method on a fully staggered grid. Second, it applies the sticky-air method (Matsumoto and Tomoda 1983; Schmeling et al, 2008) and thus approximates a free surface when the sticky-air parameters are chosen carefully (Crameri et al., 2012).

Overall, this study demonstrates the ability of small-scale convection and large-scale convection with hot mantle plumes to initiate subduction and it highlights the importance of an initial stagnant-lid phase as part of a global-overturn cycle that might be occurring on Venus.

REFERENCES

Crameri, F., et al. (2012), Geophys. J. Int., 189(1).

Matsumoto, T., and Y. Tomoda (1983), J. Phys. Earth, 31(3).

Schmeling, H., et al. (2008), Phys. Earth Planet. Int., 171(1-4).

Tackley, P. J. (2008), Phys. Earth Planet. Int., 171(1-4).