How does subduction begin?

Subduction is the fundamental driver of plate tectonics, but we do not know how it starts. Although density is a primary driving force for subduction, research to date suggests that initiation of the process is very difficult. For example self-sustaining subduction requires downwelling to reach a significant depth and pristine lithosphere is too strong to be broken by any reasonable tectonic mechanism.

Research led at Cardiff has developed detailed thermo-mechanical evolving models of subduction dynamics, incorporating multiple realistic rheologies which can help address this question (Garel et al., 2014). The numerical code (Fluidity, Davies et al., 2010) for these models is adaptive, allowing the grid to adapt to the solution. As a result large models (whole mantle scale) can still have regions of very high resolution (sub-km) in regions where required for accurate solution, but without significant computational expense. These might include narrow zones where feedbacks might weaken the lithosphere allowing subduction initiation.

Through this model we can evaluate the magnitude of downwelling required to generate self-sustaining subduction, and test models of subduction initiation resulting from (i) tectonic forcing, (ii) plume impingement, (iii) sediment loading, (iv) ridge reversal, and (v) juxtaposition of different lithosphere columns, e.g. at transform faults.

These models will make predictions of the elevation history of the overriding plate which can be compared with observations of natural subduction zones. In particular we will focus on regions of recent subduction initiation at both Vanuatu and Panama. Both Vanuatu and Panama might be an examples of induced subduction, Vanuatu following reversal of subduction polarity, and Panama during collision; one recognised mechanism (Stern, 2004). The supervisory team has unique observations relating, to the tectonic history, magmatism, surface subsidence and uplift, at both these locations.

We are looking for a student who has an interest in applying computational methods in Earth Sciences and constraining such models with real world data. The student might have a geophysics, physics, engineering or geology, or similar degree, and ideally a computational background. The student will acquire skills in numerical modelling and programming, including using supercomputing clusters and visualisation, and also an introduction to utilising a range of geology knowledge for constraining models.

These improved models of subduction initiation will revolutionise our understanding of Earth’s dynamics.