Unravelling Inter-slab Interactions in Double Subduction Systems: Insights from Dynamic Models

Subduction zones play a pivotal role in controlling Earth’s plate tectonics. Natural subduction processes are commonly modelled as a two-plate system, where the denser subducting plate sinks against the lighter overriding plate. However, many subduction systems are architecturally complex due to participation of multiple plates. Double subduction is a type of such complex systems in which two plates subduct simultaneously to accommodate the overall convergent movements. Despite significant advancement in modelling techniques and geophysical observations, the evolution of double subduction remains poorly understood, in particular, its dynamics, in terms of the physical factors controlling its initiation, evolution, and stability. To bridge this knowledge gap, this study uses scaled analogue modelling approach to simulate the dynamic initiation of in-dip double subduction systems, allowing two slabs to subduct opposite to each other with a common overriding plate. Subsequently, employing Particle Image Velocimetry, we capture the critical facets of evolving double subduction systems and its influence on inter-slab interaction, stress transfer in the lithosphere and convective behaviour of the asthenospheric mantle beneath these zones. Complementing our analogue experiments, we conducted numerical simulations on simplified double subduction setups to validate our experimental findings. Findings from both analogue and numerical models unveil pivotal relationships between competing movements of subducting slabs within in-dip double subduction systems and resultant mantle flow patterns. Finally, we compare our model findings with natural double subduction settings.    Keywords: Convergent plate tectonics, double subduction systems, dynamic subduction modelling, Analogue experiments, Finite-element-modeling.