Numerical modelling of plate deformation during subduction with application to back-arc extension

Zhang, Duo 2023. Numerical modelling of plate deformation during subduction with application to back-arc extension. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Back-arc extension is the first stage in the formation of a back-arc basin (BAB). The driving mechanism of back-arc extension is still debated. To better understand the driving mechanism and factors controlling back-arc extension, a series of 2D thermally driven subduction models with composite rheology are simulated. Initially, models are investigated with fixed rheology parameters and a homogeneous overriding plate (OP). Varying the initial ages of the plates at the trench, these models show that the most probable driving mechanism of back-arc extension is poloidal flow induced by slab subduction (enhanced by trench retreat). I investigate varying activation energy (E) and prefactor (A) in diffusion, dislocation and Peierls creeps, as well as friction coefficient (fc) and maximum yielding strength (yldmax) in yielding deformation. Many modes of plate behaviours are recognised. The models show that a weaker OP does not necessarily facilitate back-arc extension. This is because these models also have a weaker mantle flow, which further verifies the importance of poloidal flow. I investigate extension of an OP with a triangular hot region to mimic a volcanic arc. The models produce back-arc extension at different locations: splitting the arc itself or extension away from the arc. Splitting the arc shows the importance of thermal weakening to OP extension, and extension away from the arc emphasises the role of poloidal flow. These models suggest that splitting the arc is more common (e.g. Mariana Trough and Lau Basin), than not extending at the arc (potentially Japan Sea). Overall, this study shows that the poloidal flow induced by subduction is the main driving mechanism of back-arc extension together with its thermal weakening of the OP. Extension occurs when the force from the sub-OP flow exceeds the OP strength, as evidenced in the models. Testing these findings will require 3D modelling.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Earth and Environmental Sciences
Date of First Compliant Deposit:	28 June 2024
Last Modified:	28 Jun 2024 11:10
URI:	https://orca.cardiff.ac.uk/id/eprint/170153

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