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Numerical investigation of the influence of subduction on deformation within the overriding plate

Lei, Zhibin 2022. Numerical investigation of the influence of subduction on deformation within the overriding plate. PhD Thesis, Cardiff University.
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Subduction can pose a fundamental tectonic overprint on the overriding plate by generating a variety of deformation patterns incorporating both extension and shortening strains. Latest research suggests that the diversity of subduction configuration, e.g., multiple slab interaction, inherited tectonic setup, plays an important role in affecting the deformation patterns observed in the overriding plate. However, the driving mechanism accounting for the initiation of the deformation, especially extension, in the diversified subduction configuration is still much less explored, for which this thesis aims at a better understanding through thermal mechanical numerical modelling. In Chapter 3, the thesis investigates single-sided subduction (SSS). Previous investigation implies that it takes a pre-weakened or an immobile overriding plate to reproduce back-arc extension. Nevertheless, it skips answering how the overriding plate gets weakened or becomes immobile before extension initiates. Here, results show that back-arc extension can self-consistently emerge as trench retreat rate increases, even when the overriding plate is mobile and homogeneous. This is a significant advance in simulating back-arc extension, though the trench retreat rate can go higher than what has been observed in current plate framework, suggesting that additional processes may also need to be considered, e.g., melt weakening, grain size reduction etc. In Chapter 4, the thesis investigates dual inward dipping subduction (DIDS), which, as recent research suggests, can affect the deformation patterns in the overriding plate. A major improvement here is incorporating a composite rheology which enables plate to weaken self-consistently relative to previous DIDS models. It does this by inhibiting the mobility of the overriding plate and forming a stronger upwelling mantle flow underlying the overriding plate relative to SSS models. Composite rheology also enables investigation on the evolution of dominant deformation mechanism, which shows dislocation and yielding contribute most to viscosity reduction in the overriding plate. This is a significant advance in simulating DIDS, and the quantitative method proposed here to evaluate each deformation mechanism’s contribution to viscosity reduction can be a powerful tool to understand other strain localisation processes, e.g., formation of plate boundaries. Observation shows that the distance from marginal extension centre to the nearest trench ranges from ~170-850 km, of which the driving mechanism is unclear. In Chapter 5, the thesis investigates the role of heterogeneity within the overriding plate in affecting the distance from extension to trench. The results show that the location and size of the continental block can efficiently regulate if and where marginal basin develops within the overriding plate. Overall, this thesis demonstrates the strong coupling between slab induced mantle flow and deformation in the overriding plate, and improves the current understanding on how progressive weakening can influence back-arc or marginal extension.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Earth and Environmental Sciences
Date of First Compliant Deposit: 21 September 2022
Last Modified: 21 Sep 2022 10:57

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