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Preprints
https://doi.org/10.5194/se-2020-121
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2020-121
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  27 Jul 2020

27 Jul 2020

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A revised version of this preprint is currently under review for the journal SE.

Effects of basal drag on subduction dynamics from 2D numerical models

Lior Suchoy1, Saskia Goes1, Benjamin Maunder1, Fanny Garel2, and Rhodri Davies3 Lior Suchoy et al.
  • 1Department of Earth Science and Engineering, Imperial College of London, South Kensington Campus, London, UK
  • 2Géosciences Montpellier, Université de Montpellier, CNRS, Montpellier, France
  • 3Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory, Australia

Abstract. Subducting slabs are an important driver of plate motions, yet the force balance governing subduction dynamics remains incompletely understood. Basal drag has been proposed to be a minor contributor to subduction forcing, because of the lack of correlation between plate size and velocity in observed and reconstructed plate motions. Furthermore, in single subduction system models, low basal drag, associated with a low ratio of asthenospheric to lithospheric viscosity, leads to subduction behaviour most consistent with the observation that trench migration velocities are generally low compared to convergence velocities. By contrast, analytical calculations and global mantle flow models indicate basal drag can be substantial. In this study, we revisit this problem by examining the drag at the base of the lithosphere, for a single subduction system, in 2D models with a free trench and composite non-linear rheology. We compare the behaviour of short and long plates for a range of asthenospheric and lithospheric rheologies. We reproduce results from previous modelling studies, including low ratios of trench over plate motions. However, we also find that any combination of asthenosphere and lithosphere viscosity that produces Earth-like subduction behaviour leads to a correlation of velocities with plate size, due to the role of basal drag. By examining Cenozoic plate motion reconstructions, we find that slab age and plate size are positively correlated: higher slab pull for older plates tends to be offset by higher basal drag below these larger plates. This, in part, explains the lack of plate velocity-size correlation in observations, despite the important role of basal drag in the subduction force-balance.

Lior Suchoy et al.

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Lior Suchoy et al.

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Short summary
We use 2D numerical models to highlight the role of basal drag in subduction force balance. We show that basal drag can significantly affect velocities and evolution in our simulations, and suggest an explanation to why there are no trends in plate velocities with age in the Cenozoic subduction record (which we extracted from recent reconstruction using GPlates). The insights into the role of basal drag will help setting up global models of plates dynamics or specific regional subduction models.
We use 2D numerical models to highlight the role of basal drag in subduction force balance. We...
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