Effects of basal drag on subduction dynamics from 2D numerical models
<p>Subducting slabs are an important driver of plate motions, yet the relative importance of different forces in governing subduction motions and styles remains incompletely understood. Basal drag has been proposed to be a minor contributor to subduction forcing because of the lack of correlat...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-01-01
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| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/12/79/2021/se-12-79-2021.pdf |
| Summary: | <p>Subducting slabs are an important driver of plate motions, yet the
relative importance of different forces in governing subduction motions and
styles 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 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.</p> |
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| ISSN: | 1869-9510 1869-9529 |