Grima, Antoniette Greta;
(2020)
How the Relationship Between Subduction and Mantle Dynamics Shapes Slab Evolution at Mid-Mantle Depths.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Advances in seismic tomography have revealed that the Earth’s mantle is more complex than previously thought and hosts a plethora of slab morphologies. These morphologies can be broadly grouped into three main types; penetrating slabs, deflected slabs and broken, or orphan, slabs. Slab orphaning is a newly discovered phenomenon whereby slabs break directly at mid-mantle depths. This produces a flattened parent slab above 660 km and an orphan slab below it. As the orphan slab slowly sinks towards the core-mantle boundary, subduction continues through the lateral motion of the parent above 660 km. In nature, the Tonga, Arabian, Japan and Central American slabs are possible candidates for slab orphaning. Orphaning has significant implications for the interpretation of slab remnants and their inferred ages, with consequences for tectonic reconstructions. The subduction of slabs, however, does not take place in isolation and slab dynamics must be influenced to some degree by the overriding plate. The nature of the overriding plate plays a major role in the evolution of deep slab morphologies at mid-mantle depths. 2-D numerical simulations of subduction indicate that the presence of continental lithosphere at subduction zones produces markedly different slab behaviour at depth. In particular, a continental overriding plate results in bigger orphans and encourages the mid-mantle penetration of slabs that are otherwise inclined to flatten. It is therefore clear that, in contrast to the slabs of the upper mantle, the deeper slab morphologies are the result of a complex interaction between the overriding plate forcing and the changes in the relative strength ratios of the slab and mantle.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | How the Relationship Between Subduction and Mantle Dynamics Shapes Slab Evolution at Mid-Mantle Depths |
| Event: | UCL |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| Keywords: | Slab orphaning, Subduction dynamics, Deep slab break-off, Slab evolution, Slab-mantle interaction |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10091944 |
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