Constraining the relationship between mantle circulation and supercontinent cycles

Plimmer, Abigail 2025. Constraining the relationship between mantle circulation and supercontinent cycles. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Supercontinent cycles reflect countless processes acting within the Earth’s interior. Whilst their assembly and dispersal are predominantly tectonic processes, the mechanisms which drive plate motion may originate deeper in the Earth. The primary aim of this thesis has been to better constrain the relationship between mantle circulation and supercontinent cycles by exploring the interactions between mantle structures in a ‘mantle circulation cycle’. This cycle comprises slabs sinking, the interactions between slabs and basal mantle structures, and the origins of upwellings. Each phase has been investigated using 3D mantle circulation models, driven by plate velocities at the surface. I explored the relative contribution of plate and mantle properties in controlling the dynamics of slabs as they sink through the mantle, and investigated the coupling between slabs, deep mantle structures and upwellings. These dynamics are investigated across the supercontinent cycle, to assess the degree to which plate tectonics and deep Earth dynamics are interconnected. Downwellings are a fundamental driver of the mantle circulation cycle; slabs sink from the surface at a rate which is largely dependent on the interplay between mantle viscosity and plate properties which effect the surface velocity. They sweep warm material into piles at the base of the mantle, and form plumes where the flow converges. Basal mantle structures are therefore mobile in response to changing subduction girdles at the Earth’s surface. During supercontinent assembly, circum-continental subduction zones sweep material beneath the continent and antipodal ocean. Rapid reorganisation of the plates, tied to the formation of new subduction zones, leads to increasing complexity in the large-scale mantle flow pattern, disrupting these antipodal piles. Subduction zones are often long-lived features at the Earth’s surface, such that the flow pattern in the mantle eventually restabilises, and deep mantle structures return to a predominantly degree 2 configuration. The proximity of slabs and plumes can change the magnitude of upwellings, where the thermal anomaly is either dampened out by the downwelling, or plumes are swept laterally about the core-mantle boundary, entraining more warm material. When plumes are larger and hotter, their contribution to the forces driving plate tectonics is greater. The supercontinent cycle therefore comprises a fundamental component of the mantle circulation cycle (which describes the interaction of plates, downwellings, upwellings, and deep mantle structures), being both a driving force, and driven by mantle processes.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Earth and Environmental Sciences
Funders:	NERC
Date of First Compliant Deposit:	16 May 2025
Last Modified:	19 May 2025 13:49
URI:	https://orca.cardiff.ac.uk/id/eprint/178324

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