Modelling subduction zone magmatism

Lawton, Rebekah 2016. Modelling subduction zone magmatism. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Subduction zone magmatism is a well studied area due to dangerous consequences of volcanic activity at subduction zones. Whilst it is widely accepted that water leaving the slab causes the magmatism, the method in which the water leaves the slab and causes magmatism is unclear. In this thesis we will examine the hypothesis that water leaving the slab via a large hydraulic fracture will cause instantaneous ‘flash’ melting in the mantle wedge. We will test whether this flash melting occurs and whether it produces sufficient melting. We will also look at hydrous flux melting and hydrous decompression melting occuring after the initial flash melting to see if they increase the melting. A thermal model for a subduction zone is built, with the wedge flow solved analytically, to provide the temperature input for the melting models. Four melting models were tested; flash melting, flash melting followed by hydrous flux melting, flash melting followed by hydrous decompression melting and flash melting, then hydrous flux melting followed by hydrous decompression melting. Another thermal model was also made with the wedge flow solved numerically, this allowed buoyancy to be added into the model to allow investigation into the magma migrating buoyantly. We show that the flash melting model does produce flash melting from large hydraulic fractures but the melting produced is not sufficient compared to observations from volcanic arcs. The flash melting followed by hydrous flux melting model also did not produce sufficient melting however the two decompression melting cases did when compared to observations from volcanic arcs. The addition of buoyancy in to the melting model allows migration of the partial melt towards the wedge corner providing a melt focussing mechanism which is required to get a sharp volcanic front.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Earth and Environmental Sciences
Subjects:	Q Science > QE Geology
Date of First Compliant Deposit:	30 March 2016
Last Modified:	10 Aug 2021 10:49
URI:	https://orca.cardiff.ac.uk/id/eprint/87214

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