The mantle wedge: dynamic controls on geochemical and geophysical observations

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Title: The mantle wedge: dynamic controls on geochemical and geophysical observations
Authors: Perrin, Alexander
Item Type: Thesis or dissertation
Abstract: The mantle wedge is a key part of the subduction system, affecting the coupling between plates and chemical cycling, and so having implications for global-scale processes. In order to investigate this system we take three sets of data from subduction zones and ask how much the physical characteristics of subduction zones influence them. Firstly, we calculate the equilibration pressures and temperatures of intra-oceanic subduction zone lavas, and find that the these are relatively hot, shallow and span a large depth range. Comparison with numerical subduction models indicates that this is consistent with the local thermal erosion of the lithosphere immediately beneath the arc by rising magmas, which re-equilibrate within this zone as they rise. We then investigate the controls of each subduction parameter on the position of the arc and find significant correlations with slab dip. Using a set of numerical subduction models we investigate the effect of each parameter on the thermal regime in the wedge and slab. This reveals that upper plate age exerts a key control on the thermal state of the wedge, and that the observed position of the arc is most consistent with a control of where the anhydrous solidus makes its closest approach to the trench. Finally, we investigate measurements of melt generation rates, and find no significant correlations with any subduction parameter. We calculate melting rates using numerical models, and find that melting rates are sensitive to all subduction parameters, due to the effects on the thermal structure, the wedge flow field and the hydration state of the wedge. Data from the Marianas indicates that H$_2$O concentration gradients in the wedge are the primary control on melt generation rates. We conclude that the small and large scale structure of the overriding plate lithosphere has important controls on wedge conditions and processes.
Content Version: Open Access
Issue Date: Jul-2017
Date Awarded: Apr-2018
URI: http://hdl.handle.net/10044/1/67337
Supervisor: Goes, Saskia
Prytulak, Julie
Davies, Rhodri
Department: Earth Science & Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Earth Science and Engineering PhD theses



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