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Title: The mantle wedge : dynamic controls on geochemical and geophysical observations
Author: Perrin, Alexander
ISNI:       0000 0004 7658 1235
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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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 H₂O 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.
Supervisor: Goes, Saskia ; Prytulak, Julie ; Davies, Rhodri Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral