Controls on the flow regime and thermal structure of the subduction zone mantle wedge : a systematic 2-D and 3-D investigation
Arc volcanism at subduction zones is likely regulated by the mantle wedge's flow regime and thermal structure and, hence, numerous studies have attempted to quantify the princi- pal controls on mantle wedge conditions. In this thesis, we build on these previous studies by undertaking the first...
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ndltd-bl.uk-oai-ethos.bl.uk-6664652017-05-24T03:26:21ZControls on the flow regime and thermal structure of the subduction zone mantle wedge : a systematic 2-D and 3-D investigationLe Voci, GiuseppeDavies, Rhodri; Goes, Saskia; Piggott, Matthew2013Arc volcanism at subduction zones is likely regulated by the mantle wedge's flow regime and thermal structure and, hence, numerous studies have attempted to quantify the princi- pal controls on mantle wedge conditions. In this thesis, we build on these previous studies by undertaking the first systematic 2-D and 3-D numerical investigations, across a wide parameter-space, into how hydration, thermal buoyancy and toroidal flow around the slab edge influence the wedge's flow regime and associated thermal structure. We find that small- scale convection (SSC), resulting from Rayleigh-Taylor instabilities, or drips, off the base of the overriding lithosphere, is a typical occurrence, if: (i) viscosities are < 5 x 1018 Pa s; and (ii) hydrous weakening of wedge rheology extends at least 100-150 km from the forearc cor- ner. In 2-D models, instabilities generally take the form of 'drips'. In 3-D, two separate, but interacting, longitudinal Richter roll systems form (with their axes aligned perpendicular to the trench), the first below the arc region and the second below the back-arc region. These instabilities result in transient and spatial temperature fluctuations of 100-150K, which are sufficient to influence melting, the stability of hydrous minerals and the dehydration of crustal material. Furthermore, they are efficient at eroding the overriding lithosphere, par- ticularly in 3-D and, thus, provide a means to explain observations of high heat flow and thin back-arc lithosphere at many subduction zones. A preliminary study into the effects of a finite-width slab on the wedge's flow regime, which allows for toroidal flow around the slab edge, highlights that the toroidal cell can locally increase or decrease temperatures suf- ficiently to either enhance or shut down wet melting, while a hydrated wedge corner may channel trench-parallel flow. The dynamic complexities of wedge flow revealed by our mod- els may help explain the diversity in geophysical and geochemical subduction signatures.551.1Imperial College Londonhttp://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.666465http://hdl.handle.net/10044/1/26152Electronic Thesis or Dissertation |
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551.1 Le Voci, Giuseppe Controls on the flow regime and thermal structure of the subduction zone mantle wedge : a systematic 2-D and 3-D investigation |
description |
Arc volcanism at subduction zones is likely regulated by the mantle wedge's flow regime and thermal structure and, hence, numerous studies have attempted to quantify the princi- pal controls on mantle wedge conditions. In this thesis, we build on these previous studies by undertaking the first systematic 2-D and 3-D numerical investigations, across a wide parameter-space, into how hydration, thermal buoyancy and toroidal flow around the slab edge influence the wedge's flow regime and associated thermal structure. We find that small- scale convection (SSC), resulting from Rayleigh-Taylor instabilities, or drips, off the base of the overriding lithosphere, is a typical occurrence, if: (i) viscosities are < 5 x 1018 Pa s; and (ii) hydrous weakening of wedge rheology extends at least 100-150 km from the forearc cor- ner. In 2-D models, instabilities generally take the form of 'drips'. In 3-D, two separate, but interacting, longitudinal Richter roll systems form (with their axes aligned perpendicular to the trench), the first below the arc region and the second below the back-arc region. These instabilities result in transient and spatial temperature fluctuations of 100-150K, which are sufficient to influence melting, the stability of hydrous minerals and the dehydration of crustal material. Furthermore, they are efficient at eroding the overriding lithosphere, par- ticularly in 3-D and, thus, provide a means to explain observations of high heat flow and thin back-arc lithosphere at many subduction zones. A preliminary study into the effects of a finite-width slab on the wedge's flow regime, which allows for toroidal flow around the slab edge, highlights that the toroidal cell can locally increase or decrease temperatures suf- ficiently to either enhance or shut down wet melting, while a hydrated wedge corner may channel trench-parallel flow. The dynamic complexities of wedge flow revealed by our mod- els may help explain the diversity in geophysical and geochemical subduction signatures. |
author2 |
Davies, Rhodri; Goes, Saskia; Piggott, Matthew |
author_facet |
Davies, Rhodri; Goes, Saskia; Piggott, Matthew Le Voci, Giuseppe |
author |
Le Voci, Giuseppe |
author_sort |
Le Voci, Giuseppe |
title |
Controls on the flow regime and thermal structure of the subduction zone mantle wedge : a systematic 2-D and 3-D investigation |
title_short |
Controls on the flow regime and thermal structure of the subduction zone mantle wedge : a systematic 2-D and 3-D investigation |
title_full |
Controls on the flow regime and thermal structure of the subduction zone mantle wedge : a systematic 2-D and 3-D investigation |
title_fullStr |
Controls on the flow regime and thermal structure of the subduction zone mantle wedge : a systematic 2-D and 3-D investigation |
title_full_unstemmed |
Controls on the flow regime and thermal structure of the subduction zone mantle wedge : a systematic 2-D and 3-D investigation |
title_sort |
controls on the flow regime and thermal structure of the subduction zone mantle wedge : a systematic 2-d and 3-d investigation |
publisher |
Imperial College London |
publishDate |
2013 |
url |
http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.666465 |
work_keys_str_mv |
AT levocigiuseppe controlsontheflowregimeandthermalstructureofthesubductionzonemantlewedgeasystematic2dand3dinvestigation |
_version_ |
1718450981890424832 |