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Coupled chemical-thermal-mechanical modelling of magma generation and migration in subduction zones

English title Coupled chemical-thermal-mechanical modelling of magma generation and migration in subduction zones
Applicant Tackley Paul
Number 116381
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.04.2007 - 31.03.2009
Approved amount 205'760.00
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Keywords (8)

Mantle convection; Subduction; Geochemistry; melting; melt migration; magma transport; back-arc volcanism; dehydration

Lay Summary (English)

Lead
Lay summary
Subduction zones are the places where oceanic plates enter Earth’s interior. Most subduction zones display much volcanic activity, which builds volcanic arcs above the descending oceanic slabs. The production of so much magma results from the release of water-rich fluids from the sinking slab. This released water triggers melting of the hot part of the mantle located above the cold sinking slabs. However, how this magma is transported from the melt generation region above the hydrated slab surface at 100-300 km depth to the magma extraction zone at the volcanic arc surface, is not well known. There is a complex coupling between chemical, thermal, and mechanical interactions associated with melt generation and transport. As the magma rises, decreasing pressure plus changes in temperature are likely to induce significant compositional variations, especially in terms of dissolved water content. Furthermore, whether or not water is completely miscible with silicate melt depends on pressure, temperature, and composition, and has a major effect on fluid migration. Melt transport may also affect deformation in the mantle wedge.

In this project, two- and three-dimensional coupled chemical-thermal-mechanical numerical models of magma generation and transport in subduction zones will be developed and used to study these processes. This will be accomplished by coupling a melt generation and percolation model to an existing validated thermal-mechanical model of subduction based on finite differences and a marker-in-cell technique. The heat advected by the percolating liquid phase as well as latent heat effect associated with melting will be included. Chemical exchanges between the molten rock and the solid matrix will be computed. We will start by studying simple models and build to more complex ones, including such complexities as melt viscosity which is strongly dependent on composition, and a description of fluid percolation through the solid that includes solid matrix compaction/dilatation associated with melt generation/crystallization and variations in solid and fluid pressure. Modeling results will be compared to alternative magma transport models, such as diapirism and strongly channelled porous flows. We will also test our numerical results against natural data, in particular, in collaboration with the University of Montpellier (France).
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
126832 High-resolution 3D geochemical-petrological-thermomechanical modelling of subduction and magmatic arcs development 01.10.2009 Project funding
138209 Three-dimensional numerical modelling of fluid generation atop the subducting slab beneath southern Alaska 01.10.2011 Project funding

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