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Subduction modeling From 2D to 3D…

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**Subduction modeling About the plate tectonics 2D subduction model**

Future works

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**Subduction modeling About the plate tectonics 2D subduction model**

Future works

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Plate tectonics

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Plate tectonics Transform boundaries

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Plate tectonics Divergent boundaries

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**Convergent boundaries**

Plate tectonics Convergent boundaries

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**Convergent boundaries**

Plate tectonics Convergent boundaries Collision Subduction

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**Subduction modeling About the plate tectonics 2D subduction model**

Future works

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**First subduction model : 2D**

Rectangle domain Plate Upper mantle

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**First subduction model : 2D**

Lengths of the domain Plate 660 km 100 km Upper mantle Lower mantle 3120 km

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**First subduction model : 2D**

Boundary conditions Plate Upper mantle No slip Lower mantle

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**First subduction model : 2D**

Boundary conditions Plate Free slip Upper mantle No slip Lower mantle

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**First subduction model : 2D**

Boundary conditions Plate Free slip Upper mantle Free slip No slip Free slip Lower mantle

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**First subduction model : 2D**

Boundary conditions Plate Free slip No slip Upper mantle Free slip No slip Free slip Lower mantle

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Governing equations Rayleigh-Taylor Instability: dense slab sinks into a less dense mantle … conservation of mass, incompressible medium … conservation of momentum … deviatoric stress tensor with no energy equation

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Rheology Viscous mantle Viscoplastic plate Viscous Plastic

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**The software Model setup : escript PDE solver : Finley**

Escript Finley Model setup : escript PDE solver : Finley Tracking of the plate : level set method Visualization : Pyvisi, Gnuplot

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The hardware UQ

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2D subduction results

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**Velocity field : vortex**

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**Lifecycle : initiation**

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**Lifecycle : flow reorganization**

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Limits of the 2D model

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**Necessity of the third dimension**

Importance of the mantle flow Real subductions have a limited lateral extent Interactions on the lateral edges of subduction zones

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**Subduction modeling About the plate tectonics 2D subduction model**

Future works

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**3D subduction model Same governing equations Same tools used**

… only a different setup

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**3D subduction model no upper plate plate with subduction zone upper**

mantle Box size: big enough, for side walls to have little effect on subducting slab

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**The level set field use level set to define and track**

the subducting plate subducting slab only subducting part of the plate is included in the FE domain

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**Symmetry hypothesis free slip side boundary**

assume symmetry: model only half of the domain

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**Bottom boundary condition**

fixed bottom boundary higher viscosity in LM and phase boundary hinder convection

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**Slab boundary conditions**

free slip top boundary fixed end plate fixed, to isolate effects of tearing and rollback

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Edge of the slab extreme case: free slip tear zone

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**Top boundary condition**

plate bottom fixed

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**Sides boundary conditions**

Freeslip on the sides

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3D subduction results

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**Velocity field : toroidal flow**

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**Lifecycle of the subduction**

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Initiation

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**Reorganization of the flow**

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Hinge position Hinge position (km) Time (M years)

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Hinge position Hinge position (km) Time (M years)

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**Hinge rollback velocity**

(mm/year) Time (M years)

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**Hinge rollback velocity**

(mm/year) Initiation Time (M years)

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**Hinge rollback velocity**

(mm/year) Reorganization of the mantle flow Time (M years)

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**Hinge rollback velocity**

(mm/year) 2.5 mm/year Steady subduction Time (M years)

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Hinge from the top 20 My 40 My 60 My 80 My

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Why arcs ? Ping pong ball hypothesis

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**Why arcs ? Toroidal flow Inhomogeneities in the subducting plate**

Tear resistance on the edges

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**Subduction modeling About the plate tectonics 2D subduction model**

Future works

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**To be continued … weak zone, part of the FE domain fixed**

normal case: tearing follows a pre-existing weak zone subduction possible if slab strength > strength of the weak zone

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First results

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**Thank you ! Hans Mülhaus Laurent Bourgouin Klaus Gottschaldt**

… you for coming

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