Subduction modeling From 2D to 3D…. Subduction modeling About the plate tectonics 2D subduction...

Subduction modeling

From 2D to 3D…

Subduction modeling

About the plate tectonics 2D subduction model 3D subduction model Future works

Plate tectonics

Plate tectonicsTransformboundaries

Plate tectonicsDivergent

boundaries

Plate tectonics Convergentboundaries

Plate tectonics Convergentboundaries Collision

Subduction

Subduction modeling


First subduction model : 2D

Rectangle domain

Plate

Upper mantle


Lengths of the domain

3120 km

660 kmPlate

Upper mantle

Lower mantle

100 km


Boundary conditions

No slip

Plate

Upper mantle

Lower mantle


Boundary conditions

No slip

Plate

Upper mantle

Lower mantle

Free slip


Boundary conditions

No slip

Plate

Upper mantle

Lower mantle

Free slip

Free slip Free slip


Boundary conditions

No slip

Plate

Upper mantle

Lower mantle

Free slip

Free slip Free slip

No slip

Governing equations

Rayleigh-Taylor Instability: dense slab sinks into a less dense mantle

0v

… conservation of mass, incompressible medium

gp

i

j

j

iij x

v

x

v

… conservation of momentum

… deviatoric stress tensorwith

no energy equation

Rheology

Viscous mantle

Viscoplastic plate

.constmantle

yieldcreepyield

yieldcreepcreep

II

yieldyield e2

IIcreepcreep e 2

Viscous Plastic

The software

Model setup : escript PDE solver : Finley

Tracking of the plate : level set method Visualization : Pyvisi, Gnuplot

EscriptFinley

The hardware

Altix @ UQ

2D subduction results

Velocity field : vortex

Lifecycle : initiation

Lifecycle : flow reorganization

Limits of the 2D model

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

Subduction modeling


3D subduction model

Same governing equations Same tools used … only a different setup

3D subduction model

upper mantle

plate with subduction zone

no upper plate

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

The level set field

subducting slab

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

use level set to define and track the subducting plate

Symmetry hypothesis

assume symmetry: model only half of the domain

free slip side boundary

Bottom boundary condition

higher viscosity in LM and phase boundary hinder convection

fixed bottom boundary

Slab boundary conditions

plate fixed, to isolate effects of tearing and rollback

fixedend

free slip top boundary

Edge of the slab

extreme case:free sliptear zone

Top boundary condition

plate bottom fixed

Sides boundary conditions

Freeslip onthe sides

3D subduction results

Velocity field : toroidal flow

Lifecycle of the subduction

Initiation

Reorganization of the flow

Hinge position

Hingeposition

(km)

Time(M years)

Hinge rollback velocity

Hinge rollbackvelocity

(mm/year)

Time(M years)



(mm/year)

Time(M years)

Initiation



(mm/year)

Time(M years)

Reorganization of the mantle

flow



(mm/year)

Time(M years)

Steady subduction

2.5 mm/year

Hinge from the top

20 My 40 My 60 My 80 My

Why arcs ?

Ping pong ball hypothesis

Why arcs ?

Toroidal flow

Inhomogeneities in the subducting plate Tear resistance on the edges

Subduction modeling


To be continued …

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

fixed

weak zone, part of theFE domain

First results

Thank you !

Hans Mülhaus Laurent Bourgouin Klaus Gottschaldt

… you for coming

Subduction modeling From 2D to 3D…. Subduction modeling About the plate tectonics 2D subduction...

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