Subduction modeling From 2 D to 3 D
Subduction modeling From 2 D to 3 D…
Subduction modeling About the plate tectonics n 2 D subduction model n 3 D subduction model n Future works n
Subduction modeling About the plate tectonics n 2 D subduction model n 3 D subduction model n Future works n
Plate tectonics
Plate tectonics Transform boundaries
Plate. Divergent tectonics boundaries
Plate tectonics Convergent boundaries
Plate tectonics Convergent boundaries Collision Subduction
Subduction modeling About the plate tectonics n 2 D subduction model n 3 D subduction model n Future works n
First subduction model : 2 D n Rectangle domain Plate Upper mantle
First subduction model : 2 D n Lengths of the domain Plate 660 km 100 km Upper mantle Lower mantle 3120 km
First subduction model : 2 D n Boundary conditions Plate Upper mantle Lower mantle No slip
First subduction model : 2 D n Boundary conditions Plate Free slip Upper mantle Lower mantle No slip
First subduction model : 2 D n Boundary conditions Plate Free slip Upper mantle Free slip Lower mantle No slip Free slip
First subduction model : 2 D n Boundary conditions Plate Free slip No slip Upper mantle Free slip Lower mantle No slip Free slip
Governing equations n Rayleigh-Taylor Instability: dense slab sinks into a less dense mantle … conservation of mass, incompressible medium … conservation of momentum with no energy equation … deviatoric stress tensor
Rheology n n Viscous mantle Viscous Viscoplastic plate Plastic
The software Escript Finley Model setup : escript n PDE solver : Finley n Tracking of the plate : level set method n Visualization : Pyvisi, Gnuplot n
The hardware n Altix @ UQ
2 D subduction results
Velocity field : vortex
Lifecycle : initiation
Lifecycle : flow reorganization
Limits of the 2 D model
Necessity of the third dimension Importance of the mantle flow n Real subductions have a limited lateral extent n Interactions on the lateral edges of subduction zones n
Subduction modeling About the plate tectonics n 2 D subduction model n 3 D subduction model n Future works n
3 D subduction model Same governing equations n Same tools used n … only a different setup n
3 D subduction model no upper plate with subduction zone upper mantle Box size: big enough, for side walls to have little effect on subducting slab
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
Symmetry hypothesis free slip side boundary assume symmetry: model only half of the domain
Bottom boundary condition fixed bottom boundary higher viscosity in LM and phase boundary hinder convection
Slab boundary conditions free slip top boundary fixed end plate fixed, to isolate effects of tearing and rollback
Edge of the slab extreme case: free slip tear zone
Top boundary condition plate bottom fixed
Sides boundary conditions Freeslip on the sides
3 D subduction results
Velocity field : toroidal flow
Lifecycle of the subduction
Initiation
Reorganization of the flow
Hinge position (km) Time (M years)
Hinge position (km) Time (M years)
Hinge rollback velocity (mm/year) Time (M years)
Hinge rollback velocity Initiation (mm/year) Time (M years)
Hinge rollback velocity (mm/year) Reorganization of the mantle flow Time (M years)
Hinge rollback velocity (mm/year) 2. 5 mm/year Steady subduction Time (M years)
Hinge from the top 20 My 40 My 60 My 80 My
Why arcs ? n Ping pong ball hypothesis
Why arcs ? n Toroidal flow Inhomogeneities in the subducting plate n Tear resistance on the edges n
Subduction modeling About the plate tectonics n 2 D subduction model n 3 D subduction model n Future works n
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
First results
Thank you ! Hans Mülhaus n Laurent Bourgouin n Klaus Gottschaldt n n … you for coming
- Slides: 54