Time-varying subduction and rollback velocities in slab stagnation and buckling Hana Čížková Charles University in Prague Craig Bina Northwestern University Evanston
SLAB STAGNATION Fukao et al., 29
SLAB STAGNATION Obayashi et al., 1997 Huang and Zhao, 26 Widiyantoro, 1997
TRENCH ROLLBACK ADVANCE old slabs cold and heavy rollback BUT: cold old slabs are stiff good stress guide advance (Gerault et al., 212) Husson, 212 rollback is controlled primarily by mantle drag, slab rheology plays only minor role
TRENCH VELOCITY Funiciello et al., 28
NUMERICAL MODELING TRENCH ROLLBACK Target: find the parameters of slabs (rheological parameters, age?) that may control the trench migration Main focus: rheological description effects of nonlinear rheology
NUMERICAL MODELING TRENCH ROLLBACK Target: find the parameters of slabs (rheological parameters, age?) that may control the trench migration Main focus: rheological description effects of nonlinear rheology??? FREE PARAMETERS OF RHEOLOGICAL DESCRIPTION??? Activation parameters, lower mantle viscosity jump
Estimate of the lower mantle viscosity based on sinking speed of detached slabs + t break t ini depth (km) 1 2 3 S&C, 26 2 22 24 log η
MODEL: COMPOSITE RHEOLOGY Diffusion creep ε diff = A diff σ E diff + pv exp RT diff Dislocation creep ε disl = A disl n σ E disl + pv exp RT disl Stress limiter ε σ sl = CL σ L n L
MODEL: RHEOLOGICAL PARAMETERS Crust Constant viscosity 1 2 Pa s Upper mantle Activation parameters according to Hirth and Kohlstedt (23) Yield stress.5 GPa Lower mantle Diffusion creep A-family V diff = 1.1x1-6 m 3 mol -1 B-family V diff = 2.2x1-6 m 3 mol -1 (PPV: η PPV = 1 21 Pa s)
MODEL: VISCOSITY INCREASE AT 66 km A-family B-family F&M, 1996 depth (km) 1 2 depth (km) 1 2 S&C, 26 depth (km) 1 2 P, 1999 S&C, 26 M&F, 24 3 S&C, 26 2 22 24 log η 3 2 22 24 log η 3 2 22 24 log η
MODEL: THERMAL EXPANSIVITY 1 Depth (km) 2 Katsura (21) 3 2E-5 4E-5 6E-5 α
RESULTS t = 4 Myr surface CMB 19 26 log η
RESULTS: AGE vs. DEPTH A family Depth (km) 1 2 Depth (km) 3 1 2 3 S&C, 26 2 22 24 log η B family S&C, 26 2 22 24 log η Depth (km) 1 2 1.1 22 2,5.122 8,4.121 2.1 22 4.1 22 8.1 22 1,1.1 23 1 2 Age (Myr) 7,6.1 22 5.1 22 3,1.1 22 3,3.1 22 Čížková et al., PEPI 212
RESULTS: BOTTOM AND TOP OF SLAB REMNANTS 3,1.1 22 5.1 22 5.1 22, weak PPV Depth (km) 1 2 1 2 3 Age (Myr) Van der Meer et al. (21) Čížková et al., PEPI 212
3 r (km) 2 family A preferred profile 1-2 2 4 6 log (η)
MODEL SETUP ROLLBACK AND SLAB STAGNATION STUDY weak crust Sinking slabs surface 41 km 66 km locked overriding plate PPV CMB weak crust impermeable free-slip surface 41 km second ridge Rollback and stagnation 66 km PPV CMB
MODEL SETUP ROLLBACK AND SLAB STAGNATION STUDY Initial position of the trench surface CMB 19 26 log η
MODEL SETUP ROLLBACK AND SLAB STAGNATION STUDY Initial position of the trench surface CMB 19 26 log η 145 km
RESULTS rollback not allowed 19 26 log η rollback
RESULTS plate / rollback velocity (cm/yr) 16 12 8 4 plate velocity rollback velocity 4 8 time since passing 4 km (Myr) 19 26 log η rollback
RESULTS velocity horizontal vertical absolute value 29 km plate / rollback velocity (cm/yr) 16 12 8 4 plate velocity rollback velocity 4 8 time since passing 4 km (Myr) ± 7 cm/yr ± 7 cm/yr 1cm/yr
RESULTS viscosity abs(velocity) stream function plate / rollback velocity (cm/yr) 16 12 8 4 plate velocity rollback velocity 4 8 time since passing 4 km (Myr)
RESULTS: EFFECT OF THE LOWER MANTLE VISCOSITY 3 r (km) 2 A A - 2xLM A - 1xLM A - LM:5 1-2 2 4 6 log (η)
RESULTS snapshot after 5 Myr Effect of the lower mantle viscosity η LM = 3,1.1 22 η LM = 6,2.1 22 η LM = 3,1.1 23
RESULTS: EFFECT OF THE CRUSTAL VISCOSITY η crust = 1 21 Pas η crust = 5.1 2 Pas η crust = 2.1 2 Pas η crust = 1 2 Pas η crust = 1 19 Pas 19 26 log (η)
RESULTS snapshot after 5 Myr Effect of the crustal viscosity η crust = 1 19 η crust = 1 2 η crust = 2.1 2 η crust = 5.1 2 snapshot after 9 Myr η crust = 1 2 η crust = 2.1 2 η crust = 5.1 2 η crust = 1 21 penetrating slabs
RESULTS snapshot after 5 Myr Effect of the yield stress age 7 Myr age 1 Myr age 15 Myr σ y = 2.1 8 σ y = 5.1 8 σ y = 1 9
RESULTS plate and rollback velocities plate / rollback velocity (cm/yr) 16 12 8 4 plate velocity rollback velocity plate / rollback velocity (cm/yr) 16 12 8 4 plate R13-2xLM rollback R13-2xLM plate / rollback velocity (cm/yr) 16 12 8 4 plate R13-1xLM rollback R13-1xLM lower mantle viscosity 4 8 time since passing 4 km (Myr) 4 8 time since passing 4 km(myr) 4 8 time since passing 4 km(myr) plate / rollback velocity (cm/yr) 16 12 8 4 max. 5 cm/yr plate 1^19 rollback 1^19 plate / rollback velocity (cm/yr) 16 12 8 4 plate 2x1^2 rollback 2x1^2 plate / rollback velocity (cm/yr) 16 12 8 4 plate 5x1^2 rollback 5x1^2 plate / rollback velocity (cm/yr) 16 12 8 4 plate 1^21 rollback 1^21 crust viscosity -4 4 8 time since passing 4 km (Myr) 4 8 time since passing 4 km (Myr) 4 8 time since passing 4 km (Myr) 4 8 time since passing 4 km (Myr) plate / rollback velocity (cm/yr) 16 12 8 4 plate 2e8 rollback 2e8 plate / rollback velocity (cm/yr) 16 12 8 4 plate velocity rollback velocity plate / rollback velocity (cm/yr) 16 12 8 4 plate 1e9 rollback 1e9 yield stress 4 8 time since passing 4 km (Myr) 4 8 time since passing 4 km (Myr) 4 8 time since passing 4 km (Myr)
RESULTS snapshot after 5 Myr Effect of the Clapeyron slope γ 41 = 1 MPa/K γ 41 = 2 MPa/K γ 41 = 3 MPa/K γ 41 = 4MPa/K plate/rollback velocity (cm/yr) 16 12 8 4 plate velocity rollback velocity 1E+23 1E+22 1E+21 1E+2 η astenosphere (Pas) plate / rollback velocity (cm/yr) 16 12 8 4 plate velocity rollback astenospheric viscosity 1E+23 1E+22 1E+21 1E+2 η ast (Pa s) 4 8 Time since passing 4 km (Myr) 4 8 time since passing 4 km (Myr)
RESULTS snapshot after 5 Myr Effect of the Clapeyron slope γ 41 = 1 MPa/K γ 41 = 2 MPa/K γ 41 = 3 MPa/K γ 41 = 4MPa/K plate velocity (cm/yr) 2 16 12 8 4 plate velocity gamma_4 = 3 MPa/K 1 MPa/K 2 MPa/K 4 MPa/K rollback velocity (cm/yr) 8 6 4 2 rollback velocity 3 MPa/K 1 MPa/K 2 MPa/K 4 MPa/K 4 8 time since passing 4 km (Myr) -2 4 8 time since passing 4 km (Myr)
RESULTS trench distance after 6 Myr 24 24 2 2 trench retreat (km) 16 12 8 trench retreat (km) 16 12 8 4 4 1E+23 2E+23 3E+23 4E+23 lower mantle viscosity (Pa s) 1E+19 1E+2 1E+21 Crustal viscosity (Pa s) 24 24 2 age 15 Myr 2 trench retreat (km) 16 12 8 age 1 Myr age 7 Myr trench retreat (km) 16 12 8 4 4 2E+8 4E+8 6E+8 8E+8 1E+9 yield stress (Pa) 1 2 3 4 Clapeyron slope 41 km (MPa/K)
Obayashi et al., 1997 Huang and Zhao, 26 Widiyantoro, 1997
CONCLUSIONS SLAB STAGNATION AND ROLLBACK all modes display rollback (effect of ridge push?) relation between plate velocity and rollback most models predict slab stagnation in the transition zone slow slabs (due to higher friction on the contact) have slower rollback and penetrate to the lower mantle effect of higher astenospheric viscosity? more negatively buoyant slabs have faster rollback stiffer slabs have faster rollback (no reduction due to the periods of increased subduction velocity) implications of rollback periodicity to exhumation