Hi! I am Xiang and now using ASPECT to run some small tests. Recently I am testing how a spherical hot material in the deep mantle will contribute to the surface dynamics topography when a plate boundary is on the top. I use Visco Plastic section but only include radial viscosity variation and set the plate boundary material’s maximum and minimum viscosity to around 1e20:
set Model name = visco plastic
subsection Visco Plastic
# reference stuff
set Reference temperature = 1573
#set Reference viscosity = 1.0e21
set Minimum strain rate = 1.e-20
set Adiabat temperature gradient for viscosity = 9.24e-09 # 0.3 K/km
#set Adiabat temperature gradient for viscosity = 0 # 0 K/km
# Set up phase transitions so that dislocation becomes inactive in the lower mantle for all fields.
set Phase transition depths = background: 100e3|660e3 , plbd: 100e3|660e3
set Phase transition widths = background: 1e3|1e3 , plbd: 1e3|1e3
set Phase transition temperatures = background: 1573|1573, plbd: 1573|1573
set Phase transition Clapeyron slopes = background: 0|0, plbd: 0|0
# Viscosity cut offs
set Minimum viscosity = background: 1.0e18|1.0e18|1.0e19, plbd: 0.99e20|0.99e20|0.99e20
set Maximum viscosity = background: 1.0e23|1.0e23|1.0e24, plbd: 1.01e20|1.01e20|1.01e20
# density-related parameters (crust has mantle density = 3300 at T = 273 K)
set Thermal diffusivities = 1.e-6
set Heat capacities = 750
set Densities = background: 3300|3300|3300, plbd: 3300|3300|3300
set Thermal expansivities = 3e-5
# viscosity-related parameters
set Viscous flow law = diffusion
#set Viscous flow law = composite
set Viscosity averaging scheme = geometric
# None of this matters for plate boundaries, which we already pegged above at 1e20
# dislocation creep (just z < 660 km)
# We set the prefactor to a very low value in the lower mantle to effectively turn off dislocation creep.
set Prefactors for dislocation creep = background: 1e-40|1e-40|1e-40 , plbd: 1e-40|1e-40|1e-40
set Stress exponents for dislocation creep = 3.0
set Activation energies for dislocation creep = 480.e3
set Activation volumes for dislocation creep = background: 0.0|0.0|0.0 , plbd: 0.0|0.0|0.0
# diffusion creep, (gives lower/upper mantle viscosity = 100)
set Prefactors for diffusion creep = background: 4.58017051e-11|5e-21|5e-23| , plbd: 4.58017051e-11|5e-21|5e-23|
set Stress exponents for diffusion creep = 1
set Grain size exponents for diffusion creep = 0
set Activation energies for diffusion creep = background: 300e3|0|0 , plbd: 300e3|0|0
set Activation volumes for diffusion creep = background: 0|0|0 , plbd: 0|0|0
# Plasticity parameters using drucker-prager
# Lower mantle - turn off using high cohesion
# Upper mantle - turn on by using 200 MPa
set Cohesions = background: 1e20|1.0e20|1.0e20 , plbd: 1e20|1.0e20|1.0e20
#set Cohesions = background: 20.e6|20.e6, plbd: 20.e6|20.e6
#set Angles of internal friction = 0.0 # Friction coefficient of ~0.6
#set Maximum yield stress = 1e12
end
The question is, viscosity average scheme: geometric and harmonic show different reults for the top dynamics topography, even at the step 0 (I use no advection, single stokes to solve this) Does anyone have some ideas for this?
Harmonic:
Geometric
Spherical hot anomaly beneath lithosphere
Geometric.prm (10.7 KB)
Harmonic.prm (10.7 KB)
Thanks for your time!
Best regards,
Xiang He
