Latent heat material model with several compositional fields

ASPECT
1

Dear all,
I am trying to run models where I simulate the presence of crust, lithosphere, sublithospheric mantle down to a depth of 800 km, and plume (in total, I have 7 compositional fields). I would like to include the possibility for mantle materials to change properties when they cross the 410 and 660 km discontinuities, but I am facing a few issues.
More in detail, I am currently trying to prescribe density changes in the sublithospheric mantle when it crosses the MTZ (and I would like only this material to change density). However, I did not find a way to apply different reference density values for each compositional field. In addition, even though I prescribed variations in the “set Phase transition depths/temperatures/widths” for the mantle only, I realized that other materials (such as the plume field) change density too.
I was trying to use the Latent Heat model for my purpose, but likely I did not fully understand the use of the “Density differential for compositional field 1” and “Corresponding phase for density jump” items, therefore the problem could be there. I have attached one of my files

Rift_Test.prm (13.0 KB)

Maybe someone has any suggestions?
Thanks a lot.
Alessio

2

Hi Alessio,

First, apologies for a very late reply. In the future if you have not heard a response within a week or so, please feel free to post a follow-up message. I often delete the email notification before responding, and come back to it at a later time.

Second, thank you for including the PRM file, this is really helpful.

On to your question - to start, this is a really complicated model, so it make take some time and multiple iterations to sort out the best path forward.

However, I think I have some idea about what the issue is. As you noted, you are currently compositing the visco plastic and latent heat materials, which are respectively specified to compute the following properties:

    subsection Compositing
        set Compressibility                 = latent heat
        set Density                         = latent heat
        set Entropy derivative pressure     = latent heat
        set Entropy derivative temperature  = latent heat
        set Reaction terms                  = latent heat
        set Specific heat                   = latent heat
        set Thermal conductivity            = visco plastic
        set Thermal expansion coefficient   = visco plastic
        set Viscosity                       = visco plastic
    end

As defined above, the density is being calculated by the latent heat material model, but that material model is only setup to handle 2 distinct compositions. As such, it makes sense you are not getting the correct densities or phase transition behavior.

How important is compressibility for your study? If you can get away with assuming incompressibility to start, I suggest just using the visco plastic material, which is setup to handle phase transitions.

For examples on how to use phase transitions in the visco plastic material model, see the following examples in the test folder (I found these via ls *visco_plastic*phase*.prm) :

visco_plastic_phases_compositions.prm
visco_plastic_phases_temperature_limit_harzburgite.prm
visco_plastic_phases_peierls_mei_exact.prm
visco_plastic_phases_temperature_limit_pyrolite_complicated.prm
visco_plastic_phases_plasticity.prm                
visco_plastic_phases_temperature_limit_pyrolite.prm
visco_plastic_phases.prm                           
visco_plastic_phases_viscosity_max_min.prm
visco_plastic_phases_temperature_limit_basalt.prm  
visco_plastic_phases_viscosity.prm

Can you take a look at these examples, and try to modify your setup accordingly? Apologies again for the very delayed reply.

Cheers,
John