# Phase transition in visco-plastic

**URL:** <https://community.geodynamics.org/t/phase-transition-in-visco-plastic/2670>\
**Category:** ASPECT\
**Created:** [November 11, 2022, 5:25pm UTC](https://community.geodynamics.org/t/phase-transition-in-visco-plastic/2670 "2022-11-11T17:25:34Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Liu](https://avatars.discourse-cdn.com/v4/letter/l/a88e57/32.png) [@Liu](https://community.geodynamics.org/u/Liu)\
**Post date:** [November 11, 2022, 5:25pm UTC](https://community.geodynamics.org/t/phase-transition-in-visco-plastic/2670/1 "2022-11-11T17:25:34Z")

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Hello,

I am trying to add phase transition in a subduction model using visco-plastic material model. I only add phase transition to one of the material (oceanic crust). I started with adding one transition pressure, temperature, and clapeyron slope.

> set Define transition by depth instead of pressure = false  
> set Phase transition pressures= OC: 1.2e9  
> set Phase transition pressure widths= OC: 0.4e9  
> set Phase transition temperatures= OC: 803  
> set Phase transition Clapeyron slopes=OC: 4e6  
> set Densities = background: 3337.4, OC: 2950|3450, OML: 3337.4, UC: 2811.2, LC: 2929, CML: 3337.4

The transition occurs at the surface of the model, which doesn’t reach the transition pressure or temperature. I guess it is because of the clapeyron slope, or am I misunderstanding it? Is there a way to set a lower pressure/temp limit so that transition doesn’t happen below this limit? Or limit with another clapeyron slope.  
I want to include the eclogite phase transition, like in this phase diagram.  
 ![Screenshot 2022-11-11 122249](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/2X/8/8fdc87006c0ac0bbdb02232090cbfcedc6145179.png)

Thank you.

Xiaowen

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**Author:** ![bobmyhill](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/bobmyhill/32/38_2.png) [@bobmyhill](https://community.geodynamics.org/u/bobmyhill)\
**Post date:** [November 11, 2022, 6:10pm UTC](https://community.geodynamics.org/t/phase-transition-in-visco-plastic/2670/2 "2022-11-11T18:10:32Z")

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Dear Xiaowen,

The phase transition model in ASPECT implements phase changes that are linear in P-T or z-T space _under the assumption of equilibrium_.

You can choose to have multiple reactions with different Clapeyron slopes, again _under the assumption of equilibrium_.

As far as I know, ASPECT doesn’t yet include a model including metastability, although we’ve talked about it a couple of times. The problem is certainly tractable (adding an Arrhenius model to the phase function), but would require some modification to the Latent Heat model to implement if it hasn’t been done already. @mibillen or one of the other maintainers might know more.

Best wishes,  
Bob

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**Author:** ![Liu](https://avatars.discourse-cdn.com/v4/letter/l/a88e57/32.png) [@Liu](https://community.geodynamics.org/u/Liu)\
**Post date:** [November 13, 2022, 5:05pm UTC](https://community.geodynamics.org/t/phase-transition-in-visco-plastic/2670/3 "2022-11-13T17:05:38Z")

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Hi Bob,

Thank you for your reply. I was able to set the phase transition through multiple reactions.  
I am also looking forward to seeing the model including metastability in the future.

Thanks,  
Xiaowen