Fix rheology in continental extension (WIP)

[lhy11009]

Pull Request Checklist. Please read and check each box with an X. Delete any part not applicable. Ask on the forum if you need help with any step.

Fix the prefactors of dislocation creep rheology of the continental_extension cookbook

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• I have tested my new feature locally to ensure it is correct.
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[lhy11009]

Here is the real change.

[lhy11009]

This figure shows the continental strength profile before (upper panel) and after fixing the prefactors in the flow laws (lower panel).
The geotherm from the Chapman model is also shown (upper left), and two dots mark the bottom of the upper crust and lower crust and their respective temperature values.
After the correction, upper-crust dislocation creep becomes slightly stronger, while lower-crust dislocation creep becomes substantially weaker compared to the previous implementation.
As a result, the overall lithospheric strength profile returns to the classic “Christmas tree” shape expected for continental rheology.

[lhy11009]

This figure shows the strain-rate field at timestep 0.

The upper panel corresponds to the original prefactors (evaluated at ~100 km depth). In this case, the strain rate shows a sharp discontinuity at the upper–lower crust boundary.

The lower panel shows the results using the corrected prefactors. The discontinuity between the upper and lower crust becomes more moderate, while a clearer discontinuity appears at the lower crust–mantle boundary, which is more consistent with the expected rheological structure.

The following figure shows the strain-rate field and topography at t=5 Ma (as also shown in the cookbook). The results differ substantially between the two cases.

With the original prefactors, deformation localizes into a few discrete faults, leading to strong strain localization and pronounced topography.

With the corrected prefactors, deformation is distributed across numerous faults, resulting in more distributed strain and a much gentler topographic profile.

[lhy11009]

Also, feel free to check the Jupyter notebook I attached. Here I also added markdown blocks to explain what I did. One potential problem is the 1 MPa constant water fugacity I assumed for the wet anorthite flow law.

[lhy11009]

@naliboff @ryanstoner1, please take a look at this WIP PR. I updated the prefactors for the upper-crust and lower-crust dislocation creep flow laws, which leads to fairly significant changes in the results, as shown in the figures above.

I think the first step is to review these differences and then decide how we would like to proceed.