A modebox simply represents how the modal proportions of phases present in a rock (i.e. at fixed bulk composition) would vary along a path in pressure or temperature.
This information is acquired via pseudosection-type calculations along the desired path. With THERMOCALC 3.50 (Dec 2020) onward, to print mode information, add the script
to the scriptfile, tc-<project>.txt. Output is produced in CSV format (tc-<project>.csv) and Mathematica input format (tc-<project>-dr.txt).
An example scriptfile can be downloaded here:
The output files corresponding to this scriptfile are: