Figure 6.04. T or P Limiting Assemblages. Intersecting reaction curves define fixed points that can be used to place limits on temperature (T) and pressure (P) for assemblages of minerals involved in the reactions. These limits are the minimum or maximum temperature or pressure required for the assemblages to be in equilibrium. Check the assemblage boxes to see the temperature or pressure bounds on the T-P diagram for the selected assemblage. Reaction curves are based on the thermodynamic model dataset SPaC (version 4/2000) developed originally by Spear and Cheney (1989).