TCInvestigator: Automated Calculation of Contours for THERMOCALC Pseudosections

English Abstract:

Forward modelling of bulk-rock compositions to constrain pressures and temperatures (P-T) of metamorphism based on mineral assemblage is a commonly used technique. The pseudosections produced contain a wealth of information about predicted mineral compositions and abundances that goes far beyond variations in mineral assemblage. In practice, utility of these parameters is limited because calculation of compositional isopleths and contours of modal mineral abundance are time consuming to calculate for THERMOCALC pseudosections. Our new software called TCInvestigator provides a quick and user friendly way to contour all compositional parameters and mineral modes across a THERMOCALC pseudosection.

TCInvestigator takes the postscript pseudosection diagram and creates a grid of points at a user-specified resolution. THERMOCALC is then used to calculate the equilibrium mineral assemblage at each point using an initial starting guess provided by the user (this can be calculated during initial pseudosection calculation). Once all points have been tried, any that failed to calculate are re-tried using interpolated starting guess values from the surrounding points. This procedure is iterated until no more solutions are found. Any remaining unsolved points are then interpolated numerically from surrounding solutions to produce a fully quantified set of mineral modes and compositions. Following calculation, the dataset can be contoured and output as figures, output as a Matlab readable binary structure or selected compositions written to an ASCII text file. Automated contouring using TCInvestigator allows the user to consider easily all compositional variables at one time. As new P-T conditions and bulk compositions are explored using improved thermodynamic datasets this software will provide a quick and simple way to identify key compositional and modal variations in the newly-modelled systems.