RCLC, which is short for ‘recalculation’, is a program that calculates pressure-temperature (P-T) conditions of Grt-Opx-Pl-Qtz±Crd±Bt assemblages based on Al-solubility in Opx in equilibrium with Grt, corrected for late Fe-Mg exchange.
The rationale and calculation method for the program are described in Chacko et al. (1996) and in Pattison et al. (2003). Fig. 3 of Pattison et al. (2003) shows graphically how RCLC works.
The program described in Pattison et al. (2003) was written in BASIC and compiled on a PC. However, because the BASIC language is no longer compatible with newer versions of the Windows operating system, the RCLC program was converted into this Web-based application in which the underlying computer code is written in the PYTHON programming language.
RCLC was originally written by Tom Chacko and James Farquhar in 1996 and subsequently modified by Chris McFarlane, David Pattison and Tom Chacko between 1997 and 2002. The Web-based version of RCLC was developed by Justin Widney of the University of Alberta in 2018 as part of an undergraduate summer internship.
RCLC requires the following input for the calculation of P-T in a sample: mineral composition and modal abundance data for garnet and orthopyroxene and mineral composition data for plagioclase. Although not required for the calculation, if present, the modes and composition of biotite and/or cordierite can also be included in the calculations to correct for retrograde Fe-Mg exchange between those phases and garnet and orthopyroxene in the rock. The compositional data for all of these minerals must be recalculated off-line by the user into atomic proportions of cations on the following basis: Grt (12 oxygens), Opx (6 oxygens or 4 cations), Crd (18 oxygens), Bt (11 oxygens) and Pl (8 oxygens). The cation proportion data for each mineral and the modal abundance data for Grt, Opx, ± Bt, ± Crd are typed into the appropriate cell in the mineral composition/modal abundance input table below. The user must also select one or more Al-in-opx models for calculating the proportion of the octahedral site in opx filled by Al.
Once compositional and modal data are inputted and one or more Al-in-opx models are selected, click the 'Submit' button to run the program. The program will output the results of the calculations both on the webpage and as an Excel CSV file that can be downloaded.
More detailed explanations of the input and output of the RCLC program can be obtained by downloading the Web instructions at the link given above.
Reference to be cited:
Pattison, D.R.M, Chacko, T., Farquhar, J. & McFarlane, C.R.M. (2003) Temperatures of granulite-facies metamorphism: constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange. Journal of Petrology, 44, 867-900.