apg: an efficient software program for amp-pl thermobarometry based on graphical method

geothermobarometry equations are based on thermodynamic principles and appear in single or multi-variant functions. the number of variants for a specific composition or reaction usually is reduced into 2 involving temperature (t) and pressure (p). since most of planned equations have two passive or variant p and t, using these equations should be with special care. it is very effective to use graphical method to apply geothermobarometry functions. graphical method is a fundamental way to solve the math functions. in the graphical method two consistent geothermobarometry equations, which both have at least one share variant (p or t), are selected in order to achieve p and t. these selected equations should be applicable for the same reaction or rock. in this method selected thermobarometry equations are drawn on a p-t diagram and then intersection point of them which introduces asked temperature and pressure will be obtained. one of the most common geothermobarometry equations, suitable for intermediate magmatic rocks, is amphibole-plagioclase thermometry and amphibole barometry. apg software program introduced in this paper is specialized and designed for calculating equilibrium temperature and pressure of amphibole and plagioclase within an igneous rock. in this software program, pressure and temperature are estimated coincidently based on the graphical method.