Staurolite stability in metabasites: evaluation of the effect of fluid composition and Fe<sup>3+</sup> content in the rock
During the metamorphism of mafic rocks, a wide variety of new mineral species arise. Interesting from a petrological point of view is the formation of an aluminous mineral in metabasites - staurolite. It has been established that the appearance of staurolite in metabasites strongly depends on P-T conditions, the bulk chemical composition of the original rocks, and the composition of the fluid. Using the thermodynamic analysis of mineral formation, the influence of two important factors on the stability of staurolite in the metabasite system was assessed: 1) the composition of the metamorphic fluid; 2) Fe<sup>3+</sup> content in the rock. We determined that the position of staurolite- forming reactions in metabasites with an increase in the mole fraction of CO<sub>2</sub> in water-carbon dioxide fluid leads to a shift of staurolite fields on P-T diagrams to lower temperatures. The presence of iron in the form of Fe<sup>3+</sup> slightly increases the P-T stability field of staurolite.