MINERAL REACTIONS IN PELITIC ROCKS - 1. PREDICTION OF P-T-X(Fe-Mg) PHASE RELATIONS.

Abstract

The detailed behavior of mineral assemblages during progressive metamorphism of pelitic rocks may be predicted through P-T-X(Fe-Mg) relationships for the model system K//2O-FeO-MgO-Al//2O//3-SiO//2-H//2O. Continuous and discontinuous reactions may be examined in isobaric T-X(Fe-Mg) and isothermal P-X(Fe-Mg) sections, constructed simply from a knowledge of Mg/Fe partitioning between phases and relative dP/dT of end-member reactions in either Fe- or Mg-systems. The displacements of three-phase triangles on the AFM projection may be predicted as functions of changing pressure, temperature, or a H//2O. Refs.