Metamorphic Reactions

Phase Transformation Reactions

Solid-Solid Net Transfer Reaction NaAlSi 2 O 6 + SiO 2 = NaAlSi 3 O 8 Jd QtzAb dG = VdP – SdT dP =  S dT =  V Clapyron Equation

Dehydration Reaction KAl 3 Si 3 O 10 (OH) 2 + SiO 2 = KAlSi 3 O 8 + Al 2 SiO 5 + H 2 O Ms Qtz Kfs Als Slope of reaction boundary determined by properties of fluid phase dP =  S dT =  V Most dehydration reaction boundaries subparallel

Decarbonation Reactions CaCO 3 + SiO 2 = CaSiO 3 + CO 2 Parallelism of decarbonation reaction equilibrium boundaries in P-T space

Decarbonation Versus Dehydration Reactions

Theoretical Loop of Devolatilization Reactions At high enough pressures the fluid phase is so compressed that V Products < V Reactants dP =  S dT =  V Clapyron equation becomes negative

Dehydration Reaction: Effect of P H 2 O < P Total Ln K = Ln f H 2 O ( f H 2 O = P H 2 O   H 2 O ) Le Chatelier’s principle; lowering PH2OPH2O stabilizes products at the expense of reactants, displacing equilibrium boundary to lower temperature

Temperature vs Mole Fraction of Fluid Species T-X H 2 O Diagram T-X CO 2 Diagram X CO 2 + X H 2 O = 1

G T G T K A S G T A K S K S A T P3 P2 P1 P3 P2 P1 T (K) (A) (S) Energy-Temperature Diagrams: the Rules of Schreinemakers P1 P3 P2

Rules of Schreinemakers 1.Label each reaction with the missing phase 2.Arrange reactions such that the label is stable where the reaction is metastable

Application of Rules of Schreinemakers to 2-component system with 4 phases Note that there is one reaction for each phase in the system

Application of Rules of Schreinemakers to 2-Component System with 5 phases

An Example of a Petrogenetic Grid – the KMASH System for Pelites