Metamorphic Reactions

Phase Transformation Reactions

Solid-Solid Net Transfer Reaction

NaAlSiNaAlSi22OO66 + SiO + SiO22 = NaAlSi = NaAlSi33OO88 JdJd Qtz Qtz AbAb

dG = VdP – SdT

dP = S

dT = V

Clapyron Equation

Dehydration Reaction

KAl3Si3O10(OH)2 + SiO2 = KAlSi3O8 + Al2SiO5 + H2OMs Qtz Kfs Als

Slope of reaction boundary determined by properties of fluid phase

dP = S

dT = V

Most dehydration reaction boundaries subparallel

Decarbonation Reactions

CaCO3 + SiO2 = CaSiO3 + CO2

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 VProducts < VReactants

dP = S

dT = V

Clapyron equation

becomes negative

Dehydration Reaction: Effect of PH2O < PTotal

Ln K = Ln f H2O

( f H2O = PH2O H2O)

Le Chatelier’s principle; lowering PH2O

stabilizes products at the expense of reactants, displacing equilibrium boundary to lower temperature

Temperature vs Mole Fraction of Fluid Species

T-XH2O Diagram

T-XCO2 DiagramXCO2 + XH2O = 1

G

T

G

T

K

AS

G

T

AK

S

K

SA

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 phase2. Arrange reactions such that the label is

stable where the reaction is metastable

Application of Rules of Schreinemakers to2-component system with 4 phasesNote 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