Metamorphic Reactions Phase Transformation Reactions SolidSolid Net Transfer

Metamorphic Reactions

Phase Transformation Reactions

Solid-Solid Net Transfer Reaction Na. Al. Si 2 O 6 + Si. O 2 = Na. Al. Si 3 O 8 Jd Qtz Ab Clapyron Equation d. G = Vd. P – Sd. T d. P = S d. T = V

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

Decarbonation Reactions Ca. CO 3 + Si. O 2 = Ca. Si. O 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 VProducts < VReactants Clapyron equation d. P = S d. T = V becomes negative

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

Temperature vs Mole Fraction of Fluid Species T-XH 2 O Diagram T-XCO 2 Diagram XCO 2 + XH 2 O = 1

P 1 G Energy-Temperature Diagrams: the Rules of Schreinemakers K A S T P 3 P 2 G K A S T P 1 T (A) P 3 P 2 G K A S T P 1 (S) (K) T

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