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Themes of the Day:
- Magma Differentiation Processes Overview
- Introduction to Phase Diagrams
- Applying the Phase Rule and Lever Rule
- Equilibrium Crystallization in Binary Systems
- Fractional Crystallization in Binary Systems
- Equilibrium Crystallization in Ternary Systems
Magma Differentiation Processes Overview
- Magma composition is initially dictated by the starting material (solid) and the degree (percentage) of melting - mantle melts are generally of mafic (basaltic) composition
- Magma may (rarely) crystallize with little or no compositional modification
- Magma composition evolves (usually towards more felsic compositions) according to a number of factors:
- Crystallization - Equilibrium and Fractional
- Magma Mixing
- Assimilation
A Useful Web Resource on Phase Diagrams from Brock University
Introduction to Phase Diagrams
- What do they show? What are they useful for? How are they made?
- Phases (P) - physically seperable matter - solids: different mineral phases; liquids: e.g., vinegar and oil; gasses: air; fluids: supercritical H2O
- Components (C) - Minimum number of chemical species required to describe the chemical variation in a system
- Degrees of Freedom (F) - How many variables (P,T,X) can be varied independently?
- (General) Phase Rule: F = C - P + 2
Applying the Phase Rule and Lever Rule
- Divariant, Univariant, and Invariant Systems
- One component, P-T variable system - SiO2 F = C - P + 2
- Binary T-X system (Pressure constant) - An-Di F = C - P + 1
- Applying the Lever Rule - An-Di
Equilibrium Crystallization in Binary Systems
Fractional Crystallization in Binary Systems
Equilibrium Crystallization in Ternary Systems
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