Igneous Geology Petrology PDF

GEOL 102 PETROLOGY PHASE DIAGRAMS 2ndYear 2nd Semester | DGEOL -Patrick Sam M. Buenavista  SOLID SOLUTION Minerals with specific atomic sites occupied by two or more different elements in variable proportions.  SOLID SOLUTI...

GEOL 102 PETROLOGY PHASE DIAGRAMS 2ndYear 2nd Semester | DGEOL -Patrick Sam M. Buenavista  SOLID SOLUTION Minerals with specific atomic sites occupied by two or more different elements in variable proportions.  SOLID SOLUTION TYPES Substitution Interstitial Omission Solid Solution Solid Solution Solid Solution  SUBSTITUTION (IONIC) SOLID SUBSTITUTION Similar Ionic Radius Similar Ionic Charge Temperature  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 1. Simple Ionic Substitution Ions of similar radius and charge substitute for one another in a coordination site in any proportions. Composition of end member is expressed in terms of: Specificformula Mineral name Position on thetieline Proportion of eitherendmember (A % or B%)  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 1. Simple Ionic Substitution Tie Lines are lines that connect mineral phases that coexist with each other at a specific condition. 1,500 oC z 1,000 oC y x 500 oC A B 25% 50% 75% 100%  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 1. Simple Ionic Substitution Olivine (Mg,Fe)2SiO4 = Mg2SiO4 & Fe2SiO4 Fayalite Forsterite Fo0 Fo100 Fe2SiO4 X y z Mg2SiO4 Fe Mg 0 10 20 30 40 50 60 70 80 90 100  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 1. Simple Ionic Substitution (Fe,Mn,Mg)CO3 Siderite (Fe) Rhodochrosite (Mn) Magnesite (Mg)  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 2. Coupled Ionic Substitution Simultaneous substitution of ions of different charges in two different structural sites and preserves the electrical neutrality of the crystal lattice. For ion (B) to replace another ion (A) while maintaining neutral charge, an equal amount of replaced ion (A) is concurrently substituted by another ion (C). 2 A2+ → B3++ C+  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 2. Coupled Ionic Substitution Plagioclase (Na)(Si)(Al)(Si2O8) (Ca)(Al)(Al)(Si2O8) Albite Anorthite  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 2. Coupled Ionic Substitution (Na)(Si)(Al)(Si2O8) (Ca)(Al)(Al)(Si2O8) Na+ + Si 4+ Ca2+ + Al3+  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 2. Coupled Ionic Substitution An0 An100 (Na)(Si) (Ca)(Al) (Al)(Si2O8) (Al)(Si2O8) 100 0 10 20 30 40 50 60 70 80 90 An45 (Na0.55 Ca0.45)(Si0.55 Al0.45) (Al)(Si2O8)  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 3. Limited Ionic Substitution Significant differences in ionic radii or charge of ions limits the substitution, resulting to a Limited Solid Solution. Miscibility Gaps are gaps in solid solution, having immiscible liquids that do not mix with certain proportions.  SUBSTITUTION (IONIC) SOLID SUBSTITUTION 3. Limited Ionic Substitution Miscibility Gap ( unknown composition) Low-Mg Calcite High-Mg Dolomite Calcite Calcite Magnesite 4 25 40 Ca Mg 0 10 20 30 40 50 60 70 80 90 100 Ms0 %Ms Ms 100  PHASE Mechanically separable varieties of matter in a system that can be distinguished from other varieties based on their composition, structure, and/or state.  PHASE DIAGRAM Diagrams that display the stability fields for various phases separated by lines representing conditions under which phase changes occur.  TERMS Liquidus Phase boundary separating all-liquid stability field from stability fields with some solids.  TERMS Solidus Phase boundary separating all-solid stability field from stability fields with some liquids.  TERMS Eutectic Condition in which the liquid is in equilibrium with two different solids.  TERMS Peritectic Reaction where a solid and liquid phase together form a new solid phase at a specific temperature and composition.  TERMS Invariant Melting Occurs when melts of same composition are produced by melting rocks of different initial composition.  TERMS Incongruent Melting Occurs when solid mineral phase melts to produce a melt and a different mineral with a different composition from the initial material.  TERMS Discontinuous Reaction Mineral crystals and melt reacts to form a completely different mineral; negligible solid solution exists between the minerals.  TERMS Continuous Reaction Mineral crystals and melt reacts to continuously and incrementally change the composition of both; requires a mineral solid solution series  TERMS Solvus Line separating a homogenous solid solution from a field of several phases formed by exsolution or incongruent melting. It determines the solid solubility limit which changes with temperature. PHASE DIAGRAMS % Composition  GIBB’S PHASE RULE Governs the number of phases that can coexist in equilibrium in any system.  GIBB’S PHASE RULE P = C + 2 -F P = number of phases in a system C = minimum number of chemical components that define the phases in the system F = number of degrees of freedom or variance.  GIBB’S PHASE RULE Invariant Equilibria = neither P or T can be changed Univariant Equilibria = either P or T is independently changed, which changes the other variable. DivariantEquilibria = both P & T are free to change independently without changed the state of the system PHASE DIAGRAMS Examples  UNARY PHASE DIAGRAMS Silica (SiO2) H2O Carbon CaCO3  BINARY PHASE DIAGRAMS  LEVER RULE Calculates the proportions of melt (liquid) and crystals (solid) in a system. For wt.% solid: For wt.% liquid: 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑙𝑖𝑛𝑒 − 𝑤𝑏 𝑎𝑡𝑠.𝑒 % 𝑤 𝑡. %𝑏 𝑎 𝑠 𝑒 − 𝑙 𝑒 𝑛 𝑔 𝑡 ℎ 𝑜 𝑓 𝑙 𝑖 𝑛 𝑒 𝑡𝑜𝑡𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑙𝑖𝑛𝑒 𝑡𝑜𝑡𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑙𝑖𝑛𝑒  1,450oC 1,300oC 1,235oC 29 70 82 98 18 70 Plagioclase Olivine Diopside -Anorthite Diopside -Anorthite Diopside -Anorthite Diopside -Anorthite Diopside -Anorthite Albite -Orthoclase Albite -Orthoclase Nepheline -Silica Nepheline -Silica Forsterite -Silica