What happens to our PROTOLITH when acted on by AGENTS OF CHANGE??Solid-solid phase transformationSolid-solid net-transferSolid-Solid Net-Transfer IIHydration/ Dehydration ReactionsCarbonation / Decarbonation ReactionsSystemsThermodynamics PrimerThermodynamics vs. KineticsPhase diagramsSlide 11Mineral Assemblages in Metamorphic RocksThe Phase Rule in Metamorphic SystemsSlide 14Metamorphic faciesSlide 16Aluminosilicate MineralsSlide 18TopazSerpentine MineralsSlide 21Slide 22Slide 23ChloritePrehnite-PumpellyiteMicasZeolitesEpidote GroupSlide 29StauroliteActinoliteMetamorphic FaciesSlide 33Facies SeriesSlide 35IsogradsSlide 37What happens to our PROTOLITH when acted on by AGENTS OF CHANGE??•Agents of Change  T, P, fluids, stress, strain •Metamorphic Reactions!!!!–Solid-solid phase transformation–Solid-solid net-transfer–Dehydration–Hydration–Decarbonation–CarbonationSolid-solid phase transformation•Polymorphic reaction  a mineral reacts to form a polymorph of that mineral•No transfer of matter, only a rearrangment of the mineral structure•Example:–Andalusite  SillimaniteAl2SiO5Al2SiO5Solid-solid net-transfer•Involve solids only•Differ from polymorphic transformations: involve solids of differing composition, and thus material must diffuse from one site to another for the reaction to proceed•Examples:•NaAlSi2O6 + SiO2 = NaAlSi3O8 Jd Qtz Ab•MgSiO3 + CaAl2Si2O8 = CaMgSi2O6 + Al2SiO5 En An Di AndSolid-Solid Net-Transfer II•If minerals contain volatiles, the volatiles must be conserved in the reaction so that no fluid phase is generated or consumed•For example, the reaction:Mg3Si4O10(OH)2 + 4 MgSiO3 = Mg7Si8O22(OH)2 Talc Enstatite Anthophylliteinvolves hydrous phases, but conserves H2OIt may therefore be treated as a solid-solid net-transfer reactionHydration/ Dehydration Reactions•Metamorphic reactions involving the expulsion or incorporation of water (H2O)•Example:–Al2Si4O10(OH)2 <=> Al2SiO5 + 3SiO2 + H2O Pyrophyllite And/Ky Quartz waterCarbonation / Decarbonation Reactions•Reactions that involve the evolution or consumption of CO2•CaCO3 + SiO2 = CaSiO3 + CO2 calcite quartz wollastoniteReactions involving gas phases are also known as volatilization or devoltilization reactionsThese reactions can also occur with other gases such as CH4 (methane), H2, H2S, O2, NH4+ (ammonia) – but they are not as commonSystems•Rock made of different minerals•Metamorphic agents of change beat on it  metamorphic reactions occur•A closed system does not gain or lose material of any kind•An open system can lose stuff – liquids, gases especiallyHunk o’ rockOutsideworldThermodynamics Primer•Thermodynamics describes IF a reaction CAN occur at some condition (T, P, composition typically)•Second Law of thermodynamics:• G=H – TS–Where G, Gibb’s free energy determines IF the REACTION will go forward (-G=spontaneous)–H is enthalpy – has to do with heat…–S is entropy – has to do with bonds and order…Thermodynamics vs. Kinetics•Thermodynamics – comparing the potential ENERGY of things  what is more stable? Will a reaction occur at some T,P, soln, melt composition go or Not?•Kinetics  IF thermodynamics says YES, the reaction should occur (always toward lower energy!) kinetics determines how fast•Minerals out of equilibrium pass the thermodynamic test but the kinetics of their reaction is very slow…Phase diagrams•Tool for ‘seeing’ phase transitions•H2Oice  H2Oliquid•Reaction (line) governed by G=H – TS•Phase Rule:–P+F=C+2–Phases coexisting + degrees of freedom = number of components + 2–Degree of freedom  2= either axis can change and the phase stays the same  where??Phase diagrams•Let’s think about what happens to water as conditions change…•P+F=C+2•Point A?•Point B?•Point C?ABCMineral Assemblages in Metamorphic Rocks•Equilibrium Mineral Assemblages•At equilibrium, the mineralogy (and the composition of each mineral) is determined by T, P, and X•Relict minerals or later alteration products are thereby excluded from consideration unless specifically statedThe Phase Rule in Metamorphic Systems•Phase rule, as applied to systems at equilibrium:F = C - P + 2 the phase ruleP is the number of phases in the systemC is the number of components: the minimum number of chemical constituents required to specify every phase in the systemF is the number of degrees of freedom: the number of independently variable intensive parameters of state (such as temperature, pressure, the composition of each phase, etc.)The Phase Rule in Metamorphic SystemsConsider the following three scenarios:C = 1 (Al2SiO5)F = 1 commonF = 2 rareF = 3 only at the specific P-T conditions of the invariant point(~ 0.37 GPa and 500oC)Figure 21-9. The P-T phase diagram for the system Al2SiO5 calculated using the program TWQ (Berman, 1988, 1990, 1991). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Metamorphic facies•P-T conditions, presence of fluids induces different metamorphic mineral assemblages (governed by thermodynamics/ kinetics)•These assemblages are lumped into metamorphic facies (or grades)Aluminosilicate MineralsAndalusite Kyanite Sillimanite•SILLIMANITE: Orthorhombic: Octahedral Al chains (6-fold) are crosslinked by both Si and Al tetrahedra (4-fold).•ANDALUSITE: Orthorhombic: 5-coordinated Al; Same octahedral (6-fold) chains.•KYANITE: Triclinic: All the Al is octahedrally coordinated (6- and 6-fold). •Clearly, changes in structure are in response to changing P and T. Result is changes in Al coordination. •Phase transformations require rebonding of Al. Reconstructive polymorphism requires more energy than do displacive transformations. Metastability of these 3 are therefore important (Kinetic factors limit equilibrium attainment).•All 3 are VERY important metamorphic index minerals.Aluminosilicate Minerals•3 polymorphs of Al2SiO5 are important metamorphic mineralsAndalusite Kyanite SillimaniteTopaz•Aluminosilicate mineral as well, one oxygen substituted with OH, F•Al2SiO4(F,OH)2 •Where do you think Topaz forms??Serpentine Minerals•Mg3Si2O5(OH)4 minerals (principally as antigorite, lizardite, chrysotile polymorphs)•Forms from hydration reaction of magnesium silicates–Mg2SiO4 + 3 H2O  Mg3Si2O5(OH)4 + Mg(OH)2forsterite serpentine