Chapter 26: Metamorphic Reactions l If we treat isograds as reactions, we can: F Understand what physical variables might affect the location of a particular.

Chapter 26: Metamorphic ReactionsChapter 26: Metamorphic Reactions If we treat isograds as reactions, we can:If we treat isograds as reactions, we can:

Understand what physical variables might affect the Understand what physical variables might affect the location of a particular isogradlocation of a particular isograd

We may also be able to estimate the P-T-X We may also be able to estimate the P-T-X conditions that an isograd representsconditions that an isograd represents

Some workers have advocated that we distinguish Some workers have advocated that we distinguish field-field-based isogradsbased isograds in the classical sense from in the classical sense from reaction-based reaction-based isogradsisograds

1. Phase Transformations1. Phase Transformations Isochemical phase transformations (the polymorphs of Isochemical phase transformations (the polymorphs of

SiOSiO22 or Al or Al22SiOSiO55 or graphite-diamond or calcite- or graphite-diamond or calcite-

aragonite are in many ways the simplest to deal witharagonite are in many ways the simplest to deal with The transformations The transformations depend on temperature and depend on temperature and

pressure onlypressure only

1. Phase Transformations1. Phase Transformations

Figure 26-1. A portion of the equilibrium boundary for the calcite-aragonite phase transformation in the CaCO3 system. After Johannes and

Puhan (1971), Contrib. Mineral. Petrol., 31, 28-38. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

1. Phase Transformations1. Phase Transformations

Figure 26-15. The P-T phase diagram for the system Al2SiO5 showing the

stability fields for the three polymorphs andalusite, kyanite, and sillimanite. Calculated using the program TWQ (Berman, 1988, 1990, 1991). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

1. Phase Transformations1. Phase Transformations Small Small S for most polymorphic transformationsS for most polymorphic transformations small small G between two alternative polymorphs, even G between two alternative polymorphs, even

several tens of degrees from the equilibrium boundaryseveral tens of degrees from the equilibrium boundary little driving force for the reaction to proceed little driving force for the reaction to proceed

common common metastablemetastable relics in the stability field of other relics in the stability field of other Coexisting polymorphs may therefore represent Coexisting polymorphs may therefore represent non-non-

equilibrium statesequilibrium states (overstepped equilibrium curves or (overstepped equilibrium curves or polymetamorphic overprints)polymetamorphic overprints)

2. Exsolution2. Exsolution

Figure 6-16. T-X phase diagram of the system albite-orthoclase at 0.2 GPa H2O

pressure. After Bowen and Tuttle (1950). J. Geology, 58, 489-511. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

3. Solid-Solid Net-Transfer Reactions3. Solid-Solid Net-Transfer Reactions Involve solids onlyInvolve solids only Differ from polymorphic transformations: involve Differ from polymorphic transformations: involve

solids of differing composition, and thus material solids of differing composition, and thus material must diffuse from one site to another for the must diffuse from one site to another for the reaction to proceedreaction to proceed

3. Solid-Solid Net-Transfer Reactions3. Solid-Solid Net-Transfer Reactions Examples:Examples:

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

MgSiOMgSiO33 + CaAl + CaAl22SiSi22OO88 = CaMgSi = CaMgSi22OO66 + Al + Al22SiOSiO55 EnEn AnAn DiDi

AndAnd

4 (Mg,Fe)SiO4 (Mg,Fe)SiO33 + CaAl + CaAl22SiSi22OO88 = = OpxOpx PlagPlag

(Mg,Fe)(Mg,Fe)33AlAl22SiSi33OO1212 + Ca(Mg,Fe)Si + Ca(Mg,Fe)Si22OO66 + +

SiOSiO22 GntGnt CpxCpx

QtzQtz

Figure 27-1. Temperature-pressure phase diagram for the reaction: Albite = Jadeite + Quartz calculated using the program TWQ of Berman (1988, 1990, 1991). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

3. Solid-Solid Net-Transfer Reactions3. Solid-Solid Net-Transfer Reactions If minerals contain volatiles, the If minerals contain volatiles, the volatiles must be volatiles must be

conservedconserved in the reaction so that no fluid phase is in the reaction so that no fluid phase is generated or consumedgenerated or consumed

For example, the reaction:For example, the reaction:MgMg33SiSi44OO1010(OH)(OH)22 + 4 MgSiO + 4 MgSiO33 = Mg = Mg77SiSi88OO2222(OH)(OH)22

TlcTlc EnEn Ath Ath

involves hydrous phases, but conserves Hinvolves hydrous phases, but conserves H22OO

It may therefore be treated as a solid-solid net-It may therefore be treated as a solid-solid net-transfer reactiontransfer reaction

3. Solid-Solid Net-Transfer Reactions3. Solid-Solid Net-Transfer Reactions When solid-solution is limited, solid-solid net-When solid-solution is limited, solid-solid net-

transfer reactions are transfer reactions are discontinuousdiscontinuous reactions reactions Discontinuous reactions tend to run to completion Discontinuous reactions tend to run to completion

at a single temperature (at a particular pressure)at a single temperature (at a particular pressure) There is thus an abrupt (discontinuous) change There is thus an abrupt (discontinuous) change

from the reactant assemblage to the product from the reactant assemblage to the product assemblage at the reaction isogradassemblage at the reaction isograd

Discontinuous reaction: + 1 and XLiq fixed

4. Devolatilization Reactions4. Devolatilization Reactions Among the most common metamorphic reactionsAmong the most common metamorphic reactions HH22O-COO-CO22 systems are most common, but the systems are most common, but the

principles same for any reaction involving volatiles principles same for any reaction involving volatiles Reactions dependent not only upon temperature Reactions dependent not only upon temperature

and pressure, but also upon the and pressure, but also upon the partial pressure of partial pressure of the volatile speciesthe volatile species

4. Devolatilization Reactions4. Devolatilization Reactions For example the location on a P-T phase diagram of the For example the location on a P-T phase diagram of the

dehydrationdehydration reaction: reaction:

KAlKAl22SiSi33AlOAlO1010(OH)(OH)22 + SiO + SiO22 = KAlSi = KAlSi33OO88 + Al + Al22SiOSiO55 + H + H22OO MsMs Qtz Qtz Kfs Kfs Sill Sill

WW

depends upon the partial pressure of Hdepends upon the partial pressure of H22O (O (ppH2OH2O))

This dependence is easily demonstrated by applying Le This dependence is easily demonstrated by applying Le Châtelier’s principle to the reaction at equilibriumChâtelier’s principle to the reaction at equilibrium

4. Devolatilization Reactions4. Devolatilization Reactions

The equilibrium curve The equilibrium curve represents equilibrium represents equilibrium between the reactants and between the reactants and products under water-products under water-saturated conditionssaturated conditions ((ppH2OH2O = P = PLithostaticLithostatic))

P-T phase diagram for the reaction Ms + Qtz = Kfs + Al2SiO5 + H2O showing the shift in

equilibrium conditions as pH2O varies

(assuming ideal H2O-CO2 mixing). Calculated

using the program TWQ by Berman (1988, 1990, 1991). After Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

KAlKAl22SiSi33AlOAlO1010(OH)(OH)22 + SiO + SiO22 = KAlSi = KAlSi33OO88 + Al + Al22SiOSiO55 + H + H22OO

MsMs QtzQtz KfsKfs SillSill WW

Suppose HSuppose H22O is withdrawn from the system at some point O is withdrawn from the system at some point

on the water-saturated equilibrium curve: on the water-saturated equilibrium curve: ppH2OH2O < P < Plithostaticlithostatic

According to Le Châtelier’s Principle, removing water at According to Le Châtelier’s Principle, removing water at equilibrium will be compensated by the reaction running equilibrium will be compensated by the reaction running to the right, thereby producing more waterto the right, thereby producing more water

This has the effect of stabilizing the right side of the This has the effect of stabilizing the right side of the reaction at the expense of the left sidereaction at the expense of the left side

So as water is withdrawn the Kfs + Sill + HSo as water is withdrawn the Kfs + Sill + H22O field O field

expands slightly at the expense of the Mu + Qtz field, and expands slightly at the expense of the Mu + Qtz field, and the reaction curve shifts toward lower temperaturethe reaction curve shifts toward lower temperature

Figure 26-2. P-T phase diagram for the reaction Ms + Qtz = Kfs + Al2SiO5 + H2O showing the

shift in equilibrium conditions as pH2O varies (assuming ideal

H2O-CO2 mixing). Calculated

using the program TWQ by Berman (1988, 1990, 1991). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

4. Devolatilization Reactions4. Devolatilization Reactions ppH2OH2O can become less than P can become less than PLithLith by either of two ways by either of two ways

PPfluidfluid < P < PLithLith by drying out the rock and reducing the by drying out the rock and reducing the

fluid contentfluid content PPfluidfluid = P = PLithLith, but the water in the fluid can become , but the water in the fluid can become

diluted by adding another fluid component, such as diluted by adding another fluid component, such as COCO22 or some other volatile phase or some other volatile phase

In Fig. 26-2 I calculated the curves for the latter case In Fig. 26-2 I calculated the curves for the latter case on the basis of ideal Hon the basis of ideal H22O-COO-CO22 mixing mixing

4. Devolatilization Reactions4. Devolatilization Reactions An important point arising from Fig. 26-2 is:An important point arising from Fig. 26-2 is:

The temperature of an isograd based on a devolatilization The temperature of an isograd based on a devolatilization reaction is sensitive to the partial pressure of the volatile reaction is sensitive to the partial pressure of the volatile species involvedspecies involved

An alternative: An alternative: T-XT-Xfluidfluid phase diagram phase diagram

Because HBecause H22O and COO and CO22 are by far the most common are by far the most common

metamorphic volatiles, the X in T-X diagrams is metamorphic volatiles, the X in T-X diagrams is usually the usually the mole fraction of COmole fraction of CO22 (or H (or H22O) in HO) in H22O-COO-CO22

mixturesmixtures Because pressure is also a common variable, a T‑XBecause pressure is also a common variable, a T‑Xfluidfluid

diagram diagram must be created for a specified pressuremust be created for a specified pressure

4. Devolatilization Reactions4. Devolatilization Reactions

Figure 26-4. T-XH2O phase

diagram for the reaction Ms + Qtz = Kfs + Sil + H2O at 0.5 GPa

assuming ideal H2O-CO2 mixing,

calculated using the program TWQ by Berman (1988, 1990, 1991). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

4. Devolatilization Reactions4. Devolatilization Reactions

Figure 26-4. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Figure 26-2. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

4. Devolatilization Reactions4. Devolatilization Reactions Shape of ~ all dehydration curves on T-XShape of ~ all dehydration curves on T-X fluidfluid

diagrams is similar to the curve in Fig. 26-2diagrams is similar to the curve in Fig. 26-2 Maximum temperature at the pure HMaximum temperature at the pure H22O end, and O end, and

slope gently at high Xslope gently at high XH2OH2O, but steeper toward low , but steeper toward low

XXH2OH2O, becoming near vertical at very low X, becoming near vertical at very low XH2OH2O

Reaction temperature can thus be practically any Reaction temperature can thus be practically any temperature below the maximum at temperature below the maximum at ppH2OH2O = P = Plithlith

Must constrain the fluid composition (if possible) Must constrain the fluid composition (if possible) before using a dehydration reaction to indicate before using a dehydration reaction to indicate metamorphic grademetamorphic grade

Figure 26-3. Calculated P-T equilibrium reaction curve for a dehydration reaction illustrating the full loop that is theoretically possible. From Winter (2001). An Introduction to Igneous and Metamorphic Petrology, Prentice Hall.

A rare exceptionA rare exception

4. Devolatilization Reactions4. Devolatilization Reactions Decarbonation reactions may be treated in an Decarbonation reactions may be treated in an

identical fashionidentical fashion For example, the reaction:For example, the reaction:

CaCOCaCO33 + SiO + SiO22 = CaSiO = CaSiO33 + CO + CO22 (26-6)(26-6) CalCal Qtz Qtz Wo Wo

Can also be shown on a T-XCan also be shown on a T-XCO2CO2 diagram diagram

Has the same form as reaction (26-5), only the Has the same form as reaction (26-5), only the maximum thermal stability of the carbonate maximum thermal stability of the carbonate mineral assemblage occurs at pure Xmineral assemblage occurs at pure XCO2CO2

4. Devolatilization Reactions4. Devolatilization Reactions

Figure 26-1. A portion of the equilibrium boundary for the calcite-aragonite phase transformation in the CaCO3 system. After

Johannes and Puhan (1971), Contrib. Mineral. Petrol., 31, 28-38. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Figure 26-5. T-XCO2 phase diagram for the reaction Cal + Qtz

= Wo + CO2 at 0.5 GPa assuming ideal H2O-CO2 mixing,

calculated using the program TWQ by Berman (1988, 1990, 1991). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

5 types5 types of devolatilization of devolatilization reactions, each with a reactions, each with a unique general shape on a unique general shape on a T-X diagramT-X diagram

Type 3: TType 3: Tmaxmax at X at XCO2CO2

determined by the determined by the stoichiometric ratio of stoichiometric ratio of COCO22/H/H22O producedO produced

CaCa22MgMg55SiSi88OO2222(OH)(OH)22 + 3 CaCO + 3 CaCO33 + 2 SiO + 2 SiO22

TrTr Cal CalQtz Qtz = 5 CaMgSi= 5 CaMgSi22OO66 + 3 CO + 3 CO22 + H + H22O O DiDiFigure 26-6. Schematic T-XCO2 phase diagram illustrating the

general shapes of the five types of reactions involving CO2 and

H2O fluids. After Greenwood (1967). In P. H. Abelson (ed.),

Researches in Geochemistry. John Wiley. New York. V. 2, 542-567. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

5. Continuous Reactions5. Continuous Reactions

Figure 26-8. Geologic map of a hypothetical field area in which metamorphosed pelitic sediments strike directly up metamorphic grade. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

5. Continuous Reactions5. Continuous ReactionsTwo possible reasons:Two possible reasons:

1. Such contrasting composition that the garnet reaction is different1. Such contrasting composition that the garnet reaction is different

Example: garnet in some pelites may be created by the Example: garnet in some pelites may be created by the (unbalanced) reaction:(unbalanced) reaction:

Chl + Ms + Qtz Chl + Ms + Qtz Grt + Bt + H Grt + Bt + H22OO (26-11)(26-11)

Whereas in more Fe-rich and K-poor pelites, garnet might be Whereas in more Fe-rich and K-poor pelites, garnet might be generated by an (unbalanced) reaction involving chloritoid:generated by an (unbalanced) reaction involving chloritoid:

Chl + Cld + Qtz Chl + Cld + Qtz Grt + H Grt + H22OO (26-12)(26-12)

5. Continuous Reactions5. Continuous Reactions2. The reaction on which the isograd is based is the same in each 2. The reaction on which the isograd is based is the same in each

unit, but it is a unit, but it is a continuouscontinuous reaction, and its location is reaction, and its location is sensitive to the composition of the solutions (either solid of sensitive to the composition of the solutions (either solid of fluid) involvedfluid) involved

The offsets this creates in an isograd are usually more subtle The offsets this creates in an isograd are usually more subtle than for reason #1, but in some cases they can be substantialthan for reason #1, but in some cases they can be substantial

We will concentrate on this second reason hereWe will concentrate on this second reason here

5. Continuous Reactions5. Continuous Reactions

Fig. 6-10. Isobaric T-X phase diagram at atmospheric pressure After Bowen and Shairer (1932), Amer. J. Sci. 5th Ser., 24, 177-213. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

5. Continuous Reactions5. Continuous Reactions DiscontinuousDiscontinuous reactions occur at a constant grade reactions occur at a constant grade

They are actually They are actually uniunivariant (F = 1) on P-T phase variant (F = 1) on P-T phase diagrams, but pressure and temperature are not diagrams, but pressure and temperature are not really independent, but constrained to follow a really independent, but constrained to follow a geothermal gradient or P-T-t pathgeothermal gradient or P-T-t path

The P-T path crosses the reaction at a single gradeThe P-T path crosses the reaction at a single grade If If Chl + Ms + Qtz Chl + Ms + Qtz Grt + Bt + H Grt + Bt + H22OO (26-11) (26-11)

were a were a discontinuousdiscontinuous reaction (let’s say it occurred reaction (let’s say it occurred for pure Mg end-members), and is responsible for for pure Mg end-members), and is responsible for the formation of garnet in the map area above, the the formation of garnet in the map area above, the reaction should run to completion (when reaction should run to completion (when oneone of the of the reactants was consumed) at a single gradereactants was consumed) at a single grade

5. Continuous Reactions5. Continuous Reactions ContinuousContinuous reactions occur when F reactions occur when F 1 1, and the , and the

reactants and products coexist over a temperature (or reactants and products coexist over a temperature (or grade) intervalgrade) interval If If Chl + Ms + Qtz Chl + Ms + Qtz Grt + Bt + H Grt + Bt + H22OO (26-11) (26-11)

were a were a continuouscontinuous reaction, then we would find reaction, then we would find chlorite, muscovite, quartz, biotite, and garnet all chlorite, muscovite, quartz, biotite, and garnet all together in the same rock over an interval of together in the same rock over an interval of metamorphic grade above the garnet-in isogradmetamorphic grade above the garnet-in isograd

The The composition of solid solution phasescomposition of solid solution phases vary vary across the interval, and the across the interval, and the proportions of the proportions of the mineralsminerals changes until changes until one of one of the reactants the reactants disappears with increasing gradedisappears with increasing grade

ContinuousContinuous reactions occur when F reactions occur when F 1 1, and the , and the reactants and products coexist over a temperature (or reactants and products coexist over a temperature (or grade) intervalgrade) interval

Fig. 26-9. Schematic isobaric T-XMg

diagram representing the simplified metamorphic reaction Chl + Qtz Grt + H2O. From Winter (2001) An

Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

6. Ion Exchange Reactions6. Ion Exchange Reactions Reciprocal exchange of components between 2 or Reciprocal exchange of components between 2 or

more mineralsmore minerals MgSiOMgSiO33 + CaFeSi + CaFeSi22OO66 = FeSiO = FeSiO33 + CaMgSi + CaMgSi22OO66

Annite + Pyrope = Phlogopite + AlmandineAnnite + Pyrope = Phlogopite + Almandine Expressed as pure end-members, but really Expressed as pure end-members, but really

involves Mg-Fe (or other) exchange between involves Mg-Fe (or other) exchange between intermediate solutionsintermediate solutions

Basis for many geothermobarometersBasis for many geothermobarometers Causes rotation of tie-lines on compatibility Causes rotation of tie-lines on compatibility

diagramsdiagrams

Figure 27-6. AFM projections showing the relative distribution of Fe and Mg in garnet vs. biotite at approximately 500 oC (a) and 800oC (b). From Spear (1993) Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths. Mineral. Soc. Amer. Monograph 1. MSA. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

6. Redox Reactions6. Redox Reactions Involves a change in oxidation state of an elementInvolves a change in oxidation state of an element

6 Fe6 Fe22OO33 = 4 Fe = 4 Fe33OO44 + O + O22

2 Fe2 Fe33OO44 + 3 SiO + 3 SiO22 = 3 Fe = 3 Fe22SiOSiO44 + O + O22 At any particular pressure these become At any particular pressure these become oxygen oxygen

buffersbuffers

Fig. 26-10. Isobaric T-fO2 diagram

showing the location of reactions (26-13) - (26-15) used to buffer oxygen in experimental systems. After Frost (1991), Rev. in Mineralogy, 25, MSA, pp. 469-488. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

7. Reactions Involving Dissolved Species7. Reactions Involving Dissolved Species Minerals plus ions neutral molecules dissolved in a fluidMinerals plus ions neutral molecules dissolved in a fluid One example is hydrolysis:One example is hydrolysis:

2 KAlSi2 KAlSi33OO88 + 2 H + 2 H++ + H + H22O = AlO = Al22SiSi22OO55 (OH) (OH)44 + SiO + SiO22 + 2 K + 2 K++

KfsKfs aq. speciesaq. species kaolinite kaolinite aq. speciesaq. species

Can treat such reactions in terms of the phase rule Can treat such reactions in terms of the phase rule and the intensive variables: P, T, and concentrations and the intensive variables: P, T, and concentrations of the reactant speciesof the reactant species T-P diagrams for fixed or contoured CT-P diagrams for fixed or contoured C ii

Isobaric T-CIsobaric T-Cii diagrams diagrams Isobaric and isothermal CIsobaric and isothermal Cii - C - Cjj diagrams diagrams Reaction above might be handled by a T vs. Reaction above might be handled by a T vs.

CCKK++//CCHH++ diagram diagram

Reactions and ChemographicsReactions and Chemographics We can use chemographics to infer reactionsWe can use chemographics to infer reactions

MgO SiO2

Per Fo En Qtz

Fo + Qtz = EnFo + Qtz = En Mg Mg22SiOSiO44 + SiO + SiO22 = Mg = Mg22SiSi22OO66

En + Per = FoEn + Per = Fo Mg Mg22SiSi22OO66 + 2 MgO = 2 Mg + 2 MgO = 2 Mg22SiOSiO44

Per + Qtz = Fo or EnPer + Qtz = Fo or En If we know the chemographics we can determine If we know the chemographics we can determine

that a reaction is possible (and can dispense with that a reaction is possible (and can dispense with balancing the reaction)balancing the reaction)

Reactions and ChemographicsReactions and Chemographics What reaction does this ternary system allow?What reaction does this ternary system allow?

Fig. 26-12. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Reactions and ChemographicsReactions and Chemographics What reaction does this ternary system allow?What reaction does this ternary system allow?

Fig. 26-13. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Reactions and ChemographicsReactions and Chemographics What reaction is possible between A-B-C-D?What reaction is possible between A-B-C-D?

A chemographic A chemographic diagram for some diagram for some metamorphic zonemetamorphic zone

Fig. 26-14a. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

A + B = C + D

This is called a This is called a tie-line fliptie-line flip, and , and results in new groupings in the results in new groupings in the next metamorphic zonenext metamorphic zone

At the isograd

Above the isograd

Below the isograd

Fig. 26-14. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Petrogenetic GridsPetrogenetic Grids P-T diagrams for multicomponent systems that show a P-T diagrams for multicomponent systems that show a

set of reactions, generally for a specific rock typeset of reactions, generally for a specific rock type

Petrogenetic grid for mafic rocks

Fig. 26-19.Fig. 26-19. Simplified petrogenetic grid for metamorphosed mafic rocks showing the location of several determined Simplified petrogenetic grid for metamorphosed mafic rocks showing the location of several determined univariant reactions in the CaO-MgO-Alunivariant reactions in the CaO-MgO-Al

22OO33-SiO-SiO22-H-H

22O-(NaO-(Na22O) system (“C(N)MASH”). O) system (“C(N)MASH”). Winter (2001) An Winter (2001) An

Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Text figures that I don’t have time Text figures that I don’t have time to cover in my 1-semester classto cover in my 1-semester class

Fig. 26-7. T-XCO2 phase

diagram fro 2 reactions in the CaO-MgO-SiO2-

H2O-CO2 system at 0.5

GPa, assuming ideal mixing of non-ideal gases, calculated using the program TWQ by Berman (1988, 1990, 1991). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Text figures that I don’t have time Text figures that I don’t have time to cover in my 1-semester classto cover in my 1-semester class

Figure 26-15. The Al2SiO5 T-P phase

diagram from Figure 21-9 (without H2O).

Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Text figures that I don’t have time Text figures that I don’t have time to cover in my 1-semester classto cover in my 1-semester class

Figure 26-16. Schematic one-component T-P phase diagram showing the topology of a four-phase multisystem in which all invariant points are stable. Because only three phases (C+2) coexist at an invariant point, a complete system should have four invariant points, each with one phase absent. Phases absent at invariant points are in square brackets, phases absent for univariant reactions are in parentheses. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Text figures that I don’t have time Text figures that I don’t have time to cover in my 1-semester classto cover in my 1-semester class

Figure 26-17. A portion of the P-T phase diagram for SiO2 (Figure 6-6) showing two stable invariant

points [Trd] and [Liq] and two metastable ones. [b-Qtz] occurs at negative pressure, and [Crs] is truly metastable in that it is the intersection of metastable extensions. From Spear (1993) Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths. Mineral. Soc. Amer. Monograph 1. MSA.

Text figures that Text figures that I don’t have I don’t have

time to cover in time to cover in my 1-semester my 1-semester

classclass

Figure 26-18. a. Hypothetical reaction D + E = F in a two-component phase diagram. Note that the D-absent and E-absent curves must both lie on the side of the initial univariant curve opposite to the field in which D + E is stable. Likewise the F-absent curve must lie on the side opposite to the field in which F is stable. b. A second hypothetical univariant curve (D-absent) is added. c. The complete topology of the invariant point can then be derived from the two initial reactions in (b). The chemographics may then be added to each divariant field. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Figure 26-20. a. Sketch from a photomicrograph showing small crystals of kyanite (purple) and quartz (blue) in a larger muscovite grain (green). Small crystals of fibrolitic sillimanite also occur in the muscovite. Glen Cova, Scotland. b. Sillimanite needles in quartz (blue) embaying muscovite (green). Pink crystals are biotite. Donegal, Ireland. After Carmichael (1969). Contrib. Mineral. Petrol., 20, 244-267.

Figure 26-21. A possible mechanism by which the Ky Sil reaction can be accomplished while producing the textures illustrated in Figure 26-20a and b. The exchange of ions shown between the two local zones is required if the reactions are to occur. After Carmichael (1969). Contrib. Mineral. Petrol., 20, 244-267.

Text figures that I don’t have time Text figures that I don’t have time to cover in my 1-semester classto cover in my 1-semester class

Text figures that I don’t have time Text figures that I don’t have time to cover in my 1-semester classto cover in my 1-semester class

Figure 26-21. An alternative mechanism by which the reaction Ky Sil reaction can be accomplished while producing sillimanite needles associated with biotite with plagioclase occupying embayments in the biotite. The exchange of ions shown between the two local zones is required if the reactions are to occur. After Carmichael (1969). Contrib. Mineral. Petrol., 20, 244-267.