C = 3: Ternary Systems:C = 3: Ternary Systems:Example 1: Ternary EutecticExample 1: Ternary Eutectic

Di - An - FoDi - An - Fo

TT

MM

AnorthiteAnorthite

ForsteriteForsterite

DiopsideDiopside

Note three binary Note three binary eutecticseutectics

No solid solutionNo solid solution

Ternary eutectic = MTernary eutectic = M

T - X Projection of Di - An - FoT - X Projection of Di - An - Fo

Figure 7-2. Isobaric diagram illustrating the liquidus temperatures in the Di-An-Fo system at atmospheric pressure (0.1 MPa). After Bowen (1915), A. J. Sci., and Morse (1994)(1994), Basalts and , Basalts and Phase Diagrams. Phase Diagrams. Krieger Publishers.Krieger Publishers.

Crystallization RelationshipsCrystallization Relationships

An + Liq

Liquid

Di + Liq

Di + An

aAn

Pure Fo formsPure Fo formsJust as in binaryJust as in binary

= ?= ?F = ?F = ?

= 2 (Fo + Liq) F = 3 - 2 + 1 = 2

If on liquidus, need to specify

only 2 intensive variables

to determine the system T and or and

X of pure Fo is fixed

XAnliq

XAnliq XFo

liq

Lever principle Lever principle relative proportions of liquid & Fo relative proportions of liquid & Fo At 1500At 1500ooC C

Liq x + Fo = bulk a x/Fo = a-Fo/x-a

New New continuous reaction as liquid follows cotectic:continuous reaction as liquid follows cotectic:

LiqLiqAA Liq LiqBB + Fo + Di + Fo + Di

Bulk solid extractBulk solid extract Di/Fo in bulk solid extract using lever principleDi/Fo in bulk solid extract using lever principle

1400

1300

1500

12741274

12701270

13921392

DiopsideDiopside

Di +

Liq

M

b

cc

Fo + Liq

13871387

At 1300At 1300ooC liquid = C liquid = XX Imagine triangular plane X - Di - Fo balanced on bulk Imagine triangular plane X - Di - Fo balanced on bulk aa

Liq/total solids = a-m/Liq-a

total Di/Fo = m-Fo/Di-m

aa

DiDi

Liq xLiq x

FoFomm

Partial MeltingPartial Melting (remove melt):(remove melt):

Ternary Peritectic Systems:Ternary Peritectic Systems:(at 0.1 MPa)(at 0.1 MPa)

Figure 7-4. Isobaric diagram illustrating the cotectic and peritectic curves in the system forsterite-anorthite-silica at 0.1 MPa. After Anderson (1915) A. J. Sci., and Irvine (1975) CIW Yearb. 74.

3 binary systems:Fo-An eutecticAn-SiO2 eutecticFo-SiO2 peritectic

18901890FoFo EnEn

Forsterite + Liq

Ens

tatit

e +

Liq

ab

yy

x

Works the same way as the Fo - En - SiOWorks the same way as the Fo - En - SiO22 binary binary

iikk

FoFo EnEn

15571557

FoFo EnEn

Forsterite + Liq

Ens

tatit

e +

Liq

e b

f

Diopside-Albite-AnorthiteDiopside-Albite-Anorthite

Di - An EutecticDi - An EutecticDi - Ab EutecticDi - Ab EutecticAb - An solid solutionAb - An solid solution

Figure 7-5. Figure 7-5. Isobaric Isobaric diagram illustrating the diagram illustrating the liquidus temperatures liquidus temperatures in the system diopside-in the system diopside-anorthite-albite at anorthite-albite at atmospheric pressure atmospheric pressure (0.1 MPa). After Morse (0.1 MPa). After Morse (1994)(1994), Basalts and , Basalts and Phase Diagrams. Phase Diagrams. Krieger PublushersKrieger Publushers

Isobaric Isobaric polythermal polythermal projectionprojection

Figure 7-5. Isobaric diagram illustrating the liquidus temperatures in the system diopside-anorthite-albite at atmospheric pressure (0.1 MPa). After Morse (1994), Basalts and Phase Diagrams. Krieger Publishers.

Note:Note:

Binary character is usually maintainedBinary character is usually maintainedwhen a new component is addedwhen a new component is added

Eutectic behavior remains eutecticEutectic behavior remains eutectic Peritectic behavior remains peritecticPeritectic behavior remains peritectic Solid solutions remain so as wellSolid solutions remain so as well

ObliqueObliqueViewView

IsothermalIsothermalSectionSection

Figure 7-8.Figure 7-8. Oblique view illustrating an isothermal section through the diopside-albite-anorthite Oblique view illustrating an isothermal section through the diopside-albite-anorthite system. system. Figure 7-9.Figure 7-9. Isothermal section at 1250 Isothermal section at 1250ooC (and 0.1 MPa) in the system Di-An-Ab. Both from C (and 0.1 MPa) in the system Di-An-Ab. Both from Morse (1994)Morse (1994), Basalts and Phase Diagrams. Krieger Publishers., Basalts and Phase Diagrams. Krieger Publishers.

Ternary FeldsparsTernary Feldspars

1118

Ab 20 40 60 80 An

1100

1200

1300

1400

1500

1557

T Co

PlagioclaseLiquid

Liquid

plus

Liquidus

Solidu

s

Weight % An

Plagioclase

OrOrAbAb

Ab-rich feldsparAb-rich feldspar+ liquid+ liquid

liquid

single feldspar

two feldspars

12001200

10001000

800800

Tem

pera

ture

T

empe

ratu

re oo C

C

Wt.% Wt.%

a

cb

d e

f

g h

i

jk

solvus

so

l

idus

liquidus

Or-rich feldspar

+ liquid

Figure 7-10. After Carmichael et al. (1974), Igneous Petrology. McGraw Hill.

Ternary FeldsparsTernary Feldspars

Trace of solvus Trace of solvus at three at three temperature temperature intervalsintervals

Triangle shows coexistingTriangle shows coexisting feldspars and liquid atfeldspars and liquid at 900900ooCC

Figure 7-11. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

4 - Component Diagrams4 - Component Diagrams

y

An

Figure 7-12. The system diopside-anorthite-albite-forsterite. After Yoder and Tilley (1962). J. Petrol.

> 4 Components> 4 Components

Figure 7-13. Pressure-temperature phase diagram for the melting of a Snake River (Idaho, USA) tholeiitic basalt under anhydrous conditions. After Thompson (1972). Carnegie Inst. Wash Yb. 71

olivine Calcic plagioclase

Mg pyroxene

Mg-Ca pyroxene

amphibole

biotite(S

pin

el)

Te

mp

era

ture

potash feldspar muscovite quartz

alkalic plagioclase

Calci-alkalic plagioclase

alkali-calcic plagioclase

Bowen’s Reaction SeriesBowen’s Reaction Series

DiscontinuousDiscontinuousSeriesSeries

ContinuousContinuousSeriesSeries

The Effect of PressureThe Effect of Pressure

LiquidP

ress

ure

Temperature

Solid

P1

P2

T1 T2

Eutectic systemEutectic system

Figure 7-16. Effect of lithostatic pressure on the liquidus and eutectic composition in the diopside-anorthite system. 1 GPa data from Presnall et al. (1978). Contr. Min. Pet., 66, 203-220.

The Effect of Water on MeltingThe Effect of Water on MeltingDry melting:Dry melting: solid solid liquid liquidAdd water- Add water- water enters the meltwater enters the melt Reaction becomes:Reaction becomes:

solid + water = liqsolid + water = liq(aq)(aq)

Figure 7-19.Figure 7-19. The effect of H The effect of H22O O

saturation on the melting of albite, saturation on the melting of albite, from the experiments by Burnham from the experiments by Burnham and Davis (1974). A J Sci 274, 902-and Davis (1974). A J Sci 274, 902-940. The “dry” melting curve is 940. The “dry” melting curve is from Boyd and England (1963).from Boyd and England (1963). JGR 68, 311-323.JGR 68, 311-323.

Figure 7-20.Figure 7-20. Experimentally determined melting intervals of gabbro under H Experimentally determined melting intervals of gabbro under H22O-free (“dry”), and O-free (“dry”), and

HH22O-saturated conditions. After Lambert and Wyllie (1972).O-saturated conditions. After Lambert and Wyllie (1972). J. Geol., 80, 693-708. J. Geol., 80, 693-708.

Dry and water-saturated Dry and water-saturated solidisolidi for some common rock types for some common rock types

The more mafic the rockThe more mafic the rockthe higher the meltingthe higher the meltingpointpoint

All solidi are greatlyAll solidi are greatlylowered by waterlowered by water

Figure 7-21.Figure 7-21. H H22O-saturated (solid) and O-saturated (solid) and

HH22O-free (dashed) solidi (beginning of O-free (dashed) solidi (beginning of

melting) for granodiorite (Robertson melting) for granodiorite (Robertson and Wyllie, 1971), gabbro (Lambert and Wyllie, 1971), gabbro (Lambert and Wyllie, 1972) and peridotite (Hand Wyllie, 1972) and peridotite (H

22O-O-

saturated: Kushiro saturated: Kushiro et al.et al., 1968; dry: , 1968; dry: Ito and Kennedy, 1967).Ito and Kennedy, 1967).

We know the behavior of water-free and water-saturatedWe know the behavior of water-free and water-saturatedmelting by experiments, which are easy to control by melting by experiments, which are easy to control by performing them in dry and wet sealed vesslesperforming them in dry and wet sealed vessles

What about real rocks?What about real rocks?

Some may be dry, some saturated, but most are moreSome may be dry, some saturated, but most are morelikely to be in between these extremeslikely to be in between these extremes

• a fixed water content < saturation levelsa fixed water content < saturation levels

• a fixed water activitya fixed water activity

The Albite-Water The Albite-Water SystemSystem

Red curvesRed curves = melting for = melting for a fixed mol % water ina fixed mol % water in the melt (Xthe melt (Xww))

Blue curvesBlue curves tell the water tell the water content of a water-content of a water- saturated meltsaturated melt

mm

Figure 7-22. From Burnham and Davis (1974). A J Sci., 274, 902-940.

Raise a melt with a ratioRaise a melt with a ratioof albite:water = 1:1 of albite:water = 1:1

(X(Xwaterwater = 0.5) = 0.5)

from point from point aa at 925 at 925ooC andC and1 GPa pressure, toward the 1 GPa pressure, toward the Earth’s surface under Earth’s surface under isothermal conditions.isothermal conditions.

meltmelt

Figure 7-22. From Burnham and Davis (1974). A J Sci., 274, 902-940.

Conclusions:Conclusions:

A rising magma withA rising magma witha fixed % water willa fixed % water willprogressively meltprogressively melt

At shallower levels itAt shallower levels itwill become saturated,will become saturated,and expel water intoand expel water intoits surroundingsits surroundings

Figure 7-22. From Burnham and Davis (1974). A J Sci., 274, 902-940.

Another example: isobaric Another example: isobaric heating of albite withheating of albite with10 mol % water at 0.6 GPa.10 mol % water at 0.6 GPa.

Figure 7-22. From Burnham and Davis (1974). A J Sci., 274, 902-940.

Conclusion:Conclusion:

Although the addition of Although the addition of water can drastically reduce water can drastically reduce the melting point of rocks, the melting point of rocks, the the amountamount of melt produced of melt produced at the lower temperature may at the lower temperature may be quite limited, depending be quite limited, depending on the amount of water on the amount of water availableavailable

15% 20% 50% 100%15% 20% 50% 100%

Figure 7-22. From Burnham and Davis (1974). A J Sci., 274, 902-940.

Melting of Albite with Melting of Albite with a fixed activity of Ha fixed activity of H22OO

Fluid may be a COFluid may be a CO22-H-H22O O

mixture with Pmixture with Pff = P = PTotalTotal

Figure 7-23. From Burnham and Davis (1974). A J Sci., 274, 902-940.

Melting of Albite with Melting of Albite with a fixed activity of Ha fixed activity of H22OO

Fluid may be a COFluid may be a CO22-H-H22O O

mixture with Pmixture with Pff = P = PTotalTotal

Figure 7-26. From Millhollen et al. (1974). J. Geol., 82, 575-587.

The solubility of water in a melt depends on the structure ofThe solubility of water in a melt depends on the structure ofthe melt (which reflects the structure of the mineralogicalthe melt (which reflects the structure of the mineralogicalequivalent)equivalent)

Figure 7-25. The effect of H2O on the

diopside-anorthite liquidus. Dry and 1 atm from Figure 7-16, PH2O = Ptotal curve

for 1 GPa from Yoder (1965). CIW Yb 64.

Ne

Fo En

Ab

SiO2

Oversaturated(quartz-bearing)tholeiitic basalts

Highly undesaturated(nepheline-bearing)

alkali olivinebasalts

Undersaturated

tholeiitic basalts

3GPa2GPa

1GPa

1atm

Volatile-free

Ne

Fo En

Ab

SiO2

Oversaturated(quartz-bearing)tholeiitic basalts

Highly undesaturated(nepheline-bearing)

alkali olivinebasalts

Undersaturated

tholeiitic basalts

CO2

H2Odry

P = 2 GPa

Effect of Pressure, Water, and COEffect of Pressure, Water, and CO2 2 on the positionon the position

of the eutectic in the basalt systemof the eutectic in the basalt systemIncreased pressure moves theIncreased pressure moves theternary eutectic (first melt) fromternary eutectic (first melt) fromsilica-saturated to highly undersat.silica-saturated to highly undersat.alkaline basaltsalkaline basalts

Water moves the (2 GPa) eutecticWater moves the (2 GPa) eutectictoward higher silica, while COtoward higher silica, while CO22

moves it to more alkaline typesmoves it to more alkaline types