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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.
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
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
Works the same way as the Fo - En - SiOWorks the same way as the Fo - En - SiO22 binary binary
iikk
FoFo EnEn
15571557
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
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