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C = 3: Ternary Systems:Example 1: Ternary Eutectic
Di - An - Fo
T
M
Anorthite
Forsterite
Diopside
Note three binary eutectics
No solid solution
Ternary eutectic = M
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T - 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), Basalts and
Phase Diagrams.
Krieger Publishers.
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Crystallization Relationships
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An + Liq
Liquid
Di + Liq
Di + An
a
An
Pure Fo formsJust as in binary
f = ?
F = ?
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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
XFoliq
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Lever principle relative proportions of liquid & Fo
At 1500oC
Liqx + Fo = bulka
x/Fo = a-Fo/x-a
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New continuous reaction as liquid follows cotectic:
LiqA LiqB + Fo + Di
Bulk solid extract Di/Fo in bulk solid extract using lever principle
1274
1392
Diopside
M
b
c
Fo + Liq
1387
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At 1300oC liquid = X
Imagine triangular plane X - Di - Fo balanced on bulk a
Liq/total solids = a-m/Liq-a
total Di/Fo = m-Fo/Di-m
a
Di
L iq x
Fom
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Partial Melting(remove melt):
i i
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Ternary Peritectic Systems:(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 eutectic
Fo-SiO2 peritectic
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1890Fo En
a
b
y
x
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Works the same way as the Fo - En - SiO2 binary
ik
Fo En
1557
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Fo En
e b
f
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Diopside-Albite-Anorthite
Di - An Eutectic
Di - Ab Eutectic
Ab - An solid solution
Figure 7-5. Isobaric
diagram illustrating theliquidus temperatures
in the system diopside-
anorthite-albite at
atmospheric pressure
(0.1 MPa). After Morse
(1994), Basalts and
Phase Diagrams.Krieger Publushers
Figure 7-5 Isobaric
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Isobaric
polythermalprojection
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 andPhase Diagrams. Krieger
Publishers.
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Note:
Binary character is usually maintainedwhen a new component is added
Eutectic behavior remains eutectic
Peritectic behavior remains peritectic
Solid solutions remain so as well
Obli
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Oblique
ViewIsothermal
Section
Figure 7-8. Oblique view illustrating an isothermal section through the diopside-albite-anorthite
system. Figure 7-9. Isothermal section at 1250oC (and 0.1 MPa) in the system Di-An-Ab. Both fromMorse (1994), Basalts and Phase Diagrams. Krieger Publishers.
T F ld
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Ternary Feldspars
1118
Ab 20 40 60 80 An
1100
1200
1300
1400
1500
1557
T Co
PlagioclaseLiquid
Liquid
plus
Weight % An
Plagioclase
OrAb
Ab-rich feldspar
+ liquid
liquid
single feldspar
two feldspars
1200
1000
800TemperatureoC
Wt.%
a
cb
de
f
g h
i
jk
Figure 7-10. After Carmichael et al.(1974), Igneous Petrology. McGraw Hill.
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Ternary Feldspars
Trace of solvus
at three
temperature
intervals
Triangle shows coexisting
feldspars and liquid at
900oC
Figure 7-11. Winter (2001) An
Introduction to Igneous and
Metamorphic Petrology. PrenticeHall.
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4 - Component Diagrams
An
Figure 7-12. The system
diopside-anorthite-albite-forsterite. After
Yoder and Tilley (1962).
J. Petrol.
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> 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
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olivine Calcic plagioclase
Mg pyroxene
Mg-Ca pyroxene
amphibole
biotite
(Spinel)
potash feldsparmuscovite
quartz
alkalic plagioclase
Calci-alkalic plagioclase
alkali-calcic plagioclase
Bowens Reaction Series
Discontinuous
Series
ContinuousSeries
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The Effect of Pressure
Liquid
Temperature
Solid
P1
P2
T1 T2
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Eutectic 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.
Th Eff t f W t M lti
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The Effect of Water on MeltingDry melting:solid liquid
Add water- water enters the meltReaction becomes:
solid + water = liq(aq)
Figure 7-19. The effect of H2O
saturation on the melting of albite,
from the experiments by Burnham
and Davis (1974). A J Sci 274, 902-
940. The dry melting curve is
from Boyd and England (1963).JGR 68, 311-323.
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Figure 7-20. Experimentally determined melting intervals of gabbro under H2O-free (dry), andH2O-saturated conditions. After Lambert and Wyllie (1972). J. Geol., 80, 693-708.
Dry and water saturated solidi for some common rock types
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Dry and water-saturated solidi for some common rock types
The more mafic the rock
the higher the melting
point
All solidi are greatly
lowered by water
Figure 7-21. H2O-saturated (solid)
and H2O-free (dashed) solidi
(beginning of melting) for
granodiorite (Robertson and Wyllie,
1971), gabbro (Lambert and Wyllie,
1972) and peridotite (H2O-saturated:
Kushiro et al., 1968; dry: Ito andKennedy, 1967).
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We know the behavior of water-free and water-saturated
melting by experiments, which are easy to control by
performing them in dry and wet sealed vessles
What about real rocks?
Some may be dry, some saturated, but most are morelikely to be in between these extremes
a fixed water content < saturation levels
a fixed water activity
Th Albit W t
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The Albite-Water
System
Red curves = melting for
a fixed mol % water in
the melt (Xw)
Blue curves tell the water
content of a water-
saturated melt
m
Figure 7-22. From Burnham and Davis(1974). A J Sci., 274, 902-940.
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Raise a melt with a ratio
of albite:water = 1:1
(Xwater= 0.5)
from point a at 925
o
C and1 GPa pressure, toward the
Earths surface under
isothermal conditions.
melt
Figure 7-22. From Burnham and Davis(1974). A J Sci., 274, 902-940.
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Conclusions:
A rising magma witha fixed % water will
progressively melt
At shallower levels it
will become saturated,
and expel water into
its surroundings
Figure 7-22. From Burnham and Davis(1974). A J Sci., 274, 902-940.
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Another example: isobaric
heating of albite with
10 mol % water at 0.6 GPa.
Figure 7-22. From Burnham and Davis(1974). A J Sci., 274, 902-940.
15% 20% 50% 100%
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Conclusion:
Although the addition of
water can drastically reduce
the melting point of rocks,the amount of melt produced
at the lower temperature may
be quite limited, depending
on the amount of wateravailable
Figure 7-22. From Burnham and Davis(1974). A J Sci., 274, 902-940.
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Melting of Albite with a
fixed activity of H2O
Fluid may be a CO2-H2O
mixture with Pf= PTotal
Figure 7-23. From Burnham and Davis(1974). A J Sci., 274, 902-940.
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Melting of Albite with a
fixed activity of H2O
Fluid may be a CO2-H2O
mixture with Pf= PTotal
Figure 7-26. From Millhollen et al. (1974). J. Geol., 82, 575-587.
Th l bilit f t i lt d d th t t f
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The solubility of water in a melt depends on the structure of
the melt (which reflects the structure of the mineralogical
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.
Effect of Pressure Water and CO on the position
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Ne
Ab
Oversaturated(quartz-bearing)tholeiitic basalts
Highly undesaturated(nepheline-bearing)
alkali olivinebasalts
3GPa2GPa
1GPa
1atm
Volatile-free
Ne
Ab
Oversaturated(quartz-bearing)tholeiitic basalts
Highly undesaturated(nepheline-bearing)
alkali olivinebasalts
CO2
H2Odry
P = 2 GPa
Effect of Pressure, Water, and CO2 on the position
of the eutectic in the basalt system
Increased pressure moves the
ternary eutectic (first melt) fromsilica-saturated to highly undersat.
alkaline basalts
Water moves the (2 GPa) eutectic
toward higher silica, while CO2
moves it to more alkaline types