phase diagrams continued
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Phase Diagrams ContinuedPhase Diagrams Continued
15571557
MgMg22SiOSiO44
2020 4040 6060 8080 SiOSiO22
14001400
16001600
18001800
20002000
17131713T T ooC C
MgSiOMgSiO22
1543
1470ForsteriteForsterite+ Enstatite+ Enstatite
Liquid +Liquid + ForsteriteForsterite
1695
Enstatite + Tridymite
Enstatite + Cristobalite
Cristobalite + Liquid
Two Liquids
Liquid
Wt.% XWt.% X22
o
n
c
p
TT
MM
AnorthiteAnorthite
ForsteriteForsterite
- Next week Review and MidtermNext week Review and Midterm
Topics: phase diagramsTopics: phase diagrams- 2 component systems:2 component systems:
- PeritecticPeritectic
- 3 component systems3 component systems
Updates/questionsUpdates/questions
Solid Solution with Eutectic:Solid Solution with Eutectic:Ab-Or (the alkali feldspars)
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.
Effect of PEffect of PH OH O on Ab-Or on Ab-Or22
Figure 6-17. The Albite-K-feldspar system at various H2O pressures. (a) and (b) after
Bowen and Tuttle (1950), J. Geol, (c) after Morse (1970) J. Petrol.
Binary Peritectic SystemsBinary Peritectic Systems
15571557
MgMg22SiOSiO44
2020 4040 6060 8080 SiOSiO22
14001400
16001600
18001800
20002000
17131713T T ooC C
MgSiOMgSiO22
1543
1470
EnstatiteEnstatiteForsteriteForsterite
Forsterite+ Enstatite
Liquid + Forsterite
1695
Enstatite + Tridymite
Enstatite + Cristobalite
Cristobalite + Liquid
Two Liquids
Liquid
Wt.% XWt.% X22
bb
ee
a
Figure 6-12. Isobaric T-X phase diagram of the system Fo-Silica at 0.1 MPa. After Bowen and Anderson (1914) and Grieg (1927). Amer. J. Sci.
ccdd
iikk mm
FoFo EnEn
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Bulk X
The Peritectic 1: X between Fo-EnThe Peritectic 1: X between Fo-En
15431543
ccdd
iikkmm
FoFo EnEn
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bulk Xbulk X
xx
yy
CrCr
The Peritectic 2: X between En-CrThe Peritectic 2: X between En-Cr
Incongruent Melting of EnstatiteIncongruent Melting of Enstatite
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ccdd
ii
FoFo EnEn
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bulk Xbulk X
CrCr
Ternary SystemsTernary Systems
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
Crystallization RelationshipsCrystallization Relationships
Fo + Liq
Liquid
Di + Liq
Di + Fo
aAn
Pure Fo formsPure Fo formsJust as in binaryJust as in binary
= ? F = ?= ? F = ?
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 lever w/ 3 phasesTernary lever w/ 3 phases
Pressure EffectsPressure Effects
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