partial melting
DESCRIPTION
Partial melting. 1. Binary and ternary phase diagrams; melting of the mantle. 1 - C Systems. The system SiO 2. After Swamy and Saxena (1994) , J. Geophys. Res., 99 , 11,787-11,794 . AGU. 1900. 1890. Liquid. a. 1700. b. c. Olivine. T o C. plus. Liquid. d. 1500. Olivine. 1300. - PowerPoint PPT PresentationTRANSCRIPT
Partial melting
1. Binary and ternary phase diagrams; melting of the mantle
1 - C Systems1 - C SystemsThe system SiOThe system SiO22
Stishovite
Coesite
- quartz
- quartz
Liquid
TridymiteCristobalite
600 1000 1400 1800 2200 2600
2
4
6
8
10P
ress
ure
(GP
a)
Temperature oC
After Swamy and Saxena (1994), J. Geophys. Res., 99, 11,787-11,794. AGU
The Olivine SystemThe Olivine SystemFo - FaFo - Fa (Mg (Mg22SiOSiO44 - Fe - Fe22SiOSiO44))
also a solid-solution seriesalso a solid-solution series
Isobaric T-X phase diagram at atmospheric pressure (After Bowen and Shairer (1932), Amer. J. Sci. 5th Ser., 24, 177-213.
Fo20 40 60 80Fa
1300
1500
1700
1890
1205
T oC
Olivine
Liquid
Liquid
plus
1900
a
b c
d
Wt.% Forsterite
Olivine
2-C Eutectic Systems2-C Eutectic Systems Example: Diopside - AnorthiteExample: Diopside - Anorthite
No solid solutionNo solid solution
1274
Di 20 40 60 80 An
1200
1300
1400
1500
1600
T oC
Anorthite + Liquid
Liquid Liquidus
Diopside + Liquid
Diopside + Anorthite
1553
1392
Wt.% Anorthite
Isobaric T-X phase diagram at atmospheric pressure (After Bowen (1915), Amer. J. Sci. 40, 161-185.
Melting in a binary system
• An-rich composition (right of the eutectic)
• Di-rich composition
C = 3: Ternary Systems:Example 1: Ternary Eutectic
Di - 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 - 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
Melting in a ternary
• Consider a composition close to the Fo apex and with Di>An (mantle-like)
Effect of pressureEffect of pressure
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.
Pressure effects:
Figure 10-8 Figure 10-8 After Kushiro (1968), After Kushiro (1968), J. Geophys. Res.J. Geophys. Res., , 7373, 619-634., 619-634.
NeNe
FoFo EnEn
AbAb
SiOSiO22
Oversaturated(quartz-bearing)tholeiitic basalts
Highly undesaturated
(nepheline - b
earing)
alkali basalts
Undersaturated
tholeiitic basalts
EE3GPa3GPa
EE 2Gpa2Gpa
EE1GPa1GPa
EE 1atm1atm
Volatile-freeVolatile-free
NB
• Do you remember – alkaline vs. Sub-alkaline series?
Effect of waterEffect of water
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.
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.
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
> 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
Experiments on melting mantle samples:
• Tholeiite easily created
by 10-30% PM
• More silica saturated
at lower P
• Grades toward alkalic
at higher PFigure 10-17a. Figure 10-17a. After Jaques and Green (1980).After Jaques and Green (1980). Contrib. Mineral. Petrol., 73, 287-310.Contrib. Mineral. Petrol., 73, 287-310.
• Figures not used
15
10
5
00.0 0.2 0.4 0.6 0.8
Wt.
% A
l 2O3
Wt.% TiO2
DuniteHarzburgite
Lherzolite
Tholeiitic basalt
Partia
l Melt
ing
Residuum
Source, melt and residuum:Source, melt and residuum:
Figure 10-1 Figure 10-1 Brown and Brown and Mussett, A. E. (1993), Mussett, A. E. (1993), The Inaccessible Earth: The Inaccessible Earth: An Integrated View of Its An Integrated View of Its Structure and Structure and Composition. Composition. Chapman Chapman & Hall/Kluwer.& Hall/Kluwer.
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.
Partial melting
2. Melting reactions, experimental petrology
Melting of the crust
Qz-Ab-Or + H2O
At 1 kbar (supersolvus) At 5 kbar (subsolvus)
Chapter 18: Granitoid Rocks Chapter 18: Granitoid Rocks
Figure 18-3. The Ab-Or-Qtz system with the ternary cotectic curves and eutectic minima from 0.1 to 3 GPa. Included is the locus of most granite compositions from Figure 11-2 (shaded) and the plotted positions of the norms from the analyses in Table 18-2. Note the effects of increasing pressure and the An, B, and F contents on the position of the thermal minima. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
5um powder
12.7mm
Incongruent melting reactions
(Limpopo SMZ, Ga-Mathule village, E. of Bandelierkop)
Chapter 18: Chapter 18: Granitoid Rocks Granitoid Rocks
Figure 18-5. a. Simplified P-T phase diagram and b. quantity of melt generated during the melting of muscovite-biotite-bearing crustal source rocks, after Clarke (1992) Granitoid Rocks. Chapman Hall, London; and Vielzeuf and Holloway (1988) Contrib. Mineral. Petrol., 98, 257-276. Shaded areas in (a) indicate melt generation. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
• 2 generations of melt in a single outcrop ?– M1: Bt still stable
(Q+KSp+Ph+H2O=M)
– M2: incongruent melting yielding crd
(Velay dome, french hercynian belt)
Melting of an heterogeneous crust
• Orthogneiss: Qz-Pg-Bt
• Paragneiss: Or-Ab-Qz-Bt-AlS
• Shear zone: add water to the above
• What will melt, at what temperature, with which melting reaction?
NB- this is a simplified model!
• Slides not used
Figure 18-8. Schematic models for the uplift and extensional collapse of orogenically thickened continental crust. Subduction leads to thickened crust by either continental collision (a1) or compression of the continental arc (a2), each with its characteristic orogenic magmatism. Both mechanisms lead to a thickened crust, and probably thickened mechanical and thermal boundary layers (“MBL” and “TBL”) as in (b) Following the stable situation in (b), either compression ceases (c1) or the thick dense thermal boundary layer is removed by delamination or convective erosion (c2). The result is extension and collapse of the crust, thinning of the lithosphere, and rise of hot asthenosphere (d). The increased heat flux in (d), plus the decompression melting of the rising asthenosphere, results in bimodal post-orogenic magmatism with both mafic mantle and silicic crustal melts. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Partial melting
3. Migmatites and melt extraction
Partially molten rocks
MESOSOME = Not melted
LEUCOSOME = Liquid = granitic magma
MELANOSOME = Residue
Biot
Plg
QzKF
Biot
Plg
Qz KF
MetatexitesDiatexites
« Dirty » granites
Rheology of partially molten systems
Melt extraction
Brown, 1994
Melt depletion
An experimental study of melt extraction
J. Barraud, PhD 2000
Films
Exp39.avi
(Films)
Exp32.avi
Exp43.avi
Evolution de la déformation1) 5% shortening
2) 22% shortening
4) 36% shortening
3) 30% shortening
Asymetrical fold; shear zone on one flank
Strain localization in liquid patches.
Zone de cisaillement
Bande de cisaillement
Melt extraction: role of deformation
Burg et al., 1994
Melting and migmatitic domes – migmatites in orogenic belts
The Velay dome
• Slides not used