slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Geol 5310 Advanced Igneous and Metamorphic Petrology PowerPoint Presentation
Download Presentation
Geol 5310 Advanced Igneous and Metamorphic Petrology

Loading in 2 Seconds...

play fullscreen
1 / 45

Geol 5310 Advanced Igneous and Metamorphic Petrology - PowerPoint PPT Presentation


  • 465 Views
  • Uploaded on

Geol 5310 Advanced Igneous and Metamorphic Petrology. Phase Diagrams. October 26, 2009. Makaopuhi Lava Lake, Hawaii Watching a Magma Crystallize. TEMPERATURE. TIME. From Wright and Okamura, (1977) USGS Prof. Paper , 1004. Opaque. Olivine. Clinopyroxene Plagioclase. 1250. 1250.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

Geol 5310 Advanced Igneous and Metamorphic Petrology


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
    Presentation Transcript
    1. Geol 5310 Advanced Igneous and Metamorphic Petrology Phase Diagrams October 26, 2009

    2. Makaopuhi Lava Lake, HawaiiWatching a Magma Crystallize TEMPERATURE TIME From Wright and Okamura, (1977) USGS Prof. Paper, 1004.

    3. Opaque Olivine Clinopyroxene Plagioclase 1250 1250 Liquidus 1200 1200 1150 1150 1100 Temperature oc 1050 1100 Melt 1000 Crust 1050 950 900 1000 20 60 30 40 50 0 100 10 70 80 90 Percent Glass Solidus 950 0 10 10 0 10 20 30 40 0 10 20 30 40 0 Makaopuhi Lava Lake, Hawaii Winter (2001), Figs. 6-1 & 6-2. From Wright and Okamura (1977) USGS Prof. Paper, 1004.

    4. Makaopuhi Lava Lake, HawaiiCompositional Changes in Solid Solution Minerals 100 Olivine Augite Plagioclase 90 80 Weight % Glass 70 60 50 60 .7 .6 70 .9 .7 .9 80 .8 .8 Mg / (Mg + Fe) Mg / (Mg + Fe) An Winter (2001), Fig. 6-3. From Wright and Okamura, (1977) USGS Prof. Paper, 1004.

    5. Crystallization Behavior of Magmasfrom natural and experimental observations and thermodymanic predictions • Cooling melts crystallize from a liquid to a solid over a range of temperatures (and pressures) • Several minerals crystallize over this T range, and the number of minerals increases as T decreases • The minerals that form do so sequentially, generally with considerable overlap • Minerals that involve solid solution change composition as cooling progresses • The melt composition also changes during crystallization • The minerals that crystallize (as well as the sequence) depend on T and X of the melt • Pressure can affect the temperature range at which a melt crystallizes and the types of minerals that form • The nature and pressure of volatiles can also affect the temperature range of xtallization and the mineral sequence

    6. Why do Magmas Crystallize This Way?Predicted by Phase Diagrams Although magmas (melts + crystals) are some of the most complex systems in nature, we can evaluate how they form and crystallize by simplifying them into their basic chemical constituent parts and empirically determine (observe) how these simple systems react to geologically important variables – temperature and pressure. We portray this behavior through the construction of PHASE DIAGRAMS

    7. Phase DiagramsTerminology PHASE of a System A physically distinct part of a system that may be mechanically separated from other distinct parts. (e.g., in a glass of ice water (the system), ice and water are two phases mechanically distinct phases) COMPONENTS of a System The minimum number of chemical constituents that are necessary to define the complete composition of a system (e.g. for the plagioclase system, components are NaAlSi3O8– albite and CaAl2Si2O8 - anorthite) VARIABLES that define the STATE of a System Extensive – dependent on the quantity of the system – volume, mass, moles, ... Intensive – properties of the phases of a system that are independent of quantities (temperature, pressure, density, molecular proportions, elemental ratios, ...) Note that ratios of extensive variables become intensive (V/m = density,V/moles=molar volume)

    8. Gibbs Phase Rule • F = C - f + 2 • F = # degrees of freedom • The number of intensive parameters that must be specified in order to completely determine the system, or the number of variables that can be changed independently and still maintain equilibrium • f = # of phases • phases are mechanically separable constituents • C = minimum # of components (chemical constituents that must be specified in order to define all phases) • 2 = Two intensive parameters • Usually = temperature and pressure • ONLY APPLIES TO SYSTEMS IN CHEMICAL EQUILIBRIUM!!

    9. PHASE RULE IN A ONE-COMPONENT SYSTEM SiO2 F = C - f + 2 Divariant Field F = 1 – 1 + 2 = 2 Univariant Line F = 1 – 2 + 2 = 1 Invariant Point F = 1 – 3 + 2 = 0

    10. PHASE RULE IN A ONE-COMPONENT SYSTEMH2O Fluid Note that HEAT is different than TEMPERATURE. A boiling pot of water must be continuously heated to completely turn to steam, all the while sitting at 100oC This heat is called the latent heat of vaporization The heat require to turn solid into liquid is the latent heat of fusion Sublimation

    11. Two-Component System with Solid Solutioncompare X and T at a constant P System – Plagioclase Phases – Liquid and Plagioclase mineral Components – Ab (NaAlSi3O8) An (CaAl2Si2O8) coupled substitution! An content = An / (Ab + An) F = C - f + 1 (only 1 variable since P is constant) Divariant Field F = 2 – 1 + 1 = 2 Univariant Field F = 2 – 2 + 1 = 1 Phase Relationships determined by Experimental Data

    12. Two-Component System with Solid SolutionEquilibrium Crystallization a – Starting bulk composition of melt = An60 b – Beginning of crystallization T= 1475oC c – Composition of first plagioclase to crystallize = An87

    13. Two-Component System with Solid SolutionEquilibrium Crystallization a – Starting bulk composition of melt = An60 b – Beginning of crystallization T= 1475oC c – Composition of first plagioclase to crystallize at 1475oC = An87 d – Melt composition at 1450oC = An48 e – Bulk composition of Magma (Melt + Crystals = An60) f– Composition of Plagioclase at 1450oC = An81

    14. Two-Component System with Solid SolutionEquilibrium CrystallizationUsing the Lever Rule to determine Crystal:Melt Ratio %Plag %Melt %Melt 40% 60%

    15. a – Starting bulk composition of melt = An60 b – Beginning of crystallization T= 1475oC c – Composition of first plagioclase to crystallize at 1475oC = An87 d – Melt composition at 1450oC = An48 e – Bulk composition of Magma (Melt + Crystals = An60) f– Composition of Plagioclase at 1450oC = An81 g – Last melt composition at 1340oC = An18 h – Final composition of plagioclase at 1450oC = An60 i – Subsolidus cooling of plagioclase Two-Component System with Solid SolutionEquilibrium Crystallization

    16. Two-Component System with Solid SolutionFractional Crystallization As crystals form, they are removed (fractionated) from the system and thus are not allowed to reequilibrate with the cooling melt. This has the effect of incrementally resetting the bulk composition of the liquid to a lower An content with each crystallization step. Consequently, the final melt may have a composition of An0 (pure Ab end member)

    17. Two-Component System with Solid SolutionFractional Crystallization Because of coupled substitution of Ca-Na and Al-Si in plagioclase, reequilibration is difficult with T decrease, leading to chemically zoned crystals like this one. Avg. An=60 uts.cc.utexas.edu/~rmr/CLweb/volcanic.htm

    18. Two-Component System with Solid SolutionOlivine Sonju Lake Intrusion Fayalite Fe2SiO4 Fosterite Fe2SiO4

    19. Two-Component System with a EutecticPyroxene - Plagioclase Eutectic Point

    20. Two-Component System with a EutecticPyroxene - Plagioclase a– bulk starting composition = An70 Eutectic Point

    21. Two-Component System with a EutecticPyroxene - Plagioclase a– bulk starting composition = An70 b – crystallization begins at 1450oC c - pure plagioclase (An) crystallizes Eutectic Point

    22. Two-Component System with a EutecticPyroxene - Plagioclase b-d – magma composition changes as plagioclase crystallizes d – reaction stays at 1274oC until liquid is consumed a– bulk starting composition = An70 b – crystallization begins at 1450oC c - pure plagioclase (An) crystallizes Lever Rule Eutectic Point An 30% Liq 70% An 50% Liq 50% An 70% Di 30%

    23. Two-Component System with a EutecticPyroxene – PlagioclaseEvolution of Liquid and Solidduring Crystallization Equilibrium vs. Fractional Eutectic Point

    24. Two-Component System with a EutecticPyroxene – Plagioclase Equilibrium Melting

    25. Two-Component System with a EutecticPyroxene – Plagioclase Fractional (or Batch) Melting

    26. Two-Component System with a PeritecticOlivine-Orthopyroxene-Quartz Three phases 2MgSiO3 (Opx) = Mg2SiO4 (Ol) + SiO2 (Qtz) Si-rich magma (a) (eutectic relationship) Winter (2001) 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.

    27. Two-Component System with a PeritecticOlivine-Orthopyroxene-Quartz Mg-rich magma (f) i - Peritectic Point Winter (2001) 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.

    28. i 1557 Fo En Two-Component System with a PeritecticOlivine-Orthopyroxene-Quartz Bulk X Opx Ol Ol Opx –reaction rim Liq 60% Ol 40% Proportional amount of Ol that must be converted to Opx Mg2SiO4 (Ol) + SiO2 (Liq) 2MgSiO3 (Opx) Opx 67% Ol 33%

    29. x i k y m 1557 d Cr 1543 c bulk X Fo En Two-Component System with a PeritecticOlivine-Orthopyroxene-Quartz System at: - pertectic point 10%Ol +90%Liq  50%Opx+50%Liq i.e. all original Ol recrystallizes to Opx (if equilibrium is maintained) - 80% Opx + 20% Liq - eutectic point 90%Opx +10%Liq  94%Opx+6%Qtz i m c

    30. i 1543 1557 d Cr c Fo En Two-Component System with a PeritecticOlivine-Orthopyroxene-Quartz • Incongruent Melting of Enstatite • Melt of En does not ® melt of same composition • Rather En ®Fo + Liqi at the peritectic • Partial Melting of Fo + En • (harzburgite = mantle) • En + Fo also ® first liq = i • Remove i and cool • Result = ?

    31. Two-Component System with a PeritecticOlivine-Orthopyroxene-Quartz Pressure Effects Different phases have different compressibilities Thus P will change Gibbs Free Energy differentially • Raises melting point (lower volume (solid) phase is favored at higher P) • Shifts from a peritectic relationship at low P to a dual eutectic relationship at high P with a thermal divide separating them. Figure 6-15. The system Fo-SiO2 at atmospheric pressure and 1.2 GPa. After Bowen and Schairer (1935), Am. J. Sci., Chen and Presnall (1975) Am. Min.

    32. Two-Component System with a Solvus Olivine-Orthopyroxene-Quartz Liquid Immiscibility Hyper-liquidus Solvus

    33. Two-Component System with Solid Solution, a Eutectic and a Solvus Plagioclase and Alkali Feldspar Solid Solution with a Eutectic Subsolidus Solvus  Perthitic Exsolution

    34. Two-Component System with a SolvusPressure Effects

    35. Three Component System with EutecticsOlivine-Plagioclase-Pyroxene (Fo-An-Di) Liquidus surface showing temperature contours F = 3 – 2 + 1 = 2 (divariant field) Liquidus surface showing temperature contours F = 3 – 2 + 1 = 2 Cotectic (or binary eutectic) F = 3 – 3 + 1 = 1 (univariant line) Ternary eutectic F = 3 – 4 + 1 = 0 (invariant point) Pressure = 0.1 MPa Winter (2001) 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.

    36. Three Component System with EutecticsOlivine-Plagioclase-Pyroxene (Fo-An-Di) X – starting magma compositionS – starting bulk solid composition X’ – magma composition when plagioclase become saturated along with olivine S’ – bulk solid composition when magma at X’ (olivine composes ~ 30% of system) Equilibrium Crystallization Pressure = 0.1 MPa X” – magma comp at 50% crystallized (based on lever rule of tie-line through X) S” – bulk solid comp when magma at X” (composed of 68%Ol & 32%Pl) X’ X’’ X*=M – magma reached ternary eutectic at 65% crystallized S* – bulk solid comp when magma reaches ternary eutectic (composed of 60%Ol & 40%Pl) X* Sf S* X S’’ X*=M – magma comp fixed at ternary eutectic until 100% crystallized Sf – final bulk solid = X-starting liquid comp X* S S’

    37. Three Component System with EutecticsOlivine-Plagioclase-Pyroxene (Fo-An-Di) Fractional Crystallization PCO Pressure = 0.1 MPa PO X’ X’’ O X* Sf S* X S’’ X* S S’

    38. Three Component System with a PeritecticPlagioclase-Olivine-(Orthopyroxene)-Quartz (An-Fo-(En-)SiO2) 3 binary systems: Fo-An eutectic An-SiO2eutectic Fo-SiO2peritectic Liquidus contours not shown to reduce clutter Winter (2001) 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. Pressure = 0.1 MPa

    39. Three Component System with a PeritecticPlagioclase-Olivine-(Orthopyroxene)-Quartz (An-Fo-(En-)SiO2) LIQUID PATH SOLID PATH • a – Starting Liquid Comp • a-b – liquid path due to Fo • crystallization • b- En crystallization (and • partial replacement of Fo) begins • b-c – liquid path due to • Fo+En crystallization • c – An joins En and Fo as • crystallizing phases; • last liquid comp • for equilibrium crystallization • AB –Fo only crystallization • drives liquid from ab • AB-C – En crystallization • (and replacement) enriches bulk solid in En to C (where liquid reaches c) • C-F – when liquid • reaches c, An is added to bulk solid and is 100% crystallized when reach starting composition F F AB C

    40. Three Component System with a PeritecticPlagioclase-Olivine-(Orthopyroxene)-Quartz (An-Fo-(En-)SiO2) g-d leg only possible with fractional crystallization final rock is En + An under equilibrium crystallization All Ol is consumed

    41. Three Component System with Solid SolutionPlagioclase-Pyroxene (An-Ab-Di) Winter (2001) 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. Liquid – An content Tie-lines

    42. Three Component System with Solid SolutionPlagioclase-Pyroxene (An-Ab-Di) Starting Liquid Composition Last Liquid (EC) Final Plag (EC) First Plag

    43. Three Component System with Solid SolutionPlagioclase-Pyroxene (An-Ab-Di) Liquid composition arcs due to decreasing An content of plagioclase Last Liquid (EC) Starting Liquid Composition First Plag Final Plag (EC)

    44. Four Component SystemsFo-Di-An-Ab Becoming difficult to visualize Time to revert to multi-dimensional mathematical models Winter (2001) Figure 7-12. The system diopside-anorthite-albite-forsterite. After Yoder and Tilley (1962). J. Petrol.

    45. Back to Thermodynamics Think about Gibbs Free Energy again dG = VdP – SdT at a given P (0.1 MPa) and T (1300ºC) Low Volume, trumps Entropy  Minerals more stable High Entropy trumps volume  Liquid more stable Liq