1 / 23

Phase Equilibrium

Phase Equilibrium. Makaopuhi Lava Lake. Magma samples recovered from various depths beneath solid crust. From Wright and Okamura, (1977) USGS Prof. Paper , 1004 . 1250. 1200. 1150. 1100. Temperature o c . 1050. 1000. 950. 900. 20. 60. 30. 40. 50. 0. 100. 10. 70. 80. 90.

JasminFlorian
Download Presentation

Phase Equilibrium

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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Phase Equilibrium

  2. Makaopuhi Lava Lake Magma samples recovered from various depths beneath solid crust From Wright and Okamura, (1977) USGS Prof. Paper, 1004.

  3. 1250 1200 1150 1100 Temperature oc 1050 1000 950 900 20 60 30 40 50 0 100 10 70 80 90 Percent Glass Makaopuhi Lava Lake Temperature of sample vs. Percent Glass Fig. 6-1. From Wright and Okamura, (1977) USGS Prof. Paper, 1004.

  4. Olivine Clinopyroxene Plagioclase Opaque 1250 Liquidus 1200 olivine decreases below 1175oC 1150 Temperature oC 1100 Melt Crust 1050 1000 Solidus 950 0 10 0 10 20 30 40 50 0 10 20 30 40 50 10 0 Makaopuhi Lava Lake Minerals that form during crystallization Fig. 6-2. From Wright and Okamura, (1977) USGS Prof. Paper, 1004.

  5. Makaopuhi Lava Lake 100 Olivine Augite Plagioclase Mineral composition during crystallization 90 80 Weight % Glass 70 60 50 60 .7 .6 70 .9 .7 .9 80 .8 .8 Mg / (Mg + Fe) An Mg / (Mg + Fe) Fig. 6-3. From Wright and Okamura, (1977) USGS Prof. Paper, 1004.

  6. Crystallization Behavior of Melts 1. Cooling melts crystallize from a liquid to a solid over a range of temperatures (and pressures) 2. Several minerals crystallize over this T range, and the number of minerals increases as T decreases 3. The minerals that form do so sequentially, with considerable overlap 4. Minerals that involve solid solution change composition as cooling progresses 5. The melt composition also changes during crystallization 6. The minerals that crystallize (as well as the sequence) depend on T and X of the melt 7. Pressure can affect the types of minerals that form and the sequence 8. The nature and pressure of the volatiles can also affect the minerals and their sequence

  7. The 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 • 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 = 2 intensive parameters • Usually temperature and pressure for geologists

  8. OneComponent Systems SiO2 Fig. 6-6. After Swamy and Saxena (1994), J. Geophys. Res., 99, 11,787-11,794. AGU

  9. Two Component Systems Systems with Complete Solid Solution PlagioclaseAb (NaAlSi3O8 ) - An (CaAl2Si2O8) Fig. 6-8. Isobaric T-X phase diagram at atmospheric pressure. After Bowen (1913) Amer. J. Sci., 35, 577-599.

  10. Bulk composition a = An60 = 60 g An + 40 g Ab XAn = 60/(60+40) = 0.60

  11. A continuous reaction of the type: liquidB + solidC = liquidD + solidF

  12. The lever principle: Amount of liquid ef = Amount of solid de where d = the liquid composition, f = the solid composition and e = the bulk composition d f e D liquidus de ef solidus

  13. Equilibrium Crystallization of the Plagioclase Feldspars 1. Liquid of composition X (An61) cools to the liquidus 2. Crystals of approximately An87 begin to form 3. Crystals have higher Ca/Na than liquid; ppt of crystals causes L composition to become more sodic. X P=1 atm 4. Ratio of Ca/Na in both crystals and liquid decrease with decreasing temperature; proportion of crystals increases as liquid decreases 5. Crystals of An61 cool without further change in composition Composition of 1st crystal Composition of last crystal PowerPoint® presentation by Kenneth E. Windom Composition of last liquid

  14. Note the following: 1. The melt crystallized over a T range of 135oC * 4. The composition of the liquid changed from b to g 5. The composition of the solid changed from c to h Numbers refer to the “behavior of melts” observations (several slides back) ** The actual temperatures and the range depend on the bulk composition **

  15. Equilibrium melting is exactly the opposite • Heat An60 and the first melt is g at An20 and 1340oC • Continue heating: both melt and plagioclase change X • Last plagioclase to melt is c (An87) at 1475oC

  16. Fractional crystallization: Remove crystals as they form so they can’t undergo a continuous reaction with the melt At any T, Xbulk = Xliqdue to the removal of the crystals

  17. Partial Melting: Remove first melt as it forms Melt Xbulk = 0.60, first liquid = g remove and cool bulk = g ® final plagioclase = i

  18. Two Component Systems Olivine Fo - Fa (Mg2SiO4 - Fe2SiO4) also a solid-solution series Fig. 6-10. Isobaric T-X phase diagram at atmospheric pressure After Bowen and Shairer (1932), Amer. J. Sci. 5th Ser., 24, 177-213.

  19. 2-C Eutectic Systems Example: Diopside - Anorthite No solid solution Fig. 6-11. Isobaric T-X phase diagram at atmospheric pressure. After Bowen (1915), Amer. J. Sci. 40, 161-185.

  20. 1. A bulk composition of X cools to the liquidus, at which point An crystallizes. 2. Continued crystallization of An causes liquid composition to move toward Di. 3. When T=1274°C, liquid has moved to eutectic; Di begins to crystallize. No change in temperature or composition of any of the 3 phases is permitted until the liquid has completely crystallized. 4. At temperatures below 1274°C, only crystals of An and Di are present. X

  21. C = 3: Ternary Systems:Example 1: Ternary EutecticDi - An - Fo Anorthite Note three binary eutectics No solid solution Ternary eutectic = M M T Forsterite Diopside

  22. Crystallization Behavior of Melts 1. Cooling melts crystallize from a liquid to a solid over a range of temperatures (and pressures) 2. Several minerals crystallize over this T range, and the number of minerals increases as T decreases 3. The minerals that form do so sequentially, with considerable overlap 4. Minerals that involve solid solution change composition as cooling progresses 5. The melt composition also changes during crystallization 6. The minerals that crystallize (as well as the sequence) depend on T and X of the melt 7. Pressure can affect the types of minerals that form and the sequence 8. The nature and pressure of the volatiles can also affect the minerals and their sequence

More Related