Phase EquilibriumMakaopuhi Lava LakeSlide 3Slide 4Slide 5PowerPoint PresentationSlide 7One Component SystemsSlide 9Two Component SystemsSlide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Phase EquilibriumPhase EquilibriumMakaopuhi Lava LakeMakaopuhi Lava LakeMagma samples recovered from various Magma samples recovered from various depths beneath solid crustdepths beneath solid crustFrom Wright and Okamura, (1977) USGS Prof. Paper, 1004.Temperature of sample vs. Percent GlassTemperature of sample vs. Percent Glass10090706050403020100Percent Glass900950100010501100115012001250Temperature oc 80Makaopuhi Lava LakeMakaopuhi Lava LakeFig. 6-1. From Wright and Okamura, (1977) USGS Prof. Paper, 1004.Minerals that form during crystallizationMinerals that form during crystallization1250120011501100105010009500 0 0010 10 20 10 102030 40 3050 40 50LiquidusMeltCrustSolidusOlivine Clinopyroxene Plagioclase OpaqueTemperature oC olivine decreases below 1175oCMakaopuhi Lava LakeMakaopuhi Lava LakeFig. 6-2. From Wright and Okamura, (1977) USGS Prof. Paper, 1004.Mineral composition during crystallizationMineral composition during crystallization1009080706050.7.8.9 .9.8.7 .6807060AnMg / (Mg + Fe)Weight % GlassOlivine Augite PlagioclaseMg / (Mg + Fe)Makaopuhi Lava LakeMakaopuhi Lava LakeFig. 6-3. From Wright and Okamura, (1977) USGS Prof. Paper, 1004.Crystallization Behavior of MeltsCrystallization Behavior of Melts1. Cooling melts crystallize from a liquid to a solid over a range of 1. Cooling melts crystallize from a liquid to a solid over a range of temperatures (and pressures)temperatures (and pressures)2. Several minerals crystallize over this T range, and the number of 2. Several minerals crystallize over this T range, and the number of minerals increases as T decreasesminerals increases as T decreases3. The minerals that form do so sequentially, with consideral overlap3. The minerals that form do so sequentially, with consideral overlap4. Minerals that involve solid solution change composition as cooling 4. Minerals that involve solid solution change composition as cooling progressesprogresses5. The melt composition also changes during crystallization5. The melt composition also changes during crystallization6. The minerals that crystallize (as well as the sequence) depend on T 6. The minerals that crystallize (as well as the sequence) depend on T and X of the meltand X of the melt7. Pressure can affect the types of minerals that form and the 7. Pressure can affect the types of minerals that form and the sequencesequence8. The nature and pressure of the volatiles can also affect the minerals 8. The nature and pressure of the volatiles can also affect the minerals and their sequenceand their sequenceThe Phase RuleThe Phase RuleF = C - F = C -  + 2 + 2F = # degrees of freedomF = # degrees of freedomThe number of intensive parameters that must be specified in The number of intensive parameters that must be specified in order to completely determine the system order to completely determine the system  = # of phases= # of phasesPhases are mechanically separable constituentsPhases are mechanically separable constituentsC = minimum # of components C = minimum # of components Chemical constituents that must be specified in order to Chemical constituents that must be specified in order to define all phases define all phases2 = 2 intensive parameters2 = 2 intensive parametersUsually temperature and pressure for geologistsUsually temperature and pressure for geologistsOneOneComponent Component SystemsSystemsSiOSiO22Fig. 6-6. After Swamy and Saxena (1994), J. Geophys. Res., 99, 11,787-11,794. AGUFig. 6-7. After Bridgman (1911) Proc. Amer. Acad. Arts and Sci., 5, 441-513; (1936) J. Chem. Phys., 3, 597-605; (1937) J. Chem. Phys., 5, 964-966. OneOneComponent Component SystemsSystemsHH22OOTwo Component SystemsTwo Component SystemsPlagioclasePlagioclase Ab (NaAlSiAb (NaAlSi33OO8 8 ) - An (CaAl) - An (CaAl22SiSi22OO88))Systems with Systems with Complete Solid SolutionComplete Solid SolutionFig. 6-8. Isobaric T-X phase diagram at atmospheric pressure. After Bowen (1913) Amer. J. Sci., 35, 577-599.Bulk composition Bulk composition aa = An = An6060 = 60 g An + 40 g Ab= 60 g An + 40 g AbXXAnAn = 60/(60+40) = 0.60 = 60/(60+40) = 0.60A A continuous reactioncontinuous reaction of the type: of the type:liquidliquidBB + solid + solidCC = liquid = liquidDD + solid + solidFFfdededeefefThe lever principle:The lever principle:Amount of liquidAmount of liquid Amount of solidAmount of soliddedeefef==where where dd = the = the liquidliquid composition, composition, ff = the = the solidsolid composition composition and and ee = the = the bulkbulk composition compositionliquidusliquidussolidussolidusNote the following:Note the following:1.1. The melt crystallized over a T range of 135 The melt crystallized over a T range of 135ooC *C *4.4. The composition of the liquid changed from The composition of the liquid changed from bb to to gg5.5. The composition of the solid changed from The composition of the solid changed from cc to to hhNumbers referNumbers referto the “behaviorto the “behaviorof melts” observationsof melts” observations(several slides back)(several slides back)** The actual temperatures ** The actual temperatures and the range depend on the and the range depend on the bulk composition **bulk composition **Equilibrium Equilibrium meltingmelting is exactly the opposite is exactly the opposite Heat AnHeat An6060 and the first melt is and the first melt is g at Ang at An20 20 and 1340and 1340ooCC Continue heating: both melt and plagioclase change XContinue heating: both melt and plagioclase change X Last plagioclase to melt is Last plagioclase to melt is c (Anc (An8787) at 1475) at 1475ooCCFractional crystallization:Fractional crystallization: Remove crystals as they form so they can’t Remove crystals as they form so they can’t undergo a continuous reaction with the meltundergo a continuous reaction with the meltAt any T, At any T, XXbulkbulk = X = Xliqliq due to the removal of the crystalsdue to the removal of the crystalsPartial Melting:Partial Melting:Remove first meltRemove first melt as it forms as it formsMelt XMelt Xbulkbulk = 0.60, first liquid = = 0.60, first liquid = ggremove and cool bulk = g remove and cool bulk = g  final plagioclase = final plagioclase = iiNote the difference