Olivine and Phase Diagrams PDF

Olivine (and solid solution phase diagrams!!!!) Olivine § Occurrence: § Primary igneous mineral in mafic and ultramafic rocks like dunite, gabbro, peridotite, and basalt. § Ca rich varieties occur in metamorphic rocks http://imagestour.blogspot.ca/2012/04/green-sand-beaches...

Olivine (and solid solution phase diagrams!!!!) Olivine § Occurrence: § Primary igneous mineral in mafic and ultramafic rocks like dunite, gabbro, peridotite, and basalt. § Ca rich varieties occur in metamorphic rocks http://imagestour.blogspot.ca/2012/04/green-sand-beaches-in-papakolea-hawaii.html Structural formula Olivine: Composition § Ca-Fe-Mg ternary diagram § Complete simple (cationic) substitution between: § CaMg – CaFe end members § Mg – Fe end members § Limited simple between: § Mg-MgCa end members § Fe-FeCa end members § Mg:Fe ratio controls many physical properties including density, crystallization temp, T. Edward, 2011 etc. Olivine: Structure § Independent (or Isolated) tetrahedral silicates – Also called Island silicates, or nesosilicates § Crystal viewer – Number of bridging O for silicate tetrahedrons? § Zilch, nada, zero, none – Linked cations: § A and B spots, 2 different spots in structure Phase Diagrams § Phase diagrams provide a model for what happens in natural environments § Based on laboratory studies § Useful for: 1. Predicting and interpreting conditions of the environment minerals formed in. PT 2. Determining what process occurred in that environment magma -liquid -liquid -vapor cooling -plagioclase (solid phase) -olivine (solid phase) 7th (?) Phase Diagrams Variables ? Phases: § The yellow and green fields are one phase fields § The white field is a two phase field § Liquidus: § For a given temperature, a line which specifies the composition of liquid that co- exists with a solid § For any given composition, it’s the temperature at which crystals first form in a cooling magma § Solidus: § For a given temperature, a line which specifies the composition of a solid that co- exsits with a liquid § For any given composition, it’s the lowest temperature at which liquid can exist in a system § Tie-line: § Line that connects co-existing phases at any given temperature § Horizontal line on diagram Notes 1. Final group project assignment is on LEAN § Read it! § Start now! 2. Lab Nov. 19/20 is a Bancroft work session § Work on your map, etc before this lab so you can ask Q’s! § Preliminary report….. Phase Diagrams Variables ? Phases: § The yellow and green fields are one phase fields § The white field is a two phase field § Liquidus: § For a given temperature, a line which specifies the composition of liquid that co- exists with a solid § For any given composition, it’s the temperature at which crystals first form in a cooling magma § Solidus: § For a given temperature, a line which specifies the composition of a solid that co- exsits with a liquid § For any given composition, it’s the lowest temperature at which liquid can exist in a system § Tie-line: § Line that connects co-existing phases at any given temperature § Horizontal line on diagram Phase Diagrams – important concepts 1. Equilibrium crystallization (EX): § CLOSED system, crystals (solids) that are formed stay in contact with the melt and have an opportunity to continually equilibrate with it. § What you start with is what you end up with § WWPI=WWGO (what you put in=what you get out) 2. Fractional (non or disequilibrium) crystallization (FX): § OPEN system, crystals (solids) that are formed stay are extracted and DO NOT stay in contact with the melt and causes non or disequilibrium § What you start with is NOT what you end up with § WWPI≠WWGO (what you put in ≠ what you get out) § How? 1. Crystal settling § Density differences in a magma chamber § Basaltic magma = 2.7 g/cm3 § Olivine/Pyroxene = 3.3 g/cm3 § Leucite = 2.5 g/cm3 2. Filter pressing 3. Crystal zoning 4. Volcanoes (!) 5. ……etc….. Example 1 - Equilibrium crystallization X starting liquid = Fa40 Start system @1800 ºC 1. Track liquid and solid evolution with lines 2. T first crystals? 3. Composition of first crystal? a) Compo of liquid? 4. @ 1500ºC what is: a) Composition crystals (solid olivine)? b) Composition melt? c) Proportion melt? d) Proportion crystals? 5. T when all solid? 6. Composition of last bit of melt? 7. Composition of final solid? The Lever Rule § Box 8.4 (8.3 in 1st edition) in text § What are the proportions of each phase? § Lever rule gives you the relative proportions of solid (or crystals or minerals) vs. liquid (or melt or magma) at that very instant of temperature § X starting composition of liquid (X bulk) § Is the fulcrum for the lever rule § Need to keep things “balanced” a b Intersection Intersection with solidus with X starting liquid liquidus (X bulk) Example 1 - Equilibrium crystallization – Liquid and solid evolution 1. 1800 °C to 1625°C: § Liquid? Only phase, constant composition, Fa40 § Solid? N/A 2. 1625 °C to 1410°C: § Liquid? Composition evolves along liquidus, becomes more Fe rich, from Fa40 to Fa70 § Solid? Composition evolves along solidus, becomes more Fe rich, from Fa15 to Fa40 3. 1410 °C and below § Liquid? N/A § Solid? Only phase, constant composition, Fa40 Classwork - Equilibrium crystallization X starting liquid = Fa60 Start system @1800 ºC 1. Track liquid and solid evolution with lines 2. T first crystals? 3. Composition of first crystal? a) Compo of liquid? 4. @ 1350ºC what is: a) Composition crystals (solid olivine)? b) Composition melt? c) Proportion melt? d) Proportion crystals? 5. T when all solid? 6. Composition of last bit of melt? 7. Composition of final solid? Classwork - Equilibrium crystallization X starting liquid = Fa60 Start system @1800 ºC 1. Track liquid and solid evolution with lines 2. T first crystals? 3. Composition of first crystal? a) Compo of liquid? 4. @ 1450 what is: a) Composition crystals (solid olivine)? b) Composition melt? c) Proportion melt? d) Proportion crystals? 5. T when all solid? 6. Composition of last bit of melt? 7. Composition of final solid? Phase Diagrams & Fractional Crystallization Phase Diagrams – important concepts 1. Equilibrium crystallization (EX): § CLOSED system, crystals (solids) that are formed stay in contact with the melt and have an opportunity to continually equilibrate with it. § What you start with is what you end up with § WWPI=WWGO (what you put in=what you get out) 2. Fractional (non or disequilibrium) crystallization (FX): § OPEN system, crystals (solids) that are formed stay are extracted and DO NOT stay in contact with the melt and causes non or disequilibrium § What you start with is NOT what you end up with § WWPI≠WWGO (what you put in ≠ what you get out) § How? 1. Crystal settling § Density differences in a magma chamber § Basaltic magma = 2.7 g/cm3 § Olivine/Pyroxene = 3.3 g/cm3 § Leucite = 2.5 g/cm3 2. Filter pressing 3. Crystal zoning 4. Volcanoes (!) 5. ……etc….. Example 2 – Fractional crystallization X starting liquid = Fa40 Start system @1800 ºC § What happens if we allow for crystal settling § continuous removal of what phase? 1. Track liquid and solid evolution with lines 2. T first crystals? 3. Composition of first crystal? § What happens to this crystal? a) Compo of liquid? 4. @ 1500ºC what is: a) Composition crystals (solid olivine)? b) Composition melt? c) Can we apply the lever rule? d) What is happening to these phases? 5. T when all solid? 6. Composition of last bit of melt? 7. Composition of final solid? Example 2 – Fractional crystallization 1. 1800 °C to 1625°C: § Liquid? Only phase, constant composition, Fa40 § Solid? N/A 2. 1625 °C to 1100 °C § Liquid? Composition evolves along liquidus, becomes more Fe rich, from Fa40 to Fa100 § Solid? Leaving system Composition evolves along solidus, becomes more Fe rich, from Fa15 to Fa100 3. 1100 °C and below § Liquid? N/A § Solid? Only phase, constant composition, Fa100 Notes/Reminders § Lab Nov 19/20 – Bancroft Work Period and Map Check § Work on map before hand, think about what your units are, contacts between units, etc § Start working on/thinking about final assignment before hand, so you can ask q’s during work period § Q’s about feedback for Prelim report? Ask during work period, or come see me before hand § Will give a quick intro at the beginning of the about final assignments and expectations for the presentations the next week. § Lab Nov 26/27 – Bancroft Presentations!! § Attendance is mandatory § Midterm Midterm… § Marks on Learn Average/Q § Final mark is “midterm grade with bonus” 7.1, 71.2% § Average is similar to last year 8, 59.4% § Median is better 6.3, 66.3% § Use the booking link on Learn if you want to look 5.2, 73.9 % at your midterm! § Can also try dropping by, Avg=67 % Median=73% but I might be busy Classwork - Fractional crystallization X starting liquid = Fa60 Start system @1800 ºC § What happens if we allow for crystal settling § continuous removal of what phase? 1. Track liquid and solid evolution with lines 2. T first crystals? 3. Composition of first crystal? § What happens to this crystal? a) Compo of liquid? 4. @ 1350ºC what is: a) Composition crystals (solid olivine)? b) Composition melt? c) Can we apply the lever rule? d) What is happening to these phases? 5. T when all solid? 6. Composition of last bit of melt? 7. Composition of final solid? Example 3 – Fractional crystallization X starting liquid = Fa40 Start system @1800 ºC § What happens if we allow for a volcanic eruption @ 1500°C § removal of what phase? 1. Track liquid and solid evolution with lines 2. T first crystals? 3. Composition of first crystal? § What happens to this crystal? a) Compo of liquid? 4. @ 1500ºC what is: a) Composition crystals (solid olivine)? b) Composition melt? c) Can we apply the lever rule? a) What is happening to these phases? 5. T when all solid? 6. Composition of last bit of melt? 7. Composition of final solid? Phase diagram round up § Compare FX and EX – example 1 and 2, look at summary slides EX - Equilibrium Crystallization – FX - Fractional Crystallization – open closed box box (specifically crystal settling) Temp and composition of first solid formed Liquid evolution Temperature at which system is all solid Composition of final solid Phase diagram round up § Compare FX and EX EX - Equilibrium Crystallization – FX - Fractional Crystallization – open closed box box (specifically crystal settling) Temp and composition of Consistent with both FX and EX, because there is nothing to fractionate until we first solid formed start forming a second phase Liquid evolution Constrained by the solid it is co- Not constrained by the co-existing solid existing and reacting with. Can not as the solid is being removed from the evolve further along the liquidus than system and as such no reaction is the composition of the liquid that co- occurring. Evolves all the way to the point exists with the composition of the final on the phase diagram where the liquidus solid required in EX system and solidus intersect Temperature at which Generally higher than FX systems for Generally lower than EX systems for the system is all solid the same starting composition same starting composition Composition of final solid WWPI=WWGO WWPI ≠WWGO Solid is the same composition of the Different than the initial liquid and has the initial liquid same composition of the last liquid that exists in system.