L10 Ch07 TernaryPhaseEqla

L10 Ch07 TernaryPhaseEqla - Proper Usage Most of the...

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Proper Usage Most of the graphics in these slides, used to illustrate lectures in GEO 426P, are teaching aids provided by John Winter, the author of An Introduction to Igneous and Metamorphic Petrology , and modified by me to suit our purposes. You may download these slides to review on- screen, and may print out a single copy for study, but it would be inappropriate to further disseminate them or the images they contain.
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Phase Equilibrium in Three-Component Systems
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Diopside Anorthite Ternary Systems Example: Ternary Eutectic Di - An - Fo T Three binary eutectics Three binary eutectics No solid solution No solid solution Ternary eutectic = M Forsterite
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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) , Basalts and Phase Diagrams. Krieger Publishers. , Basalts and Phase Diagrams. Krieger Publishers. P = 0.1 MPa Cotectic curves
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Crystallization Path for Bulk Composition a
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At 1700 °C, forsterite forms, because our bulk composition falls in the "Fo + Liq" field, atop the 1700 °C contour. Initial crystallization of Fo
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During cooling to ~1350 °C, pure Fo continually crystallizes; this causes liquid composition to move directly away from Fo corner. Reaction is: Liq 1 –> Liq 2 + Fo "Liquid line of descent" is a –> b . Continued crystallization of Fo How do we know it's 1350 °C at which things change?
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Proportions of Liq & Fo are given by lever rule At 1500 °C, apply …to get 55% liq + 45% Fo.
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With further cooling, crystallization of Fo continues until liquid composition reaches point b at~1350 °C. Arrival at cotectic
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1400 1300 1500 1274 1270 1392 Diopside Di + Liq M b c Fo + Liq 1387 "Bulk solid extract" (with composition "c") given by tangent to cotectic New continuous reaction as liquid begins to follow cotectic: Liq 1 Liq 2 + Fo + Di Ratio of Di/Fo in bulk solid extract given by lever rule Crystallization along cotectic
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L10 Ch07 TernaryPhaseEqla - Proper Usage Most of the...

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