EARTH232 Lecture Notes - Lecture 10: Plagioclase, Diopside, Intermediate Composition

• School: University of Waterloo
• Department: Earth Sciences
• Course: EARTH232
• Professor: Shaun Frape

Document Summary

Coloured lines are tie lines joining the cotectic to the base of the triangle: ex. Initial plagioclase composition of an80 connect to point b using red line. Use to tell you the composoition of plagioclase. Hit liquidus surface at 1410c start to crystallize plagioclase: first crystals. From x to y, just crystallizing plagioclase which is becoming more na-rich as t decreases. At point y, hit the cotectic liquid1 diopside + plagioclase + liquid 2. Grow and join when temperatures are high enough. Greater vibrational energy of the crystal lattice (structure) at higher temperatures (more kinetic energy) This has the effect of opening up the crystal structure, thus allowing for a greater extent of solid solution. With slow cooling, pyroxenes of intermediate composition (that formed at high t) increasingly becoming unstable: problem of accommodating larger ions in the crystal structure (ca 2+) At low t, immiscibility gap covers entire middle of diagram.