![]() ![]() ![]() Textures: start with An-rich basaltic melt: first crystals are An - plenty of room & time to grow=> large crystals = phenocrysts. Most igneous rocks have compositions near eutectics => there is just enough thermal energy in Earth to melt the lowest-T compositions: basalts ~ Di-An eutectic granites ~Ab-Q eutectic (system is similar to Di-An) What does this phase diagram tell us about igneous rocks? Perfect fractional crystallization and equilibrium crystallization are extremes. Liquid becomes progressively depleted in phase that is crystallizing and enriched in phase that remains in the melt. Liquid composition becomes new starting composition. ![]() Def: crystals are removed from magma as they form (sink or float). This only applies if crystals remain in contact with liquid, and compositions continually change => equilibrium crystallization.ī.ĝi-An system: fractional crystallization Trace this procedure in reverse for melting. Lever Rule: starting composition X = 18%An and 82% Di: ab/ac = % liquid at temperature T bc/ac = % Di crystals at T At c, liquid is 38% An and 62% Di (thus % liquid at c = 18/38 = 47% / % Di at T = 20/38 = 52%) at eutectic, 42% An, 58% Di. Binary System with 2 phases and no solid solutionĪ.ĝiopside-Anorthite system: equilibrium melting Pyroxene system: MgFeSi2O6-Ca(Mg,Fe)Si2O6 Solid solution with a minimus: alkali feldspars NaAlSi3O8-KAlSi3O8 (Ab-Ksp) ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |