Diversification 2
Today Updates: Lab progress? Topics: Evolving melt compositions: Magma mixing Assimilation
Magmatic Differentiation
Stages in ascent Eruption (Fragmentation) Vesiculation Renewed ascent Storage mixing assimilation crystallization Buoyant ascent Partial melting
Processes during storage in magma chambers
Magma Mixing + =
Magma Mixing 5 10 15 45 50 55 60 65 70 75 SiO End-members 80%
Mixing vs fractionation 12 17 22 Al 2 O 3 5 10 MgO FeO* 4 6 Na 15 CaO 45 50 55 60 65 70 75 1 K SiO
Mixing vs mingling
Comingled basalt-Rhyolite Mt. McLoughlin, Oregon Figure 11-8 From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall Basalt pillows accumulating at the bottom of a in granitic magma chamber, Vinalhaven Island, Maine
Magma Mixing/Mingling B Magma Mixing/Mingling
Assimilation
Assimilation-diffusion http://iramis.cea.fr/Images/astImg/308_2.jpg
Assimilation-xenoliths
Zone melting Melt Crystallize
Detecting and assessing assimilation Figure 9-13. After Wilson (1989). Igneous Petrogenesis. Unwin Hyman/Kluwer.
Combinations
Compositional effects of magma chamber processes
Renewed ascent Eruption (Fragmentation) Vesiculation Renewed ascent Storage mixing assimilation crystallization Buoyant ascent Partial melting Common evidence for mixing: Eruptions (renewed ascent) driven by new magma entering magma chamber
At or near surface Eruption (Fragmentation) Vesiculation Renewed ascent Storage mixing assimilation crystallization Buoyant ascent Partial melting Vesicles show gasses unmix: volatile phases escape from melt Does not affect major or (most) trace elements
Possible Origin Eruptions are triggered by mixing events. crust Mixing in magma chambers generates andesite and dacite Partial melting of “crust” -> rhyolitic magma mantle Storage -> crystal fractionation: basaltic andesite Partial melting in mantle yields basaltic magma