Diversification 2
Updates:Lab progress?
Topics:Evolving melt compositions:Magma mixingAssimilation
Today
Magmatic Differentiation
Stages in ascentEruption(Fragmentation)VesiculationRenewed ascent StoragemixingassimilationcrystallizationBuoyant ascentPartial melting
Processes during storage in magma chambers
Magma Mixing
End-membersMagma Mixing80%
Mixing vs fractionation
Mixing vs mingling
Basalt pillows accumulating at the bottom of a in granitic magma chamber, Vinalhaven Island, MaineComingled basalt-Rhyolite Mt. McLoughlin, OregonFigure 11-8 From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall
ABMagma Mixing/Mingling
Assimilation
Assimilation-diffusionhttp://iramis.cea.fr/Images/astImg/308_2.jpg
Assimilation-xenoliths
Zone meltingCrystallizeMelt
Detecting and assessing assimilationFigure 9-13. After Wilson (1989). Igneous Petrogenesis. Unwin Hyman/Kluwer.
Combinations
Compositional effects of magma chamber processes
Renewed ascentEruption(Fragmentation)VesiculationRenewed ascent StoragemixingassimilationcrystallizationBuoyant ascentPartial meltingCommon evidence for mixing:Eruptions (renewed ascent) driven by new magma entering magma chamber
At or near surfaceEruption(Fragmentation)VesiculationRenewed ascent StoragemixingassimilationcrystallizationBuoyant ascentPartial meltingVesicles show gasses unmix: volatile phases escape from meltDoes not affect major or (most) trace elements
Possible OrigincrustmantlePartial melting in mantle yields basaltic magmaPartial melting of crust -> rhyolitic magmaMixing in magma chambers generates andesite and daciteEruptions are triggered by mixing events.Storage -> crystal fractionation: basaltic andesite
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