Diversification 2

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Topics:Evolving melt compositions:Magma mixingAssimilation

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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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