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Diversification 2

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

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Diversification 2

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  1. Diversification 2

  2. Today • Updates: • Lab progress? • Topics: • Evolving melt compositions: • Magma mixing • Assimilation

  3. Magmatic Differentiation

  4. Stages in ascent • Eruption • (Fragmentation) • Vesiculation • Renewed ascent • Storage • mixing • assimilation • crystallization • Buoyant ascent • Partial melting

  5. Processes during storage in magma chambers

  6. = + Magma Mixing

  7. Magma Mixing 15 10 5 0 45 50 55 60 65 70 75 SiO End-members 80%

  8. 22 10 Al O MgO 2 3 17 5 0 12 15 10 FeO* 10 CaO 5 5 0 0 4 6 3 Na O 2 K O 4 2 2 2 1 0 0 45 50 55 60 65 70 75 45 50 55 60 65 70 75 SiO SiO 2 2 Mixing vs fractionation

  9. Mixing vs mingling

  10. 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

  11. A B Magma Mixing/Mingling

  12. Assimilation

  13. Assimilation-diffusion http://iramis.cea.fr/Images/astImg/308_2.jpg

  14. Assimilation-xenoliths

  15. Zone melting Melt Crystallize

  16. Detecting and assessing assimilation Figure 9-13. After Wilson (1989). Igneous Petrogenesis. Unwin Hyman/Kluwer.

  17. Combinations

  18. Compositional effects of magma chamber processes

  19. 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

  20. 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

  21. 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

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