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 5 10 15 45 50 55 60 65 70 75
SiO
End-members
80%

8. Mixing vs fractionation12 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

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. Magma Mixing/MinglingB
Magma Mixing/Mingling

12. Assimilation

13. Assimilation-diffusion

14. Assimilation-xenoliths

15. Zone melting
Melt
Crystallize

16. Detecting and assessing assimilation
Figure 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