1. What happens after a supervolcano erupts and a caldera collapses ?

2. 1. Resurgent doming 2. Styles of volcanic activity 3. Magma compositions

3. Resurgence, T / D = 1 Acocella et al 2001 Principal high- angle reverse fault Normal fault Intrusion of silicone analogue magma here, due to (a) decrease in shear stength in this weak zone (see also Mathieu et al 2008) and (b) dilatation during uplift

4. Resurgence, T / D = 0.4 Acocella et al 2001 Extrusion and “eruption” of silicone magma Development of radial fractures at these shallow-level, near- surface conditions Central crestal depression due to apical tensile stresses

5. Collapse followed by resurgence Acocella et al 2001 Normal faults developed during subsidence re-used as reverse faults during resurgence Reverse faults developed during subsidence re-used as normal faults during resurgence IN ALL CASES, FAULTS NUCLEATE FROM THE BOTTOM OF THE SANDPACK ASYMMETRY: MOST UPLIFTED PART COINCIDES WITH MOST SUBSIDED PART OF CALDERA

6. Faulting during collapse and resurgence Acocella et al 2001

7. Acocella 2007, Earth-Sci Rev Rabaul Pinatubo Mt St Helens Interesting seismicity patterns from a caldera viewpoint

8. Saunders 2001 Rabaul caldera Maximum uplift

9. Saunders 2001; seismicity from Jones and Stewart 1997

10. Saunders’ model of ring fracture intrusion to cause central uplift Saunders 2001

11. Saunders’ model for Rabaul Saunders 2001

12. Dykes, cups, saucers, and sills: some ideas from Mathieu et al 2008 Nature of host material is key: is it strong, highly lithified material (e.g., granite, gneiss), or is it weak granular-like material (e.g., breccias, fault zones, pyroclastics, etc.) Does magma intrusion induce (a) hydraulic fracturing in strong country rock, (b) self-induced shear faulting in weak country rock, or (c) both processes? Should country rock be modeled using gelatin (strong) or granular material (weak) ? In Mathieu et al’s experiments, note the highly irregular and lobate nature of the intrusions, as well as the preponderance of dyke branching

13. Mathieu et al 2008 Intrusion into developing reverse faults

14. Mathieu et al 2008 Low-viscosity analogue magma High-viscosity analogue magma Branching dyke Apical graben Developing reverse fault Dome diameter > sill diameter…and note that highest viscosities produced deepest cup-shaped intrusions in the experiments Magma intrusion into weak zone

15. 1. Resurgent doming 2. Styles of volcanic activity 3. Magma compositions

16. Valles – circular moat rhyolite pattern

17. Yellowstone geology

18. Yellowstone – vents of post-caldera lavas follow regional structural grain, not a ring fault Christiansen 2001

19. Long Valley resurgent dome Note the strong regional structural grain running through the caldera Note this strong grain particularly for vents on the resurgent dome Also evident for “moat” rhyolites which may not be moat rhyolites at all Note the strong N-S vent alignment from Mammoth Mountain north out the caldera And note the unusual arcuate pattern of Mono Craters vents Hildreth 2004

21. 1. Resurgent doming 2. Styles of volcanic activity 3. Magma compositions

22. Some important observations and comments Lavas and pyroclastics erupted immediately after collapse tend to be among the most “primitive” silicic products of the entire caldera cycle. What is the significance of this observation ? Are the eruptions simply tapping the bottom-most dregs of the chamber ? Or does the primitive material signify influx of new magma from deeper crustal levels ? If so, when does this influx occur? Before, during, or after the supervolcanic eruption? All of the above ? And what can we say about eruption triggers in this regard ?

23. Valles caldera – Redondo Rhyolite is the most primitive rhyolite

24. Yellowstone – Upper Basin Member rhyolites most primitive

25. Long Valley – Dome 7403 may be immediately post-caldera and is a hornblende-bearing dacite erupted subaqueously Hildreth 2004

26. Long Valley geochemistry Hildreth 2004

27. Ossipee ring complex

28. Textural variation from inclusion mingling in the syenite ring dyke Anorthoclase Diffuse inclusion Crystal transfer Discrete inclusions Orthoclase Anorthoclase-rich patches, evidence of old inclusion 0 5cm 0 0 0

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