Hotspots/Plumes - PowerPoint PPT Presentation

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Hotspots/Plumes

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  1. Hotspots/Plumes p. 513, Bates R.L. and J.A. Jackson (eds), 1987, Glossary of Geology, 3rd ed.: published by the American Geological Institute, Alexandria, VA, 788 p: “ plume: (a) a localized body of volcanic rock rising into the crust from the mantle and thought to be the causal mechanism of a hot spot.” “ hot spot (p. 314): a volcanic center, 100 to 200 km across and persistent for at least a few tens of millions of years, that is thought to be the surface expression of a persistent rising plume of hot mantle material. Hot spots are not linked with arcs, and may or may not be associated with oceanic ridges.” Godfrey Fitton, October 2004 "A plume is an upwelling of hotter stuff from depth that carries a distinctive chemical and isotopic signature."

  2. The Classic Hotspot: Hawaiian-Emperor chain

  3. Age of volcano increases linearly away from current hot spot!

  4. Consistent with the idea that hotspot remains fixed relative to plate motion.

  5. After volcano moves away from the hotspot (fixed in the mantle), it sinks as the seafloor ages, and turns into an “atoll”. Atoll: Ring shaped coral reef enclosing a shallow lagoon.

  6. Bikini Atoll (Marshall Islands) in 1954 was the site of the largest atomic bomb test (Bravo) by the US.

  7. Canary Islands

  8. Yellowstone Hotspot

  9. Iceland Hotspot: On the mid-Atlantic ridge

  10. Possible or proposed hotspots

  11. Plate velocities assuming hotspots are fixed. “Hotspot reference frame”

  12. Plate driving forces.

  13. Global distribution of “large igneous provinces” (LIPS). Large outpourings of lava. Maybe “super-plumes”. Some people argue that they result from impacts

  14. From the core-mantle boundary? Initial plume causes flood basalt (or large igneous province) after which it turns into a hot spot.

  15. Rayleigh-Taylor type instabilities

  16. Seismic tomography: sample the same place with seismic waves from different direction allows you to work out 3-D shape of seismic anomalies. Earthquake 1 Earthquake 2

  17. D. Zhao Gondwana Research (2007)

  18. Definite slow (= hot) region below Iceland. Doesn’t seem to go through into lower mantle.

  19. Nature 2007

  20. Anyway, if you’re interested….