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."

Hotspots/Plumes

The Classic Hotspot:Hawaiian-Emperor chain

Age of volcano increases linearly away from current hot spot!

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

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.

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

Canary Islands

Yellowstone Hotspot

Iceland Hotspot: On the mid-Atlantic ridge

Possible or proposed hotspots

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

Plate driving forces.

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

Initial plume causes flood basalt (or large igneous province) after which it turns into a hot spot.

From the core-mantle boundary?

Rayleigh-Taylor type instabilities

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

D. Zhao

Gondwana Research (2007)

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Nature 2007

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Anyway, if you’re interested….