Transcript lecture9

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."
The Classic
Hotspot:
HawaiianEmperor 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
From the core-mantle boundary?
Initial plume causes flood basalt (or large igneous
province) after which it turns into a hot spot.
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 a
TIFF (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 a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Nature 2007
Anyway, if you’re interested….
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.