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Hotspots, Plumes and Mass
Extinctions
Is Hawaii more than a great vacation spot?
How does life respond to geologic catastrophes?
Plate Tectonics - Distribution of
Volcanic and Earthquake Activity
The Earth’s surface is broken into plates
Wilson Cycle
(ocean basin fm)
Examples:
1. East African Rifts
2. Red Sea
3. Atlantic Ocean
4. Pacific Ocean
5. Mediterranean Sea
6. Himalayas, Tibet
1
2
3
4
5
6
Hawaii
Easter
Galapagos
Samoa
The Hawaiian Hotspot
Volcanoes
to atolls
(Darwin)
Tahiti -- shield volcano
Moorea -- fringing reef
Raiatea - barrier reef
Bora Bora -- lagoon
Maupiti -- the oldest volcano
next stage is the coral atoll
French Polynesia from space
atoll
barrier reef
fringing reef
Pacific Hotspot Volcanic Chains
Questions:
• Where do Hotspots come from?
• How do Hotspots start?
• How long do they last?
Indian Ocean
• Hotspot tracks
and 3 spreading
ridges
• A complete record
of hotspot activity
JOIDES Resolution drillship
Reunion hotspot track,
central Indian Ocean
“flood” basalts in western India
>300 lava flows, each 1000 km3
Western
India
• An accumulation
of lava flows 5 km
thick!
• Occurred at the
same time as the
extinction of the
dinosaurs
Mass Extinction
(K-T Boundary)
• What killed the
Dinosaurs?
• 65 million yr ago
• A meteorite, or
volcanic activity,
or BOTH?
Impact Site: Yucatan Peninsula
Volcanic catastrophes and Mass
Extinctions
Greenland
• Birth of the
Iceland hotspot
• Next came the
opening of the
North Atlantic
Ocean basin
Global Distribution of large,
rapidly-erupted volcanic events
red = hotspot-related
volcanism since 250
Ma
Flood basalts, India
Columbia River Basin
Flood Basalts with
source at Yellowstone
Large Igneous Provinces are:
• BIG!!
• NOT explained by Plate Tectonics
• Initial Plume and Hotspot Activity
Mantle Plumes
•
•
•
•
Part of the circulation in the Mantle
Driven by temperature differences
Hot and cold => density differences
Gravity Rules!
http://www.youtube.com/watch?v=f37Gf6IVj6o&feature=related
Mantle convection the driving force for plate tectonics
What causes the warmer material to rise?
Mantle Plumes
Mantle convection and hotspot formation
Cross-sections of the Earth
Red = hot upwelling from core-mantle
boundary
Cold lithosphere sinks, hot plumes rise.
Cartoon Schematic
Blue = cold downwelling
Computer Model
Which is not a hotspot?
Yellowstone
Iceland
Hawaii
Mt. St. Helens
Degassing Magma
• Gases include CO2,
SO2, Cl, F that make
“acid rain”
• Shuts down
photosynthesis
Laki, Iceland (1783) -- the year without
a summer
Laki, Iceland (1783) -- the year without
a summer
Submarine: Hydrothermal Exchange –
Release of Metals
Ocean Anoxic Events
productivity or preservation?
Marine
sedimentary
layers exposed
in Italy
Hydrothermal Plumes from LIPs
Effects of Submarine Plateaus
• Release of “reduced” metals uses up
oxygen in the oceans
• Trace metals are “nutrients”, so
promote rapid growth of plankton
• Sinking organic matter also uses up
oxygen in the oceans
• Extinctions of “benthic” marine
organisms
Two Styles of Mantle Convection
Evolution of Life
• “Punctuated” by
rapid change
events
• Where there is
chaos there is
opportunity
• Extinctions lead to
new ecosystems