Earth Sciences 240A - Lecture 25 - Flood Basalts I
Introduction
Eruption global effects
‘Dust’ to atmosphere (colder,
darker)
Aerosols to atmosphere (colder,
darker)
CO2 to atmosphere (warmer
greenhouse)
Other gases (?)
(maybe poisonous?)
Scale of effects
Small:
1 year cooler
climate (no mass extinctions)
Large:
Vast atmospheric
effects (no mass extinctions)
Flood basalts?
Flood Basalts
Fed by ‘superplumes’
Deposits
Flood basalts: Continental/oceanic
flood/plateau basalts
Large igneous
provinces
‘Coincidental’
deposits?
Siberian Traps (245 mya)
Large Igneous
Provinces
More primitive composition than
MORB
Lower mantle component
Mantle plume only possible source
Continental deposits: common features
Only basalt
Mainly subaerial
Very short eruption time span
Attempted Correlations
Continental Rifting
but not: Columbia River Plateau
Siberian Traps
(maybe)
Mass Extinction
Events
~OK for
The only historical F.B. event
14.7 km3 basalt
Abnormally high (?) content gases
F, SO2 aerosols
Lowered global T by 1oC for 1 year
Was Laki typical of
Flood Basalts?
Columbia River
Plateau
~175,000 km3 deposit
~ 16 mya
Early deposit from the Yellowstone
Plume
Earliest: Imnaha and Grand Ronde Basalt
Very similar to Hawaiian basalts
Second: Picture Gorge Basalt
Less volume; strong lithosphere
component
Third:
Smallest, compositionally very
complex
The Roza flow
Traveled 300 km from vent
Flow of 30 m high, 100 km wide,
traveling at 5 km/h for 1 week
The
Traveled 600 km from vent
Longest flow on Earth
Lakes of magma created that took years to tens of years to
cool
A
weird hypothesis?
Large asteroid impacted
Lithosphere fractured
Reduced P produced huge partial
melting of asthenosphere
Flood basalts produced
Crater covered
Problem
Impact cannot
create a plume
Plume evidence
obvious
CRB, SRB,
Comparative eruption
volumes
Subduction volcanoes
Resurgent caldera
Flood Basalt
Laki: 14.7 km3
Columbia River Plateau: 175,000 km3
No mass extinction with any!
Next
Siberian (245 mya)