The impact of the Siberian traps
through CO2 release is well established and appears to be the largest such
event impacting on ancient climates.
A smaller comparable is Hawaii
I suppose that the good news is
that these flows work themselves out in geological time allowing life to
normally get out of the way. That is not
so true for the super volcanoes that flood the atmosphere with ash that is
picked up globally. Even those have
turned out to be survivable.
The take home is that massive geologic
CO2 release and large asteroids are the two prime culprits for mass extinctions
that do not entail the rejoining of two continents or mankind’s own folly.
Fortunately both are rare enough
to effectively show up once each in enough strength.
The cause of Earth's largest environmental catastrophe
by Staff Writers
Siberian Traps near lake
Lama
The eruption of giant masses of magma in Siberia
250 million years ago led to the Permo-Triassic mass extinction when more than
90 % of all species becameextinct.
An international team including geodynamic modelers from the GFZ German
Research Centre for Geosciences together with geochemists from the J. Fourier
University of Grenoble, the Max Plank Institute in Mainz, and Vernadsky-,
Schmidt- and Sobolev-Institutes of the Russian Academy of Sciences report on a
new idea with respect to the origin of the Siberian eruptions and their
relation to the mass extinction in the recent issue of Nature (15.09.2011, vol.
477, p. 312-316).
Large Igneous Provinces (LIPs) are huge accumulations of volcanic rock
at the Earth's surface.
Within short geological time spans of often less than one million years their
eruptions cover areas of several hundred thousand square kilometres with up to
4 kilometers thick lava flows. The Siberian Traps are considered the largest
continental LIP.
A widely accepted idea is that LIPs originate through melting within
thermal mantle plumes, a term applied to giant mushroom-shaped volumes of
plastic mantle material that rise from the base of the mantle to the
lithosphere, the Earth's rigid outer shell.
The high buoyancy of purely thermal mantle plumes, however, should
cause kilometer-scale uplift of the lithosphere above the plume head, but such
uplift is not always present. Moreover, estimates of magmatic degassing from
many LIPs are considered insufficient to trigger climatic crises. The team of scientists presents
a numerical model and new geochemical data with which unresolved questions can
now be answered.
They suggest that the Siberian mantle plume contained a large fraction
of about 15 percent of recycled oceanic crust; i.e. the crust that had long
before been subducted into the deep mantle and then, through the hot mantle
plume, brought back to the Earth's lithosphere.
This recycled oceanic crust was present in the plume as eclogite, a
very dense rock which made the hot mantle plume less buoyant. For this reason
the impingement of the plume caused negligible uplift of the lithosphere.
The recycled crustal material melts at much lower temperatures than the
normal mantle material peridotite, and therefore the plume generated
exceptionally large amounts of magmas and was able to destroy the thick
Siberian lithosphere thermally, chemically and mechanically during a very short
period of only a few hundred thousand years.
During this process, the recycled crust, being exceptionally rich in
volatiles such as CO2 and halogens, degassed and liberated gases that passed
through the Earth crust into the atmosphere to trigger the mass extinction. The
model predicts that the mass extinction should have occurred before the main
magmatic eruptions. Though based on sparse available data, this prediction seems
to be valid for many LIPs.
Stephan V. Sobolev, Alexander V. Sobolev, Dmitry V. Kuzmin et al.,
Linking mantle plumes, large igneous provinces and environmental catastrophes,
Nature, vol. 477, p. 312-316, 2011
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