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NSF PR 99-10 - February 17, 1999
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Ancient Volcanic Cataclysms Discovered in the Indian
Ocean
Scientists from the largely National Science Foundation
(NSF) supported Ocean Drilling Program (ODP) have
completed an expedition to one of the most remote
places on Earth, the Kerguelen Plateau. The results
of their expedition will shed new light on how and
when continents formed and broke apart millions of
years ago.
The international team of 45 scientists conducted their
research aboard the world's largest scientific drilling
vessel, the JOIDES Resolution. The drillship departed
Fremantle, Australia, on December 13, 1998, and returned
to Fremantle on February 11, 1999.
Kerguelen Plateau is located in the southern Indian
Ocean, is one-third the size of the United States,
and is described as a large igneous province (LIP).
LIPs are areas where magma wells up from deep beneath
Earth's surface and forms molten rock. The major objectives
of the ODP expedition, explains Bruce Malfait, director
of ODP at NSF, were to determine through drilling
when volcanism was active; how much of the plateau
formed above sea level and how long portions of the
feature remained above sea level; and if continental
fragments form part of the plateau.
Using evidence from fossils as well as terrestrial
plant remains, the scientific team constrained the
time period during which the Kerguelen LIP formed.
They found that the southern Kerguelen Plateau, only
hundreds of kilometers from Antarctica, formed approximately
110 million years ago. To the north, the central Kerguelen
Plateau and the once-contiguous Broken Ridge formed
between 85 and 95 million years ago. In contrast,
the northern Kerguelen Plateau is much younger, having
formed less than 35 million years ago. These results
indicate that several intense episodes of volcanism
formed this large plateau over a long time period,
rather than from a single massive volcanic event.
"We found abundant evidence that much of the Kerguelen
LIP formed above sea level," states co-chief scientist
Mike Coffin of the University of Texas Institute of
Geophysics. "Wood fragments, a seed, spores and pollen
recovered in 90-million-year- old sediment from the
central Kerguelen Plateau, just southeast of Heard
Island, unambiguously indicates that this region was
above sea level."
A spectacular result was finding uniquely continental
rocks in a conglomerate that was probably deposited
in a river on Elan Bank near the central and southern
Kerguelen Plateau, explains co chief scientist Fred
Frey of the Massachusetts Institute of Technology.
"Knowing how pieces of an ancient continent were incorporated
into the oceanic environment of Elan Bank will have
significant impact on our understanding of the approximately
130- million-year-old break-up of Australia, India
and Antarctica."
A surprising finding at three drill sites was evidence
for large-scale explosive volcanism, apparently a
common phenomenon as volcanic construction of the
plateau came to an end. Explosive volcanism can perturb
the earth-atmosphere system significantly by injecting
material into the stratosphere where, depending on
the magnitude and altitude of the material, it may
persist for several years. This can cause considerable
short- term environmental effects, such as those resulting
from the recent eruption of Mount Pinatubo in the
Philippines.
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