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By Peter Rejcek
A team of scientists working around Byrd Glacier in Antarctica
this season may shake up scientific orthodoxy about the
formation of the continent’s tallest and longest
mountain range.
The researchers, led by Audrey Huerta , an assistant
professor at Central Washington University’s Department
of Geological Sciences , believe the Transantarctic Mountains
are the remnant of an ancient plateau.
That would challenge the commonly held theory that the
mountains were uplifted through geologic forces. The plateau
theory, if correct, would have significant implications
in not only how scientists interpret Antarctica's geologic
evolution but also its glaciological history.
“Yeah, actually it is pretty significant, and there
are those who don’t believe it,” Huerta said
shortly before heading south to the Ice. “It would
change our ideas of how that region evolved. It would
seriously change our ideas of how the Transantarctics
[formed]. It’s a serious changing in the way we think
about it.”
Scientists had assumed the mountains popped up during
the Eocene, which began about 59 million years ago. The
East Antarctic Ice Sheet came along much later, and its
glaciers supposedly began carving their way through the
mountains, grinding away like slow-moving bulldozers.
Today, numerous glaciers slice through the mountain range,
pouring into the West Antarctic Ice Sheet, the Ross Sea
and the Ross Ice Shelf .
Instead, Huerta and colleagues have found evidence that
Byrd Glacier didn’t start as a glacier-carved valley
but as a river flowing in the opposite direction, from
west to east. That idea would relegate the glaciers to
a minor role in the formation of the valleys that cut
through the Transantarctics, a 3,500-kilometer-long mountain
range that splits East and West Antarctica.
“That’s going to change the way people think
about how glaciers work,” Huerta noted. “It’s
looking like in this case they haven’t done much.”
And if those outlets pre-date the glacier, then the East
Antarctic Ice Sheet has always been able to drain through
the mountains, Huerta said. “That kind of changes
how we would interpret the dynamics of [the ice sheet]
and try to understand the past variations in it.”
Part of the evidence for the plateau theory comes from
three major tributaries of the Byrd Glacier that form
acute angles that point upstream of the current east-to-west
drainage, meaning that at some time in the past West Antarctica
was higher than East Antarctica. “It would be hard
to understand if [Byrd] was formed by rivers, how it could
be going in a different direction,” Huerta said.
Previous analysis of the cooling history of the mineral
apatite from the region, from methods such as fission-track
thermochronology with samples collected by colleague Ed
Stump at Arizona State University, suggest the mountains
predate the Eocene by tens of millions of years, according
to Huerta.
The Transantarctic should have started eroding about 55
million years ago after uplift, but Stump’s samples
are about double that age, according to Huerta. “It
makes them sound like they were old mountains a long time
ago and didn’t all of a sudden pop up in the Eocene.”
Fission tracks are preserved in minerals like apatite
that contain small amounts of uranium, according to information
from the U.S. Geological Survey . The tracks come from
the spontaneous fission of uranium in the mineral.
By determining the number of tracks present on a polished
surface of a grain and the amount of uranium present in
the grain, scientists can calculate how long it took to
produce the number of preserved tracks. As long as the
mineral has remained cool, near the earth’s surface,
the tracks will accumulate. If the rock containing these
minerals is heated, the tracks will begin to disappear.
The cooling history from minerals on the east and west
sides of the mountains would be fairly symmetrical if
they had been created by uplift, according to Huerta.
“If there was a plateau, then you would expect to
see a lot of old ages on the East Antarctic side, where
the rivers would have carved through at the edge of the
plateau and run down onto East Antarctica,” she explained.
Huerta’s team includes co-principal investigator
Ann Blyth , as well as undergraduate students Meilani
Bowman-Kamahao and Stephanie Kay, all from Occidental
College , Don Voigt from Penn State University and two
professional mountaineers. “The science component
of the sampling team is all women,” Huerta noted.
The seven-person team will spend 10 days at Byrd Glacier
collecting apatite for additional analysis, making long
vertical transects of the region with the help of helicopter
support. The group will work out of a nearby Antarctica
New Zealand field camp.
The plateau theory begs all sorts of additional questions.
What happened to the plateau? How did it erode? How tall
was it? Was the slope gentle or ruggedly steep? “We’re
just starting to think it was actually there. Hopefully,
with this study, we can get a better idea of how it was
shaped and how the rivers cut through it,” Huerta
said.
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