Mystery Deepens Over Unseen Antarctic "Alps"
for National Geographic News
|November 6, 2008|
The existence of a massive Antarctic mountain range buried under miles of ice has become an even deeper mystery, a new study says.
The little-researched Gamburtsev Mountains seem to challenge geologic patterns seen in other mountain ranges on Earth.
For one, the range is situated in the middle of the continent instead of on the edge—at the plate-tectonic boundaries—like most other mountains. (See a high-resolution map of Antarctica.)
The range's high peaks reach an elevation of about 10,000 feet (more than 3,000 meters)—heights typical of relatively young mountain ranges, such as the spiky Rockies and the European Alps.
New findings based on river sediments, which suggest the range is more than 500 million years old, are intriguing, experts say.
Older mountains, such as the Appalachian range in the eastern U.S., are thought to be shorter and less rugged after hundreds of millions of years of erosion.
Because the Gamburtsev range is tall, some scientists have argued it must have formed relatively recently—within the last 60 million years or so.
And because it's not near a tectonic boundary, some have suggested the range rose up as the result of magma buildup around a theoretical volcanic hot spot.
(Related: "Under-Ice Volcano Eruption Spewed Ash Over Antarctica" [January 21, 2008].)
"The hypothesis that the mountains are derived from young volcanic activity is hard to reconcile with our data," said study lead author Tina van de Flierdt of the Imperial College London.
Hard to Reconcile
Scientists examined sediments collected from a coastal area that would have been a vast delta about 35 million years ago, when Antarctica's rivers carried flowing water instead of glacier ice.
If the mountains were made of relatively recent volcanic material, some of it should have been in the sediment as Gamburtsev runoff passed through the delta.
Instead, all mineral grains the researchers dated—such as zircon and hornblende—were more than 500 million years old.
"Volcanic activity of the extent to form a mountain range bigger than the European Alps would leave a 'geochemical fingerprint' in the preglacial to present-day sediments—we simply can't see this fingerprint," van de Flierdt said.
The study, which is based in part on van de Flierdt's work at Columbia University, was published online this week by Geophysical Research Letters.
A remaining mystery, according to study co-author Sidney Hemming, is why the mountains have not eroded more.
"The new data we're collecting makes it look like the erosion rates are so extremely low," said the Columbia University geochemist.
Hemming cautioned that researchers can't be certain the sediments are from the mountain.
It's possible, she added, that the ice has helped keep the rocks in place, but that does not explain the lack of erosion from ancient periods when the ice was not there.
"We can say that they're either not hot spot volcanic [mountains] or that they formed after the ice basically capped them off," Hemming said.
But, she said, later formation is highly unlikely: "It would be hard to imagine that it wouldn't leave some evidence in the ice or sediments."
The study makes a good case for the theory that the mountains were not formed by recent volcanic activity, said University of Arizona geochemist Peter Reiners, who was not involved with the research.
"If the mountains themselves are anywhere close to the same age as the rocks, then the Gamburtsevs are trying to tell us something about how really old topography can persist for hundreds of millions of years without being worn down by water, wind, and glaciers," said Reiners, who also studies the range.
Norm Sleep, a Stanford University geophysicist who also studies the Gamburtsev Mountains but wasn't involved with this study, agreed with the data but not the interpretation.
Sleep worried that "550-million-year-old highlands would have long since eroded away."
Instead, he suggests a gooey, semi-solid plume of material could have formed a pond deep under Earth's cooler outer lid of rock. This would have caused the mountains to rise without spewing magma all over the surface.
Such an event may have happened within the last 50 million years, he said.
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