Flying over Antarctica with geophysical instruments researchers peered through the ice to see the peaks of the Gamburtsevs.
Credit: Nick Frearson, Lamont-Doherty
Buried below more than a mile of ice, Antarctica’s Gamburtsev Mountains have baffled scientists since their discovery in 1958. How did the mountains get there, and what role did they play in the spread of glaciers over the continent 30 million years ago? In the latest study on the mountains, scientists this week in the journal Nature say they have pieced together the puzzle of the origins and evolution of this mysterious mountain chain.
An international team of scientists flew over Antarctica’s deep interior in 2008-2009 with ice-penetrating radar, gravity meters and magnetometers to reveal the peaks and valleys hidden below the ice. The data they gathered has provided insight into how the mountains arose. One billion years ago, before animals or plants appeared on land, several continents collided and the oldest rocks that make up the Gamburtsevs smashed together. From the collision, a thick crustal root formed deep beneath the mountain range. Over time, these ancient mountains were eroded but the cold dense root remained.
Between 250 and 100 million years ago – when dinosaurs walked the Earth –the supercontinent Gondwana, which included Antarctica, ripped apart, causing the old crustal root to warm. Reactivated, the crustal root and the East Antarctic Rift pushed land upwards again, reforming the mountains. Rivers and glaciers carved deep valleys and raised peaks to create a spectacular landscape that resembled the European Alps. The East Antarctic Ice Sheet, which formed 34 million years ago and at 10 million square kilometers covers an area the size of Canada, protected the mountains from erosion.
"It has been almost a billion years since the Gamburtsev first formed," said study co-author Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory. "This work shows that very old mountains can rise again, like a Phoenix from the ashes. The Gamburtsevs rose from the long eroded East Antarctic craton."
The study also resolves an apparent contradiction: how could such ancient mountains have retained their tall, jagged, and youthful peaks, said study co-author Carol Finn, a scientist at the U.S. Geological Survey. "We are accustomed to thinking that mountain building relates to a single tectonic event, rather than sequences of events," she said. "The lesson we learned about multiple events forming the Gamburtsevs may inform studies of the history of other mountain belts.
"It was fascinating to find that the East Antarctic rift system resembles one of the geological wonders of the world – the East African rift system – and that it provides the missing piece of the puzzle that helps explain the Gamburtsev Subglacial Mountains," said study lead author Fausto Ferraccioli, a scientist at British Antarctic Survey. "The rift system was also found to contain the largest subglacial lakes in Antarctica."
Radar images of the mountains revealed chiseled peaks, some towering 4,500 feet above deep valleys.
(click to enlarge)
The team's next goal is to drill through the ice and collect the first Gamburtsev rock samples. "Amazingly, we have samples of the moon but none of the Gamburtsevs," said Bell. "With these rock samples we will be able to constrain when this ancient piece of crust was rejuvenated and grew to a magnificent mountain range."
The work was funded by grants from the U.S. National Science Foundation (NSF) and was launched in conjunction with the International Polar Year, an effort to study the Arctic and Antarctic spanning 2007-2009 and involving research by thousands of scientists from more than 60 nations. "It is very fitting that the initial results of Antarctica’s Gamburtsev Province project are coming out 100 years after the great explorers raced to the South Pole,” said Alexandra Isern, program director at NSF. “The scientific explorers of the AGAP project worked in harsh conditions to collect the data and detailed images of this major mountain range under the East Antarctic Ice Sheet. The results of their work will guide research in this region for many years to come.”