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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