Enigma of Ice-buried mountains finally solved, thanks to ancient rocks

The deep history of rocks and mountain belts buried beneath the East Antarctica Ice Sheet - one of the planet's most inaccessible and underexplored environments- has been exposed thanks to a recent treasure collection of ancient rocks reported in Nature. 

Until now, scientists had only the vaguest understanding of the origins of the mountains and landscapes currently covered by Earth's most extensive ice sheet for the past 14 million years.

Finding the hidden mountains beneath Antarctica's ice

"These mountains are much more remote than Mount Everest or the deepest part of the ocean," explained first author Paul Fitzgerald in a press release, an Earth and environmental sciences professor at Syracuse University. 

Now, thanks to innovative rock sampling and radiometric dating, several of the tectonic puzzles of that inaccessible region have been solved.

Fitzgerald and his friend, John Goodge (a professor emeritus of geological sciences at the University of Minnesota Duluth), selected granite boulders ranging in age from 1 to 2 billion years old. 

They knew that rocks of this age were not found anywhere in Antarctica. Better yet, they must have originated deep within the ice sheet- may have been from the vast and enigmatic Gamburtsev Subglacial Mountains. 

These mountains, in particular, have long baffled scientists because they are entirely covered in ice, and no one is sure what types of rocks make up the range.

We know that when mountains are formed, they are uplifted and create high topography. Due to erosion, rocks are exhumed (i.e., exposed) toward the surface and cool as this happens. Geologists can measure the rate at which a rock cools to determine when mountains formed in the geologic past. 

Using a cutting-edge dating method called thermochronology, which investigates the time-temperature history of rocks through radiometric dating, the two discovered the cooling history of the granites.

'This was like having rocks to study from the moon or Mars'

The findings indicated that three significant periods of rapid cooling, brought on by substantial tectonic processes, had occurred in the interior of East Antarctica.

Initially, around 500 million years ago, a collision between two continents gave rise to the supercontinent Gondwana. Secondly, 180 million years ago, the Gondwana supercontinent began to split.

Finally, a fissure system between East and West Antarctica about 100 million years ago caused a high-elevation plateau to collapse.

As a whole, these conclusions make solid geologic sense. That said, it's only just the beginning when it comes to appreciating the geologic mysteries hidden by the enormous size of the East Antarctic Ice Sheet. If there's one thing we know about science, it's that it's constantly evolving. 

 What stands out for Fitzgerald, though, is the excitement of discovery. "We were sampling a place that we knew very little about. For us, this was like having rocks to study from the moon or Mars," he concluded. 

Study abstract:

The geology, tectonic history and landscape evolution of ice-covered East Antarctica are the least known of any continent. Lithic boulders eroded from the continental interior and deposited in glacial moraines flanking the Transantarctic Mountains provide rare constraints on the geological history of central interior East Antarctica. Crystallization ages and ice velocities indicate these glacial erratics are not sourced locally from the Transantarctic Mountains but rather originate from the continental interior, possibly as far inland as the enigmatic Gamburtsev Subglacial Mountains. We apply low-temperature thermochronology to these boulders, including multi-kinetic inverse thermal modeling, to constrain a multi-stage episodic exhumation history. Cambro-Ordovician and Jurassic rapid-cooling episodes correlate with significant exhumation events accompanying Pan-African convergence and Gondwanan supercontinent rifting, respectively. Here we show that while Cretaceous rapid cooling overlaps temporally with Transantarctic Mountains formation, a lack of discrete younger rapid-cooling pulses precludes significant Cenozoic tectonic or glacial exhumation of central interior East Antarctica.