The vast beaches of Australia seem a world away from the towering glaciers of Antarctica, yet footprints found among the Antipodean sands have led to a dazzling discovery on the frozen continent.
The incredible find was made when scientists began noticing streaks of pink washing up on the remote southern beach of Petrel Cove, about 90km (56 miles) from Adelaide.
They quickly discovered that the colored sand was made up of the mineral garnet, but were amazed to learn its age and origin.
“This journey began with the question of why there were so many shells on the beach at Petrel Cove,” University of Adelaide geologist Jacob Mulder said in a statement.
They soon realized that the grains were tiny little pink flags that signaled the existence of a buried ancient mountain, thousands of kilometers away.
“It’s fascinating to think that we were able to trace tiny grains of sand on a beach in Australia to a previously undiscovered mountain belt beneath the Antarctic ice,” added Mulder.
The pink sands of Petrel Cove have revealed a secret that has been hidden for millennia (University of Adelaide)
Garnet, a deep red-colored mineral, is fairly common—it crystallizes at high temperatures, usually where large mountain ranges emerge from colliding tectonic plates.
The crystals serve as a record of the pressure and temperature history of the metamorphic rocks in which they form, making them extremely valuable for inferring how and when mountains formed.
When the University of Adelaide team dated the garnet at Petrel Cove and nearby rock formations, they found that it mostly formed about 590 million years ago – about 76-100 million years before the local Adelaide Fold Belt Mountains formed and billions of years after the crystalline basement of the Gawler Craton formed.
“The garnet is too young to be from the Gawler Craton and too old to be from the eroding Adelaide Fold Belt,” explained Sharmaine Verhaert of the University of Adelaide, who led the investigation.
Instead, the mineral most likely formed when South Australia’s crust “was relatively cool and non-mountainous,” Verhaert added.
The Transantarctic mountain range divides the continent’s ice sheet into two parts. The larger, eastern part rests on land that is mostly above sea level; the smaller, western part lies mostly below sea level(US National Science Foundation)
Garnet is usually destroyed by prolonged exposure to waves and currents, so scientists also conclude that it originally formed millions of miles away, millions of years ago, before emerging locally. Scientific noticenews.
Their research revealed a link between the pink sands of Petrel Cove and layers of nearby glacial sedimentary rocks and distant garnet deposits previously found in the Transantarctic Mountains foothills in East Antarctica.
These rock formations protrude from the thick ice sheet that otherwise covers the area, making it impossible to sample the geology of the mountain range believed to lie beneath.
The buried mountain belt is thought to be 590 million years old, as is the garnet analyzed in Verhaert’s study, but she and her colleagues couldn’t get a good look at it.
Scientists believe that the garnet-rich glacial sands were washed out of the Antarctic mountains – which remain hidden under the ice – by an ice sheet that moved in a northwesterly direction during the Younger Ice Age.
Back then, Australia and Antarctica were connected via the supercontinent Gondwana.
“The garnet deposits were then locally deposited in glacial sedimentary deposits along the southern Australian margin,” explained fellow University of Adelaide geologist Stijn Glorie, “until erosion. [once again] freed them and the waves and tides concentrated them on the beaches of South Australia.’
It’s amazing how something as seemingly innocuous as a deposit of sand can bridge such vast gaps between space and time.
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