Australia’s vast beaches seem a world away from Antarctica’s towering glaciers, yet clues found in the Antipodean sands have led to a dazzling discovery of the frozen continent.
The incredible discovery was made when scientists began noticing pink streaks washing up on the remote southern beach of Petrel Cove, about 90 kilometers (56 miles) from Adelaide.
They quickly determined that the colored sand was composed of the mineral garnet, but were stunned to learn its age and origin.
“This journey began with the question of why there is so much garnet on the beach at Petrel Cove,” geologist Jacob Mulder of the University of Adelaide said in a statement.
They soon realized that the grains were tiny pink flags signaling the existence of a buried ancient mountain thousands of kilometers away.
“It’s fascinating to think that we’ve been able to track 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 mineral, is quite common – it crystallizes at high temperatures, usually where large mountain belts emerge from colliding tectonic plates.
The crystals serve as a record of the pressure and temperature history of the metamorphic rocks in which they formed, making them extremely valuable for inferring how and when mountains formed.
When the University of Adelaide team dated garnet at Petrel Cove and nearby rock formations, they found that it was mostly formed about 590 million years ago – about 76–100 million years before the local mountain range formed the Adelaide Fold Belt and billions of years after the formation of the crystalline basement of the Golar Craton.
“The garnet is too young to have come from the Gowler craton and too old to have come from the eroded Adelaide fold belt,” explained Charmaine Verhart of the University of Adelaide, who led the investigation.
Instead, the mineral most likely formed at a time when South Australia’s crust “was relatively cool and non-mountainous,” Verhart added.
The Transantarctic Mountains divide the continent’s ice sheet into two parts. The larger, eastern portion lies on land that is mostly above sea level; the smaller, western part is mostly below sea level(US National Science Foundation)
Garnet is usually destroyed by prolonged exposure to waves and currents, so the researchers also concluded that it originally formed millions of miles away, millions of years ago, before floating to the surface locally. Learned signalreports.
Their research revealed a link between the pink sands at Petrel Cove and layers of nearby glacial sedimentary rocks and distant garnet deposits previously found in an outcrop of the Transantarctic Mountains in East Antarctica.
These rock formations protrude from a thick ice sheet that otherwise covers the area, making it impossible to sample the geology of a mountain range believed to lie below.
The buried mountain belt is thought to be 590 million years old, just like the garnet analyzed in Verhaert’s study, but she and her colleagues haven’t been able to get a good look at it.
The researchers believe that the garnet-rich glacial sands were ground down from the Antarctic mountains – which remain hidden beneath the ice – by an ice sheet that moved northwest during the late Paleozoic Ice Age.
Australia and Antarctica were then connected by the supercontinent Gondwana.
“The garnet deposits were then stored locally in glacial sedimentary deposits along the margins of southern Australia,” explained University of Adelaide geologist colleague Steen Glory, “until erosion [once again] released them, and the waves and tides concentrated them on the beaches of South Australia.”
It’s amazing how something as seemingly innocuous as a sand deposit can bridge such vast gaps between space and time.
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