Australia’s sweeping beaches seem a world away from the towering glaciers of Antarctica, and yet clues found among the Antipodean sands have led to a dazzling discovery on the frozen continent.
The remarkable discovery was made when scientists began noticing streaks of pink on the remote southern beach of Petrel Cove, about 90 km (56 miles) from Adelaide.
They quickly discovered that the colored sand consisted 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 garnets on Petrel Cove beach,” University of Adelaide geologist Jacob Mulder said in a statement.
Soon, they realized that the grains were tiny pink flags, signaling the existence of an ancient buried 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 range under the Antarctic ice,” added Mulder.
The pink sands of Petrel’s Bucket 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 the collision of 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 understanding 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 was mostly formed around 590 million years ago – about 76-100 million years before the local mountain range, the fold belt, took shape. of Adelaide and billions of years after the Gawler Craton crystalline basement formed.
“The garnet is too young to come from the Gawler Craton and too old to come from the eroding Adelaide fold belt,” explained Sharmaine Verhaert, from 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”, Verhaert added.
The Transantarctic Mountains divide the continent’s ice sheet into two parts. The greater, eastern part lies 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 the researchers also concluded that it first formed millions of miles away, millions of years ago, before surfacing locally. Scientific alertreports.
Their investigations revealed a link between the pink sand at Petrel Bay and nearby glacial sedimentary rock layers and distant garnet deposits previously found in an outcrop of the Transantarctic Mountains in East Antarctica.
These rock formations emerge from a thick layer of ice that otherwise covers the area, making it impossible to sample the geology of a mountain range thought to lie below.
The buried mountain belt is thought to be 590 million years old, like the garnet analyzed in Verhaert’s study, but she and her colleagues haven’t been able to get a good look at it.
Researchers believe that the garnet-rich glacial sands were eroded from the Antarctic mountains – which remain hidden beneath the ice – by an ice sheet that drifted northwestward during the Late Paleozoic Ice Age.
At that time, Australia and Antarctica were connected via the supercontinent Gondwana.
“The garnet deposits were then preserved in situ in glacial sedimentary deposits along Australia’s southern margin,” explained 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 span such vast gaps between space and time.
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