Australia’s sprawling beaches seem miles away from Antarctica’s massive glaciers, yet clues found in the sands of other continents have led to a startling discovery on the frozen continent.
The incredible discovery was made when scientists noticed pink streaks washing up on the remote southern beach of Petrel Cove, about 90 kilometers from Adelaide.
They quickly discovered that the colored sand was made of the mineral garnet, but were amazed to learn of its age and origin.
“This journey began with the question of why there was so much garnet on the beach at Petrel Cove,” said geologist Jacob Mulder of the University of Adelaide in a statement.
They soon realized that the grains were tiny pink flags that indicated the existence of an ancient mountain buried thousands of kilometers away.
“It’s fascinating that we were able to trace tiny grains of sand on a beach in Australia to a previously undiscovered mountain range beneath the Antarctic ice,” Mulder added.
The pink sand of Petrel Cove revealed a secret hidden for thousands of years (University of Adelaide)
Garnet, a deep red mineral, is relatively common – it crystallizes at high temperatures, usually where large mountain ranges are formed 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 and are therefore extremely valuable for drawing conclusions about how and when mountains were formed.
When the University of Adelaide team dated the garnet in Petrel Cove and nearby rock formations, they found that most of it formed around 590 million years ago – about 76 to 100 million years before the local mountain range, the Adelaide Fold Belt, took shape, and billions of years after the crystalline basement of the Gawler Craton formed.
“The garnet is too young to have come from the Gawler Craton and too old to have come from the eroding Adelaide Fold Belt,” explained Sharmaine Verhaert of the University of Adelaide, who led the study.
Instead, the mineral most likely formed at a time when the South Australian crust was “relatively cool and not mountainous,” Verhaert added.
The Transantarctic Mountains divide the continent’s ice sheet into two parts. The larger, eastern part lies on land that is mostly above sea level; the smaller, western part lies mostly below sea level(National Science Foundation of the USA)
Garnet is usually destroyed by prolonged exposure to waves and currents, which is why researchers concluded that it originally formed millions of kilometers and millions of years ago before it reached the surface locally. Science alertreports.
Their investigations revealed a connection between the pink sand at Petrel Cove and nearby layers of glacial sedimentary rock and distant garnet deposits previously found in a rocky outcrop of the Transantarctic Mountains in East Antarctica.
These rock formations protrude from a thick layer of ice that otherwise covers the area, making it impossible to sample the geology of a mountain range that is believed to lie beneath it.
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 have not yet been able to take a close look at it.
The researchers assume that the garnet-rich glacial sand was ground out of the Antarctic mountains – which are still hidden under the ice today – by an ice sheet that moved northwest during the late Paleozoic Ice Age.
At that time, Australia and Antarctica were connected via the supercontinent Gondwana.
“The garnet deposits were then stored locally in glacial sediment deposits along the southern Australian border,” explained Stijn Glorie, a geologist at the University of Adelaide, “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 large gaps in space and time.
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