Usually, when something turns pink in nature, it’s not a good sign. But strange pink sands washed up on South Australian beaches have revealed an ancient Antarctic mountain range believed to be buried under ice.
When pink streaks first appeared in the sand at Petrel Cove, a remote beach that meets the Southern Ocean, scientists in Australia quickly figured out what the colored sand was made of, a mineral called garnet, but were surprised by its age and where is located. originally from
“This journey started with the question of why there are so many shells on the beach at Petrel Cove,” says University of Adelaide geologist Jacob Mulder.
“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.”
The earth’s crust is constantly eroding and reforming, with loose sediments blown away by wind and waters deposited elsewhere to form new lands. If geologists are lucky, they can draw connections over vast distances and long periods of time between deposits of similar age with similar properties.
Garnet is a fairly common mineral, deep red in color. It crystallizes at high temperatures, usually where large mountain ranges are eroded upward from colliding tectonic plates. This makes it probably the most important mineral for inferring how and when mountains formed, as the presence of crystals indicates the pressure and temperature history of the metamorphic rocks in which they form.
Lutetium-hafnium dating by the team showed that some of the garnets found at Petrel Cove and in nearby rock formations matched the timing of local orogenic events in South Australia.
However, their results suggest that it mostly formed about 590 million years ago, about 76–100 million years before the Adelaide Fold Belt formed and billions of years after the Gawler Craton crustal block formed.
“The garnet is too young to be from the Gawler Craton and too old to be from the eroding Adelaide Fold Belt,” explains Sharmaine Verhaert, a postgraduate geology student at the University of Adelaide who led the investigation.
Instead, the garnet probably formed when the crust of southern Australia “was relatively cool and non-mountainous,” says Verhaert.
Garnet is usually destroyed by prolonged exposure to waves and currents, so the researchers also concluded that it probably emerged locally, even though it originally formed millions of kilometers away, millions of years ago.
Their research revealed a spectacular solution, one that connects the pink sands of Petrel Cove with layers of nearby glacial sedimentary rocks and with distant garnet deposits previously found in the Transantarctic Mountains spur in East Antarctica.
The rock outcrops protrude from a thick ice sheet that otherwise completely hides the underlying area, making it impossible to sample the geology beyond the exposed tips of the mountain range believed to lie beneath. The hidden mountain belt is thought to be 590 million years old, just like the garnet analyzed in this study, but the researchers couldn’t get a good look at it.
Connecting the dots with indicators of ice flow in South Australian glacial sedimentary rocks, Verhaert and colleagues believe that the garnet-rich glacial sands were ground up from the Antarctic mountains – which have yet to see the light of day – by the northward-moving ice sheet. -west during the late Paleozoic ice age, when Australia and Antarctica were combined into the supercontinent Gondwana.
“The garnet deposits were then locally deposited in glacial sedimentary deposits along the southern Australian margin,” explains 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.’
An epic journey across land and time.
The study was published in Earth and environment communication.