Mysterious crystals discovered on Australian beach reveal astonishing connection to Antarctica

Garnets have captivated humans for millennia. The ancient Egyptians adorned their jewelry with garnets, and the Greeks called them “lamp stones,” believing they could help one see in the dark. Recently, crystallized garnet particles shed light on a fascinating geological link between Australia and Antarctica, revealing an ancient Antarctic mountain range now buried under ice. These groundbreaking findings were published in Communications Earth & Environment.

Detrital minerals and sediments found in sand can reveal the tectonic history of their location. For this study, scientists analyzed the geochronology of detrital garnet in order to reconstruct the orogenic events recorded in the sediments. Geologists from the University of Adelaide discovered these garnet crystals while exploring the beach at Petrel Cove in South Australia. “This journey started with wondering why there was so much garnet on the beach at Petrel Cove,” said researcher Jacob Mulder.

Classic detrital minerals and sediments found in sand are known to provide useful information about the tectonic history of the place where they were found. Thus, for this research, scientists determined the geochronology of detrital garnet in order to reconstruct orogenic events from sedimentary records. These garnet crystals were discovered when geologists from the University of Adelaide searched the beach at Petrel Cove in South Australia. “This journey started with wondering why there was so much garnet on the beach at Petrel Cove,” said Jacob Mulder, one of the team’s researchers.

While Australia is well known for its pink lakes, pink wildflowers and pink desert roses, the pink sand covering the beach has piqued the curiosity of researchers. They wondered what the source of these garnet crystals could be. Most garnets form when a sedimentary rock with a high aluminum content, such as shale, is metamorphosed, subjected to heat and pressure. High heat and pressure break chemical bonds in rocks and cause minerals to recrystallize, according to Geoscience Australia. Garnet is generally destroyed by prolonged exposure to the marine environment. So when geologists discovered garnet in the pink sands of Australia, they concluded that it did not come from a local source of rock. They proposed in the study that it probably came from a nearby source.

The research, led by doctoral student Sharmaine Verhaert and Associate Professor Stijn Glorie, used a cutting-edge new method to show that the garnet grains found were around 590 million years old. According to the research paper, more than 550 individual detrital garnet grains from modern ranges and permo-Carboniferous strata of South Australia were analyzed using the high-throughput laser ablation Lu-Hf dating method recently established. Called “lutetium-hafnium dating,” the method uses a laser system attached to a mass spectrometer to determine the age of the particles.

These garnet grains were separated from four modern beach sand samples and two samples from the glaciogenic Permo-Carboniferous Cape Jervis Formation, the latter part of the Troubridge Basin which once covered much of southern Australia . They also established the age of the garnet from local rock units.

From previous studies, it was known that garnet was formed primarily as a result of two events. One of these events was the Delamerian Orogeny, the event that created the Adelaide Fold Belt approximately 490 to 514 million years ago. The second event was the formation of the Gawler craton in western South Australia, approximately 1.4 to 3.3 billion years ago. Interestingly, the age of the garnet found on the South Australian beach does not fit either of these time scales.

“Garnet is too young to come from the Gawler Craton and too old to come from the eroding Adelaide Fold Belt,” Verhaert said, adding: “Garnet requires high temperatures to form and is generally associated with the formation of large mountain belts, and this was a time when the South Australian crust was relatively cool and not mountainous.

Further investigation of ice sheets and ice flows revealed that garnet-rich glacial sands were washed onto this beach by a northwestward-moving ice sheet when Australia and Antarctica were connected in the supercontinent Gondwana. About 85 million years ago, the supercontinent began to split in two. This was mainly due to mantle plumes and other tectonic activities, according to the Australian Antarctic Program.

When the discovered garnet was dated using technological equipment, its age was found to date back to the same period as the Transantarctic Mountains outcrop in East Antarctica, a region of uplifted rocks entirely covered by thick ice sheets for millions of years. Researchers have hypothesized that this area harbors evidence of a 590 million-year-old mountain belt hidden beneath Antarctica’s ice. “While it is not currently possible to sample directly beneath this ice sheet, it is conceivable that millions of years of ice transport have eroded the bedrock below and carried this cargo of garnet northwest , towards the Antarctic-Australia conjugate margin,” Glorie said. .

He added that the garnet deposits were then stored locally in glacial sediments until erosion released them, and waves and tides carried them onto the South Australian beach, painting the white sand a pink hue. “It is fascinating to think that we have been able to trace tiny grains of sand on an Australian beach to a previously unknown mountain belt beneath the Antarctic ice,” the researchers said.