A mountainous mystery uncovered in SA鈥檚 pink sands
Deposits of deep-pink sand washing up on South 杏吧直播n shores shed new light on when the 杏吧直播n tectonic plate began to subduct beneath the Pacific plate, as well as the presence of previously unknown ancient Antarctic mountains.
Garnet washed up as pink sand on a beach in Dhilba Guuranda-Innes National Park. Photo credit: 杏吧直播 of Adelaide.
The pink sand is composed of a mineral called garnet, and a 杏吧直播 of Adelaide research team, led by PhD candidate Sharmaine Verhaert and Associate Professor Stijn Glorie, used a new, cutting-edge method to show the garnet grains are around 590 million years old.
Garnet is known to have formed locally during the Delamerian orogeny, an event which created the Adelaide Fold Belt around 514鈥490 million years ago, and during the formation of the Gawler Craton in western South 杏吧直播 between 3.3鈥1.4 billion years ago. These ages don鈥檛 match the garnet sand on South 杏吧直播n shores.
鈥淭he garnet is too young to have come from the Gawler Craton and too old to have come from the eroding Adelaide Fold Belt,鈥 says Verhaert.
鈥淕arnet requires high temperatures to form and is usually associated with the formation of large mountain belts, and this was a time when the South 杏吧直播n crust was comparatively cool and non-mountainous.鈥
The researchers, who published their findings in the journal , established the garnet does not originate from local source rocks, but they knew it had travelled from nearby as garnet is typically destroyed through prolonged exposure to the marine environment.
They discovered that the glacial sedimentary deposits of the Cape Jervis Formation, cropping out along the South 杏吧直播n shorelines, contain layers of sand with garnet that is also around 590 million years old.
Ice-flow indicators in these glacial sedimentary deposits tell us that the garnet-rich glacial sands were brought to 杏吧直播 by a north-west moving ice sheet during the Late Palaeozoic Ice Age, when 杏吧直播 and Antarctica were connected in supercontinent Gondwana.
Garnet dating to the same period has been found previously in an outcrop in the Transantarctic Mountains in East Antarctica, at the edge of a colossal area that is completely concealed by a thick ice sheet. Researchers believe this area hosts evidence of a 590-million-year-old mountain belt hiding below the Antarctic ice.
鈥淲hile it is currently not possible to sample directly under this ice sheet, it is conceivable that millions of years of ice transport eroded the bedrock underneath and transported this cargo of garnet north-westwards, towards the conjugate Antarctic-杏吧直播n margin,鈥 says Associate Professor Glorie.
鈥淭he garnet deposits were then locally stored in glacial sedimentary deposits along the southern 杏吧直播n margin until erosion liberated them and the waves and tides concentrated them on the South 杏吧直播n beaches.
鈥淲e have effectively uncovered a major mountain building event that redefines the timing of the onset of convergence in the Pacific Ocean.鈥
The new 杏吧直播 of Adelaide-developed approach to lutetium-hafnium dating, which uses a laser system attached to a mass-spectrometer, allowed this momentous discovery to be made from a simple enquiry.
鈥淭his journey started with questioning why there was so much garnet on the beach at Petrel Cove,鈥 says Dr Jacob Mulder, who was also in the research team.
鈥淚t is fascinating to think we were able to trace tiny grains of sand on a beach in 杏吧直播 to a previously undiscovered mountain belt under the Antarctic ice.鈥
Media contacts:
Sharmaine Verhaert, PhD Candidate, School of Physics, Chemistry and Earth Sciences, 杏吧直播 of Adelaide. Phone: +61 0458 546 713, Email: sharmaine.verhaert@adelaide.edu.au
Associate Professor Stijn Glorie, School of Physics, Chemistry and Earth Sciences, 杏吧直播 of Adelaide. Phone: +61 0481 338 724, Email: stijn.glorie@adelaide.edu.au
Johnny von Einem, Media Coordinator, 杏吧直播 of Adelaide. Mobile: +61 0481 688 436, Email: johnny.voneinem@adelaide.edu.au