For the first time, volcanic rocks have been dated from the Wallaby Plateau – a 70,000 square kilometre underwater structure off the North West coast of Australia.
The research, led by Curtin University, looked at rocks that were once at the Earth’s surface during the time of the supercontinent Gondwana. The Wallaby Plateau, which is about the size of Ireland, now sits less than two kilometres under water off the coast of Western Australia, near Carnarvon.
Rock samples from the plateau were collected from the sea floor by the RV Sonne in 2008/09 as part of Geoscience Australia’s ‘WA Margins Reconnaissance Survey’.
Dr Hugo Olierook, of the Department of Applied Geology, WA School of Mines, Curtin University, said radioactive dating techniques enabled researchers to conclude that the samples originated from a volcanic eruption that took place during the supercontinent’s breakup.
“The samples tested in this study were shown to have an eruption age of 124 million years ago, which places them at the time during the breakup of Gondwana, specifically between the split of what are now known as Australia and India,” Dr Olierook said.
Previous studies of the Wallaby Plateau provided estimates of the area’s lava volume, but it was uncertain how these lava flows formed.
“Chemical data from this study shows that lava flowed out on a continent, rather than on the ocean floor. It is only since this eruption that the Wallaby Plateau has sunk underwater,” Dr Olierook said.
“Now that a date is known, when piecing back together the Australian and Indian continents, the research suggests that magma could not erupt before 124 million years ago.
“That means the space where the Wallaby Plateau is located was only created when India broke away from Australia, allowing the lava to flow out freely,” Dr Olierook said.
The research also suggests the volcanic samples used in the study were chemically similar to continental flood basalts – enormous volumes of lava which erupted in a geologically short period of time.
“Continental flood basalts are often associated with mass extinctions, but this is not always the case,” Dr Olierook said.
The paper, Age and geochemistry of magmatism on the oceanic Wallaby Plateau and implications for the opening of the Indian Ocean, was published by Geology.
Led by Dr Olierook, the study was completed by a team of researchers from Curtin University, Geoscience Australia, FROGTECH and Macquarie University.
Future expeditions have been proposed adjacent to the Wallaby Plateau to discover more about volcanic activity in this area during the time of Gondwana supercontinent breakup.
