Curtin’s Institute for Geosciences Research tectonics specialist, Professor Zheng-Xiang Li and Yale University collaborator, Professor David Evans, said prevailing views were that the western two-thirds of the continent had remained in their present configuration for at least 1000 million years (Ma).
Although different parts of the old continent were likely linked to each other as early as 1800 Ma, Professor Li said there were major reorganisations in their relative positions since then.
“In particular, our work suggests that the northern part of the old continent rotated about 40 degrees relative to the southern half of the continent between 650 Ma and 550 Ma,” Professor Li said.
“This led to the formation of a major mountain range running from WA’s Telfer District, across the Gibson Desert Nature Reserve and the Musgrave Ranges in Central Australia, and heading northeast to Western Queensland.
“Sediments shed from the northern slope of this 650-550 Ma east-west great divide now form the iconic geographic, cultural and spiritual features of Ayers Rock and the Olgas.”
Professor Li’s results resolve one of the longstanding controversies regarding the timing of the breaking apart of the pre-Pangaea supercontinent, Rodinia.
Previous compilations of palaeomagnetic data suggest a breakup age well before 750 Ma, but the information has been in conflict with the sedimentary basin evidence for a younger, ca. 715-680 Ma fragmentation.
“Our tectonic model resolves this discrepancy, supporting the younger breakup age with the new synthesis of palaeomagnetic data,” Professor Li said.
“This is important for our ideas on how supercontinents are related to global climate changes.
“In particular, the timing of the Rodinia breakup is more consistent with that of a globally engulfing ice age; some speculate a ‘Snowball Earth’ event, with the two processes possibly linked by changes in the carbon cycle associated with volcanism and rock weathering.
“This time period is also intriguingly close to the age of an explosion in animal evolution and diversification.”
Professor Li said although there were great changes during the transcontinental rotation period, the two halves of the Australian continent had remained more or less intact since that time.
He said the joint research finding also had implications for the relationship between Australia’s two major copper-silver-lead-zinc mineral provinces.
“There has long been a call for finding the missing southern half of the Mt Isa mineral zone, thought perhaps to be located on some other continent that could have drifted away from Australia in the deep past,” he said.
“Our answer to this call is to stop looking elsewhere. It is still within Australia’s Broken Hill mineral zone as previously hypothesised by other leading Australian geologists.”
Professor Li and Professor Evan’s study confirms that the two world-class mining regions were offset by hundreds of kilometres during the proposed 650-550 Ma transcontinental rotation.
Their study was recently published in the prestigious earth sciences journal Geology.
Professor Zheng-Xiang Li
Department of Applied Geology, WA School of Mines, Curtin University
Andrea Barnard, Public Relations, Curtin University
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