Geologists believe that around 155 million years ago, a 5,000-kilometer (3,107-mile) long chunk of land, dubbed Argoland, broke off from Western Australia, but what happened to it after that was unknown – until now.
Our planet’s continents aren’t stationary; because of plate tectonics, over the course of millions of years, they can join each other to form “supercontinents” and break apart from each other to make smaller continents. Geologists have long suspected Argoland to be one of these microcontinents, but there was little evidence to suggest where it went.
The structure of the seafloor in the Argo Abyssal Plain, the deep ocean basin left behind by the break-off of Argoland, indicates that the continent drifted off to the northwest, most likely ending up somewhere in what is today the islands of Southeast Asia.
There’s no massive continent hidden under those islands – that definitely would’ve made the news – only small, continental fragments, so researchers from Utrecht University turned to the geology of Southeast Asia to find clues as to Argoland’s fate.
Using reconstructive models and fieldwork data from several islands, including Sumatra, Borneo, and the Andaman Islands, they discovered that Argoland was never a single, coherent continent; it began splintering into fragments around 300 million years ago, forming what the researchers called an “Argopelago”.
“The situation in Southeast Asia is very different from places like Africa and South America, where a continent broke neatly into two pieces. Argoland splintered into many different shards,” explained Eldert Advokaat, one of the study’s authors, in a statement. Those fragments are now hidden beneath large parts of Indonesia and Myanmar, having arrived there around the same time.
The researchers also found that the break-up of Argoland accelerated around 215 million years ago, which explained why the “continent” became so fragmented and why it made putting all the pieces together that much harder for the team. “We were literally dealing with islands of information, which is why our research took so long. We spent seven years putting the puzzle together”, said Advokaat.
It might have taken them a long time, but as fellow study author Douwe van Hinsbergen explained, it’s important to know how lost continents became, well, lost. “Those reconstructions are vital for our understanding of processes like the evolution of biodiversity and climate, or for finding raw materials. And at a more fundamental level: for understanding how mountains are formed or for working out the driving forces behind plate tectonics; two phenomena that are closely related.”
The study is published in the journal Gondwana Research.