Dinosaurs were still alive. Argoland then extended into northwestern Australia, over 5,000 kilometers, or five times the distance separating the north and south of France. It’s hard not to notice it a priori. And yet this continent has almost disappeared! If we have assumed the existence of this “land of Argo” for thirty-five years, we have had all the trouble in the world to identify it under the ocean or among the emerging countries. Did it collapse into the bowels of the Earth due to plate tectonics? The answer is no! This ‘lost continent’, recently described in the literature as a ‘hot topic of geological exploration’, is finally being revealed. And it doesn’t really look like we imagined.
In recent years, scientists have finally found traces of it under the island of Java and in the Himalayas. However, no one could have given Argoland an overview. Until two researchers completed the puzzle, the continent had clearly fallen apart. In the journal Gondwana Research last month, the duo detailed their research: Argoland separated from Australia 155 million years ago and is now spread across Burma and Indonesia. A simulation accompanying the publication clearly shows the fragmentation and drift of the continent.
The scientific study of more than 100 pages is the result of seven years of tracking. “It is impossible to get money to carry out such long-term projects,” assures Eldert L. Advokaat, researcher at the Department of Earth Sciences at Utrecht University (Netherlands). So this required two scientists crazy enough – or patient – to continue devoting significant time to this project for so long, while busy with other full-time jobs! »
An archipelago instead of a block
For more than half a century, geologists have been dating the ocean floor using magnetic anomalies. “The Earth’s magnetic field has the funny property that it sometimes reverses: the magnetic north pole becomes the south pole and vice versa. These inversions are stored in the oceanic crust,” explains Advokaat colleague Douwe Van Hinsbergen. It is on the basis of these anomalies that a team of Australian researchers, led by Christopher McAulay Powell, first conjured up a hypothetical ‘Argo landmass’ in 1988, which they would name ‘Argo Land’ three years later.
“My interest in Argoland started during my PhD at Royal Holloway (University of London) between 2011 and 2015, says Eldert L. Advokaat. I was fascinated by the geology of central Indonesia. » The researcher knows that in Southeast Asia there are many small continental fragments that probably belonged to the supposed Argoland. However, they are separated by remnants of ocean basins that are older than the age of the ‘departure’ into Eurasia: the fault lines are therefore older.
“This fact was not taken into account in the existing reconstructions, so we wanted to know what the full history of Argoland was: it couldn’t just be a single continent like Madagascar or something. » The duo of researchers understand that Argoland, even when it was in its Australian home port, was more of an archipelago than a block. An “Argopelago”, as they eventually called it.
“We wanted to merge Argoland and reconstruct its history from its break with Australia to its current spread in Southeast Asia,” adds Van Hinsbergen. “One of the reasons it took seven years was the enormous amount of data we needed to put together this reconstruction,” says Advokaat. As much as the duo was able to draw on the existing literature for parts of Southeast Asia, other parts remained underexposed: “We had to do fieldwork to obtain the necessary data, such as on Sumatra, Borneo and the Andaman Islands.”
“First we had to reconstruct all the deformations that occurred after the arrival of the Argoland fragments in Southeast Asia, about 90 million years ago. And there have been many: Argoland, which was already fragmented, has fragmented into even more pieces over the past thirty million years,” Advokaat continues. The rest is a time machine story: “We had to know when the fragments of Argoland arrived” in Eurasia, and then “when these fragments broke away from Australia,” “when they separated” before leaving the island…
Modestly, Advokaat says that their work is mainly based on previous data: “We stood on the shoulders of giants. » Never before, however, have so many fragments been identified covering the former surface of Argoland. The ‘lost’ continent has finally resurfaced.