Geologists have found the missing continent of Argoland

The continent of Argoland once lay on the northwest coast of Australia. Geologists have discovered that this continent is now hidden in fragments off parts of Southeast Asia.

Geologists from Utrecht University have discovered that the disappeared continent of Argoland can now be found in pieces near Indonesia and Myanmar.

Mystery

For decades, geologists have believed that there once was a continent at the northwestern edge of the Australian continental plate: the so-called Argoland. Geological features on the edge of the Australian plate indicate that another plate was once attached to it.

This disappeared continent is said to have broken off from Australia in the Jurassic period, about 200 to 145 million years ago. It then traveled north. In doing so, it left a deep plain on the ocean floor next to Australia, the Argo Abyssal Plainfrom which Argoland takes its name.

What exactly happened to Argoland, how big it was, and where it is now is a great mystery. Geologists Eldert Advokaat and Douwe van Hinsbergen from Utrecht University have started looking for the lost continent. Their reconstruction of Argoland’s disappearance has been published in the scientific journal Gondwana Research.

Fieldwork

The researchers conducted fieldwork on several islands in Southeast Asia, such as the Andaman Islands, Sumatra and Borneo. There they studied the shape, type and age of rocks to look for similarities.

Southeast Asia does not consist of one very large continent, but of several small continental fragments that together form a whole. After seven years of puzzling, the researchers noticed an interesting similarity between certain fragments in Indonesia and Myanmar: together they seemed to form pieces of the missing Argoland.

The findings show that the 5,000-kilometre-wide Argoland broke up into small pieces when it was still attached to the northwest coast of Australia 300 million years ago. About 157 million years ago, the pieces were driven north by plate tectonics. Some pieces have disappeared because they have been pushed under the Earth’s mantle, a geological process called subduction. Another part of the pieces has stuck to Southeast Asia.

Earth history

According to the researchers, Argoland is important for understanding Earth’s history. ‘Reconstructions are of enormous importance for our understanding of evolution, biodiversity and climate, for example, or for finding raw materials,’ says Van Hinsbergen in a news report from Utrecht University.

Geologist Wouter Schellart of the Vrije Universiteit in Amsterdam thinks the work of Advokaat and Van Hinsbergen is a nice reconstruction. ‘There’s a lot of detail in it. In that sense it is a significant step forward compared to previous reconstructions of Argoland,” he says.

However, the mystery of Argoland is not yet completely solved. The outer layer of the Earth consists not only of continental plates, but also of oceanic plates. “A big part of the story is also what happens in the ocean,” says Schellart. ‘The tricky thing about this is that an oceanic plate usually disappears completely due to subduction.’ This makes it difficult to determine what happened to the oceanic plates around Argoland and how large they used to be.