Australia: Huge volcanic area discovered

The subsoil of Central Australia hides more than 100 ancient volcanoes

160 to 180 million years ago, more than 100 volcanoes transformed the center of Australia into a lava and fire sea. © Vershinin M / iStock
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Twice as big as Mallorca: In the center of Australia, researchers have discovered an enormous volcanic area - covering over 7, 500 square kilometers. Hidden under thick layers of sediment there are more than 100 volcanoes from the Jurassic period 160 to 180 million years ago. The unusual thing about it: These volcanoes developed in the middle of a plate of earth instead of at their edges, as was usually the case.

The Cooper Eromanga Basin in central Australia is best known for its wealth of oil and natural gas. The deposits located 1, 250 meters below the surface have been explored and exploited since the early 1960s. But this depression has even more to offer: In 2010, geologists discovered there the approximately 80-kilometer crater of an impact about 300 million years ago. In addition, the granite in the subsurface of this depression is so hot that there are tests for a geothermal project.

Enigmatic basalt finds

But a phenomenon gave the geologists puzzles: Again and again they came in addition to sedimentary rocks and granite on isolated basalts - and thus on rocks of volcanic origin. Some of these basalts appeared to be from the Triassic, others from the Jurassic. But because no volcanic activity was expected in the middle of the Australian continental plate, these findings were initially ignored.

"There is a tremendous amount of data from the underground of this region, " explain Jonathon Hardman of the University of Aberdeen and his colleagues. "But the age and nature of these basalt rocks were largely unknown." They have now re-evaluated the extensive data from past explorations, and also "screened" the area with seismic measurements to learn more about these volcanic rocks and their origins.

A volcanic area twice as big as Mallorca

The surprising result: Under the Cooper Eromanga Basin is a huge volcanic area hidden. More than 100 volcanoes, extensive lava flows and other volcanic deposits testify that there was once a violent volcanic activity here. In some places, the geological structures also indicate that there was also hydrothermal activity and thus possibly geysers and hot springs. display

"This volcanic province stretches over some 7, 500 square kilometers, " report Hardman and his team. This corresponds approximately to the size of Tyrol or the double area of ​​the island of Mallorca. These volcanoes were last active 160 to 180 million years ago in the age of the Jura, as dates showed. Today, the area baptized by the researchers Warnie volcanic province is hidden under hundreds of meters of thick sedimentary rocks.

The volcanic province is located in the middle of the Indo-Australian plate. Alataristarion / CC-by-sa 4.0

In the middle of the continent

The Unusual, however: "While the majority of terrestrial volcanism takes place at the boundaries of the tectonic plates under the oceans, this ancient Jurassic volcanic world lies deep within the Australian continent, " says co-author Simon Holford of the University of Adelaide. "That changes our idea of ​​how such processes in the past ran off the Earth."

The researchers suggest that these volcanoes were formed when hot magma burned from the Pacific plate pushed deep beneath the continent through the continent plate above it. "We interpret the Warnie volcanic province as a product of strain and intra-plate convective upwelling of rock over the subducted Pacific plate, " said Hardman and his colleagues.

Fiery past

However, the newly discovered volcanic area is not the first or only one in Australia. In the northwest of the continent lies the two million square kilometer Kalkarindji volcanic province, which may even have been involved in the first major mass extinction of Earth's history. And in the southeast, geologists recently discovered the longest continental volcanic chain on earth. A hotspot burned a 2, 000 kilometer long volcanic track through the crust. (Gondwana Research, 2019; doi: 10.1016 / j.gr.2019.06.012)

Source: University of Adelaide

- Nadja Podbregar