Double dome points to largest asteroid impact

The world’s largest asteroid impact zone – invisible at the earth’s surface – has been found in central Australia.

By studying drill cores, geophysicists at the Australian National University (ANU) discovered a 400 km wide impact zone – hidden deep in the earth’s crust – that resulted from the collision of two asteroids with Earth.

“Large impacts like these may have had a far more significant role in the Earth’s evolution than previously thought,” said research leader Dr Andrew Glikson at the ANU School of Archaeology and Anthropology.

In the study, published in Tectonophysics, the team investigated drill cores from an area near the borders of South Australia, Queensland and the Northern Territory. They found traces of rocks that had been turned to glass by the extreme temperature and pressure of the impacts.

Due to the lack of visual surface evidence of the impact zone, the researchers used magnetic modelling of the deep crust and seismic data in the area. They traced out bulges hidden deep in the Earth’s crust, rich in iron and magnesium, and estimated the total size of the impacts to be 450 × 300 km.

“There are two huge deep domes in the crust, formed by the Earth’s crust rebounding after the huge impacts, and bringing up rock from the mantle below,” Dr Glikson said.

To date asteroid impacts, geologists usually link them to large animal extinction events and other geological events that may have been triggered such as ash generation. However, in this case the lack of evidence means the impact date remains unclear.

“The two asteroids must each have been over 10 kilometres across – it would have been curtains for many life species on the planet at the time. It’s a mystery – we can’t find an extinction event that matches these collisions. I have a suspicion the impact could be older than 300 million years,” said Dr Glikson.

Next, the research team is planning on performing deep crustal seismic transects to study the geology of the area in more detail.