Miralga impact structure

The Miralga impact structure is an impact structure in the Pilbara Craton of Western Australia. With an initially estimated age of around 3.47 billion years dating to the Paleoarchean, it has been suggested to be the oldest known impact structure on Earth by over a billion years and the only one known from the Archean.^[1]

Miralga impact structure
location of the Antarctic Creek impact structure
Impact crater/structure
Confidence	Confirmed
Diameter	40–45 km (25–28 mi) (current diameter of the North Pole Dome, original study) 16 kilometres (9.9 mi) (June 2025 study)
Age	3470 ± 2 Ma (original study) ~2700-400 Ma (June 2025 study)
Exposed	Yes
Drilled	No
Location
Coordinates	21°02′54″S 119°23′35″E
Country	Australia
Province	Western Australia

The structure is found in the East Pilbara Terrane, one of the oldest parts of the Pilbara Craton. A geological dome called the North Pole Dome was suggested to represent the central uplift of the structure. Evidence of the impact is shatter cones and impact spherules (formed from condensed impact vapour) found in the Antarctic Creek Member, a 20 metres (66 ft) thick layer of sedimentary rock including "felsic to mafic volcaniclastic rocks, chert, argillite, arenite and jaspilite intruded by dolerite", located within the otherwise entirely volcanic Mount Ada Basalt, which is 2–3 kilometres (1.2–1.9 mi) thick, with the Antarctic Creek Member being overlain by pillow basalts of the Mount Ada Basalt.^[1]

In the original March 2025 study describing the structure, Uranium–lead dating of detrital zircons within the Antarctic Creek Member as well as separate dating of the overlying and underlying volcanic strata, suggested that the age of the Antarctic Creek Member and thus the impact to 3470 million years ago, ± 2-3 million years. The 40–45-kilometre (25–28 mi) diameter of the dome led the authors to suggest that the now long eroded impact crater was over 100 kilometres (62 mi) in diameter when it formed. A spherule bed found in the Barberton Greenstone Belt of South Africa of roughly the same age was suggested by these authors to have formed as a result of the impact.^[1]

However, a study published several months later in June 2025 disputed the conclusions made in the original study. While they agreed that an impact structure existed (which they dubbed the Miralga impact structure), they found that shatter cones existed in much younger overlying rocks dating to 2.71 billion years ago, so the impact must have occurred after that time, and based on other constraints the impact must have also occurred sometime before 400 millon years ago. They also found that the impact structure was smaller than initially suggested, only 16 kilometres (9.9 mi). They also found that the formation of the North Pole Dome must have predated the formation of the structure.^[2]

See also

• Dresser Formation a Paleoarchean aged geological formation that forms part of the strata of the North Pole Dome, containing some of the oldest known evidence of life on Earth