World's largest asteroid impact may be buried in Australia – Interesting Engineering

Puchan/iStock 
By subscribing, you agree to our Terms of Use and Policies You may unsubscribe at any time.
Scientists have unveiled compelling evidence pointing to the existence of the world's largest known asteroid impact structure, according to a recent study published in Tectonophysics.
Buried beneath dee in southern New South Wales, Australia, the Deniliquin structure, spanning a staggering 520 kilometers in diameter, could dethrone the previous record-holder, the Vredefort impact structure in South Africa (~300km-wide).
The Australian continent, as well as its ancient precursor Gondwana, has long been a playground for asteroid impacts. 
Glikson and Yeates, 2022 
This latest revelation adds to a list of at least 38 confirmed and 43 potential impact structures, ranging from tiny craters to massive, concealed formations.
Co-author Andrew Glikson, an Adjunct Professor at UNSW Sydney, likened this process to dropping a pebble in a pond in a recent Conversation article. Imagine the initial impact producing a central dome akin to a splash. 
However, as time passes, this dome may erode or become concealed beneath layers of history.
These central domes, remnants of impacts from eons ago, provide crucial clues about the Earth's tumultuous history. Examples like the Vredefort impact structure and the Chicxulub crater, responsible for wiping out the dinosaurs, showcase the lasting influence of these ancient cosmic collisions.
The story of the newfound impact structure in southeast Australia begins with Tony Yeates, who identified intriguing magnetic patterns beneath New South Wales' Murray Basin between 1995 and 2000. 
These patterns hinted at a buried impact structure of immense proportions. 
A recent analysis of updated geophysical data from 2015 to 2020 has strongly supported Yeates' suspicions, revealing a colossal 520-kilometer diameter structure crowned with a seismic dome at its center.
The Deniliquin structure boasts all the hallmarks of a large-scale impact site. Magnetic readings exhibit a symmetrical rippling pattern encircling the core—a fingerprint of the colossal force that once struck. 
The unique magnetic properties correspond with deformation about 30 kilometers below the surface, above a seismically defined mantle dome. This dome stands around 10 kilometers shallower than the surrounding mantle.
Further magnetic measurements tell a tale of "radial faults," fractures emanating from the impact's center. These fractures are accompanied by small magnetic anomalies that may represent igneous "dikes," sheets of molten rock injected into pre-existing fractures. 
Such features are consistent with other large impact sites worldwide, underscoring the Deniliquin structure's potential significance.
Despite these compelling findings, definitive proof of impact hinges on physical evidence—proof that only deep drilling can unearth. 
The potential impact site in the eastern portion of the ancient Gondwana supercontinent may hold the key to a mystery that dates back hundreds of millions of years. 
It's possible that the impact that formed the Deniliquin structure occurred during the Late Ordovician mass extinction event—an epoch marked by the Hirnantian glaciation stage. 
This event, characterized by colossal ice sheets and dramatic species decline, dwarfs even the notorious dinosaur-killing Chicxulub impact. Yet, mysteries remain. 
The Deniliquin structure may be even older than the Ordovician event, stretching back to the early Cambrian era. 
Determining its exact age requires sample gathering, which entails drilling deep into the structure's magnetic heart and dating the extracted materials.
The complete study was published in Tectonophysics and can be found here.
Study abstract:
Major geophysical elements of the Deniliquin multiple-ring feature, a spatially distinct buried structure in mainland southeast Australia, suggest it represents the deep-seated root zone of a large impact structure from which the upper levels, including the original crater, central uplift and associated breccia, have been eroded. Principal features include (A) a multiple ring total magnetic intensity (TMI) pattern; (B) a central quiet magnetic zone; (C) circular Bouguer gravity patterns; (D) an underlying mantle Moho rise about 10 km shallower than under the adjacent Tasman Orogenic Belt; (E) radial faults associated with magnetic and demagnetized anomalies. The minimum radius of the TMI ring is ~260 km, including a central circular quiet magnetic zone about ~120 km in radius. In the east the feature is faulted against the Early Paleozoic Lachlan Orogenic belt whereas in the west it deflects the northwest and northeast trending Early Cambrian ~525–514 Ma Kanmantoo Group. An interpretation of the Deniliquin multiple-ring feature in terms of an orocline is inconsistent with the discontinuity between the feature and surrounding regional structural trends. Limits on the age of the Deniliquin feature are defined by the onset of the Adelaide fold belt at 514 +/− 5 Ma (Foden et al., 1999) and the ~427–417 Ma age of intrusive Silurian granites. Basement drill cores within the Deniliquin multiple-ring feature show Boehm lamellae but did not reveal shock metamorphic textures. Based on its multiple-ring structure, structural distinction from surrounding regional structural trends, occurrence of a central quiet magnetic zone, an underlying shallower Moho and radial faults associated with magnetic bodies, we suggest the Deniliquin multiple-ring feature may represent the deep seated root zone of a large impact structure.

source