Acknowledgments: I would like to thank my colleague Tony Yeats for his support of this work – considering the Deniliquin multi-ring structure as an impact system.
In Recent research My colleague Tony Yeats and I published in the journal TectonophysicsWe explore what we believe — based on years of experience in asteroid impact research — is the world’s largest known impact system, buried deep within the Earth in southern New South Wales.
The Deniliquin Formation, which has not yet been tested by drilling, spans 520 kilometers in diameter. It exceeds the extent of nearly 300 km in width Castle of Peace Impact system in South Africa, which is considered to be the largest in the world to date.
Hidden traces of Earth’s early history
The history of Earth’s bombardment by asteroids is largely obscured. There are a few reasons for this. The first is erosion: the process by which gravity, wind, and water slowly wear away land materials over time.
When an asteroid hits, it creates a crater with an elevated core. It is like when you drop a pebble into a pond and a drop of water splashes upwards from an unstable trough.
This central raised dome is a key characteristic of large impact structures. However, it decays over thousands to millions of years, making the structure difficult to identify.
Structures can also be buried by sedimentation over time. Or they may disappear as a result of collisions, in which tectonic plates crash into each other and slide into the Earth’s mantle.
Nevertheless, new geophysical discoveries detect signatures of impact structures created by asteroids reaching tens of kilometers across – marking a paradigm shift in our understanding of how Earth formed over the ages. These include pioneering discoveries about impact „ejecta,” material thrown out of the crater during impact.
Researchers think The oldest layers of this ejecta, found in sediments from early terranes around the world, may represent the tail end of Earth’s late heavy bombardment. The Recent evidence Earth and the other planets in the solar system were subject to intense asteroid bombardment until about 3.2 billion years ago, and rarely since.
Some of the biggest impacts are associated with mass extinction events. For example, the Alvarez hypothesisNamed after father and son scientists Luis and Walter Alvarez, it explains how the non-avian dinosaurs were wiped out as a result of a massive asteroid strike about 66 million years ago.
Determining the structure of Deniliquin
The Australian continent and its predecessor continent, Gondwana, has been the target of countless asteroid impacts. These have produced at least 38 confirmed and 43 possible impact structures, ranging from relatively small craters to large and completely buried structures.
This map shows the distribution of circular structures of uncertain, possible or probable impact origin on the Australian continent and coast. Green dots indicate confirmed impact craters. Red dots represent confirmed impact systems with a width greater than 100 km, whereas red dots in white circles are greater than 50 km wide. Yellow dots represent potential impact systems.
As you may recall with the pond and pebble analogy, when a large asteroid hits Earth, the underlying crust responds with a transient elastic rebound. A central dome.
Such domes may have been slowly eroded and/or buried over time, all of which may have been preserved from the original impact structure. They represent the deep „root zone” of an influence. Famous examples are found in the Vredefort impact system and 170km-wide Sigsula crater In Mexico. The latter represents the impact that caused the extinction of the dinosaurs.
Between 1995 and 2000, Tony Yeats suggested magnetic patterns beneath the Murray Basin in New South Wales. Probably referred to A large, buried impact system. Analysis of updated geophysical data of the region between 2015 and 2020 confirmed the presence of a 520 km diameter structure with a seismically defined dome at its center.
Deniliquin’s structure has all the features expected of a large-scale impact structure. For example, magnetic measurements of the area reveal a symmetrical ripple pattern in the crust around the core of the structure. It may have been created during the impact because the very high temperatures created intense magnetic forces.
A central low magnetosphere corresponds to 30 km deep deformation above the seismically defined mantle dome. The summit of this dome is about 10 km shallower than the top of the Territorial Mantle.
Magnetic measurements also show evidence of „radial faults”: fractures radiating from the center of a large impact structure. It is also accompanied by small magnetic anomalies that may represent igneous „dykes,” which are sheets of magma injected into fractures in a pre-existing rock body.
Radial faults, and the igneous sheets of rocks that form within them, are typical of large impact structures and include the Vredefort system and Sudbury Impact System In Canada.
Currently, most of the evidence for Deniliquin’s impact is based on geophysical data obtained from the surface. To demonstrate impact, we must collect physical evidence of trauma, which can only come from drilling deep into the structure.
When did Deniliquin’s impact occur?
The Deniliquin system may have been located on the eastern side of the Gondwana continent, before it split into several continents (including the Australian continent).
The Deniliquin Formation formed in Eastern Gondwana during the Late Ordovician.
The impact that caused it may have occurred during the Late Ordovician mass extinction event. In particular, I think it may have prompted the so-called Hirnandian glaciation stageIt lasted between 445.2 and 443.8 million years ago and is defined as Ordovician-Silurian extinction event.
This was a massive glaciation and mass extinction event Deleted About 85 percent of the planet’s species. was more than twice the size Chicxulub Impact It killed the dinosaurs.
The Deniliquin Formation is older than the Hirnandian event and may be of early Cambrian origin (about 514 million years ago). The next step will be to collect samples to determine the exact age of the structure. This would require drilling a hole deep into its magnetic core and dating the extracted material.
It is hoped that further studies of the Deniliquin impact structure will shed new light on the nature of the early Paleozoic Earth.
This article was originally published Conversation By Andrew Glixon at UNSW Sydney. Read on Original article here.
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