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'Largest ever asteroid impact' found in Australia

Scientists in Australia have discovered what they say is the largest asteroid impact area ever found.
The 400-kilometre wide area is buried deep in the earth's crust and consists of two separate impact scars.
The team behind the discovery, from the Australian National University (ANU), said the asteroid broke into two before it hit, with each fragment more than 10km across.

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Warburton West structure
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Title: Geophysical anomalies and quartz deformation of the Warburton West structure, central Australia
Author: A.Y. Glikson, A.J. Meixner, B. Radke, I.T. Uysal, E. Saygin, J. Vickers, T.P. Mernagh

This paper reports geophysical anomalies and intra-crystalline quartz lamellae in drill cores from the Warburton West Basin overlapping the border of South Australia and the Northern Territory. The pre-Upper Carboniferous ~ 450 x 300 km-large Warburton Basin, north-eastern South Australia, is marked by distinct eastern and western magnetic, gravity and low-velocity seismic tomography anomalies. Quartz grains from arenite core samples contain intra-crystalline lamellae in carbonate-quartz veins and in clastic grains, similar to those reported earlier from arenites, volcanic rocks and granites from the Warburton East Basin. Universal Stage measurements of quartz lamellae in both sub-basins define Miller-Bravais indices of {10-12} and {10-13}. In-situ quartz lamellae occur only in pre-Late Carboniferous rocks whereas lamellae-bearing clastic quartz grains occur in both pre-Late Carboniferous and post-Late Carboniferous rocks - the latter likely redeposited from the pre-Late Carboniferous basement.

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Google earth file:East Warburton Basin.kmz (240kb, kmz)



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East Warburton impact structure
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Major asteroid site found in Aussie outback

One of the largest ancient asteroid impact zones on Earth has been discovered in outback Australia.
The impact zone, which centres on the East Warburton Basin in north-eastern South Australia, was caused by an asteroid up to 20 kilometres-wide that slammed into the planet between 298 and 360 million years ago, report scientists from the Australian National University and University of Queensland.

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Title: Shock metamorphism of a >30,000 km -large terrain, East Warburton Basin, South Australia: evidence for a Late Carboniferous asteroid mega-impact
Authors: Andrew Y. Glikson & Tonguc Uysal

The discovery of shock-produced Qz/PDF lamella in quartz grains of late Carboniferous granitoids, sediments and volcanics in drill cores extending over 220x150 km in the Warburton Basin indicates a major end-Carboniferous impact event resulting in a >300 km-diameter impact structure.

B. Evidence for shock metamorphic origin of the lamella includes (a) Ustage measurements of unique Miller indices correlated with shock levels >22 Gpa; (b) occurrence of multiple sets intersecting Qz/PDF, Qz/PFs and metamorphic deformation lamella (Qz/MDL) and (c) the narrow width of lamella <1 m and interlamellar spacings of ~4-5 m. Post-shock deformation of the Qz/PDF results in bending of Qz/PDF, producing undulating Qz/MDL overprinted on Qz/PDF. The shock-produced nature of the latter is evident from the preservation of cross lamellar sets consistent with miller indices diagnostic of impact shock effects.

C. A circular impact structure remains undefined. However, major geophysical anomalies, including the >100 km-diameter sub-Patchawarra gravity and magnetic anomaly and a corresponding low-velocity tomography anomaly hint at deep seated effects possibly related to a major impact event. The nature of a major tomographic anomaly which underlies the western Warburton Basin - the Poolawanna Basin - likewise remains to be investigated.

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South Australia asteroid strike you missed - by 300m years

Evidence of a massive asteroid strike about 300 million years ago - the third-biggest ever found on Earth - has been discovered in South Australia.
Research from the Australian National University says the East Warburton Basin in northeast South Australia contains evidence thought to be caused by an asteroid measuring 10km to 20km in diameter that hit Earth more than 298 million years ago.

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